The Biology of the Blue Swimming Crab Portunus segnis (Forskal, 1775) along the Bushehr Coasts, Persian Gulf

The size composition, growth pattern, sex ratio and feeding habits of the blue swimming crab, Portunus segnis from Persian Gulf in south of Iran, was studied. Sampling was performed by trawl net during a one- year period (July 2011 to May 2012) as processed 864 crabs was collection. The crabs carapace width ranged were from 7.5-17.5 cm for males and 7.0-16.5 cm for females. The crab carapace length was from 4-8 cm for males and 3.5-8 cm for females. An analysis of covariance indicates that there is a significant difference between the two sexes with respect to the carapace width-weight relationship.  The condition factor ranged between 3.78 and 5.46 with a mean of 4.85. The condition factor decreased with an increase in crab size. The analysis of dietary compositions showed that the main food items included crustaceans, mollusca and fish. The crustaceans included shrimp, barnacle and crab. The dominant molluscs were the bivalve Cardita bicolor and gastropod Cerithium erythraeonense. There were significant differences in the preference for food items in different seasons and size groups (p<0.05). Sex ratio during a year of study was M: F = 0.92: 1 which should be the relative frequency of females.