This study has focused on the effect of malathion on acetylcholinesterase and catalase activities on several tissues in a sentinel specie Ruditapes decussatus (Mollusca, Bivalvia). Clams were fished from the lagoon of El Mellah (North-eastern Algeria) and then immediately transferred to the laboratory. Treatment with Malathion at 100 and 300 μg/l of water lasted 24h. We evaluated protein and lipid contents and activities of acetylcholinesterase and catalase in the digestive gland, gills, adductor muscle and mantle. Results showed that treatment with Malathion caused, in the four tissues studied, a decrease of lipid and protein levels. The enzymatic activity of acetylcholinesterase was strongly inhibited by Malathion with a dose-dependent manner, whereas that of catalase increased significantly with both doses. These results confirmed the toxic effect of malathion on clams and also the status of this species as sentinel species and bioindicator of pollution. Moreover, among the tissues studied, it appeared that the gills and digestive gland were more sensitive to pollution and seemed to be the most appropriate tissue to monitor littoral pollution by organophosphorus pesticides.
