Аннотация
Abstract The levels of thyroid hormones (total thyroxine, free thyroxine, and total triiodothyronine) in the blood serum of the Caspian seal Pusa caspica are reported for the first time. The serum levels of thyroid hormones in Caspian seal were comparable to those in the harbor seal Phoca vitulina. An increased plasma level of total thyroxine was found in seals during the molting season. A tendency toward an increase in free thyroxine levels was observed in adult females in the autumn. In contrast to the data for the harbor seal, in our research there were only two cases when measured levels of thyroid hormones in the blood serum of Caspian seals dropped below the threshold.