Stocking density of nile tilapia (Oreochromis niloticus) fry during sex reversal phase

Abstract

This work aimed to evaluate Nile tilapia (Oreochromis niloticus) fry of Taiwanese strain at different stoking densities, during sex reversal phase. Experimental design was totally randomized, with four treatments and three replicates in a period of 30 days. Fish with initial weight of 7.2 ± 0.2 mg and total length of 8.2 ± 0.5 mm were stocked at 1, 3, 5 and 7 fry L^-1 in aquarium of 20 L capacity with closed water recirculation system. Fish were feed ‘ad libitum’ five times daily with commercial ration (48% crude protein) containing 60 mg of 17α-methyltestosterone kg^-1. Data were submitted to variance analyses, and means compared by Tukey’s test with 5% of significance level. Means of final weight and length were 1.66; 0.73; 0.44; 0.37g and 4.47; 3.41; 2.86; 2.70 cm, respectively to 1, 3, 5 and 7 fry L^-1. These results show that higher stoking densities lead to low fish growth. The variation coefficients of mass and length was 3.27; 1.88; 1.62; 1.29 % and 9.68; 6.04; 5.61; 4.49%, respectively to 1, 3, 5 and 7 fry L^-1. Survival, sex reversal efficiency and condition factor were not affected by stocking density. Higher stoking densities reduce growth rate and increase homogeneity of Nile tilapia fry.