Population features of Microphrys bicornutus Latreille, 1825 (Brachyura, Majidae) from Isla Margarita, Venezuela

The aim of this study is to characterize the population biology (sex ratio, size structure, relative growth of reproductive characters and realised fe cundity) of the crab Microphrys bicornutus from Isla Margarita, Venezuela. Nearly 100 crabs were collected and fixed monthly during 1998. In the labor atory, crabs were sexed and measured: maximum carapace length, chelae lengt h, chelae and abdomen width for females and first pleopod length for males. Additionally, 96 ovigerous females were collected to determine fecundity. The following measurements were taken for each female: body wet weight (BWW ), body dry weight (BDW), egg wet weight (EWW), egg dry weight (EDW) and nu mber of eggs (NE). The following determinations were made: relative fecundi ty (RF) = NE/BDW and reproductive output (RO) = (EDW/ BDW) x 100. Relative size at the onset of maturity (RSOM) was calculated as minimum ovigerous fe male/female's maximum size. The results indicate that the sex ratio is near ly 1:1 during the entire year. Ovigerous females and moulted males and fema les were observed throughout the year. Size frequency distribution and size at the onset of sexual maturity, estimated by relative growth of the sexua l secondary characters and RSOM value, differed from those estimated in stu dies done in Jamaica and Buchuaco, Venezuela.