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ABSTRACT
Aquatic environment receives industrial, agricultural and sewage outputs, which are potentially damaging to organisms. Biological responses of pollutants generally involve alterations at cellular and biochemical levels, leading to modifications in the structure and function of the cells and organs. Different species of fish and other aquatic animals have different tolerances to the level of ammonia in water. Ammonia, a metabolic waste product of fishes, is a wide spread contaminant of the aquatic environment causing autointoxication to fishes. Ammonium salts may affect severely various enzymatic processes and hamper fish health. Physicochemical changes in aquatic environment may drastically influence fish physiology. Fishes play a vital role in aquatic ecosystem and food webs. They are an important part of an aquatic ecosystem and are beneficial in indicating the aquatic pollution. The total ammonia in aqueous solution exists in two forms viz., ionized ammonia (NH4+) and unionized ammonia (NH3). The ionized ammonia is non-toxic but the unionized ammonia (NH3) is highly toxic to fish. The growth of aquaculture negatively affects the aquatic environment due to high level of nitrogen excretion from fish. The assessment of ammonia toxicity becomes necessary at this juncture to make aquaculture more eco-friendly. Symptoms of ammonia intoxication include tremor, blurring of vision and in severe cases coma and death. Ammonia is a potent neurotoxicant and may cause oxidative stress. Ammonia toxicity to aquatic organisms is largely a function of pH-and temperature-dependent chemical speciation, because ammonia toxicity is primarily dependent on the relative concentration of unionized ammonia. Biochemical markers measured in fish integrate the impacts of all toxicants, nutrients, and environmental stressors. An increase in the ambient ammonia concentration can cause a reduction in excretion and a net gain of ammonia from the environment. Therefore, the accumulation of ammonia in the body may be deleterious to the aquatic animals. Studies on such aspects must be encouraged to protect economically important fishes from ammonia toxicity.
Keywords: Aquatic pollution, ammonia toxicity, fish, enzymes, biochemical markers
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INTRODUCTION
Water is essential for survival of all forms of life. Leonardo da Vinci said that "Water is the driver of life". Water is one of the World's most precious natural resources and cannot be synthesized artificially for consumption. About 97% of earth's surface is...