Transient occurrence of chloride cells in the abdominal epidermis of the guppy, Poecilia reticulata Peters, adapted to sea water.

Chloride cells are characterized by a great number of mitochondria and a uniquely proliferated agranular endoplasmic reticulum through which ions are transported to an apical pit for secretion to the environment. Chloride cells are extremely rare in the epidermis of the guppy, Poecilia reticulata Peters, adapted to fresh water. They are frequent in the epidermis of guppies adapted to sea water three weeks after adaptation, but have disappeared in fish that were kept in sea water for approximately one year. The fine structure of epidermal chloride cells and the influence of prolactin treatment on their number are described. The significance of these cells with respect to the possible roles of the epidermis and the pituitary hormone prolactin in teleost osmoregulation is discussed.