The salt concentration inside the body of freshwater fish is higher as compared to the water in which it live . However this is not the the case with marine fish which have low salt concentration in their blood as compares to the salt in the sea water. In order to maintain sufficient salt in the fresh water fish body, specialized cell in the gills take ions from water and transport it into the blood. Thus it can be said that A freshwater fish regulate its salt levels by pumping salt inward across its gills
