Relative growth, sexual dimorphism and morphometric maturity of Trichodactylus fluviatilis (Decapoda: Brachyura: Trichodactylidae) from Santa Terezinha, Bahia, Brazil

Freshwater crabs are important elements in the aquatic biota of brooks, rivers, lakes and ponds, from both ecological and the socio-economic aspects. Trichodactylidae comprises 51 endemic species from the Neotropical region. Among all the species of this family, Trichodactylus fluviatilis Latreille, 1828 has the widest geographic distribution throughout Brazil. Despite that, there are few published contributions on the biology of this species. The present study investigated the following aspects of T. fluviatilis: relative growth, mean size at onset of morphometric maturity, sexual dimorphism, laterality and heterochely. Specimens were collected monthly from September 2010 through August 2011, from the Velha Eugenia Brook, municipality of Santa Teresinha, State of Bahia. Carapace width (CW), carapace length (CL), major cheliped length (MaCL) and minor cheliped length (MiCL), major cheliped height (MaCH) and minor cheliped height (MiCH), and width of the fifth abdominal segment (5AB) were measured to evaluate the presence of sexual dimorphism; the major difference between the sexes was in the CW vs. 5AB ratio. Heterochely was observed in males and females, with the right cheliped larger than the left in 89% of males and 81% of females. Crab size at the onset of morphometric maturity (= puberty molt) was estimated based on the ratio between CL, cheliped dimensions, 5AB and CW (independent variable). Females were larger than males when they reached morphometric maturity in all studied relations. We recommend the use of chelipeds and abdominal width relationships to estimate the size at the morphometric maturity in males and females, respectively.