The invasive Portunus segnis, an atlantic species, was recently recorded in Tunisian waters. Since its record in the Gulf of Gabes, no studies have been carried out about the biochemical analysis of this alien species. In this context, our study aims to evaluate the fatty acid profile, lipid classes (neutral and polar), and nutritional value of breast of this invasive species. Specimens sampled from the gulf of Gabes were found to be rich in protein and oil, with significant differences between sexes. The level of saturated, monounsaturated, and polyunsaturated fatty acids in neutral and polar showed a significant difference between sexes. Saturated fatty acids were significantly higher in male P. segnis compared to the female. Docosahexaenoic (DHA), eicosapentaenoic (EPA), and arachidonic (ARA) were the most predominate polyunsaturated fatty acids (PUFA) in all oil classes. Oleic (C18:1) and Palmitoleic (C16:1) were the most abundant in monounsaturated. Palmitic (C16:0) and Stearic (C18:0) were the major saturated fatty acids. Consequently, the breast of P. segnis was a valuable source of high oil quality: It is rich in essential fatty acids and has an important n‐3/n‐6 ratio in both male and female blue crab. Therefore, the atherogenicity and the thrombogenicity were also evaluated, showing that P. segnis is a shellfish of greater value for human consumption in Tunisia.

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The current study examined the concentrations of ten trace elements (TE) (nickel, chromium, cadmium, iron, zinc, manganese, aluminum, copper, selenium and lead) in the edible tissue of the Ark shell Arca noae (L. 1758) from a Mediterranean coastal lagoon, the Bizerte lagoon during 2013-2014. The analysis of several redox status biomarkers, metallothioneins (MTs), malondialdehyde (MDA), glutathione peroxidase (GPx), reduced glutathione (GSH) and acetylcholinesterase (AChE), was monitored as a response to TE bioaccumulation and environmental parameters variability. Significant differences (p < 0.05) were observed between mean seasonal TE concentrations in A. noae soft tissue. The highest TE concentrations in A. noae soft tissues were recorded during summer, which coincided with the increase of body dry weight (BDW) and the gonad index (GI). During this season, biomarker responses were enhanced, revealing significant increases of MTs, MDA and GSH levels as well as GPx activity in A. noae tissues, while a decrease of AChE activity was observed. The levels of TE analyzed in A. noae and several parameters used to assess the potential human risk (estimated weekly intake, target hazard quotient and target hazard risk) were lower than the permissible limits for safe seafood consumption. Consequently, this shellfish can be considered safe for human consumption. This preliminary study presents prospects for the valorization of this seafood product in Tunisia's food sector. It also gives basal information for future environmental assessment studies in which A. noae could be used as early warning tools in the field of biomonitoring programs and confirms the usefulness of biomarkers to monitor the health status of aquatic organisms.

The reproductive strategy of an unexploited population of Arca noae from the saltwater Bizerte Lagoon (Tunisia, western Mediterranean), including its tissue plasticity, was studied. In total 309 individuals, collected monthly from October 2013 to September 2014, were examined; 142 were females, 42 were males and five were hermaphrodites. They were used in histological and immunohistochemical (stem marker: Pou5f1; proliferation marker: proliferating cell nuclear antigen (PCNA)) analyses of gonads and adjacent tissues (N = 189) as well as to compute the monthly condition index (N = 120). Water salinity, temperature and chlorophyll a concentration were recorded. Ripe ovaries were observed in two discrete periods, October-November and April-August. Both gonad ripenings were followed by spawning periods, November-April and July-September. The mature oocyte density showed that the first spawning period was less vigorous than the second one. These data also indicated that A. noae is a multiple spawner. Five cases of protandric hermaphroditism occurred from December to April. Gonad tissue was strictly associated and intermingled with the digestive gland and mantle muscle fibres. Seasonal variations were observed in the relative proportions of digestive gland and gonads: the former predominated when the latter regressed (March) and vice versa (peak in June). Seasonal transitions from germinal to somatic tissue and vice versa were hypothesised to occur through transdifferentiation mechanisms based on the activity of stem and proliferating cells. The condition index roughly increased along with gonad ripening and decreased during the spawning periods, although it did not run parallel to gonad evolution, because it also depended on chlorophyll a concentration, a proxy for phytoplankton density. The condition index was significantly correlated, by multiple regression, to both mature oocyte density and chlorophyll a concentration. Arca noae appears to have evolved a flexible reproductive strategy that makes it capable of exploiting diverse environmental conditions, which also involves tissue transdifferentiation.