Efeitos do sistema de bioflocos e da temperatura na redução da metiltestosterona durante a masculinização da tilápia do Nilo (Oreochromis niloticus) | Effects of biofloc system and temperature on methyltestosterone reduction during masculinization of Nile tilapia (Oreochromis niloticus)

Nile tilapia larviculture is mostly carried out in ponds with a large presence of live food, temperature variations throughout the day and year, and leftover feed dissipated in the water. Therefore, the masculinization process needs to be carried out with a high concentration of the synthetic hormone 17α-methyltestosterone (MT) in the diet. Production in closed aquaculture systems, such as biofloc technology (BFT), allows controlling water temperature, using a smaller volume of water, and generating less effluent. BFT is an alternative system for the masculinization process of Nile tilapia in ponds, which requires large-volume water changes, generating effluents that may contain hormone residues that can cause environmental impacts. Due to the closed-system nature of BFT, it was hypothesized that it would be necessary to contain lower MT than those commonly used in ponds (60 mg • Kg-1 of feed) to obtain high masculinization rates. The first study of this thesis (Chapter II) showed that the use of 30 mg of MT ∙ Kg-1 of feed resulted in >99% masculinization of tilapia in a BFT system with zero water exchange. The study also verified that maintaining the same water in the tank after the end of the hormonal treatment during the growth of the fry did not result in higher male rates when compared to the management of total water replacement. In addition, MT was not detected in the water 12 hours after the last feeding with hormone-containing feed. Since it was possible to obtain a high masculinization rate using 30 mg of MT ∙ Kg-1 of feed, a new experiment was proposed by further reducing this concentration. The second study of the thesis (Chapter III) evaluated the masculinization rates of Nile tilapia larvae in a BFT system with zero water exchange, combining an even greater reduction of MT with different temperatures (25 and 28 °C). Thus, it was possible to verify whether the combination of reduced MT concentrations and high temperature would be sufficient to obtain high masculinization rates, further reducing MT dependence and the possibility of impact on the environment. In the treatment with a temperature of 28 °C, the larvae grew 2.7 times more; however, the higher temperature alone was not sufficient to increase masculinization, being statistically similar in the control treatments (0 mg ∙ Kg-1 of feed), with 68.6% and 64.9% of males at temperatures of 25 °C and 28 °C, respectively. The treatments that received hormone in the feed did not differ between temperatures of 25 °C and 28 °C, presenting masculinization rates above 98.7% and 96.9%, respectively. Therefore, it is feasible to use an even lower concentration (10 mg of MT ⋅ Kg-1 of feed) in a BFT with zero water exchange, at a water temperature equal to or above 25 °C. On the other hand, the lower temperature made the masculinization process even more sustainable, as the fish required lower amounts of feed due to the slowed growth and, therefore, there was less MT input into the system. These results support a paradigm shift in the sustainability of tilapia production and move closer to a new protocol aimed at masculinization in BFT with zero water exchange. Our study has a direct impact on the global tilapia production scenario, offering efficient and environmentally sustainable masculinization, reducing the demand for water and hormones in the process, and thus avoiding the possible release of hormonal residues into the natural aquatic environment.

FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais