Effects of thyroxine immersion on Sterlet sturgeon (Acipenser ruthenus) embryos and larvae: Variations in thyroid hormone levels during development

This study was planned to investigate the effects of immersion of Sterlet sturgeon (Acipenser ruthenus) eggs by thyroxine hormone (T4) on the embryonic survival rate (ESR), hatching rate (HR), larval survival rate (LSR), and thyroid hormone levels. Hence, oocytes of six females were pooled, fertilized with pooled semen of three males and 45 min after fertilization process, the eggs were placed 120 min in four batches that were immersed in T4 solutions as follows: D1 (the control treatment: T4-free, hatchery water), D2 (0.01 mg L−1 of T4), D3 (0.05 mg L−1 of T4), D4 (0.1 mg L−1 of T4), and D5 (1 mg L−1 of T4). Next, the eggs were transferred to the incubator. The ESR was recorded 6 h after fertilization while HR, and LSR were measured at 1 day post hatching. In addition, the levels of thyroid hormones were measured using the competitive enzyme immunoassay method three hours and three days after fertilization and at the five-day pre-larval stage. The highest ESR was obtained following D5 treatment (P