Thermal modulation of metabolic, endocrine, and immune responses in fasted juvenile stellate sturgeon (Acipenser stellatus)

This study examined the metabolic, endocrine, and immune responses of juvenile stellate sturgeon ( Acipenser stellatus ) to prolonged fasting under different thermal conditions. Ninety juveniles (55.5 ± 0.1 g) were acclimated and then distributed into nine tanks (three replicates per treatment) at low temperature (LT, 8 °C), moderate temperature (MT, 18 °C), and high temperature (HT, 28 °C). After reaching the target temperatures, fish were maintained under fasting conditions for 21 days. At the end of the trial, biochemical parameters, innate immunity, thyroid hormones, cortisol, oxygen consumption, and gill ventilation rates were assessed. Albumin and glucose levels were not affected by temperature, whereas cholesterol, lactate, total protein, and triglycerides exhibited significant temperature‐dependent variations ( P < 0.05). Cholesterol, lactate, and triglycerides were highest at HT, while total protein peaked at MT. Immune parameters displayed distinct patterns: IgM concentrations were significantly higher at LT, whereas complement components C3 and C4 increased with temperature, reaching maximum values at HT ( P < 0.05). Cortisol concentrations were significantly higher in HT group, indicating a pronounced stress response, while thyroid hormones (T3, T4) were also significantly elevated at HT compared to LT and MT groups ( P < 0.05). Metabolic measurements revealed a significant temperature effect ( P < 0.05), with oxygen consumption and gill ventilation rates increasing progressively from LT to HT. Under fasting conditions, fish at HT exhibited the highest oxygen consumption (193.6 mg O 2 kg −1 h −1 ) and ventilation rate (39.9 min −1 ), followed by MT (125.3 mg O 2 kg −1 h −1 ; 30.2 min −1 ) and LT (76.0 mg O 2 kg −1 h −1 ; 13.8 min −1 ). Overall, under fasting conditions, elevated temperatures associated with increased metabolic demand, altered biochemical and hormonal profiles, and modified immune responses, thereby suggesting the occurrence of thermal-induced stress during food deprivation. These results provide insights into the thermal physiology of stellate sturgeon and have implications for aquaculture management and conservation strategies under changing climate conditions.