THE POTENTIAL FOR DEVELOPMENT OF TILAPIA CAGE CULTURE IN FIJI

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2 THE POTENTIAL FOR DEVELOPMENT OF TILAPIA CAGE CULTURE IN FIJI BY Cherie Whippy A thesis submitted in partial fulfillment of the requirement for the degree of Master'of Science. Marine Studies Programme and School of Pure and Applied Sciences The University of the South Pacific Suva, Fiji October, 1994

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5 ABSTRACT An experiment on the growth of Tilapia (pure O. nxloticus and O.mossambicus x O.nxloticus hybrid) in cages in freshwater and brackish-water conditions was conducted for 120 days. Sixteen lm 3 cages were each stocked with 100 individuals. Eight cages were placed in a freshwater pond of which four contained the pure and four contained the hybrid (giving the categories: freshwater pure and freshwater hybrid). Another eight cages of the same composition as mentioned above were placed in a brackish-water pond (15ppt, giving the categories: brackish-water pure and brackish-water hybrid). The tilapia were given a pellet diet consisting of local agricultural by-products and fish meal with a 25% protein content. Mean daily weight gain (DWG) ranged from 0.85g to 1.08g, mean specific growth rate (SGR) ranged from 1.63% to 2.07% and mean food conversion rate (FCR) ranged from 3.07 to Although there was no significant difference in DWG between pure and hybrid tilapia between treatments, a significant difference existed within treatments. There were no significant differences in SGR and FCR between pure and hybrids between and within treatments. The mean coefficient of variation of final body weight and length did not differ significantly between and within treatments. The final condition factor ranged from 1.77 to 1.90 and differed significantly between treatments but not within iii

6 treatments. Final biomass ranged from 10.2kg/m 3 to 13.1kg/m 3 and percentage recovery ranged from 98.3% to 100%. There was 100% survival in all categories except the brackish-water pure. There were more females than males in all categories except the freshwater hybrid. iv

7 ACKNOWLEDGEMENTS I would like to express my gratitude and appreciation to the brothers of Monfort Boys Town, in particular, Brother Thomas (Director) and Brother K.M. Thomas for their assistance in offering the 0. niloticus broodstock and the four ponds for this study as well as helping out during the course of the experiment. I would like to offer my appreciation to the International Center for Ocean Development for the scholarship and research grant that made my studies at the University of the South Pacific possible. My sincere thanks to all the staff at the Marine Studies Program for their assistance with the construction and placing of the cages, transport and harvesting especially, Mahend and Suren. I would also like to sincerely thank the staff at Naduruloulou Research Station in particular, Mr. Ledua, Mr. Yamamotu, Tavenisa and Paiata for assisting with the feed-making for my experiment. The invaluable assistance offered by Mr. Satya Nand-Lal is also very much appreciated. Last but not least, I greatly appreciate the help from my friends, Craig, Liz and Johnson with the water chemistry and chlorophyll measurements for analysis of phytoplankton biomass. I am also very grateful to the Institute of Applied Sciences for analyzing the feed.

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11 1. INTRODUCTION 1.1 General The fishes of the family Cichlidae comprise three genera according to the classification by Trewavas (1983). These are, Tilapia, Sarotherodon and Oreochromis (hereafter referred to by their common name, tilapia). Tilapia belong to a group of African freshwater herbivorous and omnivorous fish (Nelson and Eldredge, 1991). The tilapia species are now distributed worldwide and are one of the most widely cultured fishes due to their hardiness, ease of culturing, relatively fast growth and ability to thrive on inexpensive feeds. The most important cultured species of tilapia belong to the genus Oreochromis which are known as maternal mouthbrooders (Gulick, 1989). The Asian countries (Philippines, Taiwan, China, Indonesia, and Thailand) are the major producers of tilapia. Other countries which make significant contributions to tilapia production include Malaysia, Latin America (Cuba, Brazil and Mexico), Europe and the South Pacific (Mistakidis 1991). In most countries, 0. niloticus (Linnaeus) is preferred over 0. mossambicua (Peters) for stocking and culture. This is probably due to the former species having a relatively better growth performance. However, in Papua New Guinea, O. mossambicus is the most important freshwater fish species (Mistakidis 1991). 1

12 Tilapia is commonly used in pond culture, cage culture and/or for stocking natural waters. Pond culture of tilapia is well established in Asia, Africa and the South Pacific. Cage culture of tilapia however, is well advanced in countries such as the Philippines and Malaysia. In Latin America and Malaysia, tilapia is stocked in reservoirs which are well managed systems (Mistakidis 1991). 1.2 Cage Culture Cage culture originated in the Far east and has rapidly developed in other regions such as the United States and Europe. Cage culture as defined by Coche (1982), is the rearing of fish generally from juvenile to market size, in an enclosed water volume through which there is a free flowing circulation water. of This intensive form of fish culture has become popular due to the reasonably high returns and the ease of management. However, it is a high risk business due to high cost of investment in addition to the possibility of losing the whole stock. Cage culture has therefore become a high technology business in the developed countries. Examples are: salmonid cage culture in Norway, Canada and Scotland and tuna culture in Japan (Christensen, 1989). Rearing fish in cages is a practical method for fish 2

13 production in various types of water bodies such as irrigation canals, old quarries and mines and can be applied to rivers, lakes, estuaries and coastal bays (Coche, 1979). One of the principal advantages of raising tilapia in cages is that the tendency of early reproduction leading to overpopulation and stunting (evident in the pond system) is eliminated. Although fertilization can still occur in cages, it is highly unlikely that the eggs will be able to develop successfully with a high density of fish present (Coche, 1979). The other major advantages of cage culture include the limited space that caged fish require, the relatively high growth rates (in areas where there is a constant flow of water) and the possibility of reducing the production costs by adopting a more accurate adjustment of feeding rates (Coche, 1982). Furthermore, it is much easier to feed, inspect and harvest the caged fish compared to any other type of fish culture. However, the caged fish need a supplemental and complete diet as the availability of natural foods are limited (McLarney, 1984). 1.3 Brackish-water Culture The euryhaline characteristics exhibited by some species of tilapia, has prompted the attempt to culture them in brackishwater and seawater. Many of these attempts have shown favorable results. The reasons for rearing tilapia in saline waters 3

