CONTROL OF THYROID HORMONE SECRETION IN SALMONIDS

甲状腺激素与鲑鱼的迁移有关，特别是与银化相关的下游迁移。本研究建立了一种从鸡蛋和全胚胎中提取甲状腺激素甲状腺素和三碘甲腺原氨酸并用放射免疫测定法定量的方法。甲状腺激素包含在蛋黄中的未受精卵不仅鲑鱼，但也所有硬骨鱼种迄今为止检查。在鲑鱼和虹鳟鱼，激素浓度逐渐下降，直到孵化，然后迅速在蛋黄absorption.The组织和血浆中的激素水平增加出现鲑鱼鱼苗从砾石床，就在下游migration.No这样的增加被认为是在非洄游虹鳟鱼。甲状腺素的血浆水平显着增加，观察到在鲑鱼鱼苗以及在amago鲑鱼在下游迁移。甲状腺激素的组织水平显着增加，也观察到在变性高潮的比目鱼幼虫。鲑鱼卵中也含有皮质类固醇，皮质醇，其浓度的变化或多或少与甲状腺激素的变化平行。这些激素在鱼类早期发育过程中起着重要作用，特别是与洄游和变态有关。

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.