Hematological and blood biochemical responses of Colossoma macropomum and Piaractus brachypomus subjected to sudden temperature reduction and thermal readjustment.

This study aimed to evaluate the physiological responses of Colossoma macropomum and Piaractus brachypomus, faced with a sudden reduction in temperature followed by thermal readjustment. Forty juveniles of each species were fasted for 24 h, after which, ten fish of each species were used as a basal group, while the others were subjected to a sudden temperature reduction from 28.7 to 18.6 °C and maintained in that condition for 24 h. The temperature was then restored, and the fish were observed for another 24 h of readjustment (R). Blood was collected at 1hATC, 24hATC and 24hR (ATC = after temperature change). There was no mortality during the experiment. C. macropomum showed a decrease in glucose without recovery after thermal readjustment, unlike P. brachypomus which experienced an increase at 1hATC. In both, C. macropomum and P. brachypomus, the lowest triglycerides levels were observed at 1hATC, with no return to the initial condition at 24hATC and 24hR. Cholesterol levels in both species showed reductions at 1hATC and 24hATC; however, there was a return to the initial condition at 24hR. The abrupt temperature change caused a reduction in lactate levels at 1hATC and 24hATC; however, only P. brachypomus returned to the initial levels. Plasma chloride was highest at 24hR and lowest at 1hATC, for both species. Therefore, we observed that the sudden drop in temperature, followed by thermal readjustment caused physiological changes, and P. brachypomus demonstrated a greater capacity to reestablish the initial condition of shape during thermal readjustment.