14 include: better growth performance, the incidence of the flesh being off-flavour is reduced and the bacteria count is lower. Growth of certain tilapia species in saline waters is enhanced due to the following factors: 1) minimal osmoregulation, 2) exposure to salinity during the early development stages, 3) increased food consumption and a lower food conversion ratio with increasing salinity and 4) suppression of territorial aggression (Suresh and Lin, 1992). Tilapia may grow better in brackish-water than in freshwater due to the following reasons: 1) greater utilization of natural food such as plankton, detritus, bacteria and water insects, 2) higher temperature and 3) the amount of metabolic energy to maintain internal osmotic gradient is reduced (Meriweather et al, 1984). Research has focussed on the feasibility of rearing tilapia in brackish-water and marine systems. Various production systems ranging from ponds to intensive systems such as tanks, raceways and cages have been tested for grow-out, most of them on an experimental basis. The majority of these grow-out experiments in saline waters have concentrated on intensive culture using formulated feeds with regular water exchanges or in an open-water environment (Suresh and Lin, 1992). The first studies were made in Hawaii in the late 1950's where attempts to culture O. mossambicus in tanks as a baitfish for the tuna industry, showed that growth was enhanced at

15 salinities of ppt (Hida et al, 1962, cited in Watanabe et al, 1989). Preliminary studies in Israel on the adaptability of commercial tilapias (0. aureus and Tilapia zilli) to various seawater concentrations, demonstrated their growth potential in saline waters. Experiments carried out in South Israel near the Dead Sea showed that hybrids of O. aureus and 0. niloticus could be reared in waters with a salinity ranging from ppt (Watanabe et al, 1989). Saltwater tilapia culture has gained remarkable interest recently as more superior species and strains have been discovered and as greater awareness of their culture potential is being made. A review of salinity tolerances of tilapias of aquaculture interest was made by Stickney (1986). Studies on methods of saltwater culture have been published, including salinity tolerance in tilapias in relation to ontogeny and early salinity exposure (Watanabe et al, 1985a,b) and reproductive performance at various salinities (Watanabe and Kuo, 1985). Other studies have indicated that 0. spilurus (Hopkins et al, 1986 cited in Watanabe et al, 1989) and the Taiwanese red tilapias (Liao and Chang, 1983; Meriwether et al, 1984) are principal candidates for saltwater culture. Reports on extensive rearing of tilapia in saline waters are not common. In the Philippines, 0. mossambicus intrudes brackishwater systems during the rainy seasons and was found to grow better than milkfish. Guerrero (1985), reported that some farmers have begun to stock 0. niloticus in their braokish-water ponds.

16 Experimental projects have been started in Kuwait and Sauolia Arabia focussing on the commercial feasibility of farming in arid areas (Watanabe et al, 1989). integrated The commercial culture of tilapia in saltwater is not well developed as yet. However, this has been recently demonstrated in Thailand using O. niloticus in brackish-water shrimp ponds (Suresh and Lin, 1992). There is not much information available on cage culture of tilapias in saline waters. Amongst reports made, is the experimental cage culture of O. niloticus and S. melanotheron in brackish-water in the Ivory coast (details not available) (Coche, 1982). Meriwether et al (1984), reported good growth of Taiwanese red tilapia hybrids (O. mossambicus x 0. niloticus) under intensive brackish-water (11-17 ppt) cage culture. According to Suresh and Lin (1992), the development of semiintensive culture or integration of.tilapia with intensive aquaculture of a highly valued species in saline ponds may be appropriate. In addition, they suggested that attention needs to be given to marketability since most work has concentrated on production systems. 1.4 Tilapia Introduction and Culture in Fiji Fishes of the genera Oreochromis are well established in a variety of habitats in the islands of the South Pacific. The

17 three basic reasons for the introduction being 1) for aquaculture, 2) for biological control of the aquatic weed, Hydrilla verticillata and 3) to improve inland fisheries. Tilapia populations can now be found in reservoirs, rivers,streams, lakes and mangroves throughout the region (Nelson and Eldredge, 1991). Fiji was the first Melanesian island in the South Pacific to introduce tilapia. In 1954, 0. mossambious was introduced from Malaya (Malaysia) (Holmes, 1954) and is now well established in freshwater habitats around the country. Oreochromis nilotiaus was first introduced in 1968 from Israel for the purpose of aquaculture (Gulick, 1989). Other strains of 0. niloticus were introduced at different times to suit the local conditions. In 1988, an 0. niloticus strain known as "Chitralada" was imported from Thailand. This strain was found to be most suitable for culture and thus formed the basis of the Fiji Fisheries Division's tilapia program (Lai and Foscarini, 1990). Tilapia culture is needed in Fiji, since it is a valuable source of protein for the inland people, considering their isolation from local markets. It will also become a valuable alternative protein source if or when inshore marine fish stocks begin to decline. The Fiji Fisheries Division developed a program (which began in 1983) in which the stocks of 0. niloticus ("Chitralada" strain) are used for fry production in a hatchery at the Naduruloulou Research Station. Fingerlings are distributed to

18 grow-out farmers for subsistence use, although the trend is shifting towards a semi-commercial level. Other tilapia species cultured are the Israel strain of 0. nilaticus and the Taiwanese strain red tilapia which is a hybridization between 0. nxloticus and the mutant 0. mossambicus (Lai and Foscarini, 1990). Tilapia provides an excellent source of animal protein especially for the people living in rural areas who are isolated from major markets. The ease of culturing this fish allows people to produce their own daily requirements for protein food (Villaluz, 1972). Cage culture can be useful in Fiji since if carefully planned, it can provide a source of cost effective protein production especially for the people in rural areas. This method of culture can easily fit into the village way of life as each family member can take part in the different phases (ie. construction, stocking, managing and harvesting) whenever they are free from their other daily tasks. Fiji has many rivers, estuaries, coastal bays and 2 main reservoirs which may provide a suitable environment for cage culture. In such environments cage culture can be an extensive or semi-intensive system depending on the productivity of the area. In an extensive system, there is no feeding whereas in the semi-intensive system, supplemental feeding of rice bran or mill mix and fish meal or even pellets (if affordable) can be used. The materials needed for construction of cages are available 8

19 locally from forests and mangrove areas. The cages may be held in place by mangrove stakes or iron bars. In 1987, a pilot study on marine cage culture of the red tilapia was carried out by the Fiji Fisheries Division in Laucala Bay. However, due to extensive damage to the cages the project was discontinued (Namotu, 1987). Some of the advantages of implementing cage culture in Fiji include: 1) production of a cost effective source of protein, 2) the elimination of the problem of frequent breeding of tilapia which leads to overpopulated ponds, 3) caged fish are easy to harvest and harvest is complete which is not obtained in pond culture and 4) the elimination of predation. On the other hand, the disadvantages of cage culture in Fiji include: 1) the possibility of the entire stock escaping into open waters, 2) poaching and 3) increase in disease or parasites due to the close association of numerous individuals. In the present experiment, wild 0. mossambicus and cultured 0. niloticus ' ("Chitralada" strain) were used as broodstock (ie. parent stock). Two crosses were made, one resulting in hybrid offspring and the other in pure offspring. Hybrids were chosen in this experiment as a comparison to the breed since hybrids are known to grow faster than either parent species.

