This study examined the physiological, biochemical, immune, endocrine, and metabolic responses of juvenile stellate sturgeon Acipenser stellatus to prolonged fasting under different thermal conditions. One hundred and fifty juveniles (43.4 ± 0.8 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). Following a gradual thermal acclimation, fish were maintained under each regime for 21 days without feeding. At the end of the trial, hematological and biochemical parameters, innate immunity, thyroid hormones, cortisol, oxygen consumption, and gill ventilation rates were assessed. Albumin and glucose levels were not significantly affected by temperature (P > 0.05), whereas cholesterol, lactate, total protein, and triglycerides exhibited significant temperature-dependent variation (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 greater at LT, whereas complement components of C3 and C4 increased with temperature, reaching maximum values at HT. 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 with LT and MT (P < 0.05). Metabolic measurements revealed a marked temperature effect, with oxygen consumption and gill ventilation rates increasing progressively from LT to HT. Fish at HT exhibited the highest oxygen consumption (193.6 mg O₂ kg^-1 h^-1) and ventilation rate (39.9 min^-1), followed by MT (125.3 mg O₂ kg^-1 h^-1; 30.2 min^-1) and LT (76.0 mg O₂ kg^-1 h^-1; 13.8 min^-1). Overall, elevated temperatures intensified metabolic demand, altered biochemical and hormonal profiles, and modified immune responses during fasting, suggesting potential thermal stress. These results provide insights into the thermal physiology of Acipenser stellatus and have implications for aquaculture management and conservation strategies under changing climate conditions.
 

Acipenser stellatus, Temperature, Starvation physiology, Immune response, Oxygen consumption