Reproductive performance and the growth of pre-stunted and normal Nile tilapia (Oreochromis niloticus) broodfish at varying feeding rates

A 119-day experiment was conducted to investigate the effects of feeding rate and reproductive performance of stunted (S) and non-stunted or normal (N) Nile tilapia (Oreochromis niloticus). Both the groups were reared in tanks re-circulated with bio-filtered water and fed with floating pellets (30% crude protein) twice daily. Seed were harvested weekly from the mouths of incubating females. The study showed that early stunting with subsequent high feeding rate can improve both growth and reproductive output in female Nile tilapia. Broodfish type and feeding rate showed significant (P<0.05) effects on both the frequency of spawning and the seed output. In general, seed output from normal broodfish increased linearly over the experimental period at all the feeding rates. However, seed output from stunted broodfish showed a linear increment for 3% feeding rate, exponential increment for 2% but quadratic for 1% showing decline after 10th week of the trial period. Results also showed that trends of seed output from stunted broodfish increased linearly with the increase in feeding rate showing that optimum rate could be higher than 3%. While from normal group the relationship was quadratic; increasing from 1%, peaked at 2% and declined at 3% feeding rate. Final GSI of the stunted females was significantly (P<0.05) higher than that of normal females. The GSI of stunted fish showed a decreasing trend with the increased feeding rate. Both the broodstock groups fed at 1% biomass grew linearly whereas at 2 and 3%, they grew exponentially. As compared to the normal, stunted broodfish had significantly (P<0.05) higher fat content in viscera although similar levels were in carcass and ovary. Carcass fat content was significantly (P<0.05) lower in fish fed at 1% biomass but significantly (P<0.05) higher in the ovary and viscera of fish fed at 3% biomass. This study shows that tilapia hatchery operators could manipulate the seed production according to the seasonal demand by using appropriate broodstock stunting and feeding strategies. (C) 2007 Elsevier B.V. All rights reserved.