20 1.5 Objectives of the study The purpose of this study was to determine the growth rates of existing tilapia species in cages under freshwater and brackish-water conditions, and to determine the feasibility of rearing tilapia in cages in Fiji. The growth rates obtained from cage culture of tilapia were then compared to that of pond culture. 10

21 2. METHODOLOGY 2.1 EXPERIMENTAL FISH Broodstock Origin O. mossambicus broodstock were collected from the wild in two different locations around Suva. The first location was in Tokatoka, Navua (about 3 0 kilometers from Suva). This area consisted of a drainage system for irrigation of rice fields where broodstock were caught on 30 and 31 January The second location was the Laqere Creek (about 7 kilometers from Suva) where broodstock were caught on 7 and 8 February. The wild broodstock were transported from the capture site to the culture site (Monfort Boys Town (M.B.T.)) in large plastic containers. O. niloticus broodstock were collected from freshwater earthen ponds (1000m 2 surface area) at M.B.T. on 19 February. Each broodstock species was held in a freshwater concrete tank (3m x 2m x 1.5m) with a volume of 6m 3 until stocked into ponds Broodstock Stocking and Feeding On 19 February, 20 O. mossambicus females (average weight: 55.9g, average length: 13.7cm) were stocked with 10 O. niloticus males (average weight: 419.8g, average length: 29.6cm) into a freshwater earthen pond at M.B.T. Throughout this document the offspring of this cross will be referred to as hybrids of which 11

22 there are 2 categories - freshwater and brackish-water. These are denoted by Freshwater Hybrid (FH) and Brackish-water Hybrid (BH) respectively. On the same day, niloticus females (average weight: 289.8g, average length: 25.7cm) were stocked with 10 O. niloticus males (average weight: 453.3g, average length: 29.8cm) into another freshwater earthen pond. The offspring of this cross will be referred to as pure throughout this document. The same categories mentioned above apply to these offspring and are denoted by Freshwater Pure (FP) and Brackish-water Pure (BP). The broodstock were fed at a rate of 4% of their total body weight twice a day for 20 days. The feed consisted of 40% copra meal, 35% mill mix and 25% fish meal in powdered form Fry Production, Acclimation and Feeding On 11 March, fry were seen swimming at the pond edge. Using a seine net, 500 of each of the crosses were transferred to separate freshwater concrete tanks (the excess number was to account for mortality). The remaining fry were acclimated to a salinity of 15ppt. This was achieved by pumping seawater from the nearby mangrove area into the ponds at a rate of approximately 3-4ppt/day using a Yanmar diesel water pump (Model YDP 30E). All fry were fed 3 times a day ad lib with a powdered feed 12

23 consisting of 50% fish meal and 50% rice pollard for another 20 days. 2.2 POND PREPARATION Liming Two earthen ponds were used for the experimental grow-out period of 4 months. Pond 1 was 38 meters x 25.5 meters in size (969 m 2 ) and was used for freshwater culture. Pond 2 was 44 meters x 22.1 meters in size (972.4m 2 ) and was used for brackishwater culture. Both ponds were drained and left to dry before applying ordinary agricultural lime (calcium oxide). Application was made directly to the dry soil at a rate of 8kg/m 2. Liming was done to improve the ph of the soil and water, to kill undesirable organisms and to improve fertilization of the water. The inlet and outlet of each pond was covered with fine netting material to minimize entry of undesirable organisms and eggs Water Depth Two days after liming, pond 1 was filled with freshwater up to a depth of 1.5 meters. Pond 2 was filled with a mixture of freshwater and seawater also to a depth of 1.5 meters. The seawater was pumped from the nearby mangrove area while maintaining a salinity of 15ppt. Once the water stabilized, the depth in each pond remained at around 1.3 meters. 13

24 2.3 CULTURE CAGES Cage Design The cages used were lm x lm x 1.3m (length x width x depth) each in size. The extra depth was to allow for the overlap required to protrude above the water surface. This protruding portion allowed for the attachment of a lid for easy inspection. However, the submerged volume was lm 3. Each cage frame was made up of 21 pieces of hardwood timber joined by nails to form the required structure (Plate 1). All six sides of each cage were covered with 18mm stretched diamond mesh (9mm in square) polyethylene (monofilament) netting material. This netting was fastened to the cage frame with wooden battens and nails. The sides of the cages were brushed weekly to eliminate algal growth. There were sixteen cages in total which were divided between two ponds. The cages were arranged in four pairs and each pair was supported by parallel wooden beams measuring 4 meters. These beams were nailed onto the cage frames at the 1 meter height mark to support the buoyancy components. This allowed a displacement of about 15-20cm above the meter depth. Each cage pair was equally spaced 1.5 meters in either direction along a floating raft (Plate 2). The raft was made up -of four 15cm P.V.C. pipes of approximately 10 meters in length. The raft also had a supporting structure in case of a sudden drop 14

25 in water level which would prevent the cages from touching the bottom. The entire set up (cages and raft) was fixed more toward the inlet end of each pond with a 10 meter clearance on either side. Access to the raft from the pond bank was by way of a 12 meter wooden walkway which was supported by mangrove stakes (Plates 3-6). 15

26 Plate 1 One of the cages made with a wooden frame and polyethylene netting used in tilapia cage culture. 16

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28 Plate 2 Experimental layout of tilapia cage culture. 18

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30 Plate 3 Experimental layout showing cages in the freshwater pond (pond 1). Plate 4 Experimental layout showing cages in the brackish-water pond (pond 2).

