Ultrastructure of the thyroid gland in goitered coho salmon (Oncorhynchus kisutch).

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 contained little or no colloid material. The follicle epithelial cells were essentially similar in fine structure to hyperactive 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 endoplasmic reticulum and large areas of Golgi membranes. A marked feature was the presence of homogeneous belectron-dense material in the intercellular spaces between adjacent follicle cells.