The African Journal of Tropical Hydrobiology and Fisheries ". 7

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2 CONTENTS Staff Vehicles...,.,.,. Lauches.....,... Library Page The African Journal of Tropical Hydrobiology and Fisheries ". 7 Publications , 10 Meetings II Scientific Work Haplochromis Studies On the Management of the Lake Naivasha Fishery Stock Assessment and Management of Lake Victoria Fisheries. 23 The Fisheries of Lake Kitangiri Feeding and Fecundity of Haplochromis guiarte and Haprochromis obesus Experimental Fisheries Surveys in some East African Lakes. 39 Ricipisculture Experiments of Ahero Irrigation Research Station Visitors

3 STAFF Director: J. Okedi, B.Sc. (Hons), Ph.D. Research Officers: G.E.B. Kitaka, B.Sc. (Hons), M.Sc Okorie, B.Sc., M.Sc., Ph. D. B. Basasibwaki, B.Sc. (Hons), M.Sc. G. Ssentongo, B.Sc. (Hons), M.Sc. Vacant (I) Research Officers (Trainee): D. L. ~cenodongo, B.Sc. (Hons) J. Okaronon, B.Sc. (Hons) B. Wanjala, B.Sc. (Hons) Research Officers (Technical Aid): J.A. Wetherall, B.Sc., Ph.D. T. Peck, B.Sc., M.Sc. J. Thrall, B.Sc., Ph.D. Experimental Fisheries Officer: Vacant Executive Officers: J. Were J. Rudatsikira Accounts Officers: E.J. Mwangi H.Onjala Supplies Officer: D.Ongodia D. Anyona Librarian Sub/Editor: Mrs. M. Peck, M.Sc. Mrs. S. L. Wanambwa, B.Sc. Maintenance Engineer: H.L. Walusimbi Laboratory Technicians: 2 Vacant Foreman Artisan (Fisheries) : G. Mutabaazi Laboratory Assistants: P. Mugerenge F. Moini J.Ogutu H.Oduke Artisans: S. Ongeso G. Ntalo E. Ndwokya

4 Personal Secretaries: Mrs. J. Wood Mrs. B. Mutesasira Senior Coxswain: W.Odongo Coxswains: E.Odwori A. Mlikholo LAKE VICTORIA FISHERIES RESEARCH PROJECT (U.N.D.P. SPECIAL FUND/EAST AFRICAN COMMUNITY/F.A.O. PROJECT) (F.A.O. Experts) Project Manager: P. B.N. Jackson, M.Sc. D. Butcher, Ph.D. Masterfishermen: Capt. G. lllugason Capt. Fjeldstad Marine Engineer: J. Johnson Sociologist: D. Butcher, Ph.D. Administrative Assistants: P. Rodrigues (E.A.F.F.R.O. Counterparts) CoManager: J. Okedi, Ph.D. Limnologist: G..B. Kitaka. M.Sc. Stock Assessment Biologist: A.W. KlIdhongania Economists: V. Babikanyisa, M.A. S.H. Jiwani, M.A. Associate Sociologists: Elsa Skjonsberg J. Colaris E. Jansen 2

5 STAFF The year 1972 has represented another successful year for the recruitment of local scientific staff at EAFFRO. It will be noted that the previous year saw some of EAFFRO's trainee scientists return from overseas Courses. This year another EAFFRO Economist, Mr. V. Babikanyisa returned from the University of Washington in the U.S.A. having successfully completed his M.A. degree under the able guidance of Professor James Crutchfield. Mr. Babikanyis3 joins his colleague Mr. S.H Jiwani as EAFFRO Economists attached to the Lake Victoria Fisheries Research Project. Training requirements for scientific staff at EAFFRO are by no means accomplished. Deliberate efforts to recruit tr3inees was maintained with full vigour and with the assistance of the East African Community Service Commission, two more research officers trainee, were recruited during the year viz. M r. J. Okaronon and M r. B. Wanjala both of whom are honours graduates from Makerere University. It is hoped, as in the past, to arrange specialised training programmes for them overseas as soon as possible. Meanwhile Mr. D. Ocenodongo, an EAFFRO trainee biologist, proceeded to the U.S.A. during the year for studies leading to the award of Master of Science degree in Fisheries. Mrs. S,:Ifa L. Wanambwa was recruited in the year to take over as Librarian/SubEditor from Mrs. M. Peck. Mrs. Wanambwa, a former school teacher, has some valuable experience to add to EAFFRO and her scientific training should be an added asset in her duties in the library as well as Subeditor of the African Journal of Tropical Hydrobiology and Fisheries. EAFFRO's fortune in getting the services of a U.S. Peace Corps biologist. Dr. James Thrall was shortlived as Dr. and Mrs. Thrall who were to be posted to Nyumba ya Mungu Dam decided to return to the United States. The arrival of M r. Fjeldstad, au. N. Gear Technologist early in the year was greatly welcomed as his role was to assist Capt. IJlugason in the fabrication of suitable fishing gear for the experimental stern trawler "Tilapia" of the Uganda Fisheries Department. Another U.N. expert, Mr. Johnson joined the team of East African Community and U.N. experts as a marine engineer and his arrival ferried the organization through a difficult period as EAFFRO Maintenance Engineer, Mr. H. Walusimbi was away in Norway on an FAO training fellowship. Mr. Walusimbi, however, arrived back after successfully completing his course towards the latter half of the yea r. 3

6 On the administrative side, EAFFRO was happy to receive Mr. J. Rudatsikira, an Executive Officer who took over from Mr. 1. Were. Similarly Mr. D. Anyona, a Supplies Officer from Nairobi arrived to relieve Mr. D. Ongodia who proceeded on a twomonths leave during the year. Although the year under report represented consolidation of training programmes and intensification of further recruitment, it is sad to report that Mr. S.H. Jiwani, an EAFFRO Economist resigned and left to settle in Canada. Similarly the UNDP Project Manager, Mr. P.B.N. Jackson left the organization in February after a long and rewarding stay at EAFFRO Headquarters at Jinja. EAFFRO would like to be associated with all friends of Mr. Jackson in wishing him prosperity and success in his new endeavours. The UNDP Project which was jointly operated with the East African Community ran into problems during the latter half of the year due to the inability of all concerned to sign the Project Document in time. Consequently the regional funds for operation of this project were exhausted and all the UNDPjFAO experts left the project in December. EAFFRO and the Partner States of Kenya, Uganda and Tanzania continued to service the project. The East African Community on behalf of the Partner States has expressed earnest desire to continue the Project and it is hoped the UNDP will be able to release the necessary funds for its reactivation in due course. To this end EAFFRO stood on the ready to initiate Phase II of the Project. Three East Africans with certificates of competency in Coastal Navigation were 'recruited for the first time as counterparts to the FAO Masterfisherman. Training aspects in the Phase I of this Project were rather unsatisfactory as far as the Counterpart Masterfisherman was concerned and this in fact led to his resignation. The recruitment of three competent and qualified counterparts should therefore enhance the chances of successful training in fishing gear and techniques where they are presently deficient in proficiency. The three counterparts viz. Messrs. C. Manyile, H.O. Okollo and L.B.M. Mukasa come from Tanzania, Kenya and Uganda respectively. They should find the 'IBIS' an excellent vessel for training purposes. Further, in preparation for intensified research activity, two more artisans were recruited during the year. Mr. G. Ntalo, Artisan Grade IT is a qualified boat builder with experience in timber, metal and fibre glass construction. He will be quite an asset to EAFFRO for the repair and maintenance of research craft which are mainly wooden or fibre glass. The second Artisan recruited during the year is Mr. E. Ndwokya, a mechanic Grade II. He will operate within the EAFFRO workshop to maintain the fleet of vehicles and other laboratory equipment. 4

7 VEHICLES In general, repair and maintenance work has been normal throughout the year although some difficulties were experienced in repairing some of the vehicles and other equipmenls. Considerable success in transport facilities was achieved during the year. Five more new vehicles were purchased in the middle of the year: Toyota Commuter Hiace KNX 872, Bedford Lorry KNY 575, VjW Kombi KPA 418, Toyota Land Cruiser K NZ 428 and Toyota Pick Up KNZ 961. The two UNDP vehicles VjW UZK 071 and UZK 072 were taken to Kampala UNDP Headquarters. Toyota Crown UG 0891 is laid off because of mechanical troubles and the UNDP Land Rover UG 0892 continued to provide service wi'th very high repair costs due mainly to its age. The organization hopes to effect in full the establishment of its Substations in Kisumu (Kenya) and Mwanza (Tanzania) during the coming year and it is apparent that more transport facilities will be required in the near future. However, operation of the vehicles during the year is indicated below: EAFFRO Vehicles: Land Rover UYM 801 Land Rover UYM 802 Peugeot 504 U UT 356 Toyota Land Cruiser KNZ 428 Toyota Pick Up KNZ 961 Volkswagen Kombi KPA 418 Bedford Lorry KNY 575 Toyota Hiace KNY 872. Miles/Km. Run 34,368 22,3J 7 45,665 24,269 13,232 14,858 7,043 13,888 Total Miles/Km. 92,4J 5 72,840 83,274 24,269 13,232 14,858 7,043 J3,888 UNDP Vehicles: Land Rover UG 0892 Toyota Crown UG 089J (Laid off because of mechanical troubles) Miles/Km. Run 13,722 Volkswagen UZK 07/) Returned to UNDP ) Volkswagen UZK 072) Headquarters, Kampala) Total Miles/Km. 56,282 Mileage information not available LAUNCHES The research vessel "IBIS" gave continuous service during the year. The vessel was involved in long offshore cruises and covered the terr:torial waters of Kenya, Uganda and Tanzania in Lake Victoria. However, the wheelhouse of this vessel was attacked by dry rot and needs complete replacement. 5

8 Launch No. I continued to give r enacing mechanical troubles as in the past year. Due to the old age of its Parkins engines, spares are a great problem to obtain. Similarly, work on the repair of its copper ~heathing, plan ks, frames, deck and cabin will be started as soon as current re~earch programmes can be serviced by procurement of another vessel. The other small canoes and dinghies underwent minor repairs ann continued to give satisfactory service during the year. LIBRARY In October the library was taken over by Mrs. Sara L. Wanambwa after the departure of Mrs. Mary Peck who returned to the U.S.A. The library's problem of lack of space continued to plague efforts to make material more easily accessible. A partial solution has been to put all periodicals from 1966 backwards in one section and to put periodicals from 1967 onwards, books and reprints in another section. This concentrates the current material in one location for easier reference. EAFFRO's library contains more information and material on fish and fisheries than most other libraries in Africa. The collection of over 11,000 reprints, 500 of which were obtained in t972, and over l,500 books, 80 of which were acquired in 1972, are an invaluable asset to scientists all over the world. Over 300 requests were received during the year for information and assistance. EAFFRO receives over 120 journals regularly. The majority are on an exchange basis for EAFFRO Annual Reports, Occasional Papers and The African Journal of Tropical Hydrobiology and Fisheries. The library has a mailing list of over 400 institutions, organizations and individuals allover the world who regularly send relevant publications. The journals and reprints received are in French, Spanish, Italian, German, Polish, Russian, Japanese, Czech, Norwegian, Swedish, Hungarian and Arabic as well as English. All reprints and books are classified by author and by subject. A special classification is given to those which deal particularly with Africa. These are again subclassified as to which country or geographical part of Africa is discussed. All reprints are sorted according to size from A to D, A bein,:\ the smallest and stored in boxes which are appropriately numbered and arranged. Books are classified as to subject and placed in the appropriate section 6

