Thyroid hormones in eggs of various freshwater, marine and diadromous teleosts and their changes during egg development.

Thyroid hormone concentrations in unfertilized eggs of 26 species of various freshwater, marine and diadromous teleosts were examined, together with changes in their concentrations during egg development in some species. Significant quantities of both thyroxine (T4) and triiodothyronine (T3) were found in eggs of all species examined. Mean T4 and T3 concentrations in eggs varied from 0.04 (marbled sole) to 15.00 ng/g (chum salmon), and from 0.07 (goldfish) to 9.95 ng/g (Pacific herring), respectively. T4 concentrations were significantly greater than T3 concentrations in eggs of most freshwater fishes, whereas T3 concentrations were greater in seawater fishes. During the course of development, thyroid hormones in eggs decreased markedly before hatching. These findings suggest that thyroid hormones are consistently present in teleost eggs, and thus may play an important role in the egg development.