Size at sexual maturity, breeding season and fecundity of three-spot swimming crab Portunus sanguinolentus (Herbst, 1783) (Decapoda, Brachyura, Portunidae) occurring in the coastal waters of Karachi, Pakistan

Size at sexual maturity of the crabs was determined by examining the condition of gonads and studying the relative growth of chelae and pleopods in male and abdomen in female crabs. Results show that the crab can attain sexual maturity at a size of 64–70 mm short carapace width (= 83–89 mm long carapace width) in male and 63–71 mm SCW (= 81–93 mm LCW) in female crabs. Fifty percent male Portunus sanguinolentus mature at 60.8 mm SCW while 50% female mature at 63.5 mm SCW. The smallest female crab having eggs on its abdominal pleopod measures 63 mm SCW. Berried females were found in all months except June. Minimum and maximum number of eggs were found to be 272,000 and 1,395,000 in crab having 63 and 120 mm SCW, respectively.