9 A record is kept of the volume and issue number ofeach journal received. The latest issue of each journal is kept on a special display rack until the next issue arrives. The older issue is then put in serial order with the other journals. Approximately, every three months, the library issues an accession list of all books and reprints received. This is distributed to all EAFFRO staff and various other institutions and individuals. Since many of the items in the EAFFRO library are irreplacable, it is impossible, under most circumstances, to lend original material to other organizations or institutions. However, arrangements can usually be made to photocopy or zerox the required information. Plans are underway to construct a new office and laboratory block which will include a large library. This will solve storage and arrangement problems and make all material more easily accessible. THE AFRICAN JOURNAL OF TROPICAL HYDROBIOLOGY AND FISHERIES The first worldwide reactions to and comments on the journal were received in The first volume of the journal was distributed to subscribers and the EAFFRO mailing list and praise and encouragement was forthcoming from the majority of the recipients. Publishing difficulties continued to slow down the processing of manuscripts and production of proofs. Lengthy consultations were held with the publisher and printers and some procedural streamlining was decided upon. It is hoped that these measures will help to eliminate any future delays. Many manuscripts were submitted to be considered for publication. They cover a wide range of topics encompassing many facets of freshwater and marine fisheries and fish species, fishing gear and techniques, limnology and the statistical and mathematical aspects of stock assessment, resource evaluation and fishery management. All manuscripts submitted are first perused by the Editor and Subeditor to evaluate their general suitability and relevance. They are then sent to a suitable r("feree who is an expert in the particular field with which the paper deals. When the manuscript is returned, it is sent to the author with suggested revisions and corrections if necessary. When the revised version is received it is forwarded to the publisher. 1

10 Galley proofs are sent to the author for correction with a two week time limit for their return. Page proofs are thoroughly scrutinized before the journal is finally printed and bound. Each author receives 60 reprinh I"n:c or charge and ('xtra copies ltlay be procured at the author's own expense. Two isslie\ comprising one volume are published every year in approximately June and December. Each issue is approximately 80 pages in length. The subscription rate is Shs. 35/ per year in East Africa and U.S. $\ 0.00 elsewhere. In November 01" 1972, the Committee for Inland Fisheries of Africa (CI FA) held its first session and a Symposium on Evaluation of Fishery Resources in the Development and Management of Inland Fisheries in Fort Lamy, Chad. Of the numerous papers presented at the meeting, fourteen were chosen and released for publication in the journal by FAO Rome of which CIFA is a subsidiary. These fourteen papers will be published in two' Special issues in This is a great honour for our journal and we are very much indebted to FAO, Rome. These Special Issues will be sent free of charge to subscribers and those On our mailing and exchange lists. Extra copies can be obtained for a small fee by contacting the Editor at EAFFRO, Box 343, Jinja, Uganda. THE AFRICAN JOURNAL OF TROPICAL HYDROBIOLOGY AND FISHERIES Vol 2 No Contents Almo J. Cardone and Observations on the influences of codend A. Kudhongania mesh size on bottom trawl catches in Lake Victoria, with emphasis on the Haplochromis population. R. Williams Relationship between the water levels and the fish catches in Lakes Mweru and Mweru wa Ntipa, Zambia. 8

11 R.G. Bailey Eugene K. Balon Observations on the biology of Nothobranchius guentheri an annual fish from the coastal region of East Africa. Possible fish stock size assessment and available production survey as developed on Lake Kariba. NOTES AND COMMENTS Richard G. Hartnoll Improved facilities for marine biology in East Africa. A.J. Bruce The rediscovery of Notopoides lalus Henderson in the Western Indian Ocean (Crustacea Decapoda, Raninidae). V.B. MeyerRochow A note on some parasites of Merluccius capensis (Pisces) and their zoogeographical significance. THE AFRICAN JOURNAL OF TROPICAL HYDROBIOLOGY AND FISHERIES Vol. 2 No Contents Patrick Denny S.A. Visser The significance of Pycnocline In Tropical Lakes. A review of the distribution of organic compounds in freshwater lakes and rivers. I.G. Dunn The commercial fishery of Lake George, Uganda (East Africa). George Ssentongo Ko Watanabe Yield isopleths of Tilapia esculenta Graham 1928 in Lake Victoria and Tilapia nilotica (Linnaeus) 1957 in Lake Albert. Chern ical, bacteriological and sensory examination of split, dried, smoked bream on the Market in Zambia. 9

12 John M. Melack and Peter Kilham Lake Mahega: A Mesothermic. chloride lake in Western Uganda. Sulphato NOTES AND COMMENTS E.A. Aderounmu and F. Adeniyi Cestodes in fish from a pond at lieife, Nigeria. PUBLICATIONS 230. CORDONE, ALMO J. and KUDHONGANIA, A.W. Observations on the influences of condend mesh size on bottom trawl catches in Lake Victoria with emphasis on the Haplochromis population. Afr. J. Trop. Hydrobiol. Fish. Vol. 2 No SSENTONGO, GEORGE Yield isopleths of Tilapia esculenta (Graham) 1928 in Lake Victoria and T. Nilotica (Limnaeus) 1957 in Lake Albert. Afr. J. Trop. Hydrobiol. Fish Vol. 2 No GEE, J.M. Problems and potentials for the development of the Haplochromis fishery of Lake Victoria. Proceedings of the Challenger Society Vol. 4 pt 3, WELCOMME, R.L. A Brief Review of the Floodplain Fisheries of Africa CIFA/72/S.17 FAO Rome, EAFFRO OCCASIONAL PAPERS No. I. ELDER, H.Y. Report on investigation into the Tilapia population of Lake Naivasha, Kenya No.2. EAFFRO. The History and Research results of the East African Freshwater Fisheries Research Organization from (1967). No.3. EAFFRO. East African Freshwater Fisheries Research Organization Annual Report (Reprinted). No.4. EAFFRO. Complete list of Published Works

13 No.5. GEE, J.M. and GILBERT, M.P. The establishment of a commercial fishery for Haplochromis in the Uganda waters of Lake Victoria, Part I, No.6. MANN, MJ. The Fisheries of Lake Rukwa, Tanzania No.8. GEE, J.M. and GILBERT, M.P. The establishment of a commercial fishery for Haplochromis in the Uganda waters and Lake Victoria part II No.9. MATHES, H. The Fishes and Fisheries of Ruaha River Basin, Tanzania No. 10. MANN, MJ. A brief report on a survey of the fish and fishery of the Tana River with special reference to the probable effects of the proposed barrages, No. 11. GEE, J.M. The establishment o( a commercial fishery for Haplochromis in the Uganda waters of Lake VictoriaPart III, No. 12. MANN, M.J. Catalogue of EAFFRO scientific archives, No. 13. CHILVERS, R.M. Bottom trawl codend mesh selectivity to Bagrus docmac (ForskahJ) from Lake Victoria, with some remarks on the proposed Trawl Fishery, No. 14. WETHERALL, JERRY A. On the Catch Assessment Survey (CAS) of Lake Victoria Part IUganda Waters of Lake Victoria Part IIKenya Waters of Lake Victoria Part IllTanzania Waters of Lake Victoria MEETINGS As in the past years, EAFFRO had the opportunity to participate in several local and international seminars and meetings. Of particular significance was the first session of the Committee for Inland Fisheries of Africa (CIFA) convened in Fort Lamy, Chad. The FAO generously made it possible for Dr. J. Okedi, Dr. O. Okorie, Mr. G. Kitaka and Mr. W. Kudhongania to attend this meeting. The CI FA meeting was conveniently preceeded by a Symposium on Evaluation of Fishery Resources in the II

14 Development and Management of Inland Waters in Africa. Dr. Okedi chaired the Symposium and the other EAFFRO participants read papers. The four EAFFRO scientists also had an opportunity to tour Volta Lake Project in Ghana and the Kainji Research Project in Nigeria. EAFFRO extends it sincere thanks to the FAO and Project staff at these Projects who made the visit most informative and valuable. The U.N. Committee on Natural Resources held in Nairobi in January was attended by Dr. J. Okedi, Dr. O. Okorie and Mr. Kitaka. Mr. G. Ssentongo attended a briefing session in Bujumbura (UN DP Project in Lake Tanganyika) in January along with Dr. Weatherall who assisted the UN Project on statistical treatment of their Lake Tanganyika data. ]n February EAFFRO team participated at the All Africa Trade Fair in Nairobi, whilst the East African Communty Committee on Papyrus in Arusha was attended by Dr. J. Okedi and Mr. G. Kitaka. The Social and Research Council of the East African Community in April was attended by Dr. J. Okedi and Mr. G. Kitaka. A seminar mounted by EAFFRO on Catch Assessment in Kisumu was attended by Dr. Okedi, Dr. Okorie, Mr. Jiwani, and Dr. Wetherall. This semina r was well attended by Fishery officials from the Partner States and was ably conducted by Dr. G. Bazigos from the FAO Headquarters. ]n August the Annual Fisheries Technical Committee was hosted in Tanga and EAFF RO joined colleagues from Kenya, Uganda, Tanzania and Zambia to discuss common problems in fisheries; Dr. Okedi, Dr. Okorie, Mr. Kudhongania and Mr. Jiwani attended this meeting. SCIENTIFIC WORK The development of research programming over the years has led EA FFRO to evolve research on five major Jines: I. Fishery Biology. 2. Stock Assessment and Resource Evaluation. 3. Limnology and Water Quality. 4. Fishery Economics. 5. Fishing Gear Development. To date East Africa is becoming increasingly aware of the availability of fishery resources in lakes and rivers and the Governments have expressed anxiety to develop these resources. For some of the smaller lakes there has been no prior fishery investigations whereas the largest lake in East Africa, i.e. Lake Victoria, has tended to be better studied. For all these lakes, ]2

15 however, it is essential to determine preliminary aspects of the characteristics of the populations in order to advise Fishery Department of the Partner States on such relevant information as species composition, size distribution, habitat selection, maturity, feeding habits and gear selection. This aspect of research has been closely related with management and a a section or division within EAFFRO was created to undertake resource evaluation research in all the important lakes and rivers in East Africa. In this regard the following lakes were covered during the year under report. LAKE WAMALA A survey in Lake Wamala was carried out during the year and involved studies of the general biology of the available fish species as well as a comprehensive evaluation of the exploited stocks of Titapia nilotica. Two sets of gillnets of mesh sizes ranging from to mm were set in two fishing grounds: Lusalira in Busuju county and Butebi in Singo County. The catch in numbers and weight from each gillnet was noted. The following biometric information for each fish species was recorded: weight, standard length, total length, sex, gonad condition and stomach condition. The incidence of parasites on each fish species was noted. This was the first lime for an EAFFRO biologist to work on the lake. Some reliable information on the status of commercial fish stocks were collected. LAKE ALBERT From the 16th June to 29th June 1972 experimental fishing was carried out on Lake Albert. Two sampling stations were chosen namely Wanseko and Ntoroko. Wanseko is located at the northern end of Lake Albert while Ntoroko is located at the Southern end. Gillnets of various mesh sizes ranging from 38.1 mm to mm were used in fishing. Since Lake Albert is deep, both surface set and bottom set gillnets were used. The catch in numbers and weight was recorded in order to obtain catch per unit effort data on the fisheries. The exploited fish species include: Atestes, Hydrocyon, Lates, Tilapia nitotica, Barbus, Mormyrus and Bagrus. Data on lengths, weights, sexes, gonads and stomach cond ition was collected for each species. LAKE KITANGIRI In August an evaluation of the harvestable fish stocks of Lflke Kitangiri in Tanzania was conducted. Gillnets of mesh sizes ranging from 38.1 mm to mm were used in fishing. Because of the shallow condition of the lake all the gillnets were surface set. 13

