Protective Effect of Chloride on Nitrite Toxicity to Coho Salmon (Oncorhynchus kisutch)

Tolerance of coho salmon (Oncorhynchus kisutch) to nitrite was increased when the concentration of chloride ion in the environment was high. The results of flow-through bioassays revealed that no mortality occurred when yearling coho salmon were subjected to nitrite-nitrogen (NO2−–N) of 29.8 mg/ℓ and chloride (Cl−) of 261.3 mg/ℓ for 48 h. When yearling coho salmon were exposed to 3.8 mg/ℓ NO2−–N and 2.5 mg/ℓ Cl− for 12 h, the resultant mortality was 58.3%. Possibly, chloride competes with nitrite for transport across the gills and integumental tissues, thereby interfering with the onset of nitrite-induced methemoglobinemia.