Thyroid hormones (THs) serve as fundamental regulators of growth, metabolism, and reproduction in teleost fish, yet their targeted applications in sturgeon aquaculture remain largely unexplored. This comprehensive research program, comprising six integrated studies, systematically investigates the dose- and stage-specific effects of thyroxine (T4) administration in Sterlet sturgeon (Acipenser ruthenus). In broodstock, chronic T4 administration (10 mg/kg BW via intraperitoneal injection) elicited profound physiological responses, including an increase in weight gain, significant improvements in hematological parameters (RBC count, hemoglobin, and hematocrit), and enhanced immune competence (IgM and complement activity). These benefits were accompanied by elevated cortisol levels, indicating a stress response. Notably, maternal T4 treatment substantially improved reproductive outcomes, increasing ovarian fluid protein content, lipid levels, and critical mineral concentrations (Ca and Mg), while boosting larval survival to 92.2% at 3 dph compared to 67.2% in controls. For early life stages, T4 immersion protocols (1 mg/L for 120 minutes post-fertilization) demonstrated remarkable efficacy, increasing embryonic survival rates and hatching success. These improvements correlated with optimized TH profiles, particularly sustained T3:T4 ratio during critical developmental windows. Metabolic studies revealed that even acute T4 exposure induced prolonged effects, with plasma triglyceride levels remaining elevated for 60 days post-treatment and glucose metabolism showing significant enhancement. Dose-response analyses established clear thresholds for therapeutic benefit, with 10 mg/kg BW optimal for broodstock conditioning and 1 mg/L for egg immersion. Lower doses (0.01-0.1 mg/L) showed intermediate effects, suggesting potential for tailored applications. These findings collectively position T4 as a powerful, multi-functional tool for sturgeon aquaculture, capable of simultaneously improving growth performance, immune function, and reproductive success.
 

Growth enhancement, Hormonal regulation, Egg hormone treatment, Spawning improvement, Immunity performance