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32 Plate 5 Experimental layout showing the walkway design. 22

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34 2.3.2 Stocking Size and Density On 1 May 1993, 400 fingerlings of each cross kept in the freshwater tanks were randomly selected by means of catching them with a net while blindfolded. The same was done for the remaining fingerlings that were acclimated in the ponds. A representative sample consisting of 200 hybrid fingerlings and 200 pure fingerlings (100 for freshwater and 100 for brackish-water) were randomly selected. They were then weighed and measured for total length (Table 2.1). MS222 (0.2mg/ml for 30 seconds) was used to anaesthetize the fish during the measurements. The rest of the fingerlings were weighed in batches of 100 pieces. The cages were then stocked with mixed sex fingerlings at a density of 100 fish per m 3 (100 fish per cage). The arrangement of fish in the cages was one of an alternate fashion, such that the pure were in the first cage, the hybrids in the second, pure in the first and so on (Fig. 2.1). TABLE 2.1 Initial weight and length for a representative sample of tilapia reared for 120 days in cages' Category 1.Freshwater pure 2.Freshwater hybrid 3.Brackish-water pure 4.Brackish-water hybrid "Data are represented as means±sem. N Weight (g) ± Length (cm) 9.7±

35 Figure 2.1 Schematic diagram of the arrangement of tilapia in cages. 25

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37 The fingerlings were fed 3 times a day with a crumble feed at a rate of 10% of their total body weight per day for the first month. A feeding rate of 4% was adopted thereafter and the fish were given pellets beginning with lmm in size and then with 3mm. A plastic feeding basket was placed in each cage after one month to contain the feed in one place and thus reduce loss through the cage walls. The feed was placed into these baskets gradually, not all at once, to achieve maximum utilization. TABLE 2.3 Composition of pellet diet fed to tilapia during the experiment. Component Crude protein Crude fat Crude fibre Ash Moisture Nitrogen Phosphorous Sodium Potassium Calcium Magnesium Iron Calorific value Quantity 25.1% 8.7% 5.0% 9.0% 10.9% 4.0% 2.8% mg/lqog mg/loog mg/loog mg/loog 21.4 mg/loog 2370 kj/loog 27

38 2.4 SAMPLING DESIGN Water Chemistry During the experimental period, the following water quality parameters were analyzed weekly between hours and between hours. Below is a summary of the methods used to measure the water quality parameters. 1. Dissolved oxygen: Used a dissolved oxygen meter (YSI model 58) to measure both ambient and incage levels (Mote: From week 9 - week 14 the D.O. meter was out of operation so no readings were taken) 2. Surface Temperature: Used a Salinity Temperature Conductivity meter (S.C.T.) (YSI model 38) to measure ambient temperature 3. ph: Used a Unilab ph meter model number Salinity: Used the S.C.T. meter to measure salinity 5. Turbidity: Used a Secchi disc Phytoplankton biomass To determine the Phytoplankton biomass, two samples of 0.4 litres of water were collected from each pond at different areas along the raft each time. The water samples were then processed 28

39 by the following method. The Chlorophyll-a pigment was extracted with 90% acetone solution. Maceration of the filter paper and centrifugation of the water samples followed. A spectrophotometer (Miltonroy Spectronic 301) was used to measure the absorbance of the extract. The Phytoplankton biomass was then determined by multiplying the chlorophyll-a content by a factor of 67. Two replicate samples were taken for each pond and the average taken after the biomass was determined (AEHA, 1989) Measurement of Fish Growth Ten percent of the total number of fish in each cage (ie. 10 fish per cage) were sampled fortnightly at first. After 2 weeks, the sampling interval was changed to fifteen days where only 50% of each cross was sampled at a time (ie.4 cages at a time where 2 were pure and 2 were hybrids). This was done to minimize disturbance. During sampling, the individual weight and total length were measured while the fish were anaesthetized with MS222. Feed was adjusted accordingly after each sampling period. For those fish not sampled, feed was adjusted based on the calculated daily mean weight gain for each of the crosses which gave an estimated increase in weight over the interval between samples. Fish mortality occurred 4 days after stocking in the brackish-water cages only where a total of 7 cultured hybrids 29

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41 At the end of the experiment the following parameters were determined after sampling all the fish. 1. All growth parameters listed above 2. Final biomass (Kg/m 3 ) 3. Final count of fish in each cage 4. Survival/% recovery 5. Sex ratio. In addition, an economic analysis of tilapia cage culture in Fiji was carried out by Vina Ram, a local economics expert, in parallel with this experiment. This report was made available for analysis to assess the economics of this study Statistical Analysis The experimental data were analyzed by a computer software, MINITAB and (One Way Analysis of Variance) ANOVA was used to determine significant differences between treatments. 31

42 3. RESULTS 3.1 Mater Quality Ambient dissolved oxygen (DO) concentration fluctuated between 3.5mg/L and 7mg/L in pond 1 and between 4mg/L and 8mg/L in pond 2 (Fig. 3.1). Incage DO concentration fluctuated between 3.3mg/L and 6.4mg/L in pond 1 and between 3.6mg/L and 6.8mg/L in pond 2 (Fig. 3.2). Generally, DO was higher in pond 2 than in pond 1 and the possible critical levels experienced throughout the experiment were the morning incage DO of 3.3nig/L during the 3rd week and 3.4mg/L during the 5th week in pond 1. Water temperatures ranged from 20 C to 30 C in pond 1 and from 20"C to 30.3 C in pond 2 (Fig. 3.3) except during the 9th week when it decreased to 17.4 C and C in pond 1 and pond 2 respectively. Temperatures remained generally low thereafter until the end of the experiment. In general, throughout the experimental period, the water temperature was low since it was the cooler season of the year and this particular year was exceptionally cooler than previous years. Although the initial ph levels were as low as 5 there was an increase towards the later part of the experiment where it reached 7.8 in pond 1 and 8 in pond 2 (Fig. 3.4). Salinity fluctuations are shown in Fig Salinity in 32

43 pond 1 did not fluctuate much, the highest being O.Sppt. In pond 2, there was a wide fluctuation with readings ranging from 8. lppt to 18ppt, the lowest readings corresponding with periods of heavy rainfall. An average salinity of 12.7ppt was realized for pond 2. Turbidity of the water in both ponds was generally high except towards the end of the experiment (Fig. 3.6). In pond 1, turbidity ranged from 15cm to 85cm and in pond 2, turbidity ranged from 25cm to 100cm. Although pond 1 was generally more turbid than pond 2, no critical levels were experienced. Detailed water quality data are presented in Appendix I and include dissolved oxygen DO (mg/l); temperature ( C); ph; salinity (ppt); and turbidity (cm). 33

44 Figure 3.1 Fluctuation of ambient dissolved oxygen in ponds 1 and 2 during the experiment. 34

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46 Figure 3.2 Fluctuation of incage dissolved oxygen in ponds 1 and 2 during the experiment. 36

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48 Figure 3.3 Fluctuation of temperature in ponds 1 and 2 during the experiment. 38

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50 Figure 3.4 Fluctuation of ph in ponds 1 and 2 during the experiment. 40

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52 Figure 3.5 Fluctuation of salinity in ponds 1 and 2 during the experiment. 42

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54 Figure 3.6 Fluctuation of turbidity in ponds 1 and 2 during the experiment. 44

