On the Effect of Thyroxine to Promote the Metamorphosis of a Conger Eel-----Preliminary Report

Abstract

It is well known that thyroid matter promotes the metamorphosis of the tadpole. The authors tested the promoting effect of thyroid matter to the metamorphosis of leptoce-phalus of a conger eel, Conger myriaster (Brevoort), with a view to improving the method of rearing of the conger eel fry, Sirasu. Thyroid matter used in the present study was synthetic D-thyroxine sodium, and thiourea was used as anti-thyroid matter (Table 1). Twenty leptocephali were treated in each solution shown in table 2 of 6 litre for 2 days, and after 3rd day all the fish of each group were bred in fresh seawater for 4 days. The value of AL/TL×l00 was used as the index representing the developmental stage of the leptocephali, and the body height and body weight were also measured supplementally. Results obtained may be summarized as follows: 1) The developmental stages of the leptocephali treated with thyroxine sodium, as compared with those of the control and of the larvae treated with thiourea, were much advanced. 2) Between the treatments with 2 ppm and 6 ppm solution of thyroxine sodium, the significant difference was not recognized in the promoting effect to the metamorphosis. 3) Development of the visceral organs and coloring of the blood were observed with the the naked eye in the half of the individuals treated with thyroxine sodium solution, but in those treated with thiourea and of control, such changes were scarecely occurred. © 1967, The Japanese Society of Fisheries Science. All rights reserved.