ISSN AQUACULTURE SECTION

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1 ISSN AQUACULTURE SECTION Review of techniques and practices in controlling tilapia populations and identification of methods that may have practical applications in Nauru including a national tilapia plan by Romeo D. Fortes, Ph. D. Secretariat of the pacific Community Noumea, New Caledonia

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3 REVIEW OF TECHNIQUES AND PRACTICES IN CONTROLLING TILAPIA POPULATIONS AND IDENTIFICATION OF METHODS THAT MAY HAVE PRACTICAL APPLICATIONS IN NAURU INCLUDING A NATIONAL TILAPIA PLAN Submitted to: TIM ADAMS Director, Marine Resources Division Secretariat of the Pacific Community (SPC), Marine Resources Division, BPD , Noumea Cedex, New Caledonia Prepared by: Romeo D. Fortes, Ph. D. Consultant, Secretariat of the Pacific Community (SPC), Marine Resources

4 Copyright Secretariat of the Pacific Community, 2005 All rights for commercial / for profit reproduction or translation, in any form, reserved. SPC authorizes the partial reproduction or translation of this material for scientific, educational or research purposes, provided that SPC and the source document are properly acknowledged. Permission to reproduce the document and/or translate in whole, in any form, whether for commercial / for profit or non-profit purposes, must be requested in writing. Original SPC artwork may not be altered or separately published without permission. Original text: English Secretariat of the Pacific Community Cataloguing-in-publication data Fortes, R. D. (Romeo) Review of techniques and practices in controlling tilapia populations and identification of methods that may have practical applications in Nauru including a national tilapia plan / prepared by Romeo D. Fortes (Aquaculture Technical Paper / Secretariat of the Pacific Community) 1. Mozambique tilapia Government policy Nauru. 2. Introduced organisms Environmental aspects Nauru. 3. Aquaculture Environmental aspects Nauru. 4. Nile tilapia Control Environmental aspects Nauru. I. Title. II. Secretariat of the Pacific Community. LC AACR2 Agdex Pacific Islands 492/679 ISSN ISBN

5 Executive summary The Mozambique tilapia (Tilapia mossambica Peters=Oreochromis mossambicus Peters=Sarotherodon mossamibics Peters) was introduced in Nauru in 1960 primarily to feed on mosquito larvae (Ranoemihardjo, 1981) and for food (Ben Ponia, Aquaculture Adviser, SPC, New Caledonia, personal communication). Instead, it rapidly became abundant in what are considered in Nauru as lagoons (sunken pools surrounded by mangroves) and ponds (depressions created by bomb craters). It also became an aggressive competitor with milkfish (Chanos chanos Forsskal) leading to the collapse of milkfish aquaculture. The Republic of Nauru then implemented a Tilapia eradication program through FAO in 1979 and 1980 where rotenone was used as the toxicant. When introductions of tilapia in many parts of the (1950 to 1970) similar problems experienced in Nauru were also felt in many countries. However, most countries such as the Philippines continued to regard it as source of food. In the early 1970 s techniques to control their reproduction were developed in the country then applied in aquaculture production. Now, most of the species of tilapia are used in aquaculture. The experiences in many countries that lived through similar problems may be given a second look and may be considered as a means of controlling tilapia in Nauru. The most important tilapias in aquaculture are the Nile tilapia (T.nilotica); Mozambique tilapia (T. mossambica); and the blue tilapia (T. aurea) plus a number of mouth brooding tilapia hybrids used in aquaculture (red T. mossambica hybrids) with T. aurea, T. nilotica, and T. urolepis hornorum including T. galilea and T. melanotheron. These species account for 99.5% of global tilapia production. Nile tilapia now dominates global tilapia aquaculture, accounting for 72% or 474,000 tons in Total world tilapia landings from capture and culture has been estimated at 1.16 million tons with cultured tilapia accounting for 57% of the total (659,000 tons). Cuba is the world s largest producer of blue tilapia. The largest tilapia producing nations are in Asia. China is the world s largest tilapia producer (315,000 tons), accounting for 48% of global production, followed by the Philippines, Thailand, Indonesia and Egypt. The USA is the world s largest tilapia consumer. In some countries like Australia, Nauru, Fiji and Palau complete eradication of tilapia were undertaken. Failure of tilapia culture in the past, has often been due to uncontrolled spawning, thus control measures were developed. There are basically seven (7) methods of controlling tilapia populations that have been carried out in some countries for aquaculture and/or plain eradication purposes. Theses are (1) periodic harvesting of fry and fingerlings; (2) monosex culture of which single-sex fish are obtained through: manual separation of sexes, hybridization, hormone augmentation and genetic manipulation methods such as androgenesis, gynogenesis, polyploidy and transgenesis; (3) culture in cages; (4) high density culture; (5) biological control; (6) sterilization and (7) eradication by means of fish toxicants. While tilapia has tremendous potential as an economic commodity, it has also a significant role to play in environmental biodiversity and impact to a number of economic activity in a number of countries such as Nauru, Australia, Fiji and Palau among others. Thus, general courses of action have been offered to prevent the infestation of undesirable species including tilapia into a country. In general, the principles behind controlling/managing of pests and nuisance species may be considered in controlling tilapia population. Preventive measures, careful surveillance and monitoring coupled with a regular procedure to prevent entry into other water bodies is the preferred approach. The general methods of control are: physical/mechanical, chemical and biological control; genetic engineering, and environmental management and cultural control. 5

6 Applicability of identified techniques to Nauru situation. Before any recommendation of the applicability of the identified methods can be made, it is important to know the situation of the island country in terms of geography, topography, climate, educational status of the citizens, aquatic environment, governance and economy. The Republic of Nauru was described by Wetland International (1990) as comprising a single raised coral limestone island with a total land area of about 2,130 hectares) and a population of 9,100 in 1990.The Republic of Nauru is one of the three great phosphatic-rock islands of the Pacific. The climate is tropical with an annual rainfall averages of 2,000 mm. Streams are non-existent. Agriculture is very limited. There is very little surface water on the Nauru s highly permeable terrain, much the largest permanent water body being Buada Lagoon. Many of the ponds and the two lagoons were used for the rearing of milkfish. Identified processes that may be used in controlling tilapia in the waters of Nauru. Among the seven (7) methods in use for the control of tilapia populations in aquaculture the following techniques may be appropriate and could be applied as soon as possible in controlling the Mozambique tilapia in the natural bodies of water in Nauru. (1) periodic harvesting of fry and fingerlings including the parents; (2) biological control; and (3) eradication of tilapia using organic toxicants and/or other chemicals. The other methods such as monosex culture through manual separation of sexes, hormone augmentation, cage culture, high density culture and probably sterilization may be performed on trial runs using the fry/fingerlings collected in activity number 1. Exercises on manual separation of sexes, hormone augmentation, may be performed. These trial runs may run up to at least one year depending upon the resources availability (manpower, financial and commitment). Implementing strategy for a national tilapia program in Nauru. Sustained control of the Mozambique tilapia from the significant waters of Nauru may be difficult, tedious and could take some time, but may not be too late yet. As suggested earlier, controlling the Mozambique tilapia in the waters of Nauru would need a thorough planning strategy that should at least consider the 5 stages in planning as recommended (Finlayson et al.2000) as follows: a. preliminary planning, where the project concept and alternatives are developed, public input is invited, and acceptance is encouraged; b. intermediate planning, incorporating an environmental analysis where the project is refined and public acceptance is encouraged; c. final planning and project implementation, involving management through the development of project-specific work plans; d. performing the treatment; and e. summation and critique of the project This planning strategy recognizes that responsibility for tilapia control lies with government, community and industry. The plan must be put together after extensive community consultation and should consider opinions from the stakeholders. The goals, priorities and activities in the plan should be identified in meetings with stakeholders using the information available. Also, some additional key issues should be considered during the process, such as: prevention of tilapia infestation is feasible if there is cooperation among the various stakeholders; sustained tilapia control, would be more realistic than complete eradication;

7 It is very important for the participants in the program to be familiar with the ecology and biology of tilapia, and that sustained research into other possible control methods be initiated Tilapia as an economic resource National tilapia plan for the Republic of Nauru. While it is important to eradicate/control the undesirable tilapia species in Nauru, it is also important to consider the desirable hybrid tilapia as an economic commodity in South Pacific. More recent advances in selective breeding and sex control technologies registered the greatest impact. As tilapia has gained in importance as an international aquaculture commodity, so has there been a considerable increase in research effort to improve tilapia stocks. Among these are hybridization, chromosome set manipulations and application of transgenesis. From the SPC Aquaculture Action Plan milkfish (Chanos chanos) and tilapia (Tilapia spp.) have been identified for aquaculture. Table 1. Issues and needs in formulating national tilapia plan for nauru Category Issues Constraints Required actions Institutional, legal and administrative aspects Human resources Demise of milkfish industry commitment by authorities Lack of skilled/technical manpower declining supply of fry Proliferation of Mozambique tilapia Ownership of the areas for fish farming Eradication/control of Mozambique tilapia Review of policies Programs to upgrade skills of technical and extension officers Organization training, seminars and workshops High cost and poor quality of feeds Need for water recycling technologies Consider other species of aquaculture commodities (e.g. hybrid hybrid species, etc.) Technical aspects poor site selection and poorly managed farms; impact on the natural ecosystem; tilapia introduced other than for farming Poor quality of seeds Poor water supply Promotion of polyculture system Research waste management and treatment Undertake research on water recycling technologies subsistence farming has had variable success. 7

