Effect of low water temperature on the stress, innate immune, and antioxidant responses of pacu, Piaractus mesopotamicus, a sub-tropical fish

The sustainability of aquaculture is subject to environmental changes, such as changes in temperature, which affect the physiological homeostasis of fish. Thermal shock (natural or anthropogenic) is a stress condition that results in a sequence of physiological responses and even mortality. Considering the impact of sudden reductions in temperature on the biological systems and that this occurrence is common in regions where pacu (Piaractus mesopotamicus) is farmed, we evaluated the stress, immune, and antioxidant responses of the species exposed to temperature drop. Two groups of fish were exposed to 28 degrees C or 16 degrees C for 24 h, and then fish were kept at 28 degrees C to recover and be sampled: before the temperature drop (baseline); after 24 h of cold exposure; and 3, 8, and 24 h after the return to 28 degrees C (recovery). The exposure of pacu to 16 degrees C did not alter the stress biomarkers after 24 h, but it activated the innate immune system (leukocyte respiratory activity, hemolytic activity of the complement system, and serum lysozyme concentration). It also promoted oxidative stress without altering most of the antioxidant system indicators, except for an initial reduction of glutathione peroxidase (GPx) activity after exposure to 16 degrees C and a late activation, besides the late activation of glutathione transferase (GST), probably as a compensatory process to reduce tissue damage. Pacu was sensitive to temperature changes, but it was able to activate immune and compensatory responses to mitigate oxidative stress. The results will help producers in the management of pacu during periods of thermal changes, such as in autumn and winter.

Automated summary

The sustainability of aquaculture is affected by environmental changes, such as temperature fluctuations, which can disrupt the physiological balance of fish. In this study, we assessed the stress, immune, and antioxidant responses of pacu exposed to sudden temperature drops commonly experienced in pacu farming regions. The results showed that pacu exhibited immune activation and oxidative stress in response to the temperature drop, but was able to activate compensatory mechanisms to mitigate tissue damage. This study provides valuable insights for pacu management during periods of thermal changes.