Comparative performance of mixed-sex and hormonal-sex-reversed Nile tilapia Oreochromis niloticus and hybrids (Oreochromis niloticus x Oreochromis urolepis hornorum) cultured in concrete tanks

Uncontrolled breeding and precocious maturity in Nile tilapia, Oreochromis niloticus can be avoided by using all-male population. This study compared the growth performance, survival rate, condition factor and final fish tank biomass (yield) of mixed-sex and hormonal-sex-reversed O. niloticus and hybrids (O. niloticus x O. urolepis hornorum) cultured in tanks. Sex-reversed males were produced by feeding newly hatched fry with a diet containing 60 mg of 17 alpha-methyltestosterone for 28 days. Fourteen O. niloticus with initial mean weight (+/- standard error) of 0.50 +/- A 0.04, 0.48 +/- A 0.06 and 0.46 +/- A 0.01 g for mixed-sex, sex-reversed and hybrids, respectively, were separately stocked in triplicate tanks at a density of two fish m(-2) and fed a 300 g kg(-1) crude protein diet for 12 weeks. Results showed that hybrids had significantly higher final mean weight (31.41 +/- A 0.33 g) than hormonal-sex-reversed (25.82 +/- A 1.51 g) and mixed-sex O. niloticus (19.50 +/- A 1.26 g; p < 0.05). Similarly, sex-reversed O. niloticus had significantly higher final mean weight than mixed-sex (p < 0.05). The condition factor of hybrids (1.71 +/- 0.05) was significantly higher than that of sex-reversed (1.46 +/- 0.01; p = 0.001) and mixed-sex O. niloticus (1.43 +/- 0.01; p = 0.001). Survival rate was not significantly different among treatments (p = 0.445). The final fish tank biomass was significantly higher in hybrids (535.24 +/- A 31.67 g tank(-1)) and hormonal-sex-reversed (486.52 +/- A 33.70 g tank(-1)) than mixed-sex O. niloticus (330.05 +/- A 17.08 g tank(-1); p < 0.05). This study demonstrates that hybrids have superior growth performance and condition factor than sex-reversed and mixed-sex but have similar yields to hormonal-sex-reversed O. niloticus. These results suggest that O. niloticus farmers can improve growth rate and yield by rearing hybrids without affecting survival rate.