Abstract
Rainbow trout (S. gairdneri) were exposed to various combinations of H2O hardness, pH and Cu. Hematocrits of exposed fish were measured after the fish were fatigued by forced swimming. In the absence of Cu, hematocrits were not significantly altered by hardness and pH. In pH 6.0, hematocrit increased with increasing Cu exposure. At pH 7.9, this response to Cu was evident only at a hardness of 30 mg/l. Data on red blood cell counts and carcass and muscle moisture suggest that hemoconcentration was accompanied by a shift in water from blood to muscle.