Morphometrical studies of the ultrastructure of the epidermis of the guppy, Poecilia reticulata Peters, following adaptation to seawater and treatment with prolactin.

Adult male guppies adapted to seawater or fresh water were treated for a period of 4 weeks with different doses of prolactin. The epidermis of scales from the midlateral body region was studied by light and electron microscopy. Prolactin treatment of guppies adapted to fresh water changes the pattern of superficial ridges and increases the numbers of cell layers, mucous cells, and subepidermal capillaries. Adaptation to seawater increases the body surface, the surface extent of superficial cells, the number of small electron-dense vesicles, and the height of the glycocalyx. The most striking finding is the occurrence of chloride cells in the epidermis of all guppies adapted to seawater. The number of chloride cells is reduced after low and medium doses of prolactin, and increased following high doses.