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56 3.2 Phytoplankton biomass Phytoplankton biomass fluctuation is shown in Fig A relatively low phytoplankton biomass persisted throughout the experiment as there was no fertilization. The highest phytoplankton level in pond 1 was 5.85g/L and 18.29g/L in pond 2. Detailed data on phytoplankton biomass are presented in Appendix II. 46

57 Figure 3.7 Fluctuation of phytoplankton biomaas in ponds 1 and 2 during the experiment. 47

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59 3.3 Fish Growth The mean weights of caged tilapia in different treatments are shown in Figs. 3.8a-d. There was no significant difference in initial weights between the pure and the hybrids. A significant difference.(p=0.4) between pure and hybrids became apparent within the brackish-water treatment after 12 days. After sampling on the 24th and 69th days a significant difference was found between pure and hybrid within the freshwater treatment (p=0.4). After sampling was carried out on the 12th, 24th and the 39th day of the experiment, significant differences became apparent between hybrids between the two treatments (p=0.4). Again, a significant difference was found between treatments (p=0.4) for the pure strain after sampling on the 54th and 69th days. Sampling data including initial and final measurements are presented in Appendix III. Coefficients of variation of initial weights and lengths plus condition factors are presented in the table below with no significant differences between pure and hybrid tilapia between or within treatments. 49

60 Figure 3.8a Mean weight of freshwater pure tilapia during the experimental period. Figure 3.8b Mean weight of freshwater hybrid tilapia during the experimental period.

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62 Figure 3. 8c Mean weight of brackish-water pure tilapia during the experimental period. Figure 3. 8d Mean weight of brackish-water hybrid tilapia during the experimental period. 52

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64 Growth rates expressed as daily weight gain and specific growth rate are shown in Table 3.1. Analysis of variance showed that there were no significant differences between pure and hybrid between treatments. However, there was a significant difference in daily weight gain between pure and hybrid within treatments (p=0.4). TABLE 3.1 Initial coefficients of variation {%) of body weight (W) and length (L) and condition factor (K) of tilapia reared for 120 days in cages. Category Initial H W L K 1.Freshwater pure Freshwater hybrid 3.Brackish-water pure 4.Brackish-water hybrid 54

65 TABLE 3.2 Daily weight gain (DWG) and specific growth rate (SGR) of tilapia reared for 120 days in cages* Category 1.Freshwater pure 2.Freshwater hybrid 3.Brackish-water pure 4.Brackish-water hybrid N DWG (g/day) SGR (%day) * ±0.29 "Data are presented as meansis.e.m. Feed conversion rates are shown in Table 3.3. There were no significant differences between pure and hybrid between treatments and within treatments. TABLE 3.3 Feed conversion rates (FCR) of tilapia reared for 120 days in cages* Category 1.Freshwater pure 2.Freshwater hybrid 3.Brackish-water pure 4.Brackish-water hybrid Data are presented as means+s.e.m. N FCR (dry wgt./wet wgt.) 3.07± ± Although overall mean coefficients of variation (CV) oi final body weights and lengths were high, ranging from 27.3%- 37.3% and 1.7%-1.9% respectively (Table 3.4), there were nf 55

66 significant differences between pure and hybrid between i within treatments. (See Fig. 3.9a-d for frequency distribut: of body weights). The final condition factors ranged from 1.78 to 1.90 {Tal 3.4) and differed significantly between pure and hybrid betw< treatments but not within treatments (p=0.1). TABLE 3.4 Final coefficients of variation (%) of body weight (W) and leni (L) and condition factor (K) of tilapia reared for 120 days cages" Category 1.Freshwater pure 2.Freshwater hybrid 3.Brackish-water pure 4.Bracki sh-water hybrid ±5.1 "Data are presented as meansis.e.m. N W ±1.8 Final L ± K 1.87±0.C 1.86±0.C 1.9O+.0.C 1.70+O.C 56

67 Figure 3. 9a Frequency distribution of freshwater tilapia final weight. Weight class 1 refers to a weight range of 40-50g with each subsequent class increasing by log. 57

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69 Figure 3.9b Frequency distribution of brackish-water tilapia final weight. Weight class 1 refers to a weight range of 40-50g with each subsequent class increasing by log. 59

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71 The final biomass, percentage recovery and sex ratio are presented in Table 3.5. Final biomass ranged from 10.2kg/m 3 to 13.1kg/m 3 and percentage recovery ranged from 98.3% to 100%. There were more females than males in all categories except the freshwater hybrid (Fig. 3.10). There is some recent evidence which explains the incidence of obtaining unexpected ratios in hybrids. Interspecific and intraapecific hybridization suggests that there are homogametic and heterogametic genders within tilapia species and that the sex chromosomes of tilapia follow the pairing system. Therefore, unexpected sex ratios indicate that other factors such as autosomes (ie. those chromosomes that are not sex chromosomes) and the environment are involved in sex determination. The evidence appears to favour a certain gonosome strategy with autosomal and environmental influences. In such a strategy, at a certain point in time during development in young hybridized tilapia, autosomes and the environment (which may be one or a combination of factors) may influence sex determination thus favouring a particular sex (cited in Trombka and Avtalion, 1993). Although there is a possibility that the unusual sex ratio obtained for brackish-water hybrid tilapia was due to the influence of autosomes and the environment, this needs to be investigated further. 61

72 TABLE 3.5 Final biomass, percentage recovery and sex ratio for tilapia reared in cages for 120 days." Category Final Biomass (kg/m 3 ) %, Recovery Sex Ratio M:F 1,Freshwater pure : Freshwater hybrid :1 3.Brackish-water pure : BrackiBh-water hybrid :5 category. Survival was excellent. There was 100% survival for the hybrids in both treatments and for the freshwater pure. Survival for the brackish-water pure was 98%. Fish escaping during the beginning of the experiment and during sampling was more of a problem. A total of 200 tilapia escaped at the beginning (100 FP, 100 BP) due to the netting not being attached to the cage frame properly in some areas and 15 fish escaped during sampling {5 FH, 6 BP and 4 BH) due to the slippery nature of the fish when handling. Detailed data on growth parameters are presented in Appendix IV and include daily weight gain, specific growth rate, food conversion ratio, coefficients of variation and condition factor.

