Effect of feed deprivation at different water pH levels on the performance and hematology of tambaqui

Feed deprivation and water pH are important stressors in aquaculture that can impair fish growth, metabolism, and homeostasis. Juvenile tambaqui (Colossoma macropomum) are frequently exposed to these stressors under intensive farming conditions. Therefore, this study evaluated the effects of feed deprivation and water pH on the growth performance and hematological parameters of juvenile tambaqui. A total of 180 fish (52.00 ± 0.06 g) were assigned to a completely randomized 3 × 2 factorial design consisting of three water pH levels (4.0, 6.0, and 8.0) and two feeding regimes (regular feeding [RF] and feed deprivation [FD]) for 15 days. Growth performance and hematological variables were analyzed using two-way ANOVA followed by Tukey's test (P < 0.05). Fish in the RF groups exhibited greater final weights, weight gain, and specific growth rates (P < 0.05), whereas FD significantly reduced these performance indicators. The greatest growth performance was observed in fish maintained at pH 6.0 under RF, indicating that this condition is optimal for tambaqui growth. In contrast, the combination of FD and pH 4.0 or 8.0 resulted in the poorest zootechnical performance (P < 0.05). Regarding hematological responses, fed fish showed higher hemoglobin concentrations and erythrocyte counts than fish subjected to FD (P < 0.05). In addition, exposure to pH 8.0 increased these parameters, particularly under RF, suggesting a compensatory response to meet the higher metabolic demand imposed by the alkaline environment (P < 0.05). In conclusion, both feed availability and water pH influence tambaqui growth performance. Maintaining fish at pH 6.0 promotes optimal zootechnical performance, whereas pH 8.0 induces compensatory hematological adjustments without improving growth, indicating a greater physiological cost associated with maintaining homeostasis.