CONTROL OF THYROID HORMONE SECRETION IN SALMONIDS

甲状腺激素与鲑鱼的迁徙有关，特别是在它们与熏蒸相关的下游迁徙中。本研究建立了一种从卵子和整个胚胎中提取甲状腺激素、甲状腺激素和三碘甲腺原氨酸的方法，并用放射免疫法进行了定量。甲状腺激素不仅存在于鲑鱼类的未受精卵的卵黄中，而且存在于所有迄今研究过的硬骨鱼物种的卵黄中。鲑鱼和虹鲑鱼的激素浓度在孵化前逐渐下降，然后在卵黄吸收过程中迅速下降。鲑鱼鱼苗从砾石床出来时，即下游迁徙之前，激素的组织和血浆水平上升，而非迁徙的虹鲑鱼则没有出现这种上升。在下游迁徙过程中，观察到鲑鱼鱼苗和Amago鲑鱼的血浆甲状腺激素水平显著增加。在比目鱼幼体的变态高潮期间，甲状腺激素的组织水平也显著增加。鲑鱼卵中也含有皮质类固醇皮质醇，其浓度的变化与甲状腺激素的变化基本一致。激素似乎在鱼类的早期发育中起着重要的作用，特别是在与迁徙和变态有关的过程中。

Thyroid hormones have been implicated in migration of salmonids, particularly in their downstream migration associated with smoltification. In this study, a method has been established to extract thyroid hormones, thyroxine and triiodothyronine, from the.egg and whole embryo and to quantify by radioimmunoassays. Thyroid hormones were contained in the yolk of unfertilized eggs of not only salmonids but also of all teleost species so far examined. In chum salmon and rainbow trout, the hormone concentrations decreased gradually until hatching, and then rapidly during yolk absorption.The tissue and plasma levels of the hormones increased during emergence of chum salmon fry from the gravel bed, just before downstream migration.No such increase was seen in non-migratory rainbow trout. A significant increase in the plasma levels of thyroxine was observed in the chum salmon fry as well as in amago salmon during downstream migration. A marked increase in the tissue levels of the thyroid hormones was also observed during metamorphic climax of the flounder larvae. Corticosteroid, cortisol, was also contained ih the salmon eggs, and changes in its concentrations were more or less in parallel with those in the thyroid hormones. The hormones seem to play important roles during early development of fishes, especially in association with migration and metamorphosis.