Enhanced survival in striped bass fingerlings after maternal triiodothyronine treatment

Elevation of the triiodothyronine (T3) content of striped bass (Morone saxatilis) eggs by maternal T3 injection confirms the uptake of T3 by oocytes. The resulting offspring were influenced favorably by the T3, as seen in quantitative indices of development. As reported previously, larvae from T3-supplemented eggs raised under laboratory conditions exhibited increased body area, length, dry weight, and rates of swimbladder inflation and survival, compared to controls. Also, the T3 content of unfertilized oocytes correlated positively and highly significantly with survival to two weeks of age within individual cohorts (Brownet al., 1988). In the present study, the survival of experimental and control striped bass was monitored through the fingerling stage, under hatchery production conditions. The rate of recovery of maternally T3-treated cohorts from pond-culture was approximately fourfold that of controls. The striking effects of T3 enrichment of eggs on offspring indicate the potential contribution of maternal hormones in striped bass development, and suggest possible applications in aquaculture.

Presence of thyroxine in eggs and changes in its content during early development of chum salmon, Oncorhynchus keta

In order to examine the role of thyroid hormones during salmonid development, techniques were developed for quantitative extraction of thyroxine from eggs, whole embryos, and alevins of chum salmon (Oncorhynchus keta) at various stages of development. Frozen eggs, embryos, alevins, or fry were homogenized in ice-cold methanol. The homogenate was centrifuged, and the supernatant was washed with a mixture of chloroform and 0.05% CaCl2. The aqueous layer was lyophilized, and the residue was redissolved in barbital buffer for thyroxine radioimmunoassay (RIA). Serial dilutions of the egg or tissue extracts gave inhibition slopes that were parallel to that of the thyroxine standard in the RIA. Immunoreactivity of the extracts coeluted with thyroxine standard in reverse-phase HPLC on an ODS column. Recovery of thyroxine from egg and tissue extracts was estimated from the recovery of 125I-labeled thyroxine added to the initial homogenates. Thyroxine content of eggs just after fertilization was 4-5 ng/egg, and this level was maintained until hatching. A decrease in thyroxine content was seen during yolk absorption. Total thyroxine increased to about 10 ng/fish, a level higher than that in the unfertilized egg, at the time of complete yolk absorption, and decreased within 10 days to a low level of 1 ng/fish. These findings are discussed in relation to the role of maternal thyroid hormones during early development and also to the onset of larval thyroid function.

Thyroid hormones in blood plasma of developing salmon embryos

Blood plasma thyroxine (T4) and 3,5,3'-triiodo-L-thyronine (T3) concentrations in developing embryos of chum (Oncorhynchus keta), coho (Oncorhynchus kisutch), chinook (Oncorhynchus tschawytscha), and Atlantic salmon (Salmo salar) were measured by radioimmunoassay between hatching and completion of yolk-sac absorption. Blood sampling was initiated when approximately 50% of the yolk that was present at hatching had been absorbed. At this time blood plasma levels of T4 (7-9 ng/ml) and T3 (1-5 ng/ml) were similar in all species. In embryos of each salmon species blood plasma levels of T4 increased to maximal values (9-16 ng/ml) when both differentiation of the abdominal body wall and absorption of the yolk sac were completed. Blood plasma levels of T3 generally decreased to low or nondetectable values during this time. There was either a trend toward a decrease or a stasis of levels of T4 and at the same time in some species an increase in levels of T3 in the blood plasma following the completion of yolk-sac absorption and the onset of exogenous feeding. These results demonstrate that thyroid hormones are present in the blood of developing teleost embryos. This finding is discussed in light of the possible role of thyroid hormones in control of the embryonic and larval development of fishes.