16 At the time of the survey the harvestable stocks of Ti/apia were very low. Most of the Ti/apia were captured in the to 76.9 mm gillnets. Very few Ti/apia were caught in the 88.9 mm gillnets. Gillnets of mesh sizes greater than 88.9 mm caught only a few Protopterus and C/arias. The information collected on size structure, sex, gonad condition or maturation revealed that there was an overfishing problem most probably caused by capture of immature fish and an excessive fishing effort prevailing on the lake. LAKE VICTORIA Sampling areas were selected depending on the present distribution of commercial units operating on the lake. Sampling was carried out in various localities primarily to assess the status of the important Ti/apia. Amongst these, T. escu/enta, T. variabi/is, T. zillii, T. ni/otica and T. /eucosticta were sampled including other genera e.g. Hap/ochromis, Protopterus, Barbus, C/arias and Schi/be. Sampling for these species was done mainly by gillnets and was intended to detect population changes and trends. Such important parameters as species composition, size distribution, sex, gonad maturity and stomach condition were collected for the major species. The areas sampled included North Ruvuma, Bukakata waters and Mwanza waters of Lake Victoria. LAKE BARINGO An intensive survey of this lake was conducted during the year. The lake has posed several problems particularly in regard to silting, stunting of the important Ti/apia ni/otica and parasitism. The lake was subdivided into two major ecological zones and a sampling design instituted. Amongst the species sampled and from which ecological and biological data were obtained included T. ni/otica, Barbus spp. and C/arias spp. ' NYUMBA YA MUNGU DAM This is a very important manmade lake in the northeast of Tanzania. The lake has developed a very lucrative fishery involving mainly Ti/apia pangani. Maximum size of this fish is diminishing indicating overfishing. There is also uncontrolled use of monofilament and small mesh nets. The lake was surveyed for resource evaluation purposes. Three major species included T. pangani, Labeo and Synodontis. Preliminary management ideas are being formulated for transmission to the Tanzania Fisheries Department. However, the lake needs more intensive surveys and these should be mounted in the next year. 14

17 HAPLOCHROMIS STUDIES The discovery in the previous years of a standing stock of 750,000 tons of Haplochromis in Lake Victoria continued to excite interest. Various plans were mounted for the commercial exploitation of this abundant resource. Biologists were, however, anxious to get some understanding ofthe ecology and biology of some of the major groups within the Haplochromis species flock. During the year, therefore, work on the Haplochromis involved accumulation and analysis of data collected previously in the trawls. Further studies were conducted sampling with different gear e.g. beach seines and gillnets. Information was therefore collected on important aspects of the populations particularly in the northern waters of the lake for example gear selectivity, predation, species composition, breeding and other aspects of the characteristics of the Haplochromis populations. NILE PERCH INVESTIGATIONS Studies on Lales nilolicus were mainly done in Lake Victoria and involved regular collection of biometric data and analysis of stomach contents to evaluate trends in the feeding cycle of Lales. Nile Perch is indeed spreading successfully in the lake and it is too early to predict its impact on the ecosystem. This predator continues to be watched with keen interest as it spreads in Lake Victoria. RICIPISCULTURE EXPERIMENTS During the year, EAFFRO collaborated with the Ahero Rice Irrigation Project of the Kenya Government. Experiments were mounted to test the fea~. bility of growing rice and fish together in rice paddies. Initially various species of Tilapia were tested but the experiments soon encountered problems of stunting and escapement of fry. L1MNOLOGICAL STUDIES Studies in Limnology were limited by nonavailability of suitable vessels for offshore work in Lake Victoria. Besides, the only Limnologist on the staff took opportunity to write up his research findings involving several years for presentation as Ph. D. disertation. FISHERY ECONOMICS Similarly, effort in fishery economics studies tended to suffer during the year. The two locally recruited economists relinquished their posts for one reason or other leaving their research programmes unattended. 15

18 HAPLOCHROMIS STUDIES BASASI BWAKI, P. Most of the available data on Haplochromis were accumula ted from surveys conducted in trawlable offshore and inshore areas using the fishing vessel 'IBIS'. This was not surprising because the selected gear, the trawl, was considered the most suitable and the most efficient gear that could adequately be employed in studying biological, economical, technological factors etc., that could aid in rational exploitation of Haplochromis resource which contributes over eighty percent by weight in Lake Victoria. Haplochromis surveys conducted in trawlable areas enabled us to obtain such information as catch per unit time for various mesh sizes in many areas of different biological, limnological and other characteristics. However, the selected gear used had limitation where the grounds were not trawlable and where the waters were extremely shallow. In such areas it is possible that the populations could be different especially in the shallows normally regarded as the breeding grounds of many fishes. It was accordingly decided to use different types of gears, seine nets and gill nets, to study fish populations which are never encountered using a trawl. The study was aimed at obtaining the following information: (a) (b) (c) (d) (e) (f) gear selectivity among Haplochromis species using gillnets and beach seine nets, Haplochromis population structure, Interaction of Haplochromis with other species in the lake, Predatory impact of some Haplochromis species in the inshore areas, Species composition of Haplochromis catches, breeding habits and behaviour and other relevant information such as taxonomy of the species undescri bed. In general, the results obtained from gillnetting and beach seining in the Northern parts of Lake Victoria close to Jinja can be summarised as follows ; (a) Mesh selectivity among Haplochromis species is very complex because of the diversity of the body shapes assumed by various species. Nevertheless, for each species there is a mesh size that gives optimum catch. For example, it was found that an optimum catch of H. longirostris was obtained using a one inch mesh size while a two and a half inch mesh gave an optimum catch of H. obesus. Using a trawl previously it was found that optimum 16

19 Haplochromis catches were obtained using a two inch mesh codend. Compared to the effect of a fleet of gillnets of various mesh sizes on Haplochromis species, the selectivity of a trawl would imply that only some species would contribute to commercial catches with the consequence that the gear in operation induces more drastic changes in species composition than gillnets or seine nets would do. (b) (c) (d) (e) In the areas where beach seining and gillnetting were conducted Haplochromis species occurred in association with small sized Tilapia species which were below the sizes recommended for exploitation though, occasionally, large sized Tilapia were caught in seine nets. It is generally suspected and stated that Tilapia stocks in the inshore areas are 0verexploited. In addition to high rates of exploitation in the inshore areas the impact of predation of the unexploited great abundances of larvalembryo feeding Haplochromis could significantly regulate Tilapia numbers in the areas. Relatively fewer species of predatory Haplochromis (excluding embryo feeders) occur in the breeding inshore areas than offshore areas. Those predatory species regularly encountered in the catches were mainly H. guiarti, "a primitive" predator, H. longirostris and H. macrognathus, both of which are highly specialised predators. Other groups were represented in catches. Monotypic genera never occurred abundantly. Astatoreochromis and Macropleurodus were regularly collected from areas with sandy bottoms. The larvalembryofeeders dominated the catches and all the species except one (H. cronus) were represented. The results also indicated that phytophagus species (e.g. H. lividus) and highly specialised streamlined predators (e.g. H. menlo and H. longiroslris) were retained by same mesh size. Studies involving predation showed that the paedophagus group contributed to heavy larval mortality. This group is composed of H. obesus, H. parviden, H. maxi/laris, H. cryplodon and H. microdon. The species in this group feed exclusively on the eggs and larvae ofother fishes especially the Cichlids. The fish stomachs examined showed that the contents were embryos and/or fish larvae. The larvae recovered from the guts never exceeded 13 mm total length. It was also found that the developmental 17

20 stages of the prey were far below those reached before the mouth brooding females normal~ release their young from the mouth. (f) Studies conducted into the breeding habits revealed that there was a large proportion of the breeding females (ripe eggs, incubating embryos or larvae) at anyone time. For example, the percentage of the breeding females in H. guiarti ranged from about 30% to 50% and for H. obesus the range was about 40% to 60% females breeding. Aquaria observations indicated that mouth brooding behaviour was widespread in many Haplochromis species and that the brooding females tended to spit their broods when handled vigorously. Further observation showed that at times the female fish tended to swallow their mouth incubating eggs or larvae. Finally, it had been proposed in the previous annual report (1971) that new techniques be applied to tackle the complex taxonomy of Haplochrornis. Immunological and electrophoretic approaches have been sought and it is a pleasure, at this time of reporting, to mention that the biochemical studies have already been started using biochemical indicators (enzymes) to try and separate Haplochromis species. It is hoped that the studies will throw some light on taxonomy of Haplochromis viewed at molecular level and the same studies will probably expose new areas of study which at the moment suffer because of inadequate knowledge on Haplochromis taxonomy. ON THE MANAGEMENT OF THE LAKE NAIVASHA FISHERY OKORIE, 0.0. INTRODUCTION At the request of the Director of Fisheries, Kenya, EAFFRO carried out two surveys of the fisheries of Lake Naivasha in August, 1971 and June The object of the exercise was to evaluate the status of the commercially important fish stocks and to make management recommendations designed to conserve the fishery resource in this important Rift Valley Lake. Specifically it was requested that the following aspects of the fisheries be investigated ; (i) The reasons for the diminution in numbers of the commercially important Tilapia. 18

21 (ii) (ii i) (iv) The impact of the predatory Black BassMicropterus salmoides on the Tilapia population. The need or otherwise for the effective conservation of the Black Bass population. The ecological aspects of the parasites in the commercial fish population with particular attention to the biojogicai basis for their control. A comprehensive experimental fish ng survey was carried out in June 1972 using graded mesh experimental nets. This was a first step towards the establishment in this lake of a routine ecological sampling on a monthly basis. Four representative sampling areas (based on their varied ecological characteristics) were chosen. During the survey period three species of fish were sampled, namely: Tilapia leucosticta, T. zi//ii and Micropterus salmoides. In addition large numbers of Ti/apia hybrids were also encountered. It is necessary to emphasize that this report has been written in a style that emphasizes the conservation objectives of this survey. Although the recommendations contained therein have been made on the basis of data accumulated during the survey, no attempt has been made to present the entin" raw data here. OBSERVAnONS The Ti/apia Fishery During the survey period it was apparent that T. leucosticta formed a large proportion of the Tilapia population in the lake. This species constitutes the mainstay of the commercial catch, and the analysis presented here is in respect of this species. Population Structure The largest fish caught in the experimental gill net was 25 cm and the maximum weight recorded was 825 gms. The range of fish caught was between 14 and 25 cm with the modal length at 19 cm. The largest fish examined from the commercial catch was 34.5 cm. 65 %of the fish sampled were males. There was a high incidence of hybridisation, the majority of the hybrids being males. Of the sample 60 % were immature, all the mature, spawning and spent fish of both sexes were found between the 17 and 25 cm size range. 19

22 Catch rates and Gear Selatil'ity Fish were caught only in the 24" to 4" meshes even though eleven different mesh sizes were used (from 2" to 7"). The 3r and 4" meshes caught Tilapia between 17 and 20 cm. The overall catch rates were very poor averaging one fish per net for those meshes. It is evident that the commercial fishermen are harvesting the Tilapia either before they reach their first maturity, or while they are spawning for the first timea situation which no doubt undermines the reproductive capacity of the Tilapia population. Spatial Distribution Of the four representative sampling areas, the Tilapia were mainly caught in the northern littoral areas with floating papyrus. This area is the main breeding ground for the Tilapia, and has the highest concentration of commercial fishermen. Generally the distribution of the Tilapia in the lake was towards patchiness rather than random. Parasites All the Tilapia caught except those from Oloidien Bay were infected with the larvae of Contraceucum spiculigerum Rud. These were found in the pericardial cavity of the infected fish. The largest number of parasites recorded in a single fish was 41 (the length of the infected fish was 17.5 cm). The Black Bass (Mieropterus salmoides) Population Structure The range of Bass caught was between 14 and 43 cm. The heaviest weighed 2700 gm (length 43 cm). Of the Bass sampled 50% were males. Of the sample 74 % were immature, the mature fish were between 14 and 35 cm. Catch rates, Gear Selectivity Catches were poor averaging less than a fish per net. This compared unfavourably with the better catches of the commercial fishermen. In the experimental fleet they were caught in 2" to 6" meshes, more catches being made in meshes between 2" and 3r'. Spatial Distribution Distribution of Black Bass in Naivasha was random and they were caught in all the sampling areas. Parasites Of the fish examined 65 % were infected with parasites. Two parasites 20

