## 3 Results and Discussion
### Metal Analysis
The content of trace metal elements in crustaceans is estimated to be higher in the exoskeleton than in other tissues, as cadmium (with an ionic radius of 0.97 and 0.99 A, respectively) and other elements such as manganese (Mn), lead, and zinc are gradually accumulated in the exoskeleton via calcium uptake routes [32]. Indeed, numerous investigations on brachyuran crustaceans have found that concentrations of metals in the exoskeleton are higher than in soft tissues [33; 34]. Figure 2: Heavy metal content s(Cd, Cu, Pb, and Zn) in _P. Segnis_ tissues (n = 20) from Ghannouch site (a) and from Djerba site (b). *: statistically significant difference between the trace element contents in the gills and hepatopancreas (\(p<0.01\)). Numerous environmental and biological factors, including molting, govern the trends of trace element bioaccumulation in crustaceans' soft tissues [35; 36]. This is an important phase because it provides a detoxifying mechanism for heavy metals to be eliminated on a regular basis [37]. Metals have been shown to have distinct bioaccumulation patterns and can accumulate in various tissues at different concentrations. As an example, cadmium accumulated mostly in the midgut and gills, copper in the gills, and zinc in the gills/muscle of _Carcinus menas_ treated with metals for 32 days [38]. According to the results obtained in our study, the Cd and Pb levels were higher than the MOH, EC, and FAO standards [39; 40; 41], while for the other two elements (Cu and Zn), the values do not exceed the prescribed standards (Table 2). It should be noted that copper and zinc are essential for the metabolism and physiology of crustaceans, and their accumulation is generally independent of environmental concentrations [42; 43]. However,  
Figure 3: Trace element contents (\(\mu\)g/g dry weight) in the gills (**a**) and the digestive glands (**b**) between the two studied sites (n = 20). *: statistically significant difference for the metal contents between the two sites (\(p\) < 0.01). when concentrations reach abnormally high levels, the ions accumulate in cytosolic proteins such as metallothioneein [44]. The zinc concentrations (Table 2) in all studied samples in this study were higher than the concentrations of the other metals in the same samples of _P. segnis_. These high levels in crabs can be attributed to the biological interest in Zn for the organism. Indeed, Zn is an essential element for the metabolic process and is associated with certain Zinc transporter metalloprotein (such as metallothioneins). The physiological functions of these metalloprotein are related to their affinities for essential cations, especially copper and zinc, and to their antioxidant characteristics. They also play a major role in cellular homeostasis by controlling the bioavailability of certain essential metals. Based on the data obtained in our study, we noted that the gill tissues at both studied sites had the highest concentrations of trace elements compared to the hepatopancreata (Table 3). These results are consistent with previous studies conducted on other crab species. A previous analysis [45] showed that _Potamonauteswarreni_ crab gills contained more Cd and Cu than the hepatopancreas. Indeed, the work of [PERSON] and [PERSON] [46] on the _Charybdis japonica_ crab also revealed that the gills are more sensitive than the digestive glands to exposure to pollutants. Moreover, DNA strand breaks were positively correlated with Cd exposure only in the gill tissue. Our results are also consistent with the work performed by [PERSON] et al. [47] on the _Uclides cordatus_ crab. This work showed that metals accumulated in a concentration-dependent manner, with the highest levels found in the gills, followed by the hepatopancreas. Different species accumulate metals at different rates, depending on how they respond to metal exposure [48; 49]. Within species that are closely related, as well as between genera, the processes of metal accumulation in aquatic crustaceans vary; some are net accumulators, whereas others are regulators.