Changes in thyroxine（T₄）concentrations in larval and juvenile marbled flounder, Pseudopleuronectes yokohamae

Abstract

There are several reports on the dynamics of thyroid hormones during metamorphosis in flatfish, but there are limited reports on the post-metamorphic juvenile stage. In this study, we investigated changes in thyroxine （T₄）, a thyroid hormone, from the larval to juvenile stages of the marbled flounder Pseudopleuronectes yokohamae. We found that the T₄ concentration from 20 days post-hatching （dph）（larval stage） to approximately 120 dph （juvenile stage） substantially increased in the juvenile stage. There was a local maximum T₄ concentration in the late developmental stage of juveniles. We also found considerable inter-annual variation in T₄ concentrations during this study（2015, 2016, 2018, and 2019）. The findings of this study can be used to inform treatment options and management of flatfish seed production to ensure the health and quality of the fish produced.