Seasonal changes in thyroidal status in the plaice, <i>Pleuronectes platessa</i> L.

Abstract

A chemically specific analysis for plasma thyroid hormones has been used to disclose a seasonal bimodality in the concentrations of thyroxine (T 4 ) and triiodothyronine (T 3 ) in the plaice; maxima in both hormone levels occur in winter and in summer. The ratio of T 4 concentrations to T 3 varies seasonally being at a minimum in summer. A highly significant correlation of T 4 plasma levels with the landings per unit fishing effort for the same area has been observed.