The Involvement of Thyroid Hormone Metabolism in Gilthead Sea Bream (Sparus auratus) Osmoregulation

: We have investigated the effect of adaptation to low salinity water on the thyroid status of the euryhaline teleost, Sparus auratus. We show that, following low salinity adaptation, the plasma T4 concentration increases and branchial deiodination activities of T4, T3, and rT3 decrease. Moreover, branchial and hepatic enzyme activities that are putatively involved in thyroid hormone metabolism respond differentially in low salinity conditions. Our results indicate the involvement of thyroid hormones in Sparus auratus osmoregulation. Moreover, the gills appear well equipped to play an important role in the modulation of plasma thyroid hormone titers.