Effect of Thyroxine Plus Thiourea on the Early Development of the Chum Salmon (Oncorhynchus keta)

Abstract

AVAILABLE evidence indicates that the effect of the thyroid hormone in fishes is morphogenetic rather than metabolic. Thyroid treatment stimulates growth differentially during development, so that proportions of fins, body-wall, weight and length are altered. Deposition of guanine in the skin of the salmonids² and the rate of formation of scales in sturgeons (genus Acipenser) are accelerated³. Working with the chum salmon, Dales and Hoar⁴ found that thiourea slowed down growth and morphogenetic processes. They found that, while the body-wall started growing over the yolk sac very early in the case of alevins treated with thyroxine, this process was considerably retarded in the forms treated with thiourea. The experiment, the results of which are presented here, was undertaken in order to ascertain the effect of a mixture of thyroxine and thiourea on the early development of the chum salmon. It was of interest to find out whether, in a mixture, the effect of thyroxine would be dominant over that of thiourea or vice versa.