A comparative histological study on early thyroid gland development in Acipenser stellatus and A. gueldenstaedtii larvae in hatchery

Abstract

The thyroid is an endocrine gland, with an important role in fish growth, development and adaptation of larvae. The aim of this study was to describe the development of the thyroid gland and to determine the initial functional activity of thyroid gland and hormones in Acipenser gueldenstaedtii and A. stellatus larvae using immunohistochemistry. For this aim, fertilized eggs of two species were reared in a hatchery and larval samples were collected daily for 20 days post hatching (dph). For immunostaining, rabbit polyclonal primary antibodies for thyroglobulin and mouse monoclonal antibodies for thyroid transcription factor-1 (TTF-1) were used. In histological analyses, it was observed that the first development of the thyroid gland in stellate sturgeon larvae occurs on the 3-4 dph and on the 4-5 dph in Russian sturgeon larvae in the ventral pharyngeal region of the fish. In the immunostaining analyses of 12-day-old stellate larvae and 19-day-old Russian sturgeon larvae, the thyroid follicles showed dispersion in great numbers around the aorta, and also it was observed that they were stained positively with antithyroglobulin staining, but the same sections gave negative results with TTF-1 staining. Also melanomacrophage centres, which are generally found in the haemopoietic tissues in some cases, were first observed around the thyroid follicles of sturgeon larvae. The results of this study revealed a similarity in the early thyroid gland development between two sturgeon species but using immunostaining methods, it was described that A. stellatus shows a faster functional development and earlier hormone production than A. gueldenstaedtii.