8 Table 2. Action plans and objectives of a national tilapia plan for Nauru Action plans Objectives Target beneficiaries Expected results Key areas of concern To eradicate/control Mozambique tilapia To develop utilization techniques for Mozambique tilapia in aquaculture Private sector Fish farmers Government Stakeholders Enable the government and other stakeholders to move on to other aquaculture species Key development areas in lagoon/pond management To formulate an effective management plan for the utilization, protection and conservation lagoons and aquatic ecosystems Government Private sector Stakeholders Formulated utilization and management plan for the aquatic ecosystems for Sustainable resource use production Immediate Plan. In order to commence a project as a strategy to initiate the program of fisheries activities in the bodies of water of Nauru, an action plan for tilapia may be in order. This action plan is divided into three phases as follows: (a). eradication and control of Mozambique tilapia; (b). stocking of lagoons/ponds with carnivorous species to serve as biological control for feral tilapia; and (c). enhancing the productivity of the lagoons/ponds for tilapia aquaculture Trial Runs.Trial runs for the following monosex method in controlling tilapia reproduction may be carried out using the fry/fingerlings collected in activity number 1. Exercises on manual separation of sexes, hormone augmentation, cage culture, high density culture and probably sterilization, may be performed. These trial runs may run up to at least one year depending upon the resources availability (manpower, financial and commitment). 8

9 REVIEW OF TECHNIQUES AND PRACTICES IN CONTROLLING TILAPIA* POPULATIONS AND IDENTIFICATION OF METHODS THAT MAY HAVE PRACTICAL APPLICATIONS IN NAURU INCLUDING A NATIONAL TILAPIA PLAN Romeo D. Fortes, Ph. D. College of Fisheries and Ocean Sciences University of the Philippines in the Visayas 5023 Miagao, Iloilo, Philippines address: telyos@yahoo.co.uk 1.0. Introduction The Mozambique tilapia (Tilapia mossambica Peters=Oreochromis mossambicus Peters=Sarotherodon mossamibics Peters) was introduced in Nauru in 1960 primarily to feed on mosquito larvae (Ranoemihardjo, 1981) and for food (Ben Ponia, Aquaculture Adviser, SPC, New Caledonia, personal communication). Instead, it rapidly became abundant in what are considered in Nauru as lagoons (sunken pools surrounded by mangroves) and ponds (depressions created by bomb craters and/or outcome of phosphate extraction). (Note: According to UNEP/ IUCN (1988) there is no true lagoon in Nauru). The Mozambique tilapia then evolved into an ecological pest and unattractive food fish.. It also became an aggressive competitor with milkfish (Chanos chanos Forsskal) in ponds leading to the collapse of milkfish aquaculture, a traditionally important fish culture activity in this island country the fry of which are just collected from the reef at low tide, acclimatized for 2-3 weeks to lower salinity, then released into these lagoons and ponds. Growth of the milkfish however, was observed to have slowed down, which was attributed on the following as the major raison d être: overcrowding due to the fast rate of spawning of tilapia resulting to massive competition with milkfish and consequently resulting insufficient availability of natural food. Concerned by this, the Republic of Nauru, implemented a Tilapia Eradication Programme through FAO in 1979 and 1980 in which the organic toxicant rotenone, an extract of the roots of tropical plants (the jewel vine or Derris spp. and the lacepod or Lonchocarpus spp. belonging to the bean family Leguminosae) that is commercially available in powder or liquid form, was applied in the aforementioned ponds and lagoons. The introductions of tilapia in many parts of the world happened within the period 1950 to Problems similar to what were experienced in Nauru were suffered by many countries where tilapia was introduced. In the Philippines, when the Mozambique tilapia was introduced in May, 1950, it became a burden to the milkfish industry, it was an ecological pest, nuisance and competitor with milkfish in ponds. However, the Philippine government continued to regard it as source of food because they are easily reared in backyard ponds. In the early 1970 s techniques to control their reproduction were developed in the country then applied in aquaculture production. Now, most of the species of tilapia are used in aquaculture and tilapia production has been increasing each year and becoming more and more a significant part of the aquaculture industry. 1 Consultant, Secretariat of the Pacific Community (SPC), Marine Resources Division, BPD , Noumea Cedex, New Caledonia 2 For the purpose of this report, the genus Tilapia shall be used in all species of tilapia following the idea that all of the tilapias belong to the single genus of Tilapia (Robins et al. 1991). After almost half century of its introduction into Nauru, the Mozambique tilapia in this country may have undergone considerable genetic 9

10 The experiences in the countries that lived through parallel predicament may be reviewed. It is worth knowing what the rest of the world has implemented for tilapia. In the Americas, the Mozambique tilapia was introduced in the majority of the tropical and semi-tropical countries in 1950s and 1960s. In the 1970s, various management practices for the control of unwanted reproduction were applied in North, Central and South America. These practices included use of predators (biological control), monosex culture (through hand-sexing, genetics and hybridization, hormone augmentation (sex reversal), high density culture and sterilization. The Nile tilapia (Tilapia.nilotica) became the dominant culture species. Production of tilapia has grown from near zero to more than 200,000 metric tons annually in the past 30 years. The advent of feeds has encouraged the intensive commercial production of tilapia. The introduction of hybrid tilapia (e.g. red tilapia) in the 1980s enhanced the domestic market value of the species particularly in Jamaica and Colombia. At present, nearly all commercial producers of farmed tilapia in the Americas rear sex-reversed fish. Grow-out techniques vary with the countries and include culture in static water ponds, with partial water exchange in raceways, cages, and indoor re-circulating systems. The leading producers of farmed tilapia in the Americas are Brazil and Colombia, which have industries of small, medium and large-scale producers. Most of the production from seven out of 10 countries producing tilapia in the Americas is consumed domestically (Popma, 2002). Total world tilapia landings from capture and culture has been estimated at 1.16 million tons (FAO 1997), with cultured tilapia accounting for 57% of the total (659,000 tons). The most important tilapias in aquaculture are the maternal mouth brooders (Schoenen 1982; Pullin 1985): the Nile tilapia (T.nilotica); Mozambique tilapia (T. mossambica); and the blue tilapia (T. aurea); plus a number of mouth brooding tilapia hybrids used in aquaculture (especially red T. mossambica hybrids) witht. aurea, T. nilotica, and T. urolepis hornorum. These species account for 99.5% of global tilapia production (FAO 1997). Of secondary importance are T. galilea and T. melanotheron (principally in West African lagoons). Since the mid-1980s, there has been a shift in producer preferences away from the Mozambique tilapia towards growing Nile tilapia. Nile tilapia now dominates global tilapia aquaculture, accounting for 72% or 474,000 tons in 1995 (FAO 1997). Cuba is the world s largest producer of blue tilapia, which are grown in an enhanced reservoir fishery supplemented by hatcheries (Fonticiella and Sonesten 2000). The largest tilapia producing nations are in Asia. China is the world s largest tilapia producer (315,000 tons), accounting for 48% of global production, followed by the Philippines, Thailand, Indonesia and Egypt (FAO 1997). The USA is the world s largest tilapia consumer. US tilapia consumption is estimated at 51,645 tons of live weight equivalent (Engle 1997). The USA imports over 3 times the amount of tilapia it grows, with the major importers (in order by value): China, Thailand, Costa Rica, Indonesia, and Columbia. Tilapia imports contribute a measurable share of the large US trade deficit in seafood products. It is the third largest imported aquaculture product to the US after shrimp and salmon and has received rapid consumer acceptance in US seafood circles as the new white fish (ATA 2000). Tilapia are the most frequently requested fish in the US restaurant trade, and new markets carrying the fish for the first time report rapid acceptance (ATA 1995). The culinary characteristics of the fish match almost perfectly the desires of the US consumer, for example, a white flesh, boneless, relatively odorless, with a very mild flavor. Tilapia are increasingly being seen as a replacement for cod and hake which are in short supply. Tilapia sales have exceeded those of trout in the US each year since 1995 (ATA 2000). As a result, tilapia production in the Americas is expected to exceed 500,000 t by 2010 (Fitzsimmons,2000). However, in some countries like Australia (Baron/Mitchell Tilapia Management Group, QFS, 2000) including the earlier efforts in Nauru (FAO 1979;1980), tilapia are not seen as an economic resource but an ecological pest, that eradication programs are being undertaken through several means (use of organic toxicants, construction of outfalls and others were undertaken unfortunately, but have not succeeded. 10

11 The various techniques that were developed and practices that were applied in controlling tilapia in many countries, mostly for aquaculture purposes, may also be used for the its prevention and control particularly in the identified water bodies of Nauru where the Mozambique tilapia was introduced forty-five years ago. It is therefore the objectives of this undertaking to: 1.1. review the past attempts to control tilapia populations elsewhere in the world and identify various techniques that may be applied in Nauru for tilapia population control; 1.2. determine the applicability of identified techniques taking note of the special environmental conditions and the level of institutional capacity in Nauru; and 1.3. develop a broad strategy to implement a national tilapia program in Nauru Review of various techniques used in controlling tilapia population in aquaculture Failure of tilapia culture in the past, has often been due to uncontrolled spawning, resulting to the production of large numbers of fry and stunted populations. Development of various techniques and practices and their appropriate applications have overcome this problem. Now, the growth of fingerlings are enhanced and can attain a commercially acceptable size in a reasonable period of time. In order to sustain and insure the success of this system, it is necessary to have a selection of strains with fast growth rate, late maturing and use of single-sex stock. It is also necessary to create an environment that is conducive in allowing the fish to carry out its activity normally. Thus it is essential to prepare the ponds by first completely draining them after each cropping then treat with environment-friendly toxicant to eradicate nuisance and harmful species. It is also important to use healthy fingerlings of one age class for stocking. Feeding with a suitable protein-rich diet is necessary. There are basically seven (7) methods of controlling tilapia populations that have been carried out in some countries for aquaculture and to some extent, eradication purposes. In a number of these countries, tilapia is considered an economic resource and an important food source for the people. The various methods and/or techniques that follow are: (1) periodic harvesting of fry and fingerlings; (2) monosex culture of which single-sex fish are obtained through: manual separation of sexes, hybridization, hormone augmentation and genetic manipulation methods (e.g. androgenesis, gynogenesis, polyploidy and transgenesis); (3) culture in cages; (4) high density culture; (5) biological control; (6) sterilization and (7) eradication using organic toxicants and/or other chemicals. Application of these methods in specific countries has been done with certain degree of success Periodic harvesting of tilapia fry and fingerlings. Pond culture is still the most popular method of growing tilapia. A mixed-sex population of tilapia is stocked in ponds and the normal pond culture procedures are carried out. However, instead of waiting to obtain the total yield at one harvest, collection of fry and fingerlings is done periodically every one to three weeks. One advantage of this method is that the fish are able to utilize natural foods. However, there is a need for a management scheme in order to maximize tilapia production - the extensive systems (using only organic or inorganic fertilizers) and the semi-intensive systems (using high-protein feed, aeration and water exchange). The systems are described by Mair (2002) in more details as follows: In the extensive system, the sexually 11

