Empirical Relationship between Percent Methemoglobin in Channel Catfish and Dissolved Nitrite and Chloride in Ponds

Abstract

Mean values for percent methemoglobin were obtained for 13 groups of channel catfish Ictalurus punctatus from commercial production ponds in west-central Mississippi. Mean percent methemoglobin was correlated with ambient nitrite concentrations (r2 = 0.51; P > 0.05). The correlation was improved when mean percent methemoglobin was regressed on the molar ratio of nitrite: chloride concentrations (r2 = 0.96; P > 0.01). These data indicate that percent methemoglobin can be predicted more accurately by nitrite-to-chloride ratios than by nitrite concentrations alone.