23 were identified, Contracaecum spiculigerum and Ligula intestinalis of which the latter predominated. The largest number of Ligula parasites found in one fish was 45. Predation and Cannibalism Examination of the stomach contents indicated incidence of both predation and cannibalism. Young Bass up to 14 cm was found in one stomach. Predation on juvenile Tilapia was not as prevalent and serious as might have been suspected, possibly because the two fish species were not similarly distributed spatially over the entire lake. MANAGEMENT RECOMMENDATIONS The Tilapia Fishery Size Restrictions It is evident from a comparison of the experimental gillnet selectivity and the commercial catches that the fishermen are using illegal 2f', 3" and 32" meshes. It is therefore necessary to enforce the use of the 4" meshes more vigorously. A system of net inspection either offshore or on the lake should be initiated. Closed Areas Commercial fishing should be banned from the identifiable breeding areas until such a time that the 'closed season' regulations are formulated. It is apparent that these breeding areas are being fished intensely by the commercial fishermen. Oloidien Bay should also be closed to commercial fishing and reserved as a restocking area. Closed Seasons Contrary to suggestions from certain quarters it is considered inexpedient to close the entire lake to commercial fishing for a period of one or two years. Instead it is hoped that data from the regular biological sampling now in progress would indicate precisely when the lake can be closed to allow the majority of the Tilapia to spawn undisturbed. Once this 'closed period' is identified, its enforcement should not be compromised. Restocking Oloidien Bay is the only part of the lake that can be restocked most conveniently, since it is partially cut off from the main Jake system. ]t offers the opportunity to study more closely the development of the introduced species. The Bay is more turbid than any other part of the lake and initial observations indicate lower growth rate in the fish population when compared to the rest of the lake. For example a 13 cm Tilapia caught in the Bay was found to be in spawning condition (stage VI). It is to be pointed out 21

24 that none of the fish caught in this bay was parasitized. Taking into account the ecology of this Bay area it is suggested that carp could be stocked here on an experimental basis. The Bass Fishery The indications are that the Bass fishery, if properly managed will in future form the mainstay of the commercial fish stock of this lake, and therefore attention should now be focused on its conservation. Size restrictions Mature females (IV) caught were 28 cm or above, but the commercial fishermen are taking Bass in the J 8 to 25 cm range. It does seem, therefore, that the majority of the Bass population are being taken before they reach their first maturity. It is suggested that the minimum catchable size for Bass be set at 35 cm. This will ensure adequate recruitment into the fishable stock. It is envisaged that on the face of it, it could be impracticable to enforce this size limit, but once the Fisheries Department demonstrates its determination to implement this regulation, the fishermen will be forced to adopt the necessary gears that would exploit this size group. Closed Seasons Data collected from the regular sampling programme now in progress should indicate the breeding seasons for this species, and as with the Tilapia fishery, regulations should be enforced to protect the breeding stock during that period. Parasite Control Although no detailed assessment has been made of the pathological effects of the endoparasites infecting the fish population in this lake, their incidence, intensity of infection and location within the fish host suggest that their pathological effects cannot be ignored. A detailed study of this aspect is called for. The biological basis for their control include the elimination of all the infected fish (an impossible task) or the elimination of the final host (the aquatic birds). This last resort would be unacceptable since this lake is regarded as a bird sanctuary. On this question therefore no solution is in sigh t. Research Priorities Biometric data collection All the options open for the rational management of the fisheries of this lake depend on the data to be collected from the regular sampling of the 22

25 fish population on the lines already mapped out for the resident biologist. It is therefore necessary that the biologist be given all the material and financial assistance needed to carry out this survey. This includes the monitoring of the commercial catches. The Salvinia problem Though the problems posed by the invading Salvinia on the ecology of the lake system cannot be ignored, yet experience from other lakes for example, Lake Kariba in Zambia suggest that the Salvinia habitat in a lake ecosystem can contribute positively to the maintenance of a viable fish population. It is therefore necessary to investigate specifically the ecology of fishes within the Salvinia areas before any recommendations are made. This investigation can easily be integrated with the overall sampling programme as presently constituted. STOCK ASSESSMENT AND MANAGEMENT OF LAKE VICTORIA FISHERIES KUDHONGANIAAKIKI Stock assessment embodies those studies planned to investigate the availability, distribution, abundance and yield potentials of actually exploited or potentially exploitable stocks. The purpose of such studies is to provide the scientific basis and methodology upon which management or development of the resources could be formulated. In a number of cases (e.g. where the information is highly urgent, or where the resource is still virgin) stock assessment studies need no high precision before reasonable management or development decisions can be mounted. An early reasonable approach, though based on low precision study results, can be more useful than a delineably precise decision made as a kind of postmortem management. Fishery resources can become highly amenable to irreparable damage if misused for limited periods, and precise answers are not always guaranteed to obtain. The preliminary studies can often provide a basic framework of scientific knowledge into which additional information could be added systematically as gained by subsequent research and experience. To experimentally assess potentials, problems and limits of the resource it is important to understand the response of the species to various exploitation regimes. Exploitation possibilities must necessarily change with knowledge and circumstances of the resource potentialsmaking regular adjustments to the desirable levels. It is, therefore, desirable to make early management decisions and subsequently sufficient if the preliminary decisions are followed up with more and more precise scientific information and advice to guide ~he decision makers in choosing the best course among possible alternatives for rational exploitation, management and utilization 23

26 of the resource. As exploitation of and research on the natural resources are both processes in time, the studies should also follow the trend of the resource potentiality and the information sought should be capable of predicting future needs in terms of both research and resource. Assessment studies and past trends of the fish stocks of Lake Victoria show that the resource has not been unresponsive under exploitation pressure. Certain stocks have been affected' by overexploitation. Though shortterm fluctuations and differential rate of exploitation of the component stocks are exhibited by all multiple stock fisheries, the present status in Lake Victoria calls for an immediate management policy to improve the resource potential. Proper interpretations and predictions of the nature and likely impact of perpetual exploitation can be made through sound management considerations. Management measures are either qualitative or quantitative in their effects on the fish stocks, fish catches and profits. There are varied biological reasons and potential benefits of the presence or absence of regulations depending on the objectives of the fishery. For developing countries the realistic single objective is obviously to perpetuate the resource as a source of human food and economic activities. The future economic and nutritional needs are great for these countries. Conservation measures, though beneficial in the longrun, are usually resisted. But with planning and understanding on the part of both the authorities and the fishing communities the measures can be enforced. Nevertheless, it is useful to consider some of difficulties associated with Lake Victoria. I. The trinationality of the lake poses difficulties in creating a uniform management policy. The econopolitisocial arrangements in the three Partner States are not exactly the same. Each state would want to pursue her national interests and claim a fair share of the available resource within the framework of her goals. "Geographical boundaries'" of the lake may be considered as if the fishes also would honour the national boundaries. Fragmented management of the lake would be detrimental to the fisheries as a whole since different policies might tend to negate each other. Besides, it is very hard to press for "conservation of the resource" where "development of our natural resources" is the national target. But the aroma from development should not transcend the capabilities of the limited resources. Fortunately, the Partner States are already cooperating in many relations and development measures within the established East African Community so that a unified management policy for Lake Victoria should not be allowed to constitute a stumbling block to the already firm cooperation. 24

27 2. There is this global tendency of trying to avoid serious sociopolitical problems that fisheries regulations might involve. Politicians are afraid of losing their votes by annoying the fishing community. Often they even promise "more fish" to get more votes. However, there should be no disparity between the need to increase exploitation and the necessity to expand management techniques. If, therefore, the popularity rhetoric of politicians (or their equivalent) has to prevail on Lake Victoria, the fisheries resources must also be preserved at economic levels for succeeding generationsunless one is after "grab what is there before another man comes". Aspirations for socioeconomic advance should not jeopardize the same aspirations for future needs. 3. To what specific species of value in Lake Victoria should our management objectives be directed? Should we manage the fisheries on the basis of "maximum sustainable yield" or "maximum net economic yield?" The basic biological matrices sufficient to give reasonable answers to these questions are not fully known for Lake Victoria. But it could be pointed out that changes in the dynamic aspects of the ecosystem might proceed either individually or in association. The positive or negative net effects might, therefore, be reflected in the entire biotope. For example, depletion of phytoplanktivorous fishes could reduce the trophic efficiency of the biocoenosis since primary consumers are trophically more economic than secondary consumers.and since much of the autotrophic productivity might be lost from the desired trophic pyramid for fish production. Besides, maximising the yield for certain specific species may not be expected to produce the maximum possible harvest from the entire fishery. Ecologically, the sum of all individual parts of a whole is greater than the whole itself. On the other hand, there are biological and economic grounds to criticise the concept of "maximum" as the basis for fishery management objectives. Even to determine the position of the "maximum" on catch effort curves may not be easy. Marked improvement in total catch can be achieved by not attempting to maximise the catch from overfished stocks. The mixed stocks of Lake Victoria are separated geographically and by their behaviour to a particular gear. It is therefore difficult to calculate the combined yield as a function of fishing effort and gear selectivity. Timeliness in implementation of management decision should not, therefore, be inhibited by waiting for "sigmoid curve theories" or "dynamic pool models" etc. Scientific precision is beyond existing data for Lake Victoria. And it may never come! It is neither possible nor necessary to have a single precisely defined management objective for Lake Victoria, apart from the general objective of improving and perpetuating the viability of the fishery resource. 25

28 4. Formulation of a management policy should not end at the executive desks. The policy has to be implemented and the difficulty is its enforcement. Policing of some 50,000 fishermen on a lake of some 69,000 km 2 cannot be a simple challenge. But if it has to be done, it must be done. The major oceans of the world have been managed to a certain successful extent, so that J have no reason to believe that Lake Victoria could be invincible to police. Given the necessary arms (e.g. money, authority, etc.) for this task the payoff would be unregrettable. It may be suggested that the necessary authority shoukl be vested in the "Lake Victoria Fisheries Commission" unlimitedly. The case for management of Lake Victoria fisheries still stands. A possible management and development strategy for the lake will be published shortly elsewhere. But it is important to bear in mind that exploitation and conservation should be considered together. THE FISHERIES OF LAKE KITANGIRI SSENTONGO, G.W. INTRODUCTION Lake Kitangiri is a small lake lying southwest of Lake Eyasi and is one of the chain of lakes in the eastern rift valley. It is connected with Lake Eyasi by the Sibiti River. Lake Eyasi is described as a salty lake with highly alkaline waters. T ALLING and TALLING (1965) report that Lake Kitangiri is considerably less saline than Lakl; Eyasi. The surface area of Lake Kitangiri is approximately 105 km 2, with a maximum length of22 km and maximum width of 9 km. The lake is very shallow, the depth being less than 3 metres. The important fishery of Lake Kitangiri was first realised in 1958 and fish production in that year was 200 tons (ANNUAL REPORT OF THE FISHERIES DIVISION 1965). This Jake has been surveyed several times by biologists of the East African Freshwater Fisheries Research Organization. In August 1964, M r. M. J _Mann visited the lake and carried out experimental fishing for the period of one month. In 1968 Messrs. M.J. Mann and G.W. Ssentongo visited the lake and carried out a second fisheries survey. In August 1972, the author visited the lake to evaluate the status of Lake Kitangiri fisheries. In all the surveys, fishing was conducted using gillnets of mesh sizes ranging from 38.1 mm to mm. Fishing was conducted during the day as well as at night. For Lake Kitangiri which is situated in a low rainfall area of Tanzania and being a lake with only seasonal inflowing rivers but with a permanent 26