12 mature fish are stocked in earthen ponds. Ponds are then fertilized and/or feeds are introduced to support broodfish and early growth of fry and fingerlings. Ponds are seined regularly then finally drained and harvested completely after a set period of three weeks to six months depending on desired efficiency. During seining broodstocks are usually captured first, in coarse mesh nets, and the pond then seined with finer mesh nets to removed fry and fingerlings of varying sizes. Brood stocks are then released back into the pond. With regular seining, ponds may not be drained completely for up to a year. Management of such ponds is quite simple and capital and labor requirements are low. Also, as a high proportion of the harvested seeds are already fingerlings, they can be sold immediately without requiring nursing. Productivity for such systems varies ranging from fry/kg female/month (Little and Hulata 2000) but is often quite as a result of fingerling mortality due to predators that might be in the pond and the effects of cannibalism both by broodstock and by the omnivorous juvenile tilapia which result from the earliest spawnings. The mixed size and age of fry collected from these systems, render them unsuitable for hormonal sex reversal and thus these systems are almost exclusively used for production of mixed sex fry and fingerlings. The collected fry and fingerlings are then graded prior to sale or further nursing. On the other hand, in the semi-intensive system, broodstocks are stocked into small, shallow ponds, typically m² in area and 0.5-1m deep. Ponds are prepared and broodstocks are stocked for a cycle of normally 3-5 weeks. Fry collection strategies, which commence about 15 days after stocking, rely on the fact that very young fry shoal together in groups, usually close to the surface of the pond. Fry can then be scooped up using long handled nets from the dyke of the pond or large scoop nets can be used to sweep the whole upper layer of water. The disadvantage of entering the water to regularly collect fry is that pond sediments are disturbed increasing turbidity and thus decreasing primary productivity, and this should be avoided as much as possible. Mixed-sex populations of fry are cultured together and harvested before or soon after they reach sexual maturity, thereby eliminating or minimizing recruitment and overcrowding. A restricted culture period limits the size of fish that can be harvested. In mixed-sex culture, tilapia are usually stocked at low rates to reduce competition for food and promote rapid growth. On the other hand, in order to allow the tilapia to approach its maximum size at a reasonable culture period, the density must be reduced by harvesting the fry and fingerlings to reduce competition for food. This method is effective in small ponds but it is labor intensive and requires little skill. In order to take advantage of this situation, the fry and fingerlings collected may be graded then sold or nursed for use later as seeds. The major drawback of pond culture is the high level of uncontrolled reproduction that may occur in grow-out ponds. Tilapia recruitment, the production of fry and fingerlings, may be so great that offspring compete for food with the adults. The original stock becomes stunted, yielding only a small percentage of marketable fish weighing 1 pound (454 grams) or more. In mixed-sex populations, the weight of recruits may constitute up to 70 percent of the total harvest weight Monosex culture. Single-sex tilapia are used as the stocks under this method of farming. Because the major problem of pond-cultured tilapia is excessive reproduction, and subsequent stunting of fish due to overcrowding use of all-male tilapia as the stocks may be able to combat this problem. Males are preferred because they grow almost twice as fast as females. This technique is called monosex culture and is used when large fish are required by the market. Monosex culture may resolve the 12

13 problem of uncontrolled reproduction in rearing ponds. Rakocy and McGinty (1989) reported the following account relevant to the all-male tilapia culture as follows: Male monosex culture permits the use of longer culture periods, higher stocking rates and fingerlings of any age. Expected survival for all-male culture is 90 percent or greater. A disadvantage of male monosex culture is that female fingerlings are discarded. The percentage of females mistakenly included in a population of mostly male tilapia affects the maximum attainable size of the original stock in grow-out phase. The stocking rate for male monosex culture varies from 4,000 to 20,000/acre ( 10,000 to 50,000/ha.) or more. At proper feeding rates, densities around 10,000/ha. allow the fish to grow rapidly without the need for supplemental aeration. About 6 months are required to produce 500-g fish from 50-g fingerlings, with a growth rate of 2.5 grams/day. Total production approaches 5.4 tons/ha. A stocking rate of 20,000/ha. is frequently used to achieve yields as high as 11 tons/ha. At this stocking rate the daily weight gain will range from 1.5 to 2.0 grams. Culture periods of 200 days or more are needed to produce large fish that weigh close to 500 grams. To produce a 500-gram fish in temperate regions, over wintered fingerlings should weigh roughly 70 to 100 grams and be started as early as possible in the growing season. A stocking rate of 20,000/ha does require night time emergency aeration when the standing crop is high. Stocking rates of 30,000 to close to 50,000/ha. have been used in 0.5 to 1-ha. ponds but this requires the continuous use of two to four, one-horse power paddlewheel aerators per pond. Yields for a single crop range from 15 to 25 tons/ha. With optimal temperatures, feeding rates depend on fish size and density. Optimal daily feeding rates for fish of 30, 50, 100, 175 and 450 grams are 3.5, 3.0, 2.5, 2.0 and 1.5 percent of body weight, respectively. If densities are high, sub-optimal feeding rates may have to be used to maintain suitable water quality, thereby increasing culture duration. One technique that allows reliable control of the population is that of stocking the pond with fingerlings and raising of a single sex. Some species of the genus Tilapia can be easily sorted into males and females. Either the colors are sufficiently differentiated to serve as reliable sex indicators or the structure of the anal papilla is used - the opening of the oviduct being distinguishable in the female and not present in the male. With experience it is possible to sex even small immature fish with speed and confidence. A second check is made when the fish have grown somewhat larger and distinctive sex-coloration s are more discernible. Since this technique fails if there is a single female present in the raising pond, care must be taken to ensure that there are no females left over from a previous stocking. The sexing of small tilapias although feasible is tedious. In addition to being not entirely reliable. (Hickling, 1963). Single-sex population maybe obtained utilizing the following methods/techniques: rear fry to fingerling size in a nursery tank/pond and then separate the male fingerlings from the females. The male fingerlings are then prepared for final grow-out. Other than manual sexing, all-male fingerlings can also be obtained by other methods such as: genetics and hybridization and hormone augmentation (sexreversal). None of these methods is consistently 100 percent effective, and thus a combination of methods is suggested Manual separation of male from female fish. This is the process of separating males from females by visual inspection of the external urogenital pores, often with the aid of dye applied to the papillae. Secondary sex characteristics may also be used to help distinguish sex. This requires skilled personnel and trained labor. It necessitates relatively large-size fingerlings (50-80 g) but errors can easily be made even by skilled workers and only about 90% efficient. The sexing of small tilapias although feasible is tedious, time-consuming and often results in a loss of percent of the fingerling production due to the discarding of females. This is difficult for large ponds inasmuch as large numbers of fish are needed and the process is slow. (Hickling, 1963). Manual sexing is commonly used by producers. 13

14 Reliability of sexing depends on the skill of the workers, the species to be sorted and its size. Experienced workers can reliably sex 15-gram fingerling T. hornorum and T. mossambica, 30-gram T. nilotica, and 50-gram T. aurea. The International Center for Aquaculture and Environment of Auburn University in Alabama, U.S.A. developed a procedure for manual separation of sexes in tilapia in graphical form and is being reproduced here (Source: Bocek,A. Ed. Undated) A farmer can readily distinguish male and female tilapia with practice. When tilapia reaches about 10 cm in length (about 20 g) the sexes are distinguished by inspecting the genital papillae on the fish s underside (Figure 1). Experienced worker can manually separate by sex about 2000 fish per day with an accuracy of 80 to 90%. Therefore, some reproduction will always occur. The method is tedious, stresses fish and is not 100% effective. However, production of manually sexed tilapia fingerlings for grow-out to market size can be accomplished by farmers with few financial resources and little fish culture experience. The procedure is illustrated in Figures 2 and 3. Procedure For Manual Separation Of Sexes Figure 1: Ventral view of a tilapia.showing the main parts. Figure 2: A farmer examining and sorting tilapia by sex. 14

15 Figure 3: Small fish may be held in one hand and examined. Large fish are held with two hands. Figure 4: This close-up shows a female (top) and male (bottom) tilapia together. Note that the female has two openings in the papilla for passage of urine and eggs, while the male has only one opening for urine and sperm passage Hybridization. Hybridization in fishes is crossing two closely related but distinct subspecies of fish. As a tilapia control measure, hybridization maybe used to produce a high percentage of male fish so that reproduction is lower therefore overcrowding and stunting is avoided and bigger tilapia are produced. Among the major constraints in producing hybrids are: maintaining the purity of brood stocks, limited fecundity of parent fish which restricts fry production, difficulty in producing sufficient number of hybrid fry due to spawning incompatibilities between the parent species 15

