This book deals with the evaluation of the concentrations of four heavy metals (Cd, Pb, Cu and Zn) in mullet fished in the bays of Oran and Beni Saf. This benthic fish, reflects very well the quality of its biotope, being a very abundant species in Algerian coastal waters. The monthly sampling was spread over a period of five months, three organs were taken into consideration: the liver, detoxification organ, the gonads, reproductive organs and the muscle representing the part consumed by man. From here it emerges that: the mullet (Mugil cephalus) contains the four metallic pollutants sought, the strongest contents are those of Zinc, Copper has more or less important concentrations; the weakest concentrations are those of Lead and Cadmium. The results obtained and statistically processed did not reveal any significant difference between the heavy metal levels of the two sexes and at the level of the targeted organs and sampling areas. The levels of concentrations of trace metals reflect a certain pollution of the sampling areas (the bay of Oran and the bay of Beni Saf).