Cadmium is one of the most toxic heavy metals. Its toxicity has been widely studied and reported. This metal is a serious environmental and occupational contaminant and may represent a serious health hazard to man and animals.The present investigation was designed to study the effects of sublethal concentration of cadmium on some water quality parameters in common carp, Cyprinus carpio and effects of zeolite on these parameters. The fish obtained from a local fish farm (Amin Abad , Tehran , Iran) were acclimated in holding tank for 1 week , then 45 apparently healthy fish , mean weight 700g were randomly divided into three groups ( I - III ), 1000 lit. indoor fiberglass tanks, without well water flow but with aeration. At the beginning the parameters were as follow: hardness 320.6 mg/ l as CaCo3, dissolved oxygen 8, pH 7 and temperature 16±2 0 C . The groups were divided as follow: Group I without cadmium and zeolite , group II exposed to 30 ppb cadmium and group III exposed to 30 ppb cadmium in addition 10ppt zeolite. Fish were not fed during the 30 days of Cd exposure . Water quality parameters including hardness and ammonia and the level of cadmium in each tank was measured two times weekly throughout the exposure. The result revealed that the level of cadmium, ammonia and water hardness in group III which contains cadmium and zeolite, significantly( P≤0.05) decreased in comparison with group I and II .
