THYROIDAL FUNCTION IN THE FISHES FUNDULUS HETEROCLITUS F. MAJALIS, AND F. DIAPHANUS1

Abstract

Groups of Fundulus majalis, a salt-water spp.; F. heteroclitus, a brackish-water species; and F. diaphanus, a fresh-water spp. were injected with tracer doses of radioiodine. Their thyroid tissue was analyzed by quantitative and chromato-graphic techniques at various time intervals after injection, up to 1 week. The organic I compounds found were monoiodo-tyrosine, diiodotyrosine, thyroxine. One unknown compound which was not di- or triiodothyronine also was noted in F. heteroclitus. When F. majalis or F. heteroclitus were kept in sea water their thyroidal I131 peak accumulation was about 10%. When they were kept in relatively fresh water after injection their peak thyroidal iodine accumulation was increased. The increase was slight in F. majalis, about 25%; it was very marked, almost threefold, in F. heteroclitus. F. diaphanus kept in running water at 15[degree]C had a relatively high I131 thyroid uptake but within a week had not yet reached a peak level. F. heteroclitus kept at [degree]C had a lower I131 uptake in the thyroid, and reached the peak value very slowly.