Normal and Altered Thyroidal Function in Domesticated Goldfish, Carassius auratus

Abstract

Normal C. auratus accumulate a peak of 3% of an injected tracer dose of radioactive iodine intra-thyroidally. 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% within a wk., indicating a greater turnover rate. Radioiodine in normal goldfish thyroids is mostly in the form of monoiodotyrosine, diiodotyrosine, with little, if any, thyroxine formed even after 1 wk. The thyrotropic hormone stimulated goldfish thyroid forms a small proportion of radiothyroxine as early as 24 hrs. after Il31 injn. Eight percent of the I131 is in the form of thyroxine 7 days after injn. of I131. Keeping the goldfish in water low in iodine had an effect on I131 metabolism similar to thyrotropic hormone treatment.