Freshwater fish
fish that live all or much of their lives in freshwater / From Wikipedia, the free encyclopedia
Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 1.05%.
Freshwater fish differ from saltwater fish in several respects. Their gills must be able to diffuse dissolved gases while keeping the salts in the body fluids inside. Their scales reduce water diffusion through the skin: freshwater fish that have lost too many scales will die.