TILAPIA FISH KILLS - A COMMON SOUTH FLORIDA OCCURRENCE

It is a common seasonal occurrence in South Florida, especially in the Spring and Fall, to have the tilapia die off. Spawning activities of tilapia, which are native to Africa and the Middle East, occur when water temperatures exceed sixty-eight degrees Fahrenheit. The males dig a deep nest with their mouth and fins in shallow water over sandy bottoms which often contain damaging rock materials. The stressed male tilapia then become subject to one of many fish diseases through open wounds and the loss of their outer protective coating.

When under stress, there are many factors that can account for a sudden fish kill. The most common reason is low dissolved oxygen in the water. The amount of oxygen dissolved in water is inversely proportional to water temperature. As water temperature rises, the amount of dissolved oxygen decreases. During hot weather, surface waters warm up more rapidly then deep water, forming layers (stratification). Because photosynthesis and oxygen production occur near the surface, water in the deep layers becomes void of oxygen and develops a substantial oxygen demand. Heavy winds and cold rain normal to the Florida environment, can cause the oxygen-deficient bottom waters to rise. If the oxygen demand is sufficient, all of the dissolved oxygen present can be rapidly removed from the water column resulting in severe oxygen depletion and subsequent fish kills.

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