Sex manipulations on Mozambique tilapia (Oreochromis mossambicus)

In this study, in order to assess the factors that control sex differenciation in general and to produce super male brooders of Mozambique Tilapia (Oreochromis mossambicus. Peters, 1852), it was tried to determine the correct amount of hormones related to both neo-females and super male production. For this, 2 days-old larvae were bred for 45 days at 28, 30, 32, 34 and 36 °C and sex-controlled at the end of the trial. Positive effects of increased water temperature up to 34 °C in terms of growth performance (live weight, height), condition factor, feed utilization rate and gonadal development of fish were determined. On the other hand, it was determined that the living rate tended to decrease at high temperatures. The highest male ratio (86.67%) was found at 36 °C water temperature while the rates at other water temperatures were not different from each other (p = 0,034 and α = 0,05). In the second part of the study, the effects of these doses on development and sex differentiation were investigated by mixing pelleted feed with different 17β estradiol (E2) doses (50, 100, 150 and 200 mg/kg) for 45 days. It has been found that fishes fed with hormone feed had weaker results in terms of feed consumption and growth parameters. Although the results showed that sex-conversion might be hormone-dependent at all rates of eating, the highest female ratio was obtained at doses of 150 and 200 mg/kg. Analyzes showed that the female ratio was significantly higher in all treatment groups than the control group (p value = 0.04 and α = 0.05). However, given the negative effects of high doses on fish, it has been concluded that lower doses of the administration shoul be better. In the last part of the study, production of YY super male individuals were studied. In this context, hormone-treated females were crossed with normal males. The highest number of fries per female was 27, which was obtained from the mating of fishes fed with 100 mg/kg estradiol diet. The male ratio of the offspring obtained after a second mating of the previous male individuals with normal females varied between 40% and 60%.