Osmotic and ionic regulation and the gill Na++K+-ATPase activity in the Japanese shore crab Hemigrapsus sanguineus

Osmotic, sodium and chloride regulations of hemolymph in Hemigrapsus sanguineus were investigated. The crabs exhibited strong hyperosmoregulation in the range of 50-75% SW. Sodium and chloride ions were also well regulated in the same salinity range. The speciffic activity of gill Na++K+-ATPase was higher in the posterior gills than in the anterior gills. In the posterior gills, the Na++K+-ATPase activity showed an increase of 1.5 times with acclimation from 100% SW to 50% SW. Absorption of sodium ion by H. sanguineus in low salinity may be attributed to the function of the posterior gills which have a high level of Na++K+-ATPase activity.