A STUDY OF THYROID FUNCTION IN FUNDULUS HETEROCLITUS

¹ The Binyham Oceanographic Laboratory and the Department of Zoology, Yale University, New Haven, Connecticut

Thyroidectomy of Fundulus heteroclitus was attempted with the use of radioactive iodine, administered in three doses of 25, 15, and 10 µC Cper five-gram fish at intervals of five 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 yielded the following results:

1. 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 salt or fresh water. Deaths occurring during the experiment in general involved fish with very few follicles or no thyroid tissue remaining.

2. Blood chloride titers were a function of the salinity of the medium and were not affected by lack of thyroid.

3. Hemoglobin titers and red cell counts indicated an effect of the medium, and were not influenced by lack of thyroid.

4. Hypothyroidism had no effect on growth, either in length or weight.

5. Hypothyroidism had no effect on the gonadosomatic index.