ABSTRACT

Studies were conducted to determine the influence of water level on the growth and survival of Helerobranchius longiflis from fry to adult stage in outdoor concrete tanks. Mature broodstocks of H. longJIlis measuring 3kg each were subjected to hormonal induced spawning for breeding. The hatchery-raised H. IongJllis fry were transferred after l3days to 12 units of 2x2x1m3outdoor concrete tanks and stocked at 50 fry/rn2at three different water levels of 0.35, 0.50 and 0.65m. Four replicates of each treatment were made. The fry were fed twice daily at 10% body weight for 12 weeks after which the stocking density was reduced to 5 fish/rn2in each tank. These were then further grown from weeks 13 to 24 under similar conditions of water parameters. The results indicated that there was no significant difference (P<0.05) in the growth parameters of the fish within the first 12 weeks of culture. However, significant differences (P><0.05) in growth parameters were observed between the treatments from weeks 13 to 24 in relation to the mean length and weight, mean weight gain, mean growth rate, specific growth rate and food conversion ratio. Monthly percentage survival increased significantly in the order: 0.35in (48.070)>0.50rn (44.3270)>0.65(42.5 170) at week 12 produced different at the end of 24 week in the order 0.50m (36%)> 0.65(35%)>0.35(31%). It was then concluded that the influence of water level on growth and survival of H. longifihis in outdoor concrete tanks depended more on the culture period. Based on the results obtained, the least 'vater level of 0.35m was recommended for rearing H. longifihis in outdoor concrete tanks but not beyond 12 weeks while the water level of 0.50rn should not be used beyond 17 weeks at the stocking rate applied in this study.