EPIZOOTIOLOGY AND PATHOGENESIS OF THYROID HYPERPLASIA IN COHO SALMON (ONCORHYNCHUS-KISUTCH) IN LAKE-ONTARIO

Abstract

The thyroid glands of coho salmon collected at different stages of their anadromous migration exhibited progressive and extensive hyperplasia and hypertrophy. The incidence of overt nodule formation rose from 5% in fish collected in Aug. to 24% in fish collected in Oct. The histological picture of the goiters was similar to that found in thiourea treated teleosts and thiouracil treated mammals. There was a concomitant, significant decrease in serum thyroxine and triiodothyronine values between Sept. and Oct. (thyroxine, 1.0 .+-. 0.3 .mu.g.100 ml and 0.4 .mu.g/100 ml in Sept. and Oct., respectively; triiodothyronine, 400.3 .+-. 51.6 ng/100 ml and 80.2 ng/100 ml in Sept. and Oct., respectively) and marked hypertrophy and hyperplasia of thyrotrophs. These data indicate a progressive hypothyroid condition which, although it may be linked to iodide deficiency, may be enhanced by other environmental factors. The evidence for involvement of other factors is discussed.