J. Salar-Amoli - Toxicology Research Center, University of Tehran
T. Aliesfehani

A significant and sudden death of fish and other aquatic animal is defined as a ‘fish kill’ characterized by large numbers of animals dying over a short period of time in a defined area. A fish kill incidence caused by chemicals may be rapidly evident in mater of hours through high mortality and morbidity affecting many species during a day or so. Though a sudden appearance of dead fish in a lake or pond attracts the attention toward pollutants, but fish mortality occur due to a wide variety of causes. A few dead fish floating on the surface of water is not necessarily a risky alarm. However, if large numbers of all sizes of fish along with any other aquatic species are found dead or morbid, the case calls for a precise investigation for the possible causes to be determined. Low level of dissolved oxygen, algal bloom (Red tide), cold weather, unhealthy or injured fish and pollutions are usually the common causes of a fish kill. Any of the environmental pollutants such as agricultural byproducts, active chlorine, gasoline, petroleum, ammoniac fertilizers, acids, swimming pool discharge, pond management chemicals and animal wastes may cause a sudden fish kill. A number of the fish kill incidences brought to Toxicology Research Center during the past few years are discussed in this article. Some of the cases had a clear history of intoxication with specific pollutants, while most of them, the "unknown cases" even had no suspicious reason, just inquired assessment of probable intoxication. Unfortunately, no clear history or study reports from any responsible organization or agency are available for the unknown cases.