Aquatic toxicology is the study of the effects of anthropogenic chemicals on organism in aquatic environment.a number of chemicals are degradedreadily in an aerobic condition; the aquatic environment frequently contains little or no oxygen,and thus some chemicals can persist in aquatic ecosystem for long time. Aqare uatic organisms may be exposed to chemicals routes that are not present in terrestrial ecosystem. Certain chemicals such as metals are not volatile in air but are soluble in water. The metals which have been studied extensively the last decades are: cd,hg. Some highly toxic properties and their effects on the environment and the living organisms.
Cadmium is one of the most toxic heavy metal and has been classified as shins carcinogen by the international agency for research on cancer. Thus,it is heavy metal of considerable environment health concern.cadmium is widely distributed in the aquatic environment.during of fossil fuels and municipal waste are know to be largest sources of cadmium release to the environment. It can enter into the fresh water by disposal of industrial and household waste and by fertilizer runoff.fish in most aquatic environments,when are mature,occupy mostly the top niche of predators in aquatic ecosystems.during their life- cycle, higher plants and other small fish. The pattern of migration of fish, linked with their feeding habits and reproductive strategies,may also have a major effect