Morphometrics and length-weight relationship in the blue swimming crab, Portunus segnis (Decapoda, Brachyura) from the gulf of Gabes, Tunisia

Ghailen HAJJEJ, Ayda SLEY, Othman JARBOUI

This The morphometric characteristics and relative growth of the blue swimming crab Portunus segnis collected in the Gulf of Gabes were examined. A total of 634 individuals of P. segnis were analyzed, being 335 males and 299 females. The allometric relationships between the characters of this set suggest that most relationships are isometric. The carapace width/length- weight relationship was studied in both sexes of crab. The exponential values (b) for the carapace width-total weight relationship was distinct between the sexes with a positive growth pattern in weight for males, and a negative allometric pattern identified for females. Males were significantly larger and heavier than females, the expected pattern to many crabs.  An analysis of variance indicates that there is a significant difference between sexes with respect to the carapace width-weight relationship. A correlation between carapace width and weight were encountered for males and females. The statistical analysis of chelar propodus length within sexes indicated a mirror-symmetry in this species, which provides more stability and balance to individuals. The condition factor ranged between 0.00691 and 0.34767 with a mean of 0.0582. The condition factor decreased with an increase in crab size.