Relative growth and reproductive parameters in a population of Microphrys bicornutus (Brachyura, Majoidea) from Bocas del Toro, Caribbean Sea, Panama

Size structure within a population, relative growth of secondary sexual characters in both sexes, and fecundity of females were assessed from field samples of Microphrys bicornutus in the vicinity of Bocas del Toro, Caribbean Sea, Panama. The study was based upon 135 individuals captured by hand and a kick net. Carapace width ranged from 6.5 to 14.4 mm for ovigerous females, 4.2 to 16 mm for non-ovigerous females, and 5.9 to 17.4 mm for males. The relative growth of carapace length versus carapace width was isometric in males and negatively allometric in females. Relative growth of the chela length and abdomen width, compared to the carapace width, exhibited 2 phases, immature and mature, for males and females, respectively. The carapace widths at which 50% of males and females reached morphometric maturity were 13.6 and 8.5 mm, respectively. The mean value of the reproductive output was 3.6, the relative fecundity was 2041.91 eggs, and the relative size at the onset of sexual maturity was 0.4. As in most brachyuran species, the studied population of M. bicornutus showed a strong positive correlation between fecundity and body size. Differences in those parameters for previously studied populations from Venezuela, Jamaica and Brazil may be due to latitudinal or regional environmental effects.