Thyroid dysfunction in Great Lakes coho salmon, Oncorhynchus kisutch (Walbaum): seasonal and interlake differences in serum T3 uptake and serum total and free T4 and T3 levels

Abstract

Sexually mature spawning and prespawning adult and ‘jack’ coho salmon, Oncorhynchus kisutch, were collected during their potamodromous migration from Lakes Ontario, Erie and Michigan in late autumn. In addition, sexually immature spring salmon were collected from Lakes Ontario and Erie. Serum total thyroxine (TT4), serum free thyroxine (FT4), serum total triiodothyronine (TT3) and serum free triiodothyronine (FT3) levels showed marked seasonal variability in salmon from Lakes Ontario and Erie with peak hormone levels evident in the spring fish and lowest levels in the sexually mature adults and ‘jacks’. Seasonal changes in serum triiodothyronine uptake (T3U) values were inverse of those of serum TT4, FT4, TT3 and FT3 levels. When data of the whole collection were combined significant positive correlation coefficients were evident as follows: serum TT3 v. serum TT4, FT4 and TT3; serum TT4 v. serum FT4 and FT3; serum FT4 v. serum FT3, and significant negative correlations as follows: serum T3U v. serum TT3, TT4, FT4 and FT3. When individual groups were examined significant correlations were either absent, or in some instances the reverse of those of whole data. The data provide further evidence of interlake differences in dysfunction of thyroid hormone metabolism in Great Lakes coho salmon; the possible involvement of environmental agents is discussed.