16 and at times an impasse in preventing the entry of wild tilapia into culture ponds. Inasmuch as not all crosses produce 100 percent males, the hybrids may still be subjected to manual separation of sexes or hormone augmentation. While hybridization saves time, space and feeds it is not without problems. In 1958 a cross between T. hornorum males and T. nilotica females was reported to have produced all-male offspring by crossing one purebred local variety of T. mossambica that was descended from the original tilapias first found in Java in 1939 with one that is indigenous to brackish swamps on the island of Zanzibar off the coast of Africa. However, it requires pure strains otherwise it is likely that some females may be produced if the broodstocks are not of pure line. The F 1 generation, being fertile, may backcross with the female parent fish in rearing ponds and produce fry of both sexes (Hickling, 1963). This was corroborated by Chevassus-au- Louis (2002) who stated that hybridization as a method to control tilapia population by producing single-sex fish, obliges fish farmers to either produce or buy F 1 hybrids or maintain and control pure tilapia parental stocks. However, it does not allow the combination of the characteristics of parental species in any other proportion than a 50/50 ratio. This is not always optimal and it always gives very heterogeneous populations. Production of F 1 hybrids that are essentially related to the production of monosex varieties has been the passion in tilapia. Considerable efforts have been made to use hybridization to control overpopulation in tilapia pond culture systems however, this is hardly sustainable. It must be kept in mind that the method of producing a population of monosex tilapia through hybridization sometimes results in failures and there now exist other and more efficient methods based on sexual inversion or population control. In order to improve the future performances of F 1 hybrids, two parental species must be selected, which is a heavy and complex process. Performing it otherwise, may only obtain half of the possible genetic progress (Chevassus-au-Louis, 2002). It was suggested that using hybridization in building founder gene pools between interesting tilapia species presents several advantages. Due to the need to maintain pure line stocks to satisfy these requirements, special hatchery facilities and skilled labor are required. Thus, production of hybrid fingerlings expensive. Due care must be exercised to avoid contamination by other tilapia to insure purity among the crossbred fingerlings (Hickling, 1963). Hybridization can also be illustrated by the Molobicus Program now being conducted in the Philippines by BFAR, PCAMRD and CIRAD (Westly del Rosario, Head, National Fisheries Training and Research Center, Bureau of Fisheries and Aquatic Resources, Department of Agriculture, Bonoan, Pangasinan, Philippines, personal communication).the idea of the program is to produce a hybrid population that is tolerant to salinity through successive production of F 1 hybrids between mossambicus and niloticus and successive backcrosses with mossambicus then the hybrid population is selected for growth. The evolution of salinity tolerance between pure niloticus and pure mossambicus and of the F 1 and first backcross has illustrated that the progress through successive generations is regular. The strategies using F 1 are not completely the simple use of F 1 for or direct use of F 1 in aquaculture. It is complementary to the new strategies of combining selection and hybridization and so the founding pool of genes can be associated with the F 1 and a selected fish obtained from a strain or pure species. This program while not a method for tilapia control, aims at selecting a fast-growing tilapia resisting high salinity. A set of genes in proportions between 1/8 and 7/8 of genes of one species is obtained and pooled. From this pool of genes, it is possible to conduct a genetic selection within a hybrid population in the same way one would conduct selection with pure species. That genetic selection, when achieved, can easily be extended to the farmers in a sustainable way since they can breed and grow the selected strain as they would for the pure species. There was a suggestion however, that for a genetic and hybridization programs to be credible, an evaluation process must be created by a common structure (Mr. Pierre Morissens 16

17 (c/o PCAMRD-CIRAD Project Los Baños, Laguna). This is necessary in order to know exactly what the benefits of the different approaches are. With all the speculations developed abroad, it is hard to assess that any one strategy or approach is automatically better than another. Furthermore, what is true for a given generation may not be true after a few successive generations. It therefore becomes a necessity to set up a system to check objectively and independently the performances of any strain produced. These tests should cover the use of the different strains under various farming systems especially in places where many farmers are producing tilapias intensively. The intensive and the very extensive production of tilapia with the framework of polyculture is very important also so that the testing should cover the different farming systems. The results of these tests should be accessible to any user Hormone augmentation. This is a technique which has been adopted with some degree of success. The principle behind this method lies on the fact that at the stage when the tilapia larvae are said to be sexually undifferentiated (right after hatching up to about 2 weeks or up to the swim-up stage) the extent of the androgen (male hormone) and the estrogen (female hormone) present in a fish is equal thus, augmenting one of the hormones that is originally present in the fish will direct the fish to either male or female depending upon the hormone introduced. Accordingly, if the tilapia larvae are fed with feeds that are incorporated with male hormone (e.g. 17α-methyltestosterone), the fish will develop into phenotypic male (physically appears and functions as male but possesses the female genotype (XX); in the same way, if a female hormone is mixed with the feed that is taken by the fish, then the fish will be directed to phenotypic female (physically appears and functions as female but possesses the male genotype (XY). This is commonly referred to as sex reversal wherein the sex of the fish that is produced after having been fed with hormone-treated diet is either male or female depending upon what hormone (androgen or estrogen) was taken in by the fish. To insure that the hormones shall function effectively, it is very important that the fry or larvae must eat only the specially prepared artificial feeds containing the hormone with the exclusion of any other food sources. This means that the larval rearing facilities must be absolutely clean to prevent the fry from eating other food sources (e.g. algae) that may develop inside the rearing container. Feeding the larvae with hormone-treated diet, e.g., 17α-methyltestosterone or estrogen between the second and sixth week after hatching has been observed to have produced high percentage of males and females, respectively. Some constraints in the use of hormones in fish is that the presence of hormone residue in adult fish has not yet been studied thus its effect on the consumers is not yet known. Hormones may also be difficult to obtain in some countries and hatchery facilities and skilled labor are required Genetic manipulation methods. (Androgenesis, gynogenesis, polyploidy and transgenesis). Genetic improvement in tilapia has been achieved through the exploitation of qualitative variances (e.g., selective breeding, hybridization and crossbreeding and genetic manipulation (e.g., sex control chromosome manipulation and transgenesis). Two examples of successful selection programs in tilapia are the ICLARM-coordinated Genetically Improved Farmed Tilapia (GIFT) Project and the Freshwater Aquaculture Center (FAC) Central Luzon State University (CLSU) Project which produced the YY Super males. The GIFT and the YY Super Males produced through YY male technology are not considered genetically modified organisms. The GIFT Project reported a 70% increase in growth rate over 7 generations of combined selection in a synthetic Nile tilapia strain developed 17

18 from newly introduced African and domesticated Asian stocks. The FAC/CLSU Project reported a cumulative response of 18.4% after 16 generations of within family selection using a Philippine strain. Recently, traditional selective breeding methods have been enhanced by advanced DNAbased technologies. Molecular markers have been used to identify quantitative trait loci (QTLs) that can enable selection for desirable traits in marker-assisted selection (MAS) programs. Successful genetic manipulation methods, (i.e., gynogenesis, androgenesis, polyploidy and transgenesis) their potential as well as risks to commercial aquaculture have been reported. Future prospects in the applications of traditional selection methods and new molecular technologies in the genetic improvement of tilapias are now available. The continuation of selection and sex control programs for growth and environmental tolerance traits possible using indigenous species or strains from Africa is foreseen. The importance of markers in bioinformatics (e.g., pedigree analyses in farm based trials and breeding programs) washad been stressed. To avoid the deterioration in quality of tilapia culture stocks, farmers are advised to choose their cultured strains carefully. The following basic management guidelines should be adopted: 1. Keep high effective population size, 2. Avoid unconscious selection 3. Transfer stocks between hatceries, and 4. Maintain stock/strain purity. Adopting viable traditional selection methods can improve commercially desirable strains in tilapia. Applying novel DNA-based techniques (e.g., MAS) in genetic stock improvement schemes may consequently give faster results in enhancing tilapia production (Dr. Graham Mair during the International Forum on Tilapia Farming in the 21 st Century held at Los Baños, Laguna, Philippines on February 25-27, 2002). The realization of the need to improve the tilapia stocks brought about the creation of the GIFT (Genetically Improved Farmed Tilapia). This started in 1988 when direct transfers of Nile tilapia to the Philippines from Egypt, Ghana,.Kenya and Senegal were made. The tilapias were held at the National Freshwater Fishery Training and Research Center/Bureau of Fisheries and Aquatic Resources (NFFTRC/BFAR), Muñoz, Nueva Ecija. These served as the founder stock. From these stocks, production of mixed base population (synthetic breed) was initiated and run for at least one generation of selection. The tilapia that were produced from these are called the GIFT tilapia and it is claimed that they grow at an average of 60% faster than the other breeds. In order to sustain the quality of the stocks, the genetic pool is being maintained by continuous broodstock selection. The beneficial role of genetics in aquaculture has been demonstrated in this specific project by showing that growth of a fish can be improved and its quality enhanced through the application of the science of genetics. This is consistent with its objective to increase the quantity and quality of fish protein from aquaculture and to obtain continuous long term progress in productivity.the GIFT fish was a result of the selection program designed to improve the breeds of tilapia for low-cost sustainable aquaculture in developing countries. It was evaluated by DEGITA (A Project on the Dissemination and Evaluation of Genetically Improved Tilapia) before the GIFT was released to the farmers. Today, the GIFT fish has been disseminated to the farmers through the six accredited operators and one pilot hatchery in the original site in Central Luzon State University, (Abella, Tereso, CLSU, Nueva Ecija,Philippines personal communication). Androgenesis is a mechanism that can directly produce YY-males, at least in theory, to be used as broodstock to breed all-male progeny. It is the diploidization of the paternal genome 18

