Aquaculture is a promising and developing industry world over. One of the first step in increasing productivity is by culturing of monosex fingerlings, all-male fry by the use of hormones particularly in tilapia species.To this effect, a study was carried out to determine the optimal level of hormone diet with four inclusion levels of 17α-Methyltestosterone (17α-MT), that is 0mg MT/kg-1, 40mg MT/kg-1, 60mg MT/kg-1 and 90mg MT/kg-1. The four treatments were replicated thrice and laid out in a Completely Randomized Design (CRD). Fry of average weight 0.307±0.002g were stocked in 12 concrete tanks each measuring (1m x 1m x 1.5m) at the rate of 500 fry/m2. The fry were fed with the treated diet for 28 days starting from their first feeding stage. They were then shifted into hapas (1m x 1m x 1.5m) set up in a semi concrete pond and fed on a hormone diet. After three months of growth, microscopic evaluation of gonads was conducted to determine the sex of fish by gonad squashing and aceto-carmine staining method. The proportions of males were 54 %, 90 %, 94 % and 70 % for treatments 0
MT/kg-1 (T-1), 40mg MT/kg-1(T-2), 60mg MT/kg-1 (T-3) and 90mg MT/kg-1(T-4), respectively (Table 1). The maximum mean body weight gain after 90 days was observed in fry fed 60mg/kg-1 17 α-MT (T-3), which was 15.31±0.14g. However, this was not significantly different from 40mg MT/kg-1(T-2) (P>0.05). Furthermore, the highest dose 90mg MT/kg-1(T-4), produced a significantly lower (P<0.05) male proportion (70%) compared to treatments; (T-2 and T-3). The anabolic effect of 17α-MT diminished over time. Survival rates of 98%, 97%, 97% and 96 % for treatments 0mgMT/kg-1, 40mg MT/kg-1, 60mgMT/kg-1 and 90mgMT/kg-1, respectively, were recorded. The study revealed a 60mgMT/kg-1 of hormone inclusion level that yielded the highest treatment efficacy at 94% and a mean weight gain of 15.31±0.14g after 90 days. However, 51.10mgMT/kg-1 was determined to be optimal with an efficacy of 93.71 (%) after exposing the data to quadratic contrasts.
The study recommends for production of mono sex O. tanganicae, 51.10mgMT/kg-1 should be used.