Taxa de alimentação de juvenis de tilápias criados em temperaturas subótimas

Abstract

Two experiments were conducted to determine the optimal feeding rates for Nile tilapia (Oreochromis niloticus) fingerlings and juveniles reared in recirculating aquaculture systems. In the first experiment, conducted over 53 days under water conditions of 19.83 ± 5.18°C, pH 6.27 ± 0.77, dissolved oxygen 7.32 ± 1.98 mg L⁻¹, and toxic ammonia 0.001 mg L⁻¹, five feeding rates (21%, 18%, 15%, 12%, and 9% of body weight) were tested in fingerlings (2.80 ± 0.10 g), distributed into 20 tanks (80 L) with eight fish per tank, and fed five times daily. No significant differences were observed in hepatocyte nuclear histomorphometry or zootechnical performance (P > 0.05), except for feed conversion ratio and feed intake (P < 0.05). The 9% feeding rate provided better feed conversion compared to the 18% and 21% rates. Digestive enzyme activities (amylase, lipase, and alkaline phosphatase) were lower in this group, possibly due to reduced substrate availability, while hepatic enzymes AST and ALT showed higher activity at the 9% rate, indicating increased amino acid catabolism in response to suboptimal temperature. These results suggest that a 9% feeding rate reduces feed intake without compromising fish performance, representing an economically advantageous strategy. In the second experiment, conducted over 90 days under water conditions of 19.21 ± 5.14°C, pH 7.29 ± 0.23, dissolved oxygen 6.53 ± 0.64 mg L⁻¹, and toxic ammonia 0.002 ± 0.001 mg L⁻¹, five feeding rates (1%, 2%, 3%, 4%, and 5%) were evaluated in juvenile tilapia (150.5 ± 9.0 g) stocked in 15 tanks (2000 L) under continuous water quality monitoring. Data were analyzed by ANOVA followed by Tukey’s and Duncan’s tests (p < 0.05). The 3% feeding rate resulted in greater weight gain, final biomass, and improved feed conversion ratio, as well as improved intestinal villi morphology and lower ALT and AST levels, suggesting reduced protein catabolism. Feeding rates of 1% and 2% reduced visceral fat deposition, whereas the 5% rate showed poorer feed efficiency and a higher hepatosomatic index, with no significant changes observed in hepatocyte histomorphometry (P > 0.05). Regarding flesh quality, the 3% rate produced favorable results for cooking loss, drip loss, and texture. It can be concluded that under low temperature conditions, a feeding rate of 9% of body weight is recommended for Nile tilapia fingerlings, while a 3% feeding rate is most suitable for juveniles, promoting improved zootechnical performance and fillet quality, as well as greater productive efficiency and economic sustainability in tilapia farming.