Changes in the mucous cells of the gills, buccal cavity and epidermis of the nine-spined stickleback, Pungitius pungitius L., induced by transferring the fish to sea water

A histochemical analysis of mucous cells in the gills, buccal cavity and epidermis of the nine-spined stickleback, Pungitius pungitius L., using alcian blue and PAS, showed that most cells contained more than one type of glycoprotein. In all regions, the cell content of sialylated glycoproteins increased, and of sulphated glycoproteins decreased during adaptation to sea water. The histochemical properties of the cuticle-secreting cells in the epidermis were less easy to study, but it seems that their content of neutral glycoproteins increased and their content of acid glycoproteins decreased, during adaptation to sea water. Mucous cells were generally less common in seawater-adapted animals, though in the epidermis of fish kept in sea water for 21 days, there were as many as in the freshwater controls. Sulphated glycoproteins may be more effective than others in freshwater osmoregulation for they are highly charged and could attract cations strongly. They may also help to combat bacterial and fungal infections, and perhaps these are less likely when laboratory fish are transferred to sea water.