Fish Diseases and Management

6.3.1.1 Environmental hypoxia

Environmental hypoxia refers to low concentration of dissolved oxygen (DO) in the water. It is of two types namely Acute Environmental hypoxia and Chronic Environmental hypoxia. Acute Environmental hypoxia is defined as the rapid drop in DO to lethal or near lethal levels. It is accompanied by acute and frequently catastrophic mortalities. So, immediate exchange of oxygenated water or aeration is necessary. Chronic Environmental hypoxia is defined as the long-term suboptimal dissolved oxygen level in a culture system. It does not kill fish, but causes considerable stress. Reducing feeding will reduce fish and algal oxygen consumption.