High male proportions of Nile tilapia in a zero-water exchange biofloc system even at lower methyltestosterone concentration in the feed and water temperature below ideal

Ramírez, José Fernando PazAlvarenga, Érika Ramos deCosta, Franklin Fernando Batista daKeller, Kelly MouraCampos, Ana PaulaPio, Natan Paulo BentoIto, Rafael HiroakiMansur, Lee Deyver Carvalho PenaTorres, William Gleidson AlvesBezerra, Vinícius MonteiroPires, Dara CristinaSoares, Laryssa Evelyn SantosGonçalves, Guilherme FigueiraBiscoto, Gabriela LagoLuz, Marcelo RezendeTurra, Eduardo Maldonado

Abstract Since temperature plays an important role in feed consumption, chemical reactions and metabolism, it was hypothesized that it is below ideal it could interfere in the masculinization of tilapia in biofloc system (BFT) and the ideal methyltestosterone (MT) concentration in the feed. The masculinization rates of Nile tilapia in a zero-water exchange BFT (and without clarification) at 25°C and 28 °C combined with concentrations of MT in the feed (0 (control), 10, 20, 30 and 40 mg ∙ Kg-1 of feed) were evaluated using 3 replicates per treatment (30 tanks of 50 liters, 2 larvae ∙ L-1). Larvae were fed five times a day for 28 days. The water quality and growth performance did not diverge between MT concentrations (p > 0.05). Larvae grew 2.7 times higher in 28°C than 25°C. The control treatments did not differ from each other for male proportion (mean = 66,75%) but differed from all hormonal treatments. These treatments presented masculinization rates above 98.7% and 96.9%, at temperatures of 25°C and 28°C, respectively, and did not differ from each other at the same MT concentrations. Therefore, it is feasible to use an even lower concentration (10 mg of MT ⋅ Kg-1 of feed) in a zero-water exchange BFT, regardless of these temperatures. At the lower temperature, the input of MT in the system was smaller due to smaller feed intake, however the fingerlings would take longer to reach commercial body weight. Furthermore, after 2 hours of the last hormone feeding, MT residues were not detected in any biofloc/water mixture samples.