Aquatic Toxicology is the study of the effects of environmental pollutants on aquatic organisms, such as pesticides especially the insecticides, on the health of fish or other aquatic organisms. Pesticides are substances used to control pests, including insects, aquatic weeds, plant diseases, and Aquatic snails that carry the cause of schistosomiasis. Pesticides have been found to be highly toxic not only to fish but also to the other organisms, which constitute the food chain. Pesticides in general, are used very extensively in agriculture, forestry, public health and in veterinary practices. Pesticides are categorized according to their target use. The three major pesticides are herbicides (weed control), insecticides (insect control), and fungicides (Mycotic control), but the more acute toxicity are insecticides. Since fishes are important sources of proteins and lipids for humans and domestic animals, so health of fishes is very important for human beings. Insecticides are the chemicals used to control insects by killing or preventing them from engaging in unwanted behaviors or destructive. The contamination of surface waters by insecticides is known to have ill effects on the growth, survival and reproduction of aquatic animals. Different concentrations of insecticides are present in many types of waste water and numerous studies have found them to be toxic to aquatic organisms, especially fish species. Application of insecticides used for control a wide variety of insectivorous and herbaceous pests which would otherwise diminish the quantity and quality of food production. Unfortunately, in spite of its advantages, chemistry has great disadvantages as well as insecticides are threatening the long-term survival of major ecosystems by disruption of ecological relationships between organisms and loss of biodiversity. The major Chemical groups of insecticides that are usually applied Organophosphate, Carbamates, Organochlorine, Pyrethroids, and Necotenoides. The insecticidal residues which contaminate the water are mainly due to the intensive agriculture combined with surface runoff and surface drainage, usually within a few weeks after application. Insecticides lead to decrease rate of growth, reproductive disorders. Also, cause spinal deformities and histopathological changes in gills, liver, hematopoietic tissue such as spleen, head of the kidney and renal tubules, endocrine tissues as well as brain, neurological, behavioral disorder and genetic defect are other biological indicators of exposure to insecticides. Fishes are particularly sensitive to the environmental contamination of water. Hence, these pollutants such as insecticides may significantly damage certain physiology and biochemical processes that different kinds of insecticides can cause serious impairment to physiological and health status of fishes. Aquaculture is one of the fastest growing food producing sectors, supplying approximately 40% of the world's fish food. Besides such benefit to the society, the industry does have its problems. Potentially harmful substances are often release into the aquatic environment. When is the launch of large quantities of pollutants there might be an immediate impact as measured by mortality the sudden large-scale aquaculture, for example, fish kills caused by pollution of water ways with agricultural pesticides. Lower levels of discharge may result in accumulation of pollutants in aquatic organisms. The final results, which may occur after a long period has passed pollutants through the environment, and include immune suppression, low metabolism, and damage to the gills and epithelia. This review presents further information concerning effects (Acute, sub chronic and chronic) of the different concentrations of pesticides (including insecticides) on various aspects of fish's biology and physiology. Also, depicts behavior, genetic and immune system of fish. The information given in this review facilitates the evaluation of potential toxic hazard resulting from exposure to different levels of these compounds. Data could be acquired useful in environmental risk assessment of freshwater organisms and marine. The histopathological changes in fish tissues used as a biological indicator for pollution with pesticides with special reference to insecticides. Finally, Protection of wildlife and water quality is possible when rationalize the use of pesticides. Also, when Pesticides must choosing judiciously and are used in combination with other pest management tools, and applied safely, the surface water pollution and contamination of our aquatic life could be avoided.
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