19 (androgenote) which is accomplished by interference with first mitosis for eggs that have been genome-neutralized before activation (Shelton, 2001). It is also the selection of individuals for sex inheritance characteristics that will be used in monosex production. Intraspecific breeding programs have been developed to exploit the sex inheritance mechanism in the tilapia T. nilotica to produce male populations. These programs are built on the premise that the mechanism of sex inheritance must conform closely to a mono-factorial sex determination with a heterogametic male. Sex inheritance in tilapia, however, appears to be more complicated. The sex ratio of an individual spawn often does not conform to the expected 1:1 ratio. A better understanding of sex inheritance in tilapia and the identification of tilapia populations with a minimum variation in progeny sex ratios from individual spawns is needed for a successful intra-specific breeding program to produce male tilapia. In a study by Phelps and Carpenter (2001) sex ratios in tilapia did not appear to be passed on from one generation to another. A realized heritability for sex ratio of 0.09 was calculated. No family with skewed sex ratios produced progeny from sibling matings with similarly skewed sex ratios. The androgenetic approach to developing YY males simplifies the identification of YY males as all males produced should be of the YY genotype. This is based on the theory that interand intraspecific breeding programs can result in populations with highly skewed sex ratios and often give inconsistent results. Interspecific crosses have not proven to be practical due to difficulties in maintaining the parent species integrity. Intraspecific breeding programs have been developed to exploit the sex inheritance mechanism in Nile tilapia, T. nilotica. YY-Male Technology for production of monosex tilapia. It has been shown that all-male tilapia population can be obtained from a cross between the offsprings of T. mossambica x T. hornorum. Furthermore, a cross between T. hornorum and T. mossambica could yield 75% males and 25% females as follows: Knowing that chromosomal mechanism of sex determination in tilapias is possible, super male tilapias were thought of because of its desirable characteristics in aquaculture. The YY-male technology is nothing but genetic manipulation of sex in tilapia. In this method, sex reversal to female is done initially. This is carried out by hormone augmentation. The female hormone (estrogen) is mixed into the feeds then fed to one week old tilapia fry which at this stage are still T. hornorum X T. mossambica WZ X XY WX WY XZ ZY Figure 5. Illustration of a cross between T.hornorum x T. mossambica showing a yield of 75% males and 25% females. sexually undifferentiated and the amount of the male and female hormones in their systems are equal. Feeding the fish with the treated diet is done up to 2 weeks and the sexually undifferentiated tilapia fry would develop into females. These sexually reversed females are actually phenotypic females (physically appears and functions as female but possesses the male genotype (XY). When these phenotypic females are crossed with normal males (XY) the resulting progeny contains approximately ¼ of the novel genotype YY. Further crosses of YY-males with YY 19

20 (sex reversed females) followed by a second generation of sex reversal could produce YY-females which could then be crossed with YY-males for the production of all-male producing YY-male broodstock. The success of this technology has been tried and the large scale production of allmale tilapia is now possible. The super male YY tilapia has shown to have produced genetically male tilapia with reports from studies that the fish grew better than the mixed sex tilapia by about 50% and 23% better than the sex-reversed tilapia. Today, there are about 40 accredited hatchery operators supplying the industry with the needed all-male quality fingerlings (Abella, Tereso, CLSU, Nueva Ecija,Philippines). The methods described above may be practical to use in countries such as the United States of America where technical requirements are easily accessible. Work on the development of tilapia breeding and genetic improvement program is a continuing process in the Philippines to produce improved breeds and strains of tilapia for culture. Pond and cage culture of saline tilapia for brackish and sea water environment is being pursued vigorously. The GIFT-PNTBP (Genetically Improved Farmed Tilapia-Philippine National Tilapia Breeding Program) is a major program of the Philippine government in support of tilapia aquaculture. The GIFT tilapia strain is now called Genomar Supreme Tilapia. Dr. Graham Mair (International Forum on Tilapia Farming in the 21 st Century held at Los Baños, Laguna, Philippines on February 25-27, 2002) further reported the following: The small founding population of tilapias (i.e.,tilapia mossambica and T.nilotica) introduced in the region has resulted in low genetic variability and poor performance of the cultured Asian stocks compared to the indigenous African stocks. Poor broodstock management has led to the genetic deterioration of domestic tilapia populations. The breeding of tilapias is fairly easy and can be done extensively, semi-intensively and intensively in tank, cage and pond-based hatchery systems. Productivity in these systems varies widely but is often sub-optimal. Breeding efficiency can be optimized through proper stock management, broodstocks nutrition and improved nursery techniques. In the same forum (Tilapia Farming in the 21st Century) Dr. Hans Magnus Gjoen of Biosoft (Philippines) remarked that the continuation of the GIFT strain which is now called Genomar Supreme Tilapia is a conventional set-up for a selection program for additive genetic effects. The main strategy is to keep the families separate using a conventional tagging system placed in a communal rearing facility to avoid the common environment effect. There are several drawbacks to this: (1) the common environment introduced by this separate rearing facilities becomes very difficult to separate from genetic effects later on when one does the genetic evaluation; (2) there will be low numbers within each compartment because of the high costs linked to the tagging. The whole system is quite costly both in investment and in operation Culture of fish in cages. The rearing of fish and other organisms in a structure that is suspended in water above the pond bottom but anchored and where the water maintains free circulation that may come from a natural or man-made lake or the water body is referred to a cage culture or the practice of rearing fish/aquatic organisms in cages. It can be applied in other existing bodies open water such as large reservoirs, farm ponds, rivers, cooling water discharge canals, estuaries and coastal embayments. In the southern U. S., tilapia are among the most suitable fishes for cage culture. Cage culture of tilapia is considered a method of controlling tilapia population because spawned eggs fall through the cage mesh and die. Furthermore, the breeding cycle of tilapia is disrupted in cages, and therefore mixed-sex populations can be reared without the problems of recruitment and stunting, which are major constraints in pond culture. Also, eggs fall through the cage bottom and do not develop even if they are fertilized. However, reproduction could occur in cages 20

21 with 1/10-inch mesh or less, being small enough to retain eggs (McGinty and Rakocy, Undated). It was observed that male tilapia that are loose in open waters could still mate with female tilapia inside the cage (mating behind bars ). The observation can be described as follows: Female tilapia releases eggs in one corner of the cage then picks them up with its mouth. The eggs stay in the mouth until a male outside the cage gets near it. The male then allows the female to suck its genital papillae until it releases the sperm which fertilizes the eggs inside the mouth of the female. The eggs after fertilization hatch into fry and swims inside the cage when they reach the swim-up stage (Fortes, R. D., College of Fisheries and Ocean Sciences, University of the Philippines in the Visayas, Miagao, Iloilo, Philippines). McGinty and Rakocy (Undated) considered Tilapia nilotica (Nile Tilapia), T. aurea (blue Tilapia), Florida red tilapia, Taiwan red tilapia and hybrids between these species and strains as the most appropriate species or strains of tilapia for cage culture. The choice of a species for culture in the United States of America depends mainly on availability, legal status, growth rate and cold tolerance. Many states prohibit the culture of certain species. Unfortunately, T. nilotica, which has the fastest growth rate, is frequently restricted. The ranking for growth rate of the remaining species or strains are Florida red tilapia > Taiwan red tilapia > T. aurea.. Hybrids of T. nilotica x Taiwan red tilapia grow as fast as T. nilotica. Hybrids of T. aurea x Florida red tilapia grow at an intermediate rate between Florida and Taiwan red tilapia. Cold tolerance, which is important in northerly latitudes, is greatest in T. aurea.. Other advantages of cage culture are: (1) ease and low cost of harvesting; (2) close observation of fish feeding response and health; (3) ease and economical treatment of parasites and diseases; and (4) relatively low capital investment compared to ponds and raceways. On the other hand there are also some disadvantages as follows: (1) risk of 1oss from poaching or damage to cages from predators or storms; (2) less tolerance of fish to poor water quality; (3) dependence on nutritionally-complete diets; and (4) greater risk of disease outbreaks. Cage culture offers several important advantages. Culture of fish in cages however, requires intensive feeding with high quality ration and cage materials may also be expensive Culture at very high densities. High density culture in ponds, cages, pens or raceways is considered a control measure for tilapia. It works on the principle that crowding reduces the urge to reproduce. When carried out in mesh cages that maintain free circulation of water, high density culture could attain significantly higher fish production. However, it requires intensive feeding with a high quality ration, availability of good water supply, needs electric, gas or diesel aeration devices and skilled management Biological control. This is a means of controlling certain fish population by stocking predacious fish as fingerlings or adults in a pond. This concept and method was developed by Dr. Homer W. Swingle, recognized as the Father of Aquaculture in the United States of America who hailed from Auburn University in Alabama. It needs an effective predatory fish that can control excessive reproduction. This method produces at least two different kinds of fish the predatory fish and the prey species. The successful stocking of the large new lakes created by dams in Southeastern United States was based on the predation of the black bass (Micropterus salmoides) on the bluegill sunfish (Lepomis sp). In the case of tilapia, large fish must be stocked initially or they will be eaten by the predators. The predators will not only crop down the surplus fry and thereby permit better growth in the Tilapia population; they will also contribute to the variety and value of the total fish crop. It has been shown that excessive production of tilapia fry can be overcome by the addition of a predatory species to control the population by feeding on fry and fingerlings. Predator species such as Lates niloticus, Hemichromis fasciatus and Clarias lazera have been used for this purpose (FAO/UNDP Task force onaquaculture Development and Coordination Programme,1980) 21

