Responses of Blue Catfish and Channel Catfish to Environmental Nitrite

Abstract In nitrite-exposure experiments, percent methemoglobin, plasma nitrite concentration, and plasma chloride ion concentration were compared between channel catfish Ictalurus punctatus and blue catfish I. furcatus exposed to sublethal levels of nitrite for 48 h at 25°C. In nitrite-recovery experiments, fish exposed to elevated environmental nitrite for 12 h were transferred to freshwater, and blood characteristics were monitored during the 24-h recovery period. Blue catfish appeared to be more resistant to environmental nitrite than channel catfish. Methemoglobin levels (percent of hemoglobin in methemoglobin form) were significantly lower in blue catfish than in channel catfish. Maximum plasma nitrite concentrations were 137 mg NO2-/L plasma in blue catfish and 164 mg NO2-/L plasma in channel catfish. Percent methemoglobin and plasma nitrite concentration were closely correlated. Plasma chloride decreased initially with exposure to nitrite but quickly returned to control levels. Blue catfish expose...