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mass death of aquatic animals, mainly fish.
It is caused by a decrease in the amount of oxygen dissolved in the water (to 5-30 percent of normal saturation) or by the appearance of toxic substances in the water (owing to the discharge of untreated industrial effluent or washing of toxic chemicals from land). The amount of oxygen decreases in bodies of water rich in organic matter (for example, bog water) and in stagnant water where algae (responsible for the blooming of water) and zooplankton are well developed. Fishkills generally occur in winter (from January to April) and at night in the summer in calm, warm weather. Fishkills sometimes occur in seas (for example, in the Sea of Azov in calm weather in summer). Certain fish (salmon, sturgeon, perch), crustaceans, and mollusks (pearly mussel, freshwater mussel) are particularly sensitive to an oxygen deficiency. Tench, Carassius, loach, chironomid larvae, and other organisms are less sensitive and survive longer. Control measures include saturating the water with oxygen and preventing toxic substances from entering the body of water.
REFERENCEZernov, S. A. Obshchaia gidrobiologiia, 2nd ed. Moscow-Leningrad, 1949.
N. S. STROGANOV