Thyroid Enlargement in Lake Erie Coho Salmon

Summary

Pennsylvania, New York, and Ohio introduced stocks of coho salmon, Oncorhynchus kisutch, into Lake Erie. Of 117 mature salmon examined during the 1972 spawning migration, 44% had grossly enlarged thyroids. Microscopic examination of the thyroids revealed marked hyperplasia. Local invasion was not considered evidence of neoplasia because of the diffuse nature of the normal fish thyroid. The presence of intravascular thyroid cells in one enlarged gland raised the possibility of superimposed carcinoma in some fish