29 effluent river (the Sibiti) climatic fluctuations have considerable effect on fish production. For this season a brief account on the rainfall pattern is given. Lake Kitangiri has had an uncontrolled fishing effort and restrictions on mesh sizes of gillnets have not been enforced effectively. This might partly explain the decline in catches and a reduction in the mean size of fish being caught. CLIMATE AND ITS EFFECTS ON THE FISHERIES Lake Kitangiri is situated in an area with low rainfall. The average annual rainfall ranges from 600 mm to 800 mm. Lake Kitangiri receives most of its rainfall during the period December to March and Table I shows the average monthly rainfall for Lake K itangiri. Table I. Average monthly rainfall for Lake Kitangiri MOnlh Average rainfall in mm. January mm. February mm. March mm. April mm. May Less than 25 mm. June Less than 25 mm. July Less than 25 mm. August Less than 25 mm. September Less than 25 mm. October Less than 25 mm. November mm. December mm. Lake Kitangiri lacks permanent in flowing streams and increase in volume of water is solely dependent on ra;i1fall. In 1970, the level of Lake Kitangiri dropped considerably so that it was possible to cross the lake on foot (ANNUAL REPORT 1970). The total fish production in that year was4113 metric tons valued at Shs. 705,400/. Fish production in that year showed a 25 %drop in tonnage compared to the 1969 figure of 5,465 metric tons. Because of a considerable reduction in the vorume of the lake, the fishing effort dropped below the 1967 level. In an area with a long dry season and high temperatures loss of water through evaporation is bound to be excessive. This execessive evaporation coupled with a lack of permanent inflowing rivers and low rainfall, greatly increase the salinity of the water. A review of literature on Tilapia reveal that high catches are obtained in the years following heavy rains and rise in water level. WELCOM ME (1966) reports that the spawning grounds of Tilapia esculenta in Lake Victoria 27

30 were increased considerably by flooding in LOWE (1956) reports that the breeding activity of Tilapia escli!enla increases with heavy rainfall. It can therefore be deduced that years with heavy rainfall are followed by good year classes of fish and vice versa. It is expected that in Lake Kitangiri with populations of T. escu!enla, T. amphime!as, T. zil!ii and Tilapia hybrids, absence of enough rain could seriously affect recruitment. A reduction in volume of water of Kitangiri greatly increases the salinity of the water. The increased salinity affects the Ti!apia fisheries by possibly causing stunting. I have observed that T. escu!enla of Lake Kitangiri tend to be smaller and mature at a relatively smaller size than T. escu!enla in Lake Victoria. This is characteristic of stunted fish populations to which the salinity of the water might be a contributing factor. Water loss from Lake Kitangiri is by the effluent Sibiti river and evaporation. Water loss through evaporation is controlled by climatic factors. The only way by which the volume of the lake can be controlled is through manipulation of the volume of water leaving the lake by the Sibiti river. Damming the Sibiti river at its source is an expensive undertaking and should be proceeded by the following studies: (1) The Water Development Department should study the water fluctuations of the Sibiti river and determine fairly accurately the volume of water leaving the lake by this river. Having established the water discharge from the lake by way of the Sibiti, the Water Development Department should ascertain whether damming the Sibiti will result in an appreciable increase in volume of the lake. (2) The rate of evaporation on Lake Kitangiri should also be determi n(d Determination of the rate of evaporation will lead to a fairly reliable estimate ofthe volume ofwater lost through evaporation. A comparison of water Joss through evaporation and the Sibiti river might ease the decision on the damming of the Sibiti river at its source. (3) Damming the Sibiti river might be followed by changes in the physical and chemical characteristics of Lake Kitangiri. A qualified limnologist should assess whether these changes will be beneficial or destructive to the fish populations in the lake. (4) The Rural Development Bank of Tanzania should study the economic feasibility of this project. The capital needed for damming the river and the running expenses should be costed. It is also important to 28

31 assess whether the benefits from the fisheries can offset the capital for development plus the running expenses. RESULTS OF SURVEYS Lake Kitangiri contains about twenty fish species belonging to seven families. The families represented are Lepidosirenidae, Mormyridae, Characidae, Cyrinidae, Schilbeidae, Clariidae and Cichlidae. The fish species examined included Protopterus sp., A testes sp., Labeo sp., Barbus pa/udinoses. Barbus jacksoni, Barbus lineomaculatus, Barbus rogersi, Leptog/anis sp. Schilbe sp., C/arias sp., Ti/apia amphimelas, Tilapia escu/enta, Ti/apia hybrids, Hemihaplochromis sp. and Hap/ochromis sp. Until 1957 only Protopterus sp. and Clarias mossambicus were taken by long lines, but since J958 a rapidly developing gillnet fishery has exploited the stocks of four Ti/apia spp. During the 1968 survey, it was observed that the commercial fishery depended on Protopterus sp., C/arias mossambicus and the Ti/apia species. The 38.1 mm gillnets caught mostly Schilbe. It was noted that almost all the Schi/be caught in the 38.1 mm gill nets were immature. Ranking second in numbers was Labeo but most of these fish were immalure. The Tilapia spp. caught in the same gillnets were immature and had a standard length ranging from 79 em. The 50.8 mm gillnets caught mostly Schi/be and these were noted to be immature. The catch in the 63.5 mm gillnets comprised of Protopterus, Schi(be sp. C/arias sp. and Tilapia spp. With the exception of some Scllilbe, all the fish species caught were immature. The catch of Tilapia in the 72.6 mm gillnets was good but more than 50 % of the catch was immature. The Ti/apia caught in the 88.9 mm gill nets consisted of 90 % mature fish. The size range in the catch was 16 to 19 em. The Ti/apia catch in the lo 1.6 mm gill nets was good with almost all the fish having reached the ripe maturity stage. The size range of these Ti/apia was 17 to 25.5 em. Very few Ti/apia were caught in the mm gillnets. From the foregoing observation, it is apparent that in order to optimize the fish catch from Lake Kitangiri there must be control on the mesh size of gillnets used in order to protect the immature fish from exploitation. The foregoing results show that the mesh size which should be used forcommercial fishing should be 88.9 loi.6 mm. In 1968, the mean size of Ti/apia caught in the 88.9 lo 1.6 mm gillnets was 17 em. By August 1972, the commercial fishermen were using the mm gillnets. The mean size of Ti/apia caught in these gillnets was 14.7 em. About 50% of the fish caught were immature. All these 29

32 observations suggest that the Lake Kitangiri Tilapia stocks were being ovcrtlshcd. There is therefore, a strong need for regulating the fishery so that the exploitable stocks can build up. FISH PRODUCTION AND CONTROL OF FISHING The important fishery of Lake Kitangiri was first realized in 1958 and fish production in that year was 200 tons. Since that year fish production from the lake has been substantial. Table 2 shows the annual catch in metric tons and the value' of the catch for the period The catches and value of the catch show clearly the contribution of the Lake Kitangiri fishery to the national economy. Table 2: Lake Kitangiri Fish Production and the value for the Period Year Weight in Tons Value in Shs , , , , ,753 1,500, ,000 1,568, ,000 1,600, ,785 1,259, ,035 1,564, ,465 1,533, , ,500 There are several factors which might be contributing to the fluctuations in catch. Climatic factors like rainfall can explain the low catches in In that year the volume of water of Lake Kitangiri was greatly reduced. Lack of working space forced some fishermen to pullout of the fishery. These fluctuations can also be explained by changing fishing effort. In the early years of the commercial exploitation of Lake Kitangiri there was abundant mature large sized fish. This attracted many fishermen to the lake. With a build up in fishing effort the exploitable stocks declined. Also the mean size of fish in the catch dropped. But the fisherman has to maintain the catch in numbers and weight and consequently resorted to using smaller mesh sized gillnets. This shift from a large size of fish capture to a smaller size of fish capture greatly affects recruitment and is a sign of overfishing. Figures on the fishing effort since the early days of the commercial fishery are not complete. Nevertheless, some inferences on the magnitude 30

33 of fishing effort can be made from Table 3 and Table 4. Table 3 gives the fishing effort for the years There has been an increase in fishing effort as exemplified by number of fishermen, fishing canoes and fishing gears. Table 4 gives the number of gill nets of various mesh sizes from the period There has been a reduction in the use of large mesh sized gill nets and a considerable rise in the use of small mesh size gillnets. Table 3: Fishing effort for Ihe Year Year Fishermen Canoes Gillnets Fishing gear HooksLongline \ Hooks Table 4: Number of Gillnets of Various Mesh Sizes for Year Mesh Size in mm It must be noted that in 1968 the commercial fishermen used gillnets of mesh size mm and above. A year later 362 gill nets of mesh size 88.9 mm were used for commercial fishing. By 1970 more than 70 % of the total gillnets were of mesh size less than JO 1.6 mm permissable on Lake Kitangiri. If this type of fishing is allowed to continue the Tilapia stocks in Lake Kitangiri will soon be depleted. There are several problems to be solved in order to develop the fisheries. Most of the fishes are processed by sun drying and this is difficult during the rainy season. It is probably for this reason that maximum fishing effort is between the months of May and August (dry season). There is also need for provision of stable fishing canoes to replace the unstable bottle palm dugout canoes which are very risky to operate. An all weather road will greatly ease the distribution of fresh fish from Lake Kitangiri to distant market!' like Singida and Shinyanga. 31

34 GENERAL DISCUSSION It is common experience that an excessive fishing effort such as that on Lake Kitangiri results in a decline in catch, catch per effort and the mean size of fish being caught. Basically a fisheries manager wants to maximize biomass yield which is a prod uct of number of fish being harvested and their average weight. It is important to distinguish biomass yield from standing crop and productivity. Standing crop is the biomass present in the population at any time we happen to measure it and productivity is a measure of energy flux per unit area per unit time. In order to manage the Lake Kitangiri fisheries on a maximum sustained yield basis, we must keep productivity as high as possible. The fishing gears and the total fishing effort expended on the lake must be adjusted so that the entire productivity can be cropped as biomass yield. There are several ways in which the productivity of fish populations can be regulated: the reproductive rate, mortality rate and individual growth rates. The reproductive rate is influenced through fecundity, the production of eggs or fertility and the proportion of laid eggs that develop into living offsprings. Survival is the proportion surviving at each age group or length group. The individual growth rate governs the biomass productivity. Several factors all operate through each of the above named pathways to regulate productivity. These factors are the fish species (one individual), other individuals belonging to the same species, other fish species of the same genus, fish species of other genera, fqod availability, disease, the fishermen and climatic factors. Some of these factors are densitydependent while others are densityindependent. Note, however, that climate varies in its effects in proportion to the density of fish population. The effect of climate on the success of the Lake Kitangiri has been discussed under the section on climate. The fish itself is an important factor in population productivity because the reproductive rate, mortality rate and growth rate are all agedependent or sizedependent. Therefore, a change in age composition or length composition in response to fishing will have an important effect on all attributes of that population. The fishing gear commonly used on Lake Kitangiri is the gillnet. It is a passive fishing gear for which certain conditions must be satisfied so that the fish should try to swim through it. Development of the Lake Kitangiri fishery would require the fisheries manager to know the properties of this fishing gear. The most important property of the gillnets is that they are made in such a way that they do not look like an impenetrable wall which 32

35 SUMMARY (I) The fish species that are commercially exploited are Protopterus aethiopicus, Clarias mossambic/ls, Tilapia esculenta, Tilapia amphimelas and Tilapia hybrids. The other fish species present in the lake but not commercially exploited are: Gnathonemus sp. Alestes sp. Labeo sp., Barbus paludinoses, Barbus jacksoni, Barbus lineomaculatus, Barbus regersi, Leptogrlanis sp., Schilbe sp., Haplochromis spp. and Hemihaplochromis sp. the fish would avoid. It is essential that the gillnets contrast as little as possible with the surroundings. During experimental fishing in 1972, this property was investigated. Normally, a white gillnet would contrast greatly with the dark surroundings in transparent waters. In the case of Lake Kitangiri with very opaque waters, white gillnets do not form an impenetrable walland therefore catch the Tilapia efficiently. Other colours noted to be effective in catching fish on Lake Kitangiri are bluish and brownish colours. The green gillnets were found to be inefficient in catching fish. Besides visibility, two other factors influence the efficiency of gill nets. One is that the gillnets should be soft and the other is that it should swell as little as possible. Both factors are interdependent and also dependent on the diameter of twines and knots. As the fish swims, it pushes a wave forward. The wave is reflected by any objects (e.g. a wall of gi/lnets) in the water and the return swell is recorded by the lateral line of the fish which operates like a teleprinter. The thicker the twine, the stronger the return swell and the more will the fish try to avoid the gillnet. The gill net twines for use should be made rather fine. Typically the use of gillnets gives the advantage of fish stocks being exploited more selectively than by any fishing gear. On Lake Kitangiri the commercial gillnets are not a passive gear in which fish swim by themselves. The gillnets are set in the morning hours and the fishermen drive the fish into the net by beating on the water with poles. Consequently, the Lake Kitangiri gill net fishery is actually a drivein fishery. This type of fishing destroys the gillnet selective characteristics. Both small and large fish could get caught in a certain mesh size because the fish are entangled in the net through fright. It can be expected that this factor has also contributed to the decline of the Tilapia stocks of Lake Kitangiri. (2) Protopterus sp. and Clarias sp. are mostly caught with hooks on long lines. There has been a steady increase in number of hooks on the 33

