Some endocrine aspects of fish migration

Abstract

The aim of the present investigation was to analyze the cooperation between thyroid and gonadal activity in the induction of migration-disposition and migratory behavior. These two glands were selected, because it is known that in most species migration is associated with augmented thyroid and gonadal activity. It was shown that administration of TSH and thyroxine induces a fresh water preference in sticklebacks, whereas antithyroid agents like thiourea, thiouracil and thiocyanate induce a preference for salt water. The effect of TSH is mediated by the thyroid gland, as it was found that this hormone is ineffective when administered simultaneously with thiourea. These results show that changes in the level of circulating thyroid hormone induce changes in salinity preference, which are known to reflect the induction of migration-disposition. Administration of TSH and testosterone propionate cause a significant increase in the number of swimming movements and the performance of fluttering bouts in gonadectomized sticklebacks. As migration is associated with an increase in locomotory activities these findings indicate that TSH (or thyroid hormone) and male hormone are involved in the induction of migratory behavior. A discussion of the results obtained in the present investigation together with earlier findings indicate that thyroid hormone may induce migration-disposition and migratory behavior in the absence of the gonads, but that the latter may play a role in migration by timing its onset through providing additional stimulation to the thyroid gland, and by a direct effect on the mechanism causing migratory behavior.