73 Figure 3.10 Sex ratio of freshwater and brackish-water tilapia. 63

74 M 38.9% BP BH 64

75 4. DISCUSSION Concentrations of both ambient and incage dissolved oxygen were within the tolerance range of tilapia and did not go below 3mg/L, therefore did not appear to cause any problems (Chervinski, 1982). The fluctuation in incage DO concentration resulted from the wind-water interaction as the culture area received a fair amount of wind during the experimental period. During the 9th week when the temperature suddenly dropped, activity and feeding were somewhat reduced but did not cease. A difference in feeding activity between experimental groups was observed at the time. This resulted in a slightly reduced growth rate of the brackish-water pure tilapia and an obvious* reduced growth rate of the freshwater hybrid tilapia, each decline apparent at different time intervals depending on their feeding response. There was no apparent effect of the sudden temperature drop on the growth rate of the freshwater pure tilapia and the brackish-water hybrid tilapia. It appeared that a sufficient proportion of these two categories of tilapia were feeding, so the overall growth was not affected. However, throughout the experimental period, the temperature was relatively low thus affecting overall growth. In general, ph values during the experimental period were 65

76 lower than the recommended value of 7-8 for tilapia culture (Chervinski, 1982). This confirms that the pond soil is acidic and this would have influenced growth of the tilapia. The wide fluctuation of salinity in pond 2 was due to the weather as well as problems encountered with the pond outlet pipe being knocked down resulting in some water loss. This fluctuation of salinity in pond 2 may have affected the growth of tilapia in this treatment considering that they were not acclimated to a. salinity higher than 15ppt. According to Suresh and Lin (1992), the best growth of 0. mossambiaus was achieved in 17ppt salinity and that of 0. niloticus in 5-10ppt. The decline in turbidity towards the end of the experiment was due to the cages in both ponds touching the sediment at the bottom. This was caused by the sinking of the supporting structures in turn caused by the weight of people frequently walking on the walkway. Heavy rainfall did not seem to affect turbidity to a great extent since the pond dikes were covered with grass. Phytoplankton biomass was low obviously due to no fertilization. Fertilization was omitted so that the exact quantity of feed input could be calculated. Measurement of phytoplankton was carried out to give an indication of the amount of natural food present in the ponds. The sudden increase in phytoplankton biomass in pond 2 towards the end of the experiment was initially due to the replacement of water pumped in as a 66

77 result of water loss caused by the outlet pipe being knocked over. The phytoplankton flourished during this period which coincided with a decline in turbidity. It was very unlikely that this change in phytoplankton biomass affected the growth of tilapia in pond 2. The significant difference in DWG between pure and hybrid tilapia within treatments was probably due to the difference in sex ratio. There was a greater percentage of hybrid males in the freshwater treatment and a greater percentage of pure males in the brackish-water treatment. The relatively high FCRs obtained in this experiment may be attributed to the loss of feed through the cage walls as a result of agitation by the fish (McGinty, 1991). According to Carro- Anzalotta and McGinty (1986), O. nilotious reared in cages at 250/m 3 in ponds fed with 32% protein sinking pellets had food conversion of Coche (1979), suggested that FCR of caged fish is influenced by the interaction between the fish (size and density), the food (quality, ration and distribution) and the physio-chemical environment (particularly water temperature, DO and rate of water renewal). Coche (1979) also reported that FCR in intensive fish culture in cages generally ranges from 1.2 to 1.7 using floating pellets. The condition factor gives an assessment of the physiological state of the fish. The low final condition factors obtained, indicated that the fish were in poor physiological 67

78 state at the end of the experiment which was probably due to stress. The condition factor is also used to determine the way in which fish utilize catabolic fuels during metabolism. The significant difference in condition factor between pure and hybrids between treatments indicates the difference in the amount of stress imposed on the fish between freshwater and brackishwater environments. The growth of O. nilotiaus and the hybrid (0. mossawblcus x 0. niloticus) are compared to similar experiments in the Philippines and the Ivory coast in the tables below. Each category is presented in a separate table. 68

79

80

81

82 In the Ivory coast experimental work on 0. niloticus with average initial weight of 2 9g, stocked at 340/m 3 in lin 3 cages for 125 days, produced an average final weight of 197g (Table 4.1) (Coche, 1979). Due to the low potential of 0. mossambxcus for cage culture, not many studies have been done on this species. However, growth of the freshwater hybrid tilapia in the current experiment when compared with results from the Philippines seemed to be good. In 15m 3 cages, with a stocking density of 50/m 3, hybrids reached g in 4 months (Table 4.2) (Beveridge, 1987). There is little information available on cage culture of tilapias in saltwater. Experimental work on the growth of O. niloticus cages in saline waters in the Ivory coast where salinity reached about 20ppt, proved to be very good although details were not available. Using commercial size cages (27 and 53m 3 ) a growth rate of was achieved (Coche, 1982). The growth of this species in the current experiment is slow compared with that from the above example (Table 4.3). In saline water trials in the Philippine coastal areas, O. mossambicus and hybrids reached g in 3-5 months. Cages were 3m x 3m x 1.5m in size and fish were fed at a rate of 3-5% of the biomass (Guerrero, 1991). The growth of the hybrids in the current experiment is somewhat slow when compared with the example above (Table 4.4). 72

83 From the above comparisons of tilapia growth rates in cages, it is evident that the Fijian hybrid tilapia in freshwater showed reasonably good performance where as the Fijian hybrid tilapia in brackish-water and pure O. nxloticus in fresh and brackish water did not do so well. However, comparisons are difficult to make for different lengths of culture periods. The two major factors influencing the growth of caged tilapia in the current experiment was,probably due to 1) the relatively low temperatures experienced and 2) the sex ratio where the majority were females. The growth rate of tilapia is greatly dependent on water temperature. According to Balarin and Haller (1982), the optimum water temperature for tilapia is 22 C- 28"C, where as the preferred temperature range is 28 C-35 <1 C. It is known that male tilapias grow faster than females due to the shift of energy by the females to the egg forming process and to the time of incubation when feeding ceases (Bondari, 1982 cited in Carro-Anzalotta and McGinty, 1986). Other factors which may have influenced growth of the caged tilapia include: feeding technique (frequency and presentation), size at stocking and stocking density. Each factor is discussed below. The feed ration was divided into three times a day at the convenience of the farm-hand who did not live on or near the site. If the farm-hand lived close to the site, it would have been practical to increase utilization by increasing the feeding 73.

