THE INFLUENCE OF TEMPERATURE ON THYROID HISTOLOGY AND RADIOIODINE METABOLISM OF YEARLING STEELHEAD TROUT, SALMO GAIRDNERI

Abstract

The thyroid activity of yearling steelhead, as measured by radioiodine methods (CR and T/S), increased with temperature from 6 to 18 °C. The thyroid uptake of I¹³¹ peaked at 12 °C. However, this method was found unreliable, since plasma I¹³¹ clearance, upon which it depends, also increased with temperature.The staining reaction of the colloid (Azan stain) indicated greater thyroid activity at high temperatures. On the other hand, measurements of thyroid mean epithelial height implied greater activity at low temperatures.A hypothesis resolving; anomalies between various criteria of thyroid activity, based on a TSH-independent influence of temperature on the poikilotherm thyroid, is presented.