Toxicity of Nitrite to Channel Catfish (Ictalurus punctatus), Tilapia (Tilapia aurea), and Largemouth Bass (Micropterus salmoides): Evidence for a Nitrite Exclusion Mechanism

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Abstract
The 96-h median lethal concentrations of nitrite to channel catfish (Ictalurus punctatus), tilapia (Tilapia aurea), and largemouth bass (Micropterus salmoides) under similar water quality conditions were 7.1 ± 1.9, 16.2 ± 2.3, and 140.2 ± 8.1 mg NO2-N/L (mean ± SE), respectively (pH 7.7–8.2; temperature 23 °C). During 24-h sublethal exposures to nitrite, methemoglobin concentrations in the blood of all three species generally increased with increasing nitrite concentrations. Channel catfish and tilapia concentrated nitrite in their blood above environmental levels and generated higher methemoglobin concentrations than largemouth bass at all nitrite concentrations tested. Largemouth bass did not develop elevated methemoglobin concentrations until NO2-N concentrations reached 48.7 mg/L, and plasma nitrite concentrations in largemouth bass were never observed higher than environmental concentrations. These data indicate that differences in resistance to nitrite among species may be partially due to a differential ability of some species to prevent the concentration of nitrite in the plasma.