Heatwave duration modulates physio-biochemical responses in genetically improved farmed tilapia (Oreochromis...

Inland heatwaves (HW) are increasingly recognised as potent environmental stressors affecting aquatic ecosystems. This study investigated the physiological, biochemical, and molecular stress responses in juvenile GIFT (Oreochromis niloticus) exposed to simulated short-term (STHW) and long-term (LTHW) heatwave conditions. A total of 144 fish (15.79 ± 0.21 g) were randomly assigned to three treatment groups-control, STHW, and LTHW-with four replicates each. At the end of each experimental heatwave exposure, parameters such as survival, physio-biochemical responses from different organs, serum, and whole-body proximate and fatty acid profiles were assessed. Despite no statistically significant differences in survival rates, HW exposure induced marked alterations in serum biochemical parameters, including elevated glucose and decreased hormone profiles (T3, T4, cortisol). HW significantly impacted serum lipid profiles, with notable reductions in LDL, HDL, and cholesterol, particularly in the LTHW group. Oxidative stress enzyme activities revealed organ-specific responses: liver SOD decreased while CAT and GPX increased under LTHW, indicating heightened oxidative stress. The CAT and GST activities of the gill were suppressed, whereas GPX surged in LTHW-exposed fish. Upregulation of hsp-70 and nka-1α mRNA in STHW, and a decline in LTHW, indicate changes in the cellular stress protein markers and ion transport. Whole-body composition analysis revealed reduced crude protein and ash, increased lipid content, and depleted muscle glycogen under heatwave exposure. Fatty acid profiling and PCA analysis demonstrated significant shifts in fatty acid metabolism, with increased levels of palmitic acid, ARA, and DPA under LTHW, alongside reduced MUFA and SFA/PUFA ratios. Overall, these findings underscore the multifaceted physiological disruptions caused by inland heatwaves in GIFT juveniles, with LTHW eliciting more pronounced stress responses.