Effect of thyroid hormones on morphogenesis and growth of larvae and fry of telescopic-eye black goldfish, Carassius auratus

Abstract

Three-day-old larvae of telescopic-eye black moor goldfish, Carassius auratus, were treated with different concentrations of Eltroxin (L-thyroxine-sodium, T 4) by immersion (0.01, 0.02, 0.05 and 0.10 ppm). The hormone treatment significantly accelerated the differentiation and growth of all the fins. The number of dorsal and anal fin rays was significantly higher in hormone-treated groups than in controls after 15 days of treatment. The highest dose of 0.10 ppm T 4 resulted in abnormalities especially in the vertebral column and pectoral fins. At the end of 25 days when the experiment was terminated, the eyes were still not telescopic and the body not yet black in any of the treatments, but the larvae exposed to 0.02 ppm and 0.05 ppm were significantly larger than controls. In another experiment, 30-day-old fry were treated with T 4 (0.02, 0.05 and 0.10 ppm) and triiodothyronine (T 3; 0.01 and 0.02 ppm). The hormone treatments accelerated scale formation: after 5 days the body was completely covered with scales, whereas in controls only a few scales were found. After 40 days of treatment, the number of black fish was greater after hormone treatment compared to controls. The number of melanophores on the scales was significantly greater after exposure to 0.10 ppm T 4 and 0.02 ppm T 3 than in controls. T 4 and T 3 treatments also accelerated the telescoping of eyes (exophthalmia). Among the different treatments used, only 0.05 ppm and 0.10 ppm T 4 and 0.01 ppm T 3 significantly accelerated the growth of fry over controls.