36 la ke. Since the stocks of Protopterus and C/arias in the lake have a limit, we should control the number of hooks used by each of the fishermen in order to avoid overharvesting. (3) All the previous studies on Lake Kitangiri fisheries suggested the use of gill nets with mesh size greater than 88.9 mm in order to avoid the capture of immature Ti/apia spp. But if the fishermen are to obtain economic gains from the fishery, the optimum mesh size for use is mm. (4) The gillnet is a passive gear with very beneficial selective characteristics. Unfortunately the drivein fishery which exists on Lake Kitangiri more or less destroys the gillnet selectivity characteristics. It is therefore recommended that the beating of water with poles be discouraged and stopped. (5) There is need for provision of stable fishing canoes to replace the unstable bottle palm dugout canoes which are currently being used and which are very risky to operate. (6) The fish processing facilities on Lake Kitangiri are still inadequate. Most of the fish is sun dried, Since sun drying is very difficult during the rainy season, most fishermen carry out intensive fishing during the dry season, Concentrating most of the fishin'g effort in anyone season instead of spreading evenly this effort over the whole year could damage the age structure of the exploitable stocks. (7) There are considerable fluctuations in the volume of water of the lake. The feasibility of regulating the water loss through the effluent Sibiti river should be investigated by the Water Development Department. (8) Dammi'ng the Sibiti river is an expensive undertaking and therefore, the Rural Development Bank of Tanzania should be asked to assess the economic feasibility of such a project. Literature Cited ANNUAL REPORT (1965). Ministry of Natural Resources and Tourism, Fisheries Division, 1965 Annua/ Report, Tanzania. ANNUAL REPORT (1970). Ministry of Natural Resources and Tourism Fisheries Division, 1970 Annua/ Report, Tanzania. 34

37 LOWE, MCCONNELL R.H. (1956). Observations on the biology of Tilapia (Pisces: Cichlidae) in Lake Victoria. East Africa. EAFFRO. Supp. pub. I: 172. TALL/!':G, J.F. and TALLlNG, LB. (1965). The chemical composition of African lake waters. Int. Revue ges. Hydrobio/. 50, 3, WELCOMME, R. L. (J 966). The effect of rapidly changing water level in Lake Victoria upon the commercial catches of Ti/apia (Piscess: Cichlidae). In: Obeng (ed) 1969; Manmade Lakes. The Accra Symposium, Ghana University Press, Accra. FEEDING AND FECUNDITY OF HAPLOCHROMIS GUIARTI AND HAPLOCHROMfS OBESUS BASASIBWAKI, P. INTRODlJCTION Hap/ochromis guiarti is one of the predatory Hap/ochromis species thought to have evolved from one or more insectivorous species. Within Hap/ochromis species flock of Lake Victoria H. brownae seems to provide annectent feeding habits and certain anatomical details linking the generalised insectivores with anatomically least specialised piscivores, that is, it bridges the gap between the insectivorous species and H. guiarti, another "generalised" predator but' at a slightly higher level of differentiation where the early stages in the development of an "extreme" predator type characters are still preserved GREENWOOD (1962). H. guiarti may therefore represent an ancestral type from which the "extreme" predator group (or groups) might have evolved mainly by modifications in the anatomical characters which involved (J) an increase in adult size (2) differential lengthening in the neurocranium (3) narrowing of the entire neurocranium and a decrease in its length and (4) development of unicuspid curved and often strong teeth. Like H. guiarti, H. obesus is thought to have evolved from an insectivorous species but the structural specialisation took different lines that included a large and extensible jaw, associated with a great reduction in the oral dentition which is deeply embedded in the oral mucosa. It is proposed GREENWOOD (1964) that the mouth brooding parental care practised by Hap/ochromis, coupled with continuous breeding, led to the evolution of such species as H. obesus that prey exclusively on the embryos and larvae from the mouths of female fishes. 35

38 FISH ING OPERATIONS Fishing operations were conducted in the inshore areas using gillnets whose mesh sizes ranged from an inch to three inches. The gillnets were set in the afternoon (around 3 p.m.) and then collected the following morning (around 10 a.m.) once or twice every week. Beach seining was conducted early in the morning (around 9 a.m.) and, at times, in the afternoon (around 3 p.m.) using a beach seinenet of a half an inch mesh. Beach seining was done at least twice a week. FEEDING HABITS Feeding habits of both H. guiarti and H. obesus slightly overlap and very briefly GREENWOOD (1959, 1962) mentioned these habits in his taxonomic studies. H. obesus is a predator but, more precisely, it is an embryolarval feeder preying exclusively on the em bryos and larvae of fishes especially the Cichlid group. The species is distributed in shallow breeding areas of fishes because of its feeding habits. Table I shows the quantities of fish embryos (defined as nonmotile zygotes) and fish larvae (defined as motile zygotes) recovered from the stomachs of H. obesus. It is evident that the embryos constitute a greater portion of the diet than do the fish larvae. This is probably because, firstly, there are more embryos than the fish larvae (operation of mortality from the embryo stage to the larval stage) and, secondly, it is easier to prey on the fish embryos (immobile) than on the fish larvae (mobile). The third reason could probably be related to the digestibility of both types of the diet. More quantities of digested fish larvae than digested fish embryos are encountered in many stomachs of H. obesus. Table I data examined as the quantity of food (number of embryos plus number of larvae) against the body weight shows a faint positive relationship indicating a slight increase in the predatory habit as the fish grows larger. It was found that the prey larvae never exceeded 13mm total length. H. guiarti was found 10 have a varied diet. Stomach analysis and aquaria observations in~icated that fish diet especially young Cichlids and insects mainly termites constituted the main diet. Occasionally stomachs were found filled with insects. In this particular case the insect eating habit could be considered as a facultative response to a sudden abundance of readily available food. 36

39 Table I: Number of fish embryos and fi sh larvae recovered from the stomachs of H. obesus of various sizes. Weight Number of Number of Total number of Fish Embryos larvae of embryos (gm) and larvae IS IS 73 IS IS SO SO 82 II II

40 FECUNDITY Fecundity studies were carefully followed for a period of only five months from July to November. The ovaries from "ripe" and "riperunning" females were removed and split longitudinally and then turned inside out to assist the penetration of the preservative, Gilson's Fluiddescribed by RICKER (1971)whose composition was alcohol (60 %), nitric acid (80 %), glacial acetic acid, mercuric chloride and water. The mixture hardens the eggs and liberates them by breaking down the ovarian tissues. Fecundity distribution of both species is shown in Table II. BREEDlNG Table II shows the proportion of the breeding H. obesus and H. guiarti females for a period of five months, from July to November, 1972, in the Northern parts of Lake Victoria close to Jinja. The percentage of breeding H. obesus (fish in ripe or ripe running or spent condition) ranged from 24% in July to 60% in October and H. guiarfi ranged from 37% in September to 50 % in July and August, both species showing that, on the average, more than 40 % females (H. obesus=46 %), and H. guiarfi=44 %) breed every month for the period considered. Table It. The percentage of females breeding in H. obesljs and H. gulartl from July \0 November. H. OBESUS H. GUIARTI Month Total Tolal 0' I number of Number of /0 number of Number of females females females females females caught breeding breeding caught breeding % females breeding July AuguSl September October November

41 REFERENCES GREENWOOD, P.H A revision of the Lake Victoria Haplochromis species (Pisces, Cichlidae). Part III. Bull. Sr. Mus. Nat. Hist., Zool. 5 No.7, GREENWOOD, P.H A revision of the Lake Victoria Haplochromis species (Pisces, cichlidae). Part V. Ibid. 9: No.4. GREENWOOD, P.H Explosive Proc. Roy. Instn. 40, No. J 84, speciation In African Lakes. RICKER, W.E Methods/or Assessment 0/ Fish Production in Fresh Waters. Second Edition P IBP Handbook No.3. Blackwell Scientific Publications Oxford and Edinburgh. EXPERIMENTAL FISHERIES SURVEYS IN SOME EAST AFRICAN LAKES OKORIE, 0.0. INTRODUCTION During May 1972 experimental fisheries surveys were carried out in the littoral shores and bays of Lake Victoria notably off Mwanza (Kamanga Bay) in the South, and 6ff Bukakata (Luku Bay, Nabisukiro Channel) in the north west (Fig. I). In July and August similar surveys were carried out in Lake Baringo (Fig. 2) Kenya, and in Nyumba ya Mungu Dam near Moshi (Fig. 3,) Tanzania. These preliminary surveys were intended to provide the basic information required for the formulation of a detailed ecological sampling programme to be carried out on the fisheries of these water bodies. Information was collected on the characteristics of the population structure of the various fish species caught. The efficiency of the various gears used was ascertained, and various ecological zones were delimited as future permanent sampling areas. MATERIALS AND METHODS Two fleets of identical multifilament nylon gillnets were used. Each fleet was made up of II gillnets of graded meshsizes in approximately ~" increments from 2" to 7" tied end to end and set to sink. Both fleets were fished simultaneously in different locations within the same sampling zone. The nets were set in the late afternoon and lifted very early the next morning. 39

42 In the Mwanza region of L<lke Victoria one of the 25 HP trawlers was used to obtain an estimate of the efficiency and usefulness of this gear for ex perimental sampling vis a vis the multifilament gill nets. All the fish taken from the gil1nets were sorted out <lccording to the fleet and meshsizes in which they were taken, and then separated into the various species. A note was made of the total number and weight of each species caught in a given meshsize. For each fish the sex, length (Standard) and weight were recorded. The state of maturity of the gonads was assessed according to a scale modified from that proposed by NIKOLSKY (1963) as follows: I and II Immature and Resting stages Sexual products have not yet begun to develop; gonads of very small size; eggs not distinguishable to the naked eye. III Maturation Eggs distinguishable to the naked eye; a very rapid increase in weight of the gonad is in progress; testes change from transparent to a pale rose colour. IV Maturity Sexual products ripe; gonads have achieved their maximum weight, but the sexual products are still not extruded when light pressure is applied on the belly. V Ripe but not running Sexual products are extruded in response to very light pressure on the belly. VI Spawning Sexual products running (that is extruded involuntarily). vrr Spent Condition Sexual products have been discharged; gonads have the appearance 40

43 of deflated sacs { the ovaries usually containing a few Jeft over eggs and the testes some residual sperm. The number of fish of each species in the same maturity stage in each sample was noted. The stomach of every fish caught was examined. In order to estimate the degree of fullness of each stomach, points were allotted as follows (slightly modified from BALL, 1961). Empty Stomach collapsed no food present o point Trace Trace of food present. i point t full Food occupying about onequarter of the total volume of the stomach. I point! full Food filling about half of the total volume of the t full stomach. 2 points Food occupying about three quarters of the total volume of the stomach. 3 points Full Stomach completely filled with food. 4 points The number of points allotted to each species was then totalled for each sample, and the mean number of points per stomach calculated. The resulting figure is termed the "Fullness Index" and this gives an estimate of the feeding intensity of the fish at the time of sampling. The percentage of empty stomachs in each sample was also computed. Examination fo'r parasites was carried out macroscopically in the field, attention being focussed on the endoparasites of the gillnetted fish specimens. Parasites were isolated from the pericardial cavity and the intestinal tract. A record was made of the incidence, type, location and number of any parasites found on each fish. RESULTS I. Lake Victoria (Off Blikakata) Two areas (Luku Bay and Nabisukiro Channel) were sampled on four consecutive days in May 1972 (Fig. 1). The details of the catches in the multifilament gill nets are shown in Table I. Five Ti/apia species were caught namely, T. escu/enta, T. zillii, T. variabilis, T. nilotica and T. /eucosticta. Other species of fish sampled included Hap/ochromis, Schi/be, Protopterus Barbus and C/arias. 41

