Hormonal control of migration in salmon

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The endocrine systems have important roles in controls of various aspects of fish migration. It is well accepted that, in salmonid fish, prolactin is a hormone necessary for fresh water adaptation, while growth hormone is responsible for seawater adaptation. Nonetheless, we do not know modes of actions of these hormones in migratory fish, mainly because of a lack of homologous hormones. Recent progress in molecular biology now makes it possible to have micro-organisms synthesize so-called recombinant hormones which in turn allow us to conduct receptor studies, such as a radio receptor assay (RRA). In the present project, we therefore tried to apply molecular techniques in a study on endocrine mechanisms of salmon migration. Since recombinant salmon growth hormone is available, a radio receptor assay system was rather easily established to examine physiological changes in its kinetics. Contrary, recombinant salmon prolactin is not available, so that tilapia whose hormone is available was used to establish prolactin RRA.