Normal and Altered Thyroidal Function in Domesticated Goldfish,Carassius auratus ∗

Summary

1. Normal goldfish, Carassius auratus accumulate a peak of 3% of an injected tracer dose of I¹³¹ intrathyroidally. This small amount of radioiodine remains in the thyroid at the same level for more than a week. Thyroids of thyrotropic hormone-injected goldfish accumulate 9% or more of the tracer I¹³¹, but lose at least 40% of it within a week, indicating a greater turnover rate. 2. Radioiodine in normal goldfish thyroids is mostly in the form of monoiodotyro-sine and diiodotyrosine, with little, if any, thyroxine formed even after one week. The thyrotropic hormone stimulated goldfish thyroid forms a small proportion of radiothyrox-ine as early at 24 hours after injected I¹³¹ and as much as 8% of the I¹³¹ is in the form of thyroxine by 7 days after injection of I¹³¹. 3. Keeping the goldfish in water low in iodine had an effect on¹³¹ metabolism similar to thyrotropic hormone treatment.