84 to perhaps four times a day and the stocks could be more closely monitored. The pellet feed used was in between a floating and sinking type. It floated for about 5 minutes before sinking and often breaking up into smaller pieces indicating poor water stability. The loss of feed caused by agitation of the caged tilapia combined with the poor water stability of the feed could be an important influence on growth. There was some evidence of a size hierarchy in this experiment as a consequence of dominant individuals. In addition, the low stocking density (100/m 3 ), seemed to produce a wide size variation which is reflected in the high coefficients of variation of final body weight and length (Table 3.4). In some cages, there were a few small individuals. Possible explanations for this are that these individuals were subordinate siblings whose growth was stunted due to the presence of dominant individuals combined with low temperatures during the experiment. All these small individuals were females and it is known that female tilapia have a slower growth rate than that of males. In a study by Watanabe et al (1990), on red tilapia, it was revealed that there was a significant effect of stocking density on final size variation with greater coefficient of variation of body weight and length among fish reared at a density of 100/m 3 in lm 3 cages compared to densities of 200 and 300/m 3. 74

85

86 In comparison with tilapia pond culture, the average growth rate of tilapia in cages is lower using artificial feed. A 25% protein feed was used for cage culture and 3 feed formulations with 25.6%, 28% and 29.3% protein was used for pond culture. The same ingredients were used in both cage and pond experiments but in different quantities (Yamamoto and Vereivalu, 1993). When comparing stocking density in terms of number of fish per pond surface area of the two experiments, it was noted that for cage culture in ponds, stocking density was 1.2 fish/iri 2 which was close to that of pond culture (1.5 f ish/m 2 ). By comparing production costs obtained (from the economic analysis report by Vina Ram prepared in parallel with this experiment), with local market prices (Table 4.5), it is evident that cage culture is not economically feasible on an artisanal scale. However, from the table above, it is obvious that the total production of tilapia in cages obtained from this experiment is far lower than that obtained from pond culture. Total production from ponds is about 3 to 5 times higher than that obtained from these experimental cages. Therefore, due to the very low production from tilapia cage culture (as a result of poor growth), the production cost is higher compared to that of pond culture. If higher growth rates were achieved in cage culture, then it may become economically feasible. Ways in which better growth of tilapia may be achieved include: 1) growing tilapia in higher water temperatures, 2) 76

87 placing cages in a natural water body where tilapia can utiliz natural food organisms and 3) using fertilizers production of phytoplankton for tilapia to feed on. to enhano However, pond culture involves high capital costs such a; the digging of the pond and pond construction. Therefore, i: capital costs were considered, the production cost of tilapia ii ponds may be as high as that in cages if not higher. In conclusion, the growth rates of tilapia reared in 1m cages for 120 days at an average temperature of 23.7 C ii freshwater and 24.1 C in brackish-water given a 25% protein diet were as follows: FP=0.85g/day; FH=l.08g/day; BP=0.91g/day and BH=0.86g/day. The overall growth rates of tilapia reared in cages were lower than those obtained in experiments in the Philippines and the Ivory coast except that of the hybrid in freshwater. In comparison to ponds in Fiji, the growth rates of tilapia reared in cages were lower. However, it should be noted that the pond stocking rates practiced in Fiji are lower than they could be. : This experiment has shown that cage culture of tilapia in Fiji is biologically feasible for hybrids in freshwater and j pure O. nilotiaus in brackish-water conditions. From an economic} point of view, this experiment has shown that tilapia cage culture is not feasible under such conditions. > 77

88 It is apparent from this experiment that tilapia have the potential to grow reasonably well in brackish-water. Therefore, this opens up the possibility of exploiting this resource for tilapia culture in Fiji, as there are many sites available such as mangrove and estuary areas. It would even be possible to culture tilapia in cages on a commercial scale and this could be a profitable venture if one has the capital and the resources available to pursue this type of business. 78

89 5. RECOMMENDATIONS FOR FUTURE STUDIES It would be advisable to carry out tilapia grow-out trials during the warmer months (November to April) as temperatures are more suitable for growth. The stocking density in cages can be increased to minimize the variation in size and to increase production. Although the initial stocking size was quite large, even larger sizes can be stocked so that growth diversion of the sexes would have taken place and selection of larger individuals which would most likely be males is possible. This would reduce size hierarchy and thus prevent stunting. Larger cages are recommended to reduce feed loss and locally available material eg. bamboo can be used for cage construction to reduce costs. The cage design and construction must be carefully considered or else stocks will be lost. A stronger netting material could be used, and taking into consideration corrosion of metal especially in saltwater, I recommend that plastic mesh material be used in order to eliminate the incidence of fish destroying the net and escaping. A semi-intensive cage culture system should be looked into, whereby growth of natural food is enhanced so that feed costs are reduced. If cage culture is carried out on a commercial scale, 79

90 5. RECOMMENDATIONS FOR FUTURE STUDIES It would be advisable to carry out tilapia grow-out trials during the warmer months (November to April) as temperatures are more suitable for growth. The stocking density in cages can be increased to minimize the variation in size and to increase production. Although the initial stocking size was quite large, even larger sizes can be stocked so that growth diversion of the sexes would have taken place and selection of larger individuals which would most likely be males is possible. This would reduce size hierarchy and thus prevent stunting. Larger cages are recommended to reduce feed loss and locally available material eg. bamboo can be used for cage construction to reduce costs. The cage design and construction must be carefully considered or else stocks will be lost. A stronger netting material could be used, and taking into consideration corrosion of metal especially in saltwater, I recommend that plastic mesh material be used in order to eliminate the incidence of fish destroying the net and escaping. A semi-intensive cage culture system should be looked into, whereby growth of natural food is enhanced so that feed costs are reduced. If cage culture is carried out on a commercial scale, 79

91 trials can be done using different feed formulations and the development of a more stable pellet is recommended. In addition, feeding of caged fish is of fundamental importance and a suitable feeding technique must be adopted especially if culture is intensive. For example, the feeding rate can be gradually decreased according to the weight of the fish and the temperature especially during the cooler months. This will reduce feed costs and improve the utilization of the feed. An alternative feeding method such as demand feeding should also be considered, or if cages are in shallow waters, placing them on the bottom may contain the falling food. In addition to the water quality parameters measured in this experiment, ammonia could also be measured especially if a high stocking density is used in a closed system, such as ponds. 80

92 6. REFERENCE APHA (American Public Health Association), Standard Methods for the Examination of Water and Waste Water, 17th Edition. American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington DC, USA. Balarin, J.D. and R.D. Haller, The Intensive Culture of Tilapia in Tanks, Raceways and Cages, pp In J.F. Muir and R.J. Roberts (Eds). Recent Advances in Aquaculture. Westview Press, Boulder, Colorado. Beveridge, M., Cage Aquaculture. Fishing News Books. Blackwell Scientific Publications Ltd., 351 pp. Carro-Anzalotta, A.E. and A.S. McGinty, Effects of Stocking Density on Growth Of Tilapia nilotioa Cultured in Cages in Ponds. Journal of the World Aquaculture Society, Vol. 17, Nos. 1-4, pp Chervinski, J., Environmental Physiology of Tilapias, pp In R.S.V. Pullin and R.H. Lowe-McConnell (eds). The Biology and Culture of Tilapias. Proceedings of the International Conference on the Biology and Culture of Tilapias, Italy. International Center for Living Aquatic Resources Management, Manila, Philippines, 432 pp. 81

