A STUDY OF THYROID FUNCTION IN FUNDULUS HETEROCLITUS

Abstract

Thyroidectomy of Fundulus heteroclitus was attempted with the use of radioactive I, administered in 3 doses of 25, 15, and 10 ucuries/5g fish at intervals of 5 weeks. A screening method was developed whereby the degree of thyroidectomy could be determined by the rate of activity loss in the throat region of the fish following a tracer dose of I131. Thyroidectomy was not complete, and in some cases there was considerable regeneration. However, in general the resulting condition was one of extreme hypothyroidism, and physiological studies conducted with these fish gave the following results There was no special effect on the fishes'' ability to survive in fresh water, although there seemed to be an impairment of their ability to survive at all, in either fresh or salt water. Deaths occurring during the experiment in general involved fish with very few follicles or no thyroid tissue remaining. Blood chloride titers were a function of the salinity of the medium and were not affected by lack of thyroid. Hemoglobin titers and red cell counts indicated an effect of the medium and were not affected by lack of thyroid. Hypothyroidism had no effect on growth, either in length or weight. Hypothyroidism had no effect on the gonadosomatic index.