LAUSR

Abstract Photoperiod and temperature often change concomitantly in nature and regulate physiological responses that ultimately determine the health of species. However, the impact of these changes is poorly investigated from the perspective of optimal conditions for the management of fish, and the association of these variables. In this study, we evaluated the levels of oxidative stress, antioxidant response and the numbers of leukocytes in specimens of Colossoma macropomum submitted to the combination of three photoperiods (0 L:24D, 12 L:12D, and 18 L:6D) and three temperatures (26, 29 and 32 °C) during 60 days. Our main findings showed an increase in oxidative damage of up to 141% and an antioxidant response of up to 167% in animals under 18 L:6D – 32 °C. The results showed an interaction between photoperiod and temperature on immunity, with an increase in the number of lymphocytes (37%), monocytes (60%) and eosinophils (226%) between 26 and 32 °C. Thrombocytopenia (−96%) occurred with the rise in temperatures and thrombocytosis (139%) occurred with a simultaneous decrease in photoperiod and a temperature of 26 °C. A reduction in neutrophils was observed in animals exposed to 18 L:6D – 32 °C in relation to the group 12 L:12D – 32 °C (−67%). The data suggested that, due to increased oxidative damage, the farming of tambaqui in an extended photoperiod under high temperatures makes the animal more susceptible to inflammation and alters its ability to deal with infections. In addition, variations in the profile of thrombocytes suggested that the increase in the photoperiod at lower temperatures requires physiological adjustments to support changes in the farming conditions.