産卵回帰シロザケのブナ化にともなう血中各種イオンおよびホルモン濃度の変化〔英文〕

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Returning chum salmon Oncorhynchus keta captured by set-nets placed along the Shiretoko Peninsula Hokkaido contain both silvery and nuptial colored fish. The nuptial color further develops in spawning fish in the river. To clarify physiological changes during nuptial coloration, plasma osmolality, electrolite concentrations, and plasma levels of testosterone, estradiol-17β, growth hormone, thyroxine, and the thickness of the skin were investigated using the fish captured in September and October. Plasma osmolality and concentrations of sodium and chloride significantly decreased in the spawning group but there was no significant difference between the silvery and the nuptial colored groups. Plasma calcium and magnesium significantly decreased during nuptial coloration in both sexes. The thickness of the skin, especially the epidermis, closely correlated with the development of nuptial color. Plasma testosterone level also increased during nuptial coloration in both sexes, but the level of females captured in the sea was much lower than that of corresponding males. Plasma concentration of thyroxine of females captured in the sea was significantly lower than that of males. Growth hormone levels increased during nuptial colora-tion in both sexes, and stayed high even in the river. These results indicate that the nuptial colored salmon captured in the sea have the same adapting ability to the seawater as the silvery fish, and that testosterone might promote the nuptial coloration and thickening of the skin. Sexual differences of the testosterone levels detected in the seawater salmon suggest that other hormones, such as thyroxine, may act as an antagonist to testosterone.
日本水産學會の論文

産卵回帰シロザケのブナ化にともなう血中各種イオンおよびホルモン濃度の変化〔英文〕

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