Masculinization protocol for Nile tilapia (O. niloticus) in Biofloc technology using 17-α-methyltestosterone in the diet

Abstract Sexual control through hormone treatments is widely used in Nile tilapia due to its simplicity and high efficiency. However, possible impacts of hormone residues introduction on the environment are still a topic of concern. One way to minimize the environmental impact of hormonal treatments is to use close aquaculture systems, such as the Biofloc Technology (BFT). However, BFT system can provide constant additional feed and there is the possibility that the feed with masculinization hormone offered would not be fully ingested, resulting in a lower ratio of males in relation to the traditional hormonal inversion protocols. Hence, different feeding frequencies and hormonal concentrations, superior to conventional protocols of masculinization, should be tested. Thus, our goal was to elaborate a masculinization protocol that would allow better growth and higher masculinization percentages for Nile tilapia (O. niloticus) in BFT. Nile tilapia fry were raised in BFT and submitted to different concentrations of 17α-methyltestosterone (60, 90, 120, 150 and 180 mg · kg−1) which was offered five or eight times a day. The control group consisted of fry raised in clear water tanks fed with 60 mg · kg−1 hormone diet provided five times a day. The experimental design was a factorial arrangement (5 × 2), plus control, on two random blocks, each block having two replicates per treatment. Stocking density applied was of 2 fry· L−1 (300 fry· tank−1). Water quality variables did not diverge between BFT systems and control group, except for settable solids, a result already expected. Animals submitted to BFT systems presented higher survival (%) and uniformity when compared to the clear water group. Higher hormone concentration treatments presented less proportion of males in contrast to 60 mg · kg−1 groups and no differences were found between feed frequencies tested. In conclusion, it was possible to achieve ≥94% masculinization rates in tilapia using 17α-methyltestosterone at 60 mg · kg−1 on BFT systems, under a five times per day feeding regime.