Effects of thyroid drugs on the larvae of the Brown trout, Salmo trutta

Abstract

Brown trout larvae, Salmo trutta L., were reared from hatching in solutions of the thyroid hormone, thyroxine, and the thyroid inhibitors, thiourea and thiouracil. Thyroxine treatment profoundly affected morphogenesis, while thiourea and thiouracil had little morphogenic effect. Thyroxine treatment caused abnormal growth of the head, and stimulated the rate of differentiation of the fins from the primitive fin fold, and the absorption of the external yolk sac. The epidermis and dermis were considerably thicker in thyroxine‐treated larvae than in control fish, and silvering of the skin was induced. Thiourea and thiouracil produced few morphogenic effects, but such effects as were evident were usually similar with both drugs, and opposite to those caused by thyroxine treatment.