Seasonal Changes in the Cytomorphology of the Thyroid Follicles and its Co-relation with the Testicular Cycle in the Asian Striped Catfish Mystus vittatus (Bloch, 1794)

摘要

The seasonal changes in the cellular morphology of the thyroid gland were studied in male Mystus vittatus. It was found to be composed of discrete follicular structures dispersed mainly in the sub pharyngeal region around the ventral aorta.The follicles were found to be composed of single layered epithelial cells with agranular eosinophilic colloids in their central lumen. The secretary activity of the follicular cells was found to be in accord with the seasonal phasic changes of the male reproductive cycle. The maximum secretary activity of the thyroid was studied during the spawning phase while the minimum activity of the follicles was traced during the post-spawning and resting phases. So, it was established that the thyroidal secretional activity corresponds to the seasonal testicular cycle of Mystus vittatus and hence, the breeding behaviour of male is controlled by the thyroid gland.