Population Structure of the Freshwater Crab Trichodactylus Fluviatilis Latreille, 1828 (Decapoda, Trichodactylidae) in Ubatuba, Northern Coast of Sao Paulo State, Brazil

The available information on the biology of freshwater crabs, in contrast with marine crabs, remains very scarce making it an important and interesting target for new studies. The objective of the present study was to determine basic parameters of the population structure of Trichodactylus fluviatilis in Ubatuba, northern coast of the State of Sao Paulo, Brazil. Monthly nocturnal collections were carried out by hand, from March 1998 to February 1999. A total of 306 individuals were captured, 138 males and 168 females. Ovigerous females were not caught during the sampling period, which is probably the result of their cryptic behavior during egg incubation. Female mean size (23.53 ± 4.8 mm CW) was significantly larger than males (22.32 ± 4.8 mm CW). There was no significant deviation from a 1:1 sex ratio during the studied period and the size distribution of the sampled population presented a normal distribution.