22 Using the predator-prey method, one reservoir in Malaca had produced more than 6000 pounds a year of good-sized tilapias weighing between three-quarters of a pound and two pounds each (Hickling, 1963). In order to keep the predator-prey balance at an advantageous level, there must be frequent stocking. Several species of predatory fishes have also been used for this purpose in other parts of the world. In East Africa the Nile perch (Lates niloticus), a fine sporting fish, has been tried; in the Cameron s the black bass and a fish related to the Tilapia called Hemichromis fasciatus have been stocked in tilapia ponds; in Jamaica the local tarpon (Megalops cyprinoids) has served as an effective predator. At the College of Fisheries and Ocean Sciences, University of the Philippines in the Visayas, Leganes, Iloilo, Philippines, three species of fish were used to control the reproduction of tilapia in pond culture. These are: tenpounder (Elops hawaiiensis) (Fortes, 1979;1980); tarpon (Megalops cyprinoides) (Fortes, 1979; 1980) and sea bass (Lates calcarifer) (Fortes, 1986).A predator-prey ratios of 1:20, 1:10 and 1:10 were found to be effective in controlling tilapia fry and fingerlings, respectively. In Nigeria, Fagbenro (2000) conducted a quantitative evaluation of the predation efficiency of two hybrid clariid catfishes (Heterobranchus longifilis x Clarias gariepinus) and (H. bidorsalis x C. gariepinus) in controlling recruitment of Nile tilapia (Tilapia niloticus) while producing market-size fish. This was conducted in small earthen ponds (200 m 2 ) using three tilapia : hybrid catfish stocking combinations (5:1, 10:1, 20:1). After 180 days the treatments 5:1 and 10:1 showed better production. In the United States, largemouth bass (Micropterus salmides) has been used as the predator for tilapia (T. aurea). A forage/predator ratio of 0.7 and 1.4 are suitable for controlling spawn and producing large tilapia and large bass, respectively The technique of culturing predatory fish with a prolific forage species has potential for other game fish, particularly species of high economic value and whose food requirements are not readily satisfied with commercial feeds. Maintaining tilapia: bass ratio seems feasible for one production cycle in a temperate climate. Both the tilapia and bass could be marketed as a food fish crop. The carnivore (bass) harvested from such a system could be used for management of sport and recreational fisheries (Wurts et al., 2001). At the Asian Institute of Technology, Thailand, Yi et al. (2002) tested the efficiency of snakehead (Channa striata) in controlling recruitment of mixed-sex Nile tilapia (T.nilotica) in ponds and to assess growth and production characteristics of Nile tilapia in monoculture and polyculture with snakehead in fertilized earthen ponds from March through October There were six treatments: A) monoculture of sex-reversed all-male tilapia; B) monoculture of mixed-sex tilapia; C) polyculture of snakehead and mixed-sex tilapia at 1:80 ratio; D) polyculture of snakehead and mixed-sex tilapia at 1:40 ratio; E) polyculture of snakehead and mixed-sex tilapia at 1:20 ratio; F) polyculture of snakehead and mixed-sex tilapia at 1:10 ratio. Sex-reversed and mixed-sex Nile tilapia were stocked at 2 fish m -2 at sizes of 10.5 to 11.6 g and 7.2 to 8.1 g, respectively. Results show that snakehead were able to completely control Nile tilapia recruitment at all tested predator:stocked-prey ratios, and the best predator:stocked-prey ratio was 1:80. The addition of snakehead into Nile tilapia ponds did not result in significantly greater tilapia growth, but it significantly lowered total net and gross yields of adult plus recruited tilapia. Snakehead growth was density-dependent, decreasing significantly with increasing stocking densities. While snakehead biomass gain was not significantly different at stocking densities from to 0.1 fish m-2, the gain was significantly lower at a stocking density of 0.2 fish m -2. The present experiment demonstrates that snakehead are able to control Nile tilapia recruitment completely and provide an alternative technique for Nile tilapia culture. 22

23 Various predatory fish species have been used with varying success in combination with different tilapia species depending on their availability. These species include snakehead (Channa striata or Ophiocephalus striatus) (Pongsuwana, 1956; Chimits, 1957; Tongsanga, 1962; Chen, 1976; Cruz and Shehadeh, 1980; Hopkins et al., 1982; Wee, 1982; Balasuriya, 1988); Ophiocephalus obscuris (de Graaf et al., 1996); Micropterus salmoides (Swingle, 1960; Meschkat, 1967; McGinty, 1985); Lates niloticus (Meschkat, 1967; Planquette, 1974; Lazard, 1980; Bedawi, 1985; El Gamal, 1992); Hemichromisfasciatus (Bardach et al., 1972; Lazard, 1980); Cichla ocellaris (Lovshin, 1977; McGinty, 1983; Verani et al., 1983); Clarias sp. (Meecham, 1975; Bard et al., 1976; Lazard, 1980; Janssen, 1985; de Graaf et al., 1996); Cichlasoma managuense (Dunseth and Bayne, 1978); Elops hawaiiensis (Fortes, 1980); and Megalops cyprinoides (Fortes, 1980). However, the difficulty in breeding or obtaining predators of the correct size often resulted in limited application of this population control method (Balarin and Hatton, 1979; Penman and McAndrew, 2000). Biological method to control the forage species requires draining of the pond, sorting out the fish and restocking with the right proportion of predator and prey. The technique is a sophisticated one, with plenty of room for error. Another drawback of this strategy is that often, it is difficult to get adequate numbers of predator fingerlings (Hickling, 1963) Sterilization. In Nigeria, Ekanem and Okoronkwo (2003) tried pawpaw (Carica papaya) seed as fertility control agent on male Nile tilapia. Mature male tilapia with mean weight 40 g were treated for 30 days with 4.9 g/kg/day (low dose) and a 9.8 g/kg/day (high dose) of ground pawpaw seeds incorporated into their feed. In order to determine the effect of the treatments, a control treatment was added using fish of similar sizes fed with feed that did not contain pawpaw seed. No spawning occurred in any of the replicates in the high dose treatments during the 30-day treatment period. Fish in the control experiment spawned two weeks and five weeks after while fish in the low dose treatment spawned three weeks after the treatment was discontinued. When sections of the testes were examined histologically, swollen nuclei in the low dose treatment and disintegrated cells in the high dose treatment were observed. This indicated the positive effect of pawpaw seeds in inducing sterility in Nile tilapia. The application of this method of controlling reproduction in tilapia is straightforward and can easily be adopted by poor fish farmers inasmuch as pawpaw seeds are available all year round in the tropics and subtropical regions. Pawpaw seeds contain active ingredients such as caricacin, an enzyme carpasemine, a plant growth inhibitor, and oleanolic glycoside, the last of which had been found to cause sterility in male rats (Das 1980). Other means to carry out sterilization program is the use of irradiation to cause sterility to the target fish Eradication with organic toxicants and other means. The desire to get rid of noxious species that was introduced into a country, legally or illegally, necessitated the use of toxicants that could eradicate the deleterious species. Toxicants such as rotenone has been used for this purpose. Substances such as potassium chloride, hydrated lime (CaOH), ROCCAL (Benzalkonium chloride) and other molluscicides/toxic compounds that are effective and highly toxic to most fish species have also been used in eradicating noxious species. The rapid proliferation of tilapia in an area when introduced can be demonstrated by the experience in the Mexican State of Quintana Roo. Tilapia was introduced into this state in 1974 by direct releases into water bodies and later in 1982, raising tilapia in cages. After 18 to 22 years, surveys were conducted (1992 to 1996) to determine the distribution of tilapia and its relative abundance. Escape from floating cages was the major cause of tilapia proliferation. Tilapia was found in 50% of the intensive culture sites visited and T. mossambica and hybrids, probably with 23

24 T. nilotica, were collected in four sites where it had not been introduced. Others were believed to be by invasions from nearby lakes and unauthorized introductions and became dominant (>20% of the total number of individuals) in most localities where it appeared ( Schmitter-Soto and Caro, 1997). As mentioned earlier, similar occurrence occurred in the Republic of Nauru when T. mossambica or the Mozambique tilapia was introduced. Because of the widespread distribution of tilapia in the Republic of Nauru, the government implemented a Tilapia eradication program through FAO in 1979 and The import of tilapia to Queensland was prohibited in 1963 but tilapia was able to enter the country and became widespread in Queensland. The proliferation of tilapia was attributed to: Movement through the irrigation channel into the Walsh River (major Mitchell River tributary); Movement through water releases or overtopping of the spillway and into a catchment via a flooded low lying area and by irrigation pumps and drains; Direct translocation (i.e. by humans) Movement directly into a river via irrigation channel and into the wetlands The problem of tilapia in the Barron and tributary streams was first reported in They were all well established in the southern parts of the dam. Spot eradication of T. mossambica was performed in Townsville in small, contained water bodies (e.g. ponds, dams) with the use rotenone. Unfortunately eradication of tilapia by this method was not successful. Prevention of further spread of the Mozambique tilapia into the river systems became a priority and one attempt was to place screen on the outfall of some dams (e.g. Tinaroo Dam). (Baron/Mitchell Tilapia Management Group, QFS, 2000). Based on the information described earlier, the infestation of undesirable species may be prevented if protocols shall be strictly followed. The following courses of action may not apply to all but there are provisions that could be applied to noxious aquatic animals including tilapia. (See Attachment A). 24

25 3.0. Application of indentified techniques to Nauru situation 3.1. The Republic of Nauru (a) (b) Figures 6a and 6b. A photograph of the island of Nauru (a) and a (b) sketch showing the Buada Lagoon and othe important structures. (Photo source: Department of Economic Development, National Tourism Office, Republic of Nauru through Jane s Nauru Home Page) Before any recommendation of the applicability of the identified methods can be made, it is important to know the situation of the island country in terms of geography, topography, climate, educational status of the citizens, aquatic environment, governance and economy. The Republic of Nauru as described by Wetland International (Scot, 1993) was the major reference material (See Attachment B). 25

26 3.2. Identified techniques that may be used in controlling tilapia in the waters of Nauru The important aquatic resources of Nauru which have been utilized for fish culture and to certain extent, fishing are: the Buada Lagoon, Anabar Lagoon and the 28 small ponds created out of bomb craters (assuming that the latter are still existing up to this time) (Scot, 1993; Ranoemihardjo, 1981) and depressions out of phosphate extraction. These bodies of water especially Buada Lagoon, were among the first recipients of Mozambique tilapia (Wetland International, 1990; Ranoemihardjo, 1981). It is also possible that the introduced Mozambique tilapia into Nauru did not come directly from Africa because it was reported that outside of Asia exotic tilapiine fishes were not imported directly as native genetic resources from Africa but arrived as transits from third or fourth party sources (Trewavas 1983). As a result, feral tilapias have hybridized and introgressed in aquaculture settings before escaping to the wild (Costa-Pierce 2003). The most widely dispersed tilapia species has been the Mozambique tilapia which was once known as the Java tilapia because most introductions of this fish originated from West Java, Indonesia, its first established locale outside Africa (Hickling 1960). By in the mid-1970s the Mozambique tilapia deteriorated in many recipient environments, and the small sized, poor quality fish lost consumer acceptance (Pullin 1988). After 45 years in Nauru, Mozambique tilapia may have undergone tremendous transformation and consequently, introgression as a result of the genetic depression through continuous in-breeding. Based on existing information, the attempts to rid Nauru of this poor quality and small sized tilapia that has lost consumer acceptance have not succeeded thus, attempts to apply the methods used of controlling tilapia in aquaculture shall be attempted. The following techniques and practices that are used for the control of tilapia populations in aquaculture may be appropriate and could be applied as soon as possible to control the Mozambique tilapia in the natural bodies of water in Nauru as follows: (1) periodic harvesting of fry and fingerlings including the parents; (2) biological control; and (3) eradication of tilapia using organic toxicants and/or other chemicals Periodic harvesting of fry, fingerlings including parents. This can be carried out in the ponds (bomb craters) that are infested with the Mozambique tilapia. (Note: There is need to identify which of the 28 ponds, if still existing, are infested with Mozambique tilapia). Harvesting may be done by the following methods Seining. Requirements: a. Fine mesh seine net with holding pole on its side (seine is 6 x 4 meters, Length x Width; pole is 6 meters in length) b. Buckets (at least 2 buckets to keep the catch) c. Two (2) persons Procedure. The seine is held at both ends by each person then hauled across and/or around the pond. The catch is then emptied into the bucket. This procedure is repeated several times in one day until no more fish is caught. After 2 weeks and every other 2 weeks (if still necessary), the method is done again until no more tilapia is caught. 26