93 Christensen, M.S., The Intensive Cultivation of Freshwater Fish in Cages in Tropical and Subtropical Regions. Animal Research And Development 29:7-20. Coche, A.G., A Review of Cage Fish Culture and its Application in Africa, pp In T.V.R. Pillay and Win. A. Dill (Eds). Advances in Aquaculture, FAO Technical Conference on Aquaculture, Kyoto, Japan Fishing News Books Ltd., England, 653 pp. Coche, A.G., Cage Culture of Tilapias. In R.S.V. Pullin and R.H. Lowe-McConnell (Eds)., 1982, pp Guerrero, R.D., Tilapia farming in the Philippines: practices, problems and prospects, p In Smith, I.R., B.B. Torres and E.O Tan (Eds.) Philippine Tilapia Economics. ICLARM Conference Proceedings 12, 261 pp. Philippine Council for Agriculture and Resources Research and Development, Los Banos, Laguna and International Center for Living Aquatic Resources Management, Manila, Philippines. Guerrero, R.D., Farming Tilapia in the Philippines. Infofish International, 6, pp Gulick, C.T., A Review of Aquaculture in Fiji. Rural Aquaculture Program. Report to the U.S. Peace Corp, Suva, Fiji. 82

94 Holmes, S., Report on the Possibility of Using Tilapia mossambica as Human Food. Fiji Agriculture Journal, 25 (3-4):79. Lai, S.N. and R. Poscarini, Introduction of Tilapia Species and Constraints to Tilapia Farming in Fiji. Fisheries Division, Ministry of Primary Industries, Fiji, 23 pp. Liao, I.-C. and S.-L. Chang, Studies on the Feasibility of Red Tilapia Culture in Saline Water. In L. Fishelson and Z. Yaron (compilers) Proceedings of the International Symposium on Tilapia in Aquaculture, Nazareth, Israel, May Tel Aviv University, Tel Aviv, Israel, pp Meriwether, F.H., E.D Scura and W.Y. Okamura, Cage Culture of Red Tilapia in Prawn and Shrimp Ponds. Journal World Mariculture Society, 15: of McGinty, A.S., Tilapia Production in Cages: Effects of Cage Size and Number of Honoaged Fish. The Progressive Fish-Culturist, 53: McLarney, W., The Freshwater Aquaculture Book. Hartley and Marks Publishers. Vancouver B.C., pp ,

95 Mistakidis M.N. (Ed)., Workshop on Tilapia in Capture and Culture-Enhanced Fisheries in the Indo-Pacif ic Fishery Commission Countries. Indo-Pacific Fishery Commission. Food and Agriculture Organisation Aquaculture Bulletin, 8(2):8-14, Food and Agriculture Organisation of the United Nations, Rome, Italy. Namotu, T.M., The preliminary Study of the Technical Feasibility of Culturing the Red Hybrid Tilapia in Fiji - Semi-Intensive Culture in Earthen Freshwater Ponds. Annual Progress Report. Fiji Fisheries Division, Ministry of Primary Industries, 14 pp. Nelson, S.G. and L.G. Eldredge, Distribution and Status of Introduced Chichilid Fishes of the Genera Oreochromis and Tilapia in the Islands of the South Pacific and Micronesia. Asian Fisheries Science, 4: Pullin, R.S.V. and R.H. Lowe-McConnell, The Biology and Culture of Tilapias. Proceedings of the International Conference on the Biology and Culture of Tilapias, Italy. International Center for Living Aquatic Resources Management, Manila, Philippines, 432 pp. Bam, V A Report on the Economic Assessment of Tilapia cage Culture in Fiji. Marine Studies Program, The University of the South Pacific, 13pp. 84

96 Stickney, R.R Tilapia Tolerance of Saline Waters: A Review. Progressive Fish-Culturist, 48(3): Suresh, A.V. and C.K. Lin, Tilapia Culture in Saline Waters: A Review. Aguaculture 106:(3-4) Trombka, D. and R. Avtalion, Sex Determination in Tilapia - A Review. Israel Journal of Aquaculture 45(l): Bamidesh, Israel. Trewavas, E. f Tilapine Fishes of the Genera Sarotherodon, Oreochromis and Danakilia. Comstock Publishing Association. Cornell University Press, Ithaca, New York, pp , Villaluz, D.K., Aquaculture Possibilities in Some Islands of the South Pacific. Report Prepared for the South Pacific Islands Fisheries Development Program. FAO/DP/RAS/69/102/12. Watanabe, W.O. and CM. Kuo Observations on the Reproductive Performance of Nile Tilapia [Oreochromis niloticus) in Laboratory Aquaria at Various Salinities. Aquaculture 49: Watanabe, W.O., CM. Kuo and M-C Huang. 1985a. Salinity Tolerance of Nile Tilapia Fry (Oreochromis niloticus), Spawned and Hatched at Various Salinities. Aquaculture 48:159-85

97 Watanabe, W.O., CM. Kuo and M-C Huang. 1985b. Salinity Tolerance in the Tilapias Oreochrojnis aureus, O. niloticus and an 0. mossambicus x O. niloticus Hybrid Spawned and Reared in Freshwater. Aguaculture 47: Watanabe, W.O., R.I. Wicklund, B.L. 011a, D.H. Ernst and L.J. Ellingson Potential for Saltwater rilapza Culture in the Caribbean. Proceedings of the 39th Annual Conference of the Gulf and Caribbean Fisheries Institute, Hamilton, Bermuda, pp Watanabe, W. 0., J.H. Clark, J.B. Dunham, R.I. Wicklund and B.L. 011a, Culture of Florida Red Tilapia in Marine Cages: the effect of Stocking Density and Dietary Protein on Growth. Aquaculture 90: Yamamoto, H. and T. Vereivalu, Report on Experimental Tilapia Feed. Fisheries Division, Ministry of Primary Industries and Japan International Co-operation Agency, 15pp. 86

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104 APPENDIX III This appendix contains all the data that was recorded in the field. On the first two pages are the initial measurements of 400 individuals being a representative sample of both the hybrid (200) and of the pure (200) tilapia used in the two different conditions. The third page gives the total initial weights. The sampling data follows the initial measurements. The sample number and dates are given and samples are divided into two, a and b which represent the freshwater pond and brackishwater pond repectively. The column headings correspond to the cage number where w represents weight and 1 represents length. Ordinary numerals are used to denote the freshwater pond and Roman numerals are used to denote the brackish-water pond. The harvest data follows the sampling data where the measurements (weight and length) and sex of individuals in each cage is given. 93

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