Levels of Thyroid and Sex-Steroid Hormones in Brown Trout Salmo trutta L. in the Rivers of Karelia

Abstract

The correlation between the levels of thyroxine and sex-steroid hormones in the blood of brown trout and its life cycle in different rivers and age has been analyzed. It has been revealed that the concentrations of the studied hormones in the blood of juvenile specimens and mature male brown trout from the Alats-oya River (Lake Ladoga basin) are significantly lower than in the blood of fish from the Orzega and Shoksha rivers (Lake Onega basin). It is shown that the concentrations of thyroid hormones in the blood of brown trout change insignificantly with age. On the contrary, the level of sex-steroid hormones increases significantly by the beginning of sexual maturity.