44 FIGURE I 200 /,r!~ _. T n;'nti~" ~ ~ (PADDY4) (PADD / ~ ~.' ~~ ~l' ~,ucosljciq(pa '" ~... _.'...,.' _~ T I DDY 4' ~ 150 / /. ""li", [, ~ / / /::../ :I:... /~ // /' <:> z ~/C.;:/' PAOO'" w 100 "/",,,11,/11 WATER LEVEL ' FLUCTUATiONS ;/// /., FLOODED FIELDS 60!. I I I,, NUMBER OF DAYS AFTER STOCKING THE PADDIES twater ONLY IN TRENCH

45 T. nilo/iea were caught in all of the eleven different meshsizes, whilst the majority of the rest of the species were caught in meshsizes between 2.0" and 4.5". The size ranges of the Tilapia species and their sex ratios are shown in Table II. 50 % of the stomachs of both the Ti/apia nilo/iea (64 fish examined) and Tilapia variabilis (22 fish sampled) were empty, and for both the 'Fullness Index' was 2 indicating an average degree of feeding intensity. The smallest mature female Tilapia nilo/iea was 22.5 cm. and spawning fish were found in all but the Tilapia zillii and Tilapia eseulen/a (Table JII). 2. Lake Vic/aria (Off Mwanza) Both the trawling and gill netting operations were carried out near Kamanga Bay (Fig. I). The details of the catches are shown in Table IV Of all the Tilapia species introduced into Lake Victoria only Tilapia niloliea were evident in the samples, and of the endemic species Tilapia eseulenla predominated in the trawl catches even though none was caught in gijlnets. 50~~ of the total catch of Tilapia csculen/a were females (66 fish sampled) and of all the stomach samples examined 42 % were empty (Table V) with a 'Fullness Index' of 2 (1 empty). Spawning fish were found only in Tilapia eseulcnla (33 % of the females and 17 % of males. Table VI). The smallest mature female was 19.5 em. and male 18.0 cm. The smallest mature female Tilapia nilo/iea caught was 22.5 em and the male was 23.0 cm. 3. Lake Baringo Three ecological zones were delimited for the purpose of the sampling programmethe south, central and north zones (Fig. 2). Sampling was carried out in August 1972 in all three zones. The details of the catches are shown in Table VII. Tilapia nilo/iea were caught in all but the 6.5" mesh size from all the three zones. However catches of Tilapia nilo/ica per net were better in the northern zone. Catches of Bm'bus and Clarias decreased progressively from south to north. For both Tilapia nilo/iea and Barbus gregorii male and female were in about equal numbers (Table VII). The smallest mature female and male Tilapia nilo/iea sampled were 12 and 17 em. respectively, and only 4 out of 122 females caught were in spawning condition (Table IX). Two endoparasites were isolated from Tilapia nilo/iea and only one from Barbus. Clarias had no parasitic infection. A nematode (possibly Conlraceacum sp.) and a trematode (unidentified) were found in the pericardiai and abdominal cavities of the infected Tilapia nilo/ica, Only 43

46 o )~;.;;;,,,,, O'.,~rw "<1~! SAl 1.40 (f. \ )6'0' FIG. 2, N 1 LAKE BARINGO SCALE,' SO..Q.Q.Q LOIYAMARO~'i //' I \J I (/ ~l \" NORTH \ ZONE l. ll "o:j" r? 'fi' ()S_,~ V... I, """" It. d. Se"fNTRAL~ '0'.0 "I'Dltl\ l:0u,.lno PlCII'H ZONE /', e". l$ll,"o.', 0", "" _ (...,... t:t.:7'iu' L. ".". NJEMPS,>1 i I ~~ ~../// :;'~I, I."." 'llhd

47 the nematodes were identified from the gut of Barbus, The average number of the nematode and trematode found in the Tilapia nilotica was 4 and 2 respectively. The gut and other related organs in the Barbus were completely invaded by the nematode worms, each fish harbouring over a thousand worms in the musculature of these internal organs. 1t is significant that 100% of the 49 Barbus stomachs examined were empty. (Table VIIJ). 4. Nyumba ya Mungu Dam Nyumba ya Mungu Dam, a manmade lake near Moshi in Tanzania was sampled in July Four sampling areas were chosen namely, the Dam site, Kambi la Dagaa, Magadini and Korogwe (Fig. 3). Details of catches are shown in Table X. Three species of fish were caught; Tilapia pangani, Labeo, and Synodontis, of these Tilapia pangani forms the main stay of the commercial fishery. The smallest mature female and male were 16 and 21 cm. respectively and only I spawning female was identified (Table XII). Endoparasites identical to those found in Lake Baringo (the Contracaecum sp.) were also isolated from the pericardial cavity of the Tilapia pangani. The average number of parasites per infected fish was 8. (TableXI). DISCUSSION The surveys indicated very poor catches in gillnets especially in the northwestern shores and the Mwanza Gulf of Lake Victoria. It is thought that the Tilapia stocks have developed "net avoidance" tendencies. The significance of this "netavoidance" phenomenon was apparent during the simultaneous gillnetting and trawling operations. The marked difference in biometric characteristics between the vibrant Tilapia nilotica stocks in Lake Victoria and the stunted population in Lake Baringo can be attributed to the widely different ecological conditions in these two water bodies. This aspect of the study is well amplified in the comprehensive technical paper being published on certain aspects of the ecology of the Lake Baringo fishery. In both Lake Banngo and Nyumba ya Mungu Dam an attempt was made to delimit the total areas of distribution of the commercially important fishes, and to establish the behaviouristic and ecological determinants of these general limits of distribution. Whilst in Nyumba ya Mungu Dam 45

48 MAP OF NYLM!A VA MUNGU DAM SHOWING SAMPLING AREA S r... ~ \, \ \ " '\I(jlo...."" 0 SofnGroVO : ARUSHA CHIN! KilOl'II SiMI...O... DIHI~.. "_ M,1o.CKfI'''' E'I.U ; ;, ~ M ASAI : ~ NORTH STEPPES MOUNTAINS K" "" 001 fl oy1 IoIoi\RoGds... EI.C1rjc"~uionTl'Qc, ~_. t=::::::::l "#,.;... e S~ILLW"'V NOTE. SurlQ(1 "',ea 17,000 Ac'" Of ~.qjlolll... j1501<!..,lom"...1 SlOfQ" 'l'dtuly'4 no,ooo,ooo.ooo..,.. GeMor..'.l\".OCKl,OCl)Cu.~I"

49 for instance differential distribution of the predominant Tilapia pangani was not immediately apparent from catches in the four sampling areas, the reverse was the case in Lake Baringo. Here, best catches of Tilapia nilotica were made in the northern zone; 8Q1'bus were caught in the south and central zones, and Clarias were confined to the south zone. Parasitic incidence (Contracaecum sp.) was identified in the Tilapia populations of Lake Baringo and Nyumba ya Mungu Dam (both Rift Valley lakes with resident aquatic bird populations). In both lakes practically all the fish examined were infected. In the case of the Lake Baringo Barbus these parasites completely invaded the gut and other associated organs, but inspite of this adverse pathological disintegration of the musculature of these infected internal organs, the fish were still in very good condition. Clarias were not infected. In lakes Baringo, Naivasha and Nyumba ya Mungu Dam further comprehensive monthly ecological sampling programmes were instituted as from August 1972 for a twelve month period. It is hoped that analysis of the data at the end of this extended survey would throw more light on the biology and other facets of the exploitation of the fishery of these lakes. Literature Cited BALL, J.N. (1961): On the food of the brown trout of Llyn Tegid. Proc. Zool. Soc. Lond. 137 (4): NIKOLSKY, G.V. (1963): the Ecology offishes London: Academic Press 352 p. Table II: Lake Victoriaoff Bukakata. May 1972Experimental Fisheries Survey. Size range wi. range No. of No. of Fullness Species (em) (g) females Males Index %of empty Stomachs Tilapia nilo/ica Tilapia variabilis Tilapia leucos/ic/a Tilapia zillii Tilapia esculenta

50 Table III: Lake Victoria{Off Bukakata)May 1972Gonad Condition. Species Size range (cm) Nos. of fish in each stage of sexual maturity II III IV V VI VII Tilapia nilotica female male II Tilapia variabilis female 132J 4 3 I 2 male I Tilapia leucosticta female 1719 I I I male I Tilapia zillii female I I male Tilapia esculenta female 2230 I I male Table V: Experimental Fisheries Survey Mwanza GulfMay 1972 Size wi. No. of No. of Fullness,%ofempty Species range (cm) range (g) females males Index stomachs Tilapia esculenta Tilapia variabilis I 9 I 60 Tilapia nilotica

51 Table J: Lake Victoria (Off Bukakata) Summary of Catches May, 1972.j>. '0 I Sampling I Species Area Luku Bay Nabisukiro Luku Bay Nabisukiro Luku Bay Nabisukiro Luku Bay Nabisukiro Luku Bay Nabisukiro Luku Bay Nabisukiro IT. escu/en/a I I I I T. zi//ii T. variabi/is T. ni/o/ica T. /eucos/ic/a Hap/ochromis Schi/be sp. Luku Bay Nabisukiro Pr%p/erus sp. Luku Bay Nabisukiro Barb"s sp. Luku Bay Nabisukiro Clarias sp. I Luku Bay Nabisukiro Gillnets (mesh sizes in inches) 2.0 2,5 3., , no. w!. no, w!. no. W!. no. w!. no. w!. no. W!. no. W!' no. W!. no. W!' no. W!' no, w!.1 40 l' I ~ I~ I' '00 I I ~ 210 I I , I I I I I J 3.00,, I 550 II 3.25 I II I ' I I 1550 I I I I I I, 150 I~ I I I I I 80 I 1 20 J I II 801 I I I I 2 ]02 1, II II I I I 5000 I I I, I 5450 I I I I I 450 I I I II I I I I I 2600 I I I I 3.150

52 Table IV: Summary of Catches Mwanza GUlfMay, 1972 Experimental Gears Species Trawl Gillnets (mesh sizes) 2.0" 2.5 " 3.0 " 3.5 " 4.0 " 4.5 " 5.0 " 5.5 " 6.0" 6.5 " 7.0" ~ Ti/apia ni/o/ica no. 7 I 1 wl.(g) Ti/apia escu/en/a no. 66 wi Tilapia variabi/is no I I wi Hap/ochromis sp. no I wi C1arias sp. no wi Pr%p/erus sr. no wi Barbus sp. no. I 1 wi Bagrus sp. no. 5 wi ScM/be sp. no wi A/es/es sp. no. 1 wi. 70

53 Table VI: Experimental Fisheries SurveyMwanza GulfMay 1972 Gonad Condition Species Tilapia exculenla female male Tilapia variabilis female male Size range (cm) Nos. of fish in each stage of sexual maturity II IJI IV V VI VII I II 13 II I Tilapia nilolica female male IX: Lake Bartngo Gonad ConditionAugust 1972 Species Size range Nos. of fish in each stage of sexual maturity II III IV V VI VII Tilapia nilolica female male Barbus gregorii (South zone) female male Table XII: Gonad Conditionjuly 1972Nyumba ya Mungu Dam Species Tilapia pangani Size range (em) Nos. of fish in each stage of sexual maturity II III IV V VI VII female male I 51

