Regulation of physiological properties by endocrire system in migrating fishes

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The present project of research has been held in 1984 and continued for 3 years in order to deeply underestand the mechanisms underlying the migration of fishes with special reference to (1) osmoregulatory mechanism, (2) migration and reproduction, and (3) migrating behavior. From our studies using fishes which are migrating in the ocean or fresh water to seawater and vice versa, the following findings were newly obtained.(1) Osmoregulatory mechanism: It was found that prolactin, well-known trigger of the freshwater adaptation of fishes, has another important role on the reproduction of anadromous fishes during migration. In addition, it was also found that growthhormone contributes to not only the growth but also the seawater adaptation of fishes during the migration. The detailed mode of actions of both hormones in the osmoregulatory process was investigated using modern technigues, for example radioimmunoassay or immunohistochemistry.(2) Migration and reproduction: The contribution of endocrine system to this subject has be poorly understood for a long period. Our research project recently demonstrated the contributic of both sex steroid and thyroid hormones to the catadromous migration. The former acts as a suppressor and the latter as an inducer of this phenomenon. From another stand point, the mechanism underlying the maturation of oocytes and spermatozoa were investigated. It was clearly shown that gonad stimulating hormone induces the vitellogenesis and oocyte maturation through the synthesis of steroid hormones such as estradiol, 17 <alpha> 20 <beta> -dihydroxy-4-pregnen-3-one and cyclic nucleotides. Contribution of cAMP-dependent phosphorylation process in the initiatic of sperm motility was also clearly demonstrated.(3) Behavior; Effects of terrestial magnetism or underwater magnetism on the recurrent migration to the river in chum salmon or eating responce of catfish were investigated and these studies are now progressing successfully.