A study on the relative growth of two populations of Uca rapax (Smith, 1870) was performed primarily to determine the size at onset sexual maturity. The species was sampled monthly in Itamambuca (23º24'43"S and 45º00'73"W) and Ubatumirim (23º20'17.8"S and 44º53'2.2"W) mangroves. Carapace width (CW) and length (CL), abdomen width (AW), major cheliped propodus length (PL) and height (PH) for each sex, and gonopod length (GL) for males were measured with a calliper (0.01 mm). Allometric analyses were used to estimate size at maturity. The relationships that most precisely indicated the size at onset of sexual maturity were AW vs. CW, for females and PL vs. CW, for males. Males and females are mature, respectively at 15.2 and 12.1 mm CW in samples from Itamambuca and 13.5 and 11.2 mm CW in samples from Ubatumirim mangrove. Positive allometric growth of females abdominal width is likely related to the incubation process, while positively allometry growth of male's cheliped almost certainly relates to reproductive behaviour.
Allometric growth; morphologic maturity