54 Sampling Area Table VII: Summary of Catches, Lake Baringo, August, 1972 Gillnets (mesh sizes in inches) Species no. wi. no. wt. no. wi. no. wt. no. wt. no. wi. no. wi. no. wi. no. wt. no. wt. no. wi. Tilapia nilotica South zone Central zone North zone Barbus sp. South zone Central zone I, I v North zone I I.) Clarias sp. South zone I Central zone I North zone Table VllI: Experimental Fisheries Survey, Lake Baringo, August, 1972 Size range WI. range No. of No. of Fullness % Empty IAverage No. of para Species I (em) (g) females males Index Stomachs sites per fish Tilapia nilatira I I Nematodes 4 (South zone) (South zone) Trematodes 2 Barbus gregarii I 1361 I I 27 I 22 I very heavy infestation (South zone only)

55 ~ Table X: Nyumba ya Mungu Dam, Summary of Catches, July, 1972 Gillnets (mesh sizes in inches) Sampling area Species no. wt. no. wi. no. wi. no. w!. no. w!. no. w!. no. w!. no. w!. no. w!. I. Korogwe T. pangani LabM sp. Synodonlis I 270 I 120 I 490 Vl.~ 2. Magadini T. pangani Labeo sp. Synodon/is I I Kambi la Dagaa T. pangani Labeo sp. Synondon/is II 2250 I 240 I Dam site T. pangani Labeo sp. Synondon/is I 750

56 Table XI: Nyumba ya MunguDam July, 1972 Sampling Area Species Size range (em) Wt. range (g) No. of females No. of males Fullness Index % of empty stomachs Average No. of parasites per fish Dam Site Tilapia pangani v, +: Kambi la Dagaa Tilapia pangani ~ Korogwe Magadini Tilapia pangani Tilapia pangani ~ I ~

57 RICIPISCULTIJRE EXPERIMENTS AT AMERO IRRIGATION RESEARCH STATION HENDRIKS, J. AND ENDERLEIN, O. INTRODUCTION For centuries ricipisculture has been practiced in Asia (JapanChina) on an economical basis (HICKLING, 1971). In many parts of East Africa the climate is suitable for rice growing and there is a great need for animal protein. Very little work has been done in Africa. It was felt that some research into ricipisculture should be conducted. Therefore a small observation trial was done at the Ahero Irrigation Research Station. MATERIAL AND METHODS The trial was done in 4 square rice paddies each of 750 m 2 On three sides a trench was dug I x I m making the total area of each paddy 890 m 2 This trench would serve as a refuge for the fish when paddies were drained. It was decided that the growing period of the fish should be two growing periods of rice (approx. 250 days). To obtain a maximum number of observations the trial was composed of four treatments. Paddy I: Rice + Tilapia nilotica (Linne) 2: Rice+T. leucosticta (Trewavas) 3: Rice without fish 4: No rice+half the weight of stock fish T. leucosticta+half T. nilotica (stocking data see table I). Each paddy that was stocked received a total of 2.5 kg. stock fish (between 7 and II cm.). The fish came from different ponds in the Kisumu area. Fishing of the ponds was done twice. The first time with a special seine net (mesh size 10 mm.) just after harvesting the rice when the fish were all in the trench (not all fish were caught). The second fishing was done after the second rice harvesting. This time the trench was pumped empty by a motor pump and all fish were caught. 55

58 Rice: Variety Basmati 217 Fertilizer: one application of 52 kg. P205/ha (single superphate of ammonia) Drainage: 90 days after transplanting Harvest: 100 days after transplanting Insecticides: 8, 30, 50 and 70 days after transplanting with Dimecron 50 against insect damage. RESULTS Fish: The data obtained from the seining (paddy I and 2 the 24th of August, and paddy 4 the 25th August 1972) and the final draining of the paddies (paddy I the 15th of January, 2 the 16th of January, and 4 the 22nd of January 1973) are shown in table 2. The wild fish Clarias mossambicus (Peters) did not show up until the draining of the paddies because they went down in the mud of the trench and escaped the seine net. They must have entered the paddies during irrigation which is conducted each week. The growth of the Tilapia is shown in diagram 1. Rice: Rice yields in kgiha* Rice+ Til. nil. Rice+ Til. leuc. Rice without fish Crop I Crop Average "Note. To come to figures that are economically comparable, the yield for the paddy with fish is calculated over the total area= The yiejd for rice paddy is calculated over the inside area= when comparing the yields calculated over the same area= figures are as follows: Rice+7 Til. nil. Rice+TiI. lei/c. Rice without fish Crop J Crop Average * Comparing these actual yields it is found there is a difference in yield between the rice with fish and the rice without fish of about 400 kg/ha which may be an indication that the fish has a beneficial effect on the yield. (CaCHE, 1967, HICKLING 1971). 56

59 Fi 1.'.~ ENYA Nobisukiro Chamel Mwonzo Gulf (J(omanoo Boy) 'OOkm.!, I MAP OF LAKE VICTORIA SHOWING SAMPLING AREAS 1 & 2

60 DISCUSSION Fish: The experiment has been a bit biased by the infiltration of Clarias into the paddies but still it can be said that (a) T. nilotica did better than T. leucostica, (b) at the moment it is not economical to grow fish and rice together because of the high costs to build and maintain the trenches but it may be feasible in the long run. Estimated price for the catch of each paddy (beach price) in Kenya Shilling (I U.S. $=7.14 Kenya Shs). Paddy Small fish Big fish C1arias Total I , Total per ha Further experiments might be done with other species of fish or fish combinations that can give a higher yield per ha. than what has been obtained here. One combination might be to have Clarias mossambicus as the main fish and Tilapia nilotica to produce fry on which Clarias can feed *. The problem with Bilharzia must also be considered. Today the water that goes into the irrigation canals is sprayed every three months with FRESCON, a molluscicide that also kills fish. If a rice culture is to be considered on a bigger scale the Bilharzia problem also must be solved in any other way. than today. A possible way to solve that may be with Astatoreochromis alluaudi (HYTHON, unpublished) which is a good mollusc eater. As can be seen in the above table the amount of small fish is lowest in paddy number one which had the highest amount of Clarias in weight and mostly fry were found in paddy number four (especially a high catch the filst seining) that also had the lowest content of Clarias in weight. 58

61 Month Temperature max. min. ph value January February March April May * June July August September October November December * Average *The highest ph occurred when the paddies were drained and water remained in the trench. Literature CaCHE, A.G. (1967)Fish Culture In Rice Fields A WorldWide Synthesis. Acta Hydrobiologica Hyrographica Et Protistologica 30: 144. HICKLING, c.f. (197 L)Fish Culture, Faber and Faber, LONDON pp

62 Table I: Data of Fish and Rice Fish Data Rice Data Rice paddy No. Date of stocking fish Number of fish Number ha weight of fish kg weight kg/ha Type of fish Transp!. rice 1st time Drainage 1st time Harvest 1st time Transp!. 2nd lime Drainage 2nd time Harvest 2nd time 1 5/5/72 15/5/72 17/5/72 29/6/72' T. nilolico " " " 14/4/72 12/8/72 14/9/72 14/10 111/73 13/1/73 0 o /5/72 12/5/ T. leuco51icla " 14/4/72 12/8/72 4/9/72 14/10 1/1/73 13/1; /4/72 12/8/72 4/9/72 14/10 1/1/73 13/1 / /5/72 12/5/72 15/5/ T. leuco51 ioa " T. ni/olica 12/8/72 1/1/ 'By mistake this paddy received few fish at the first stocking and thai was compensated on the 29/6/72.

63 Table II: Fish caught Rice paddy No. I Date I Type of fish Number Stocked fish Weight Average kg length Survival Rate% Fry INumberlweight kg Wild fish 1* I Yield Numberl Weight I kg kg kg I Yield kglha 1. I Stocking 24/8 15/1 T. nilolica " " I I o58[ 2 \2 I Total minus the the stocking I I I j I Stocking 24/8 16/1 I Stocking 25/8 22/1 T. feucoslica " ", T. nilolica T. feucoslica I T. nilolica T. feucoslica I T. nifotica T. feucostica I [ \ I I Average I I ' 180 I I ,57 Total minus the stocking ~I I I I 2\ 3.54 Total minus the stocking, I I I I I 159 I 282 *I Clarias mossoll7bicus *2 Estimated from random samples of the catch.

64 VISITORS As in previous years, EAFFRO continued to attract interest from International, national and local institutions. A large number of visitors called at EA FFRO for various reasons and it is of special interest to record that three Hon. Ministers visited EAFFRO during the year viz. Hon. W. Rwetsiba, East African Community Minister for Research, Communications and Social Services, Hon. Al Noor Kassum, East African Community Minister for Finance and Administration and the Hon. William Banage, Uganda Minister for Animal Resources. During the latter half of the year, the East African Community, Deputy Minister for Research Hon. S.B. Tambwepaid a visit to EAFFRO. Similarly the Hon. Members of the East African Legislative Assembly in the company of the East African Community Officials paid a visit to EAFFRO. The Hon. Ministers as well as the Hon. Members of the East African Legislative Assembly were shown around and taken on experimental fishing trips on the lake during which modern fishing gear proposed for use in Lake Victoria was demonstrated. EAFFRO was also fortunate to be host to a team of Community Commissioners (Members of the Community Service Commission) when they paid a visit to EAFFRO during the year. A comprehensive list of visitors to EAFFRO during 1972 is given below: A LIST OF VISITORS TO E.A.F.F.R.O. JANUARY Mr. W. Wafula Mr. B.W. Brauer Mr. W.L. Masengeta Mr. A.O. Obota Mr. L.J. Okot Mr. D. Kitching Mr. George Corry Mr. F. Byabato Mr. A.J. Mukins Mr. G. Gulbransen Mr. D.G.L. Ringby East African Community, Arusha Department of Marine Biology, University of North Carolina, U.S.A. East African Community, Arusha East African Community, Arusha East African Community, Arusha Overseas Development Administration, London East African Veterinary Research Organization, lv[uguga East African Community, Arusha Parkins Engines Groys, PeteJ'brough FAO/Rome Parkins Engines Ltd., Peterborough, U.K. 62

65 Mr. D.S. Mehta FEBRUARY Mr. Justina Maclean Mr. B. Kenney Mr. J.e. Early Dr. H. Nagtegaal Mr. G.K. Mukasa Mr. B. Mayboon Mr. J. MigudaAlila MARCH Hon. J.J. Ferunzy, M.L.A. Mrs. A.J. Ferunzy Hon. William Rwetsiba Mr. Al Haj Iddi Kateta Mr. H.F. Henderson Mr. M.T. Abwzzo Mr. e.o. Graham APRIL Mr. A.G. Woodland Mr. G. Christensen Mr. C.H. Clay MAY Mr. J.e. Aime Mr. R.E. Stout Mr. M.R.M. Mutabihirwa Mr. Saidi Ndika Mr. Arnold Omondi Mr. R.S. Walker Mr. K.H. LloydDavis Mr. J. Wanyonyi Hon. Orinda Sibuor, M.L.A. Mr. M.N. Grey Hon. AI Noor Kassum Hon. J.S. Ferunzy Farm Machinery Distributors, (U) Ltd., Kampala Fellowships FA.O./Rome Ministry of Animal Resources, Kampala FA.O. Fisheries, Rome l)ureau of International Projects TNO, the Hague, Holland Ministry ofplanning, Entebbe Fisheries Laboratory, Netherlands East African Community, Arusha East African Legislative Assembly, Mombasa East African Community Minister of Research Communications and Social Services East African Community, Arusha FA.O./Rome US. Department of State, Washington US. Department of State, Washington F.A.O./Rome FA.O./Rome FA. 0./Rome UNDP, Arusha UNDP, Kampala Fisheries, Dar es Salaam Fisheries Department, Mwanza Fisheries Headquarters, Nairobi Fisheries Department, Entebbe Animal Feeds, Jinja East African Community, Kampala East African Legislative Assembly Kampala East African Community Minister for Finance and Administration Member, East African Legislative Assembly 63

66 fast AfRICAN COMMUNITY

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