Fish Diseases and Management

6.3.1.5 Nitrite poisoning

Nitrite poisoning causes hypoxia, lethargy and congregation of fishes near the water surface. Nitrite is actively transported across the gill, where it enters the bloodstream and oxidizes hemoglobin to methaemoglobin. Methhaemoglobin cannot transport oxygen efficiently, so tissues are deprived of oxygen leading to death. Addition of chloride, nitrifying bacteria, biological filters reduces the accumulation of nitrite.