Background color may modulate seawater adaptability in fish

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We previously found that masu salmon (Oncorhynchus masou) reared on a white background showed better seawater adaptability than those reared on a black background. Herein, we investigated the association of the hypothalamo-pituitary system, in which the production of hormones varies in response to background color changes, with seawater adaptability and electrolyte metabolism. The following important results were obtained. Firstly, rearing masu salmon on a white background resulted in a paler body color and an increase in the activity of Na+K+ATPase (NKA) in gills. Secondly, in vivo treatment with melanin-concentrating hormone, which is produced in the hypothalamus, increased gill NKA activity. Finally, expression of the melanin-concentrating hormone receptor gene was detected in the chloride cells in gills. These results suggest that background color influences osmoregulation in gills via melanin-concentrating hormone.