BROODSTOCK DIETS WITH ADDED CRUDE PALM OIL RESULTED IN IMPROVED REPRODUCTIVE PERFORMANCE , EGG HATCHABILITY AND LARVAL QUALITY OF NILE TILAPIA Oreochromis niloticus

The intensive farming of tilapia is rapidly expanding and the need to produce sufficient quantities of quality fry is becoming crucial to meet increasing global demands for stocking tilapia farms. Furthermore, it is increasingly important to produce high quality tilapia fry due to the low fecundity of broodfish. Tilapias of the Oreochromis genus, the major farmed species, are female mouth-brooders and exhibit high parental care with relatively low number of eggs produced in each clutch. The problem in the mass production of tilapia seed is further exacerbated due to the low degree of female spawning synchrony and reduction in spawning rigor with time. Broodstock nutrition is recognized as a major factor that can influence fish reproduction and subsequent larval quality of many fish species. The development of cost-effective and nutrient optimized broodstock feeds for tilapia is both pertinent and crucial. The present study was conducted to evaluate the effects of dietary lipid source on the reproductive performance of tilapia broodfish. Four isonitrogenous (35% protein) and isolipidic (10%) casein-based diets were formulated with added fish oil (FO), FO and crude palm oil (FO+CPO; 1:1), CPO or linseed oil (LSO) as the lipid source, respectively. Pre-spawning female Nile tilapia (Oreochromis niloticus, GIFT strain) was individually color-tagged, and six females and two males were stocked into a one-tonne breeding tank. Each diet was fed to two tanks of broodfish and the reproductive performance of 12 individual female fish was monitored over 25 weeks. Female broodfish fed the two CPO-based diets showed significantly (P < 0.05) larger gonad sizes and lower intraperitoneal fat compared to fish fed the FO or LSO diets. First spawning occurred earliest in broodfish fed the CPO diet at 30.8 ± 9.9 days compared to 44.1, 45.5 or 76.3 days for fish fed the FO+CPO, FO or LSO diet, respectively. The highest number of actively spawning tilapia was observed in fish fed the FO+CPO diet, followed by fish fed the CPO, FO or LSO diet, respectively. At the end of 25 weeks, tilapia fed the two CPO-based diets produced the highest total number of eggs per fish due to the shorter inter spawning interval and higher spawning frequency. Mean diameter, volume and weight of eggs did not vary among dietary treatments. Egg hatchability was significantly higher in broodfish fed the CPO-based diets. The fatty acid composition of the muscle, gonad, egg and newly hatched larvae was influenced by dietary lipid source. However, evidence of preferential fatty acid conservation, conversion and utilization was also observed in these tissues. The fatty acid composition of tilapia eggs did not vary over four consecutive spawns. The gonads, eggs and larvae of tilapia fed the CPO diet contained the highest relative concentration of saturates, monoenes, arachidonic acid and n-6/n3 ratio. The high total n-3 PUFA concentration observed in the gonads of fish fed the LSO diet, and to a lesser degree the FO diet, seemed to be detrimental to the reproductive performance of tilapia. In conclusion, the ability to replace expensive dietary FO with CPO will augur well in reducing the costs of broodstock diets as well as contributing to the environmental sustainability of wild fishing stocks from which FO is derived. The beneficial impact of dietary CPO on female tilapia reproductive performance included larger gonad sizes, earlier first spawning activity, shorter inter-spawning interval, a longer period of broodfish fertility, higher overall total egg production, higher egg hatching rates and lower incidence of larval deformities as compared to broodfish fed a FO-based diet.