Heavy metals induced histopathological alterations in snakehead fish
Of the many different toxic compounds present in aquatic ecosystems, the heavy metals are considered to be the most hazardous. It is clear that the anthropogenic input of heavy metals is much higher than the natural input. Therefore they are of prime interest, particularly in view of their high toxicity in relation to aquatic organisms (hydrobionts). The environmental impact of metals is of particular concern because, unlike organic compounds, they cannot be subject to chemical degradation beyond the elemental state; they can only be redistributed between abiotic and biotic components and interact with their components. The changes of physical, chemical and biological parameters of water alter the behaviour of fish besides causing mortality. The studies carried out on various fishes have shown that heavy metals may alter the physiological activities and biochemical parameters both in tissues and in blood. It is a widely known by histological examination of tissues that these metals show biological accumulation of hazardous levels on the surface of the sediment in benthic and planktonic organisms and other organism by entering the food chain.
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Snakeheads (family Channidae) are airbreathing freshwater fishes containing two genera, Channa with 26 species native to Asia, Malaysia, and Indonesia; and Parachanna with 3 species native to tropical Africa. Some snakeheads are small, reaching about 17 centimeters, but most are much larger, the largest reported to be 1.8 meters in length. All are considered thrust predators with most being piscivorous as adults. A few of the smaller snakeheads and colorful juveniles of some larger ones have been available to hobbyists through the aquarium fish trade. Several species are highly valued as food fishes within parts of their native ranges, especially in Asia where they are an important part of capture fisheries and aquaculture. Because of these uses by humans, introductions far beyond native ranges have occurred. One Asian snakehead has been established in Oahu, Hawaii, since before 1900. Another species was discovered established in southeastern Florida in 2000, and a third in a pond in Maryland in 2002. Others have been captured from natural waters of the United States without evidence of reproduction and likely represent released aquarium fishes. That snakeheads at or near sexual maturity were being sold alive in ethnic food markets raised fears that they could be introduced into novel waters. These concerns led to this study on the biology of snakeheads. A risk assessment is included that examines environmental and related aspects of snakehead introductions.
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