Salinity effects on development of chloride cells in the larvae of ayu (Plecoglossus altivelis)

Salinity effects on ultrastructure, size and density of chloride cells in the larvae of ayuPlecoglossus altivelis (Temminck and Schlegel) were examined. Ayu larvae hatched in freshwater were reared in seawater and freshwater at the Fisheries Laboratory, University of Tokyo, and the Institute of Zoology, Academia Sinica, between 1984 and 1986. Freshwater-hatched larvae modify the intercellular organization and the junctional structure of skin chloride-cells within 1 h after direct transfer to 30 seawater. The gills of seawater-reared larvae develop chloride cells earlier than those of freshwaterreared larvae. Following the development, a more rapid decrease in number of skin chloride-cells occurs in the freshwater group, while a more significant increase in size of skin chloride-cells occurs in the seawater group. These results indicate that chloride cells possibly play a critical role in osmoregulation in the early life stages of ayu as in the adult, and that the skin chloride-cells may perform this function until the development of the gill chloridecells is complete.