Integrated multitissue analysis reveals distinct oxidative stress responses during recovery from cold shock in the Amazonian fish Colossoma macropomum

Tambaqui ( Colossoma macropomum ) is a tropical fish widely cultivated in South America. The increasing demand for this species has heightened interest in its cultivation in subtropical regions with greater thermal variability, where cold shock may induce oxidative stress. This study evaluated the effects of cold shock and subsequent recovery on antioxidant enzyme activity, which included superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S‐transferase (GST) and oxidative damage biomarkers (lipid peroxidation and protein carbonyl) in different tissues of juvenile tambaqui exposed to cold shock at 20°C for 24 h. Samples were collected before temperature reduction (baseline) and at 1, 24 and 48 h after returning to 28°C (recovery phase). Because sampling was restricted to the recovery period, the biomarkers primarily reflected post‐stressor physiological reorganization. Recovery responses were strongly tissue‐specific. The liver exhibited the broadest biomarker modulation, whereas the gills showed the highest integrated disturbance and the earliest response according to Integrated Biomarker Response version 2 (IBRv2). The brain displayed the clearest tendency towards restoration of basal redox homeostasis, while the intestine and muscle retained oxidative demands during later recovery. These findings demonstrate that post‐cold recovery in juvenile tambaqui is a dynamic and tissue‐dependent process and highlight the importance of multibiomarker and multitissue approaches for physiological monitoring and thermal stress assessment in tropical aquaculture species.