27 Complete draining of ponds. When no more tilapia is caught by seining every 2 weeks, the pond is completely drained, if this is possible, the remaining fish picked up individually then held/kept in containers (buckets, etc) Poisoning. This should be done only after no more Mozambique tilapia is caught by draining and/or seining. It is highly recommended that an organic toxicant be used (e.g. rotenone). After 24 hours the pond is allowed to be filled with water then neutralized with potassium permanganate. If refilling of water is not possible, the pond may be left alone until water gets in Biological control. This method may be applied in bigger water bodies (e.g. Buada and Anabar lagoons). However, before doing so, estimation of fish population from catch statistics or other means should be done and the predatory fish identified. The estimate of fish population shall determine the number of predatory fish to be released in the lagoons. It is highly recommended that the predatory fish should be chosen from among those which have already been used successfully in other places and the species is available within the waters (fresh or marine waters) of Nauru and neighboring islands. However, native species may be tried on an experimental basis to determine the predator prey dynamics between the species. Based on geographical distribution, the following predatory fishes are candidate species for the needed carnivore in the tilapia-carnivore relationship. All these fishes marine fishes are found in the areas of the Pacific Ocean and can easily be acclimatized to low saline waters (e.g. 2 to 10 ppt). a. Lates calcarifer (sea bass or barramundi) b. Elops hawaiiensis (lady fish or tenpounder) c. Megalops cprinoides (tarpon) The following freshwater fishes may be considered, if they are already established in Nauru: a. Channa striata or Ophiocephalus striatus and Ophiocephalus obscuris (snakehead) b. Lates niloticus (Nile perch); c. Hemichromis fasciatus d. Cichla ocellaris e. Clarias sp. f. Cichlasoma managuense Biological control as a means to control undesirable fish must also be done with care. That is why, the carnivore to be used as the biological agent must have already been successfully used. For example, it is often thought that stocking northern pike, muskellunge or walleye (predators) should result in reducing the excessive population of sunfish. It turned out that the stunted sunfish are too large to be consumed by predators in the sizes normally stocked thus, more predation on bass than on sunfish was observed. In carrying out biological control method to control the proliferation of tilapia or other forage species, the following should be considered: 27

28 a. Depending upon the forage/carnivore (f/c) ratio that have been established for the selected forage and carnivorous fishes, the number of predators to be used shall be determined based on the assessment of the stocks of tilapia in the lagoons. b. The above list of potential predatory fish (specifically the freshwater species) that could serve as control agents for tilapia may not be endemic to Nauru and therefore a period for acclimatization may be necessary. Slow process of acclimation should be done (from zero parts per thousand of salinity to the salinity of water in the lagoon). c. In the case of sea bass or barramundi, tenpounder and tarpon, which are all marine species, can be acclimatized to waters with low salinity (a slow acclimation process will also be necessary from sea water salinity to the salinity of the water in the lagoon). d. The marine species (sea bass, tenpounder, tarpon, etc.) do not reproduce in low saline waters hence, they can not multiply. Only the number released less the mortality therefore, remains and grows in the given body of water (lagoon, pond, etc.) to control the nuisance species. Also, the size of forage fish that can be eaten by some predatory fishes is limited according to the size of the predator because they prey only on the certain size range of the forage species. Procedure: a. Estimate the fish population in the body of water by catch statistics or by other means. The number and kind of species other than tilapia must also be known. This is important because the role of the other species must also be considered. b. Choose the predatory species to serve as the biological control agent for tilapia then obtain the f/c ratio from the procedures that are available. c. Based on the information obtained in the population estimation and assessment, determine the number of predators required. d. Based on the status of the tilapia population and reproduction checks, the stocking size of the predator and the time they will be released can now be determined. e. On the designated date and time, the carnivorous fish are released into the pond and the initial observation recorded. f. After 2 weeks, a population check by fishing in the lagoon with ordinary fishing gears and reproduction checks by making several hauls along the shoals of the lagoon by means of fine mesh net are performed. The catch from fishing and reproduction checks are then examined and analyzed. This is done regularly every two weeks within a period of 6 months. g. Using the data from the above, evaluate the condition of the lagoon in terms of the presence of tilapia. h. OPTIONAL: If necessary, use of organic toxicants may be resorted to Eradication by means of toxicants and/or other chemicals. As have already been mentioned, it is not a good practice to rely solely on chemicals, such as the special pesticide or fish toxicant technically known as piscicide, as a means of controlling undesirable fish. Only if necessary, should the use of piscicides be resorted to but it is important that it should form part of an integrated pest management strategy. The chemical (organic or inorganic) must complement rather than obstruct other elements in the design. It should also limit the neg- 28

29 ative effects on the environment. It is therefore advised that use of registered products must be observed in using chemicals as control agents. In aquaculture, the use of most chemicals can be regarded as wholly beneficial with no attendant adverse environmental effects or increased risks to the health of aquacultural workers, if carried out properly. However, its over-use and misuse could bring about negative effects on the aquatic environment and on the physical condition of persons using them in fish farming (GESAMP 1997). There are several piscicides which are extensively used in fisheries management in the United States of America, Canada and Australia but only four are currently registered for general or selective fish control or sampling. These products include the general piscicides, Antimycin (Fintrol), rotenone (Noxfish), lampricides (Lamprecid) and Bayluscide. In a number of countries, commercial use of piscicides is a regulated activity. For example, in Michigan, U.S.A, it is classified under pesticide applicator certification category 5, aquatic pest management, according to the Michigan Pesticide Control Act 171. In developed countries, the primary reasons for use of piscicide were mainly to control undesirable fish populations so that sport fish could be stocked and managed for recreational purposes in lakes, ponds, and streams without competition, predation, or other interference by the undesirable fish (Lennon et al cited by Finlayson et al. 2000). Today, the most frequently reported uses of piscicide (in order of the amount of active ingredient used) are (1) control of undesirable fish to support recreational fisheries, (2) eradication of exotic fish, (3) eradication of competing fish species in rearing facilities or ponds, (4) quantification of populations of aquatic organisms, (5) treatment of drainages before initial reservoir impoundment, (6) eradication of fish to control disease, and (7) restoration of threatened or endangered species (Finlayson, et al. 2000). The rapid proliferation of tilapia in an area when introduced can be demonstrated also by the experience in the Mexican State of Quintana Roo. As pointed out earlier, tilapia was introduced into this state in 1974 and about a score later these were already found in abundance even in areas where they were not introduced (Schmitter-Soto and Caro, 1997). Similarly, when the Mozambique tilapia was introduced into Queensland, Australia, they proliferated the Barron and tributary streams which was first reported only in Attempt to eradicate tilapia in Queensland using the rotenone, an organic toxicant derived from the root extract of the plant known as Derris sp. was not successful. The same was true where rotenone was applied in spot eradication of T. mossambica in Townsville in small, in contained water bodies (e.g. ponds, dams). (Baron/ Mitchell Tilapia Management Group, QFS, 2000). In the case of Nauru earlier attempts (1979 and 1980) to eradicate Mozambique tilapia using rotenone was not also successful (Ranoemihardjo, 1981). (See Attachment C, Principles and Procedure) 29

30 4.0. Strategy for a national tilapia program in Nauru 4.1. The Mozambique tilapia must be controlled. There is a significant concern that the Mozambique tilapia (Tilapia mossambica) which have not yet been completely eradicated in the important bodies of water of Nauru (Buada Lagoon and other smaller water bodies) shall continue to be a threat to the aquaculture initiatives of the Nauruans and on the native aquatic communities. They are very effective competitors and can quickly form self-maintaining populations because of their efficient reproductive strategy, flexible habitat preferences and simple food requirements. Invoking the precautionary principle, it is essential that effective action be undertaken now to control the spread of the undesirable tilapia. Experiences in Nauru and Australia have shown that it is very expensive and almost impossible to cope with tilapia once they have established in an area and therefore from both an economic and conservation perspectives their spread should be prevented. Earlier attempts of eradicating the Mozambique tilapia in Nauru did not succeed for whatever reason. As a consequence of the unsuccessful attempts to rid Nauru of Mozambique tilapia, it is highly possible that after about 45 years since its introduction to Nauru, they may already be well established. Sustained control of the Mozambique tilapia from the significant waters of Nauru may be difficult, tedious and would take some time, but may not be too late yet. As suggested earlier, controlling the Mozambique tilapia in the important water bodies of Nauru would need a thorough planning strategy that should at least consider the 5 stages in planning as recommended (Finlayson et al. 2000) as follows: a. preliminary planning, where the project concept and alternatives are developed, public input is invited, and acceptance is encouraged; b. intermediate planning, incorporating an environmental analysis where the project is refined and public acceptance is encouraged; c. final planning and project implementation, involving management through the development of project-specific work plans; d. performing the treatment; and e. summation and critique of the project This planning strategy recognizes that responsibility for tilapia control lies with government, community and industry. The plan must be put together after extensive community consultation and should consider opinions from the stakeholder group who may have some ideas on how to approach the problem. The goals, priorities and activities in the plan should be identified in meetings with stakeholders using the information available. Also, some additional key issues should be considered during the process, such as: prevention of tilapia infestation is feasible if there is cooperation among the various stakeholders; sustained tilapia control, would be more realistic than complete eradication; 30

