Study of thyroid histophysiological alterations in Chiloscyllium arabicum from the Persian Gulf in breeding and non - breeding seasons

In the present investigation, 50 mature Arabian carpet shark (Chiloscyllium arabicum) were caught at the Bahrakan Port, located at the north of the Persian Gulf, in both autumn (non-breeding) and spring (breeding) seasons. Blood samples were collected from the caudal vein and the plasma was separated. Triiodothyronine (T3), Thyroxin (T4) and thyroid stimulating hormone (TSH) were measured in plasma samples using ELISA method. Also, tissue samples were taken from thyroid and fixed in bouin,s solution. Tissue samples pass through the routine histological method and 5-6 μm thick sections were prepared. Tissue sections were stained using hematoxylin and eosin method. Based on the results, the thyroid gland was observed as a capsulated compact unilobed gland in C. arabicum. Thyroid gland composed of round follicles coated with follicular cells varied in shape based on the thyroid activity during two breeding and non-breeding seasons. Thyroid follicles were filled with the gelatinous colloid with vacuoles. In the reproduction season, most of the thyroid follicles were small in size with a layer of high cuboidal epithelial cells and high number of vacuolated colloid; however, the large follicles coated with squamous epithelium and less vacuolated colloid were common in the non-breeding season. On the other hand, the amounts of T3, T4 and TSH were significantly higher in the breeding than that in the non-breeding seasons.