What causes brown blood disease in fish and how is it dealt with?

Excess nitrate levels in water bodies where fish are farmed cause brown blood disease. It can be also be addressed as nitrate poisoning because the nitrate in water oxidizes the hemoglobin in the fish blood cells and converts it into a compound called met hemoglobin. This compound obstructs the oxygen intake due to which the fish in water experience oxygen stress and die immediately. Administering proper antibiotics can help overcome this problem, but most importantly care should be taken such that the disease doesn’t occur.