31 It is very important for the participants in the program to be familiar with the ecology and biology of tilapia, and that sustained research into other possible control methods be initiated Tilapia as an economic commodity Vision. The infestation of tilapia in the waters of Nauru is controlled, proper management of their impacts developed and new and desirable species and tilapia hybrids accepted (including hybrid tilapia) as an economic commodity. Goals Involve stakeholders in planning and implementing on-ground actions and control measures; Prevent the spread of the Mozambique tilapia to other water bodies and restrict its further spread within the island; Ensure that the Mozambique tilapia, within its present distribution within the island, is maintained at a level that does not impact on biodiversity and economic values Increase community understanding of the pros and cons of the various tilapia species; In the long term maintain and sustain Mozambique tilapia control programs in Nauru but without forgetting that tilapias in general are established economic resource; Constraints Ownership of the lagoons and ponds. (As the Buada Lagoon is owned by several groups living on the embankment of the lake, all members must agree in any utilization efforts to be implemented in the lagoon) Many of the ponds have been abandoned Limited knowledge of behaviour and ecology and impacts of tilapia and no research being done to redress this situation. Limited resources and technical know-how of potential community participants Lack of public knowledge about tilapia species Perception by some members of the public that tilapia having lost its acceptance as food, should be considered as an economic resource Stakeholders - Department of Island Development and Industry - Nauru Marine Resources and Fisheries Authority - Nauru community/owners of the lagoons and ponds - Industry 31

32 Key Group (To be identified) The Problem. Tilapia was first introduced into Nauru in 1960 primarily for mosquito control and later for food security. However, it soon proliferated into the significant waters of the island which became out of control leading to the demise of milkfish farming (a very important economic activity) and became an ecological pest. Eradication programs were implemented but to no avail. Present status of the water bodies. Important bodies of water are believe to be proliferated by tilapia which caused the demise of milkfish farming. The lagoons and ponds are used as dumping places for rubbish. Potential impacts of tilapia on Nauru There is the possibility that tilapia will establish in the estuaries and coastal areas which may impact on the nursery grounds for many important commercial species including prawns. It is probable that Mozambique tilapia populations has already built up and established in the lagoons Risk Assessment. The degree of risk maybe determined by qualitatively assessing the extent of of infestation of the Mozambique tilapia in significant water bodies of Nauru and the impact of the infestation on ecological, social and commercial factors such as biodiversity, tourism and the commercial fisheries. Strategies for Implementation 1. Organization of the Key Group. Identify representatives from the various stakeholders who shall compose the Key Group. 2. Formulation of Programs/Activities a. Meeting(s) of the Key Group to formulate programs/activities (Understanding the situation/awareness Programs, etc.) b. Consultations with the stakeholders c. Information campaign (dissemination of information about the situation, possible programs/activities, etc.) 3. Management of fish populations and other aquatic organisms in the existing bodies of water in Nauru (possible transfer of tilapia from one body of water to another e.g. movement by persons deliberately/unwittingly translocating fish directly into the the bodies of water, Priority Actions Increase public awareness of the issue Instigate research into biological control of tilapia Monitor all sites of infestation and to determine the rate of population increase and the success of any control measures 32

33 Education and Extension Need for technical manppower Community Service announcements Training of volunteers on Mozambique tilapia and other pest fish issues Research into general biology of tilapia and biological control options Link in with universities to instigate research into the biology/ecology of tilapia Implement relevant research projects Monitoring Utilize existing baseline information/data gathered through various projects (if any) Data collection of fish species present in the bodies of water Long term Actions Development of an Aquatic Resources Management Program in Nauru 33

34 5.0. National tilapia plan for the Republic of Nauru The increasing importance of tilapia in the world is demonstrated by its increasing production, demand and attention. Considerable information are available demonstrating the role positive role of tilapia in the economy of many nations. As pointed out earlier, the total world tilapia landings from capture and culture has been increasing and many countries are convinced that tilapia has attained the status of a world fish. The increasing production of tilapia in the world can be seen in Figure 7. Figure 7. Worldwide tilapia production according to species demonstrating that expansion in production in recent years has come from the expansion in culture of Tilapia nilotica (Data source: FAO, 2002 cited by Mair, 2001). Taking into account the increasing importance of tilapia in the world while respecting the action of other countries to get rid of the obnoxious tilapia species, the following plan regards both as critical because of tremendous development in tilapia aquaculture while attempting to preserve environmental biodiversity. Furthermore, there are advantages of integrating fisheries into the development plan of the Small Island Developing States (SIDS) in view of the suggestion that among the specific national measures deemed essential to ensure the sustainable development of the SIDS are establishment/strengthening of institutional, administrative and legislative arrangements in evolving fisheries development strategies including its integration into national development plans as well as a design of comprehensive monitoring programs for coastal and marine resources (Thorpe et al. 2004). Thus, the following specific plan integrates fisheries management as a strategy in controlling the population of undesirable species of tilapia while opening the door to the new and desirable breeds for future deliberation. This National Tilapia Plan may be discussed in more details in the future. It was learned from the SPC Aquaculture Action Plan that here are only two species of fin fishes that are listed as aquaculture commodities to be addressed within the said period, namely: milkfish (Chanos chanos) and tilapia (Tilapia spp.). Several issues were identified as among the lessons learnt which are enumerated in the following table (Table 1). While the Republic of Nauru is not a focus country, it is assumed that tilapia, particularly the hybrids is being considered as an economic resource like the other SIDS. 34

35 The major thrust of the national tilapia plan is to control the feral tilapia in the different water bodies of Nauru and at the same time manage its population in these environments. The use of hybrid tilapia will be introduced 5.1. Policy needs. Policies that are essential for sustained management and protection of lagoons/ponds must be formulated, among these are: Protection and conservation of fisheries and aquatic resources Review ownership policy of aquatic resources Conservation of spawners and/on fry/fingerlings Review of policies Strategy The major strategy in increasing production of tilapia while controlling its population is through: a. increasing the yield per hectare of inland waters; b. concentrate resources on targeted tilapia species 35

36 Table 1. Issues and needs in formulating national tilapia plan for Nauru Category Issues Constraints Required actions Institutional, legal and administrative aspects Demise of milkfish industry commitment by authorities Proliferation of Mozambique tilapia Ownership of the areas for fish farming Eradication/ control of Mozambique tilapia Review of policies Human resources Lack of skilled/ technical manpower Programs to upgrade skills of technical and extension officers Organization training, seminars and workshops declining supply of fry Technical aspects High cost and poor quality of feeds Need for water recycling technologies poor site selection and poorly managed farms; impact on the natural ecosystem; tilapia introduced other than for farming subsistence farming has had variable success. Poor quality of seeds Poor water supply Consider other species of aquaculture commodities (e.g. hybrid hybrid tilapia, & other species, etc.) Promotion of polyculture system Research waste management and treatment Undertake research on water recycling technologies 36

37 With these identified issues and needs as the take off point, a national tilapia action plan and objectives for Nauru is hereby prepared (See Table 2). Table 2. Action plans and objectives of a national tilapia plan for Nauru Action plans Objectives Target beneficiaries Expected results Key areas of concern To eradicate/ control Mozambique tilapia To develop utilization techniques for Mozambique tilapia in aquaculture Private sector Fish farmers Government Stakeholders Enable the government and other stakeholders to move on to other aquaculture species Key development areas in lagoon/pond management To formulate an effective management plan for the utilization, protection and conservation lagoons and aquatic ecosystems Government Private sector Stakeholders Formulated utilization and management plan for the aquatic ecosystems for Sustainable resource use production Research and extension needs Training for technical manpower needs of the government Non-formal Formal Programs to upgrade skills of technical and extension officers Organization training, seminars and workshops Research Needs Water recycling technologies Consider other species of aquaculture commodities (e.g. hybrid tilapia and other species, etc.) Promotion of polyculture system Research on waste management and treatment Undertake research on water recycling technologies Fertilization methods 37

38 Feeds and feeding (Identification and screening of potential feedstuffs; studies on locally available supplementary feeds such as utilization of Mozambique tilapia as a protein source of fish feeds Other Needs Fingerling production New areas for aquaculture activities Production targets. Define production target and come up with programs in the pursuit of this target. Marketing 5.2. Immediate Plan. In order to commence a project as a strategy to initiate the program of fisheries activities in the bodies of water of Nauru, an action plan for tilapia may be in order. This action plan in divided into three phases as follows: (a). eradication and control of Mozambique tilapia; (b). stocking of lagoons/ponds with carnivorous species to serve as biological control for feral tilapia; and (c). enhancing the productivity of the lagoons/ponds for tilapia aquaculture Phase 1. Eradication/Control Of Mozambique Tilapia As suggested earlier, from among the seven (7) methods in use for the control of tilapia populations in aquaculture only the following techniques may be appropriate to apply in Nauru at this time and as soon as possible, in controlling the Mozambique tilapia. (1) periodic harvesting of fry and fingerlings including the parents; (2) biological control; and (3) eradication of tilapia using organic toxicants and/or other chemicals. These shall be implemented wherever and whenever appropriate. Potential Bodies of Water for Aquaculture As described in Section 3.1 above the Republic of Nauru has bodies of water that are potential for aquaculture. Foremost of this is the Buada Lagoon and the other bodies of water such as Anabar Lagoon and several other small ponds. These two lagoons and the small ponds are the areas that are being considered where the national plan for tilapia in Nuaru shall be carried out. Figure 8. Buada Lagoon: See description on Section 3.1. (Source of photograph: SPC Fisheries Newsletter #111 October/December 2004) 38