Olufemi Oluseun Ajiboye, Victor Azubuike Okonji and Adams Femi Yakubu
The study aimed at determining the effect of testosterone-induced sex reversal on the sex ratio, growth enhancement and survival of Nile tilapia, Oreochromis niloticus fed two feed type (coppens and farm produced feed of 56% and 25% crude protein respectively) and reared intensively under controlled conditions in a semi flowthrough culture system in twelve fibre glass tanks. The present study also examine the effectiveness of water flowthrough culture system in controlling unwanted reproduction during culture of mixed sex O. niloticus. The experiment was designed as 4 treatments × 24 weeks factorial replicated thrice. The fry was treated with a steroid hormone, 17α-methyltestosterone and cultured for a period of 21 days to reverse the sex to male fishes. After completion of the trial period of 21 days, nursing of the experimental fry (mixed sex and sex reversed) was continued for further 24 weeks with the two feed type. The results of the study showed that the highest sex occurrence of 95% and 90% males was recorded in the sex reversed fishes fed Coppens (Treatment II) and Farm Produced Feed (Treatment IV) respectively. Survival rate was 100% among all the treatments. Treatment II had the highest/best mean body weight gain (19.97 g), daily weight gain (0.12 g) and highest final weight (50.11 g). The study clearly indicated that the inclusion of the steroid hormone, 17α-methyltestosterone in the diets significantly altered the sex ratio towards male and enhanced the growth performance and survival rate in the sex reversed group in Treatments II and IV (P<0.05) irrespective of the feed type and thus recommended for tilapia culture. In spite of the overall best performance recorded in 56% CP of the commercial diet (Coppens) fed the tilapias in Treatments I and II, which is outside the recommended levels for the growth of tilapia, a significant growth rate (P<0.05) was also observed in the tilapias fed Farm Produced Feed with 25% CP content and is also recommended. The inability of O. niloticus to reproduce during the 24 weeks of the culture period in this study is an indication that the semi flow-through culture system using fibre glass tanks is a successful reproduction control method for O. niloticus and thus should be adopted in the aquaculture industries.