The Effects of Heavy Metals on Aquatic Animals

Heavy metals consist less than one percent of living mass organisms, and their different density cause to some disorders. Surface waters and also acidic rains can transfer these metals to oceans via washing polluted environment. Heavy metals naturally exist in very little amount in watery places. Metals pollution of the sea is less than other types of watery pollution but its effects on marine ecosystems and humans are very extensive. Industrial wastes in aquiculture cause toxic effects in aquatic organisms specially in fishes. Aquatic organisms absorb the pollutants directly from water and indirectly from food chains. Some of the toxic effects of heavy metals on fishes and aquatic invertebrates are; reduction of the developmental growth, increase of developmental anomalies, reduction of fishes survivalespecially at the beginning of exogenous feeding or even cause extinction of entire fishes population in polluted reservoirs. These consequences can affect on geological, hydrological and finally on biological cycles. Thus it seems that more consideration of bioconservation protocols are so important. Introduction Water is one of the most valuable natural resources . The quality of water is of vital concern for the mankind since it is directly link with human welfare [15]. A major environmental concern due to dispersal of industrial and urban wastes generated by human activities is the contamination of soil and water. Controlled and uncontrolled disposal of waste, accidental and process spillage, mining and smelting of metalliferous ores, sewage sludge application to agricultural soils are responsible for transferring of contaminants into non-contaminated sites as dust or leachate and contribute towards contamination of our ecosystem[11]. A wide range of inorganic and organic compounds cause contamination, includes heavy metals, combustible and putrescible substances, hazardous wastes, explosives and petroleum products, Phenol and textile dyes. Major component of inorganic contaminates are heavy metals. They have some different problems than organic contaminants [11, 10,13]. Metal pollution of the sea is less visible and direct than other types of marine pollution but its effects on marine ecosystems and humans are very extensive. The presence of metals varies between fish species; depend on age, developmental stage and other physiological factors. Fish accumulate substantial concentrations of mercury in their tissues and thus can represent a major dietary source of this element for humans. Fish are the single largest sources of mercury and arsenic for man. Mercury is a known human toxicant and the first sources of mercury contamination in man are fishes. Biotransformation of mercury and methyl mercury formation constitute a dangerous problem for human health [7]. Soil microorganisms can degrade organic contaminants, while metals need immobilization or physical removal. Although many metals are essential, all metals are toxic at higher concentrations, because they cause oxidative stress by formation of free radicals. Another reason why metals may be toxic is that they can replace essential metals in pigments or enzymes disrupting their