Evaluation of the protective role of zeolite aginst toxicity by cadmium in skin and muscles of the Nile catfish clarias gariepinus

ABSTRACT

Aquaculture in Egypt plays a vital role in protein production. Pollution by heavy metals poses a real threat to this successful system because of their toxicity and tendency to accumulate in different body organs of fish and in turn represent a considerable threat to the general health of human beings. The present study was initiated to obtain a more comprehensive knowledge of the toxic effects of cadmium on skin and muscle tissues of Clarias. It also emphasizes the role of zeolite as an ion-exchanging agent used in the reduction of metal toxicity in aquaculture pounds to assess its prophylactic activity against cadmium toxicity. Adult Nile catfish Clarias gariepinus [Burchell, 1822] of both sexes were exposed to a low dose [3 ppm] of cadmium under static laboratory conditions for an overall experimental duration of 45 days. Among the most important histological alterations in skin and muscles tissues of cadmium-treated fishes were degeneration, stagnated blood through dilated blood vessels, haemorrhages, chronic inflammatory infiltration and prominent necrosis. On the other hand fish exposed to zeolite at a dose level of 4.0 g/l for a similar duration showed normal histological structure of the studied tissues. While addition of zeolite to cadmium to the aquatic media presents ameliorated skin and muscle architecture with attenuated histological alterations after 45 days. Moreover, the present histochemical study implied reduction of total protein content, RNA, DNA, SDH, ALP and an increase of NSE, in cadmium treated fishes. Similarly, zeolite supplementation to cadmium revealed marked improvement of the histochemical parameters, which were able to reach more or less normal pattern. The bioaccumulation rate of cadmium recorded the highest value in muscles of cadmium-treated fishes after 45 days. Addition of zeolite to cadmium- contaminated media reduced the cadmium level in fish muscle to near to normal control values. In conclusion, zeolite was capable to reduce cadmium level in fish muscles and improve the histological as well as the histochemical alterations in the studied tissues