To find the effects of thyroxine (T4) on the physiological and reproductive performances of sterlet broodstock, three groups of fish were considered and administrated 0, 1, and 10 mg of T4 per kg of body weight (BW) via peritoneal injection during post-vitellogenesis until before the final maturation. The fish were tagged, injected three times with 45-day intervals and held in circular concrete tanks, each containing five fish with two replicates for each treatment. At the water temperature of 15-16 °C the germinal vesicle migration was checked and the fish were injected with 4 μg of LHRHa2/kg BW. Additionally, blood samples were taken to assay physiological parameters. The ovulated eggs were fertilized with sperm and incubated in a Yushchenko incubator. The results showed that the highest triiodothyronine and T4 concentrations in plasma and eggs were found in fish that received the highest T4 level. Furthermore, the highest levels of sex steroids were found in this group. The best reproductive performance in terms of egg diameter and survival at 3 days post-hatch was achieved in 10 mg/kg group. This study highlights the role of T4 in fish physiology and reproduction and suggests its potential application for enhancing performance in sturgeon breeding programs.
 

Blood biochemistry; Reproduction; Sturgeon; Triiodothyronine; Thyroxine