Ultrastructure of the Thyroid Gland in Goitered Coho Salmon (Oncorhynchus kisutchy

Thyroid tissues in coho salmon (Oncorhynchus kisutch) goiters showed marked regional variation in structure and ultrastructure. For the most part the follicles were small, were composed of tall epithelial cells, and con tained little or no colloid material. The follicle epithelial cells were essentially similar in fine structure to hyperac tive thyroids in mammals and one type of follicle in congenital goiters in humans. A second type of follicle, present in human goiters, was not found in coho salmon. The follicle cells in coho salmon contained dense bodies similar to lysosomes in other species, together with larger organelles which could be colloid droplets. There was also an extensive system of dilated rough endoplasmi reticulum and large areas of Golgi membranes. A marked feature was the presence of homogeneous electrondense material in the intercellular spaces between adja cent follicle cells.