The relative growth and sexual maturity of the freshwater crab Dilocarcinus pagei (Brachyura, Trichodactylidae) in the northwestern region of the state of São Paulo

Abstract

ABSTRACT. The aim of the present study was to determine the size at sexual maturity in the freshwater crab Dilocarcinus pagei Stimpson, 1861, from a population located in Mendonça, state of São Paulo, Brazil. The crabs were sampled monthly (July 2005 to June 2007, at Barra Mansa reservoir. The specimens were captured manually or in sieves passed through the aquatic vegetation. The crabs were captured and separated by sex based on morphology of the pleon and on the number of pleopods. The following dimensions were measured: carapace width (CW); carapace length (CL); propodus length (PL); and abdomen width (AW). The morphological analysis of the gonads was used to identify and categorize individuals according to their stage of development. The morphological maturity was estimated based on the analysis of relative growth based on the allometric equation y = ax b . The gonadal maturity was based on the morphology of the gonads by the method CW 50 which indicates the size at which 50% of the individuals in the population showed gonads morphologically mature to reproduction. The biometric relationships that best demonstrated the different patterns of growth for the juvenile and adult stages were CW vs. PL for males and CW vs. AW for females (p<0.001). Based on these relationships, the estimated value to morphological sexual maturity was 21.5 mm (CW) in males and 19.7 mm (CW) in females. The determination of the size at sexual maturity and the adjustment of the data based on the logistic curve (CW 50 ) resulted in a size of 38.2 mm for males and 39.4 mm for females (CW). Based on the data obtained for sexual maturity for D. pagei, we can estimate a minimum size for capture of 40 mm (CW). This minimum size allows at least half of the population to reproduce and retains the juveniles and a portion of the adults in the population.KEYWORDS. Allometric growth, gonadal maturity, morphological maturity, reproduction. Os caranguejos foram separados por sexo, de acordo com a morfologia do abdome e pleópodos. As dimensões mensuradas foram: largura da carapaça (LC); comprimento da carapaça (CC); comprimento do própodo (CP) e largura do abdome (LA). Além disso, análise morfológica das gônadas foram realizadas e caracterizadas em relação ao estágio de desenvolvimento. A maturidade morfológica foi estimada com base no estudo do crescimento relativo, esta análise é baseada na equação alométrica y = ax b e a maturidade gonadal através da morfologia das gônadas, utilizando o método LC 50 indicando o tamanho em que 50% dos indivíduos encontram-se com gônadas desenvolvidas para a reprodução. As relações biométricas que melhor indicaram os diferentes padrões de crescimento das fases jovem e adulta foram LCxCP para os machos e LCxAB para fêmeas (p<0,001). Baseado nessas relações, o valor estimado para a maturidade sexual morfológica em machos foi de 21,5 mm (LC) e de 19,7 mm de (LC) para fêmeas. Na determinação da maturidade sexual gonadal, o ajuste da curva logística (LC 50 ) resultou em um tamanho de 38,2 mm para os machos e 39,4 mm para...

Population structure, recruitment, and mortality of the freshwater crabDilocarcinus pageiStimpson, 1861 (Brachyura, Trichodactylidae) in Southeastern Brazil

“…The bimodality obtained for male and female size combined supports the hypothesis of seasonal reproduction, which is common in tropical species (Mansur & Hebling 2002;Pinheiro & Taddei 2005b;Taddei & Herrera 2010;Venâncio & Leme 2010;Davanso et al 2013). The monthly distribution of individuals (males and females) in size classes consisted mostly of two modes, one of juveniles and one of adults, stages defined by Herrera et al (2013). This pattern is probably related to the seasonality of reproduction and recruitment (Tsuchida & Watanabe 1997).…”

“…Female decapods are often larger than males, and a larger abdomen allows a female to carry more eggs and hatchlings (Hines 1988;Taddei & Herrera 2010). In freshwater species, this specialization helps to optimize the reproductive potential (Herrera et al 2013) since species with epimorphic development produce larger eggs than those with abbreviated development (Vogt 2013). The amount of available calf fosters the survival of hatchlings (Beck & Cowell 1976) during the period in the incubation chamber (Sternberg & Cumberlidge 2003;Senkman et al 2015).…”

“…These authors worked with the same population and found for males a maximum size of 52.6 mm CW and a growth rate (K) of 0.68 and for females, a maximum size of 63.65 mm CW and a growth rate (K) of 0.73. Males measuring 21.5 mm CW or larger, and females 19.7 mm CW or larger were considered adults; individuals smaller than these measurements were considered juveniles (Herrera et al 2013).…”

“…Several biological and ecological aspects of freshwater decapod crustaceans are still scarce in the literature, such as trophic ecology, behavioral ecology, functional diversity, population dynamics studies, sex ratio, reproductive period, size at maturity, population delimitation, and the relation of the species with different environments (Davanso et al 2013;Herrera et al 2013;Sharma & Gupta 2013;Williner et al 2014). Approximately, 20% of brachyurans inhabit fresh waters (Yeo et al 2008), and they can be found on every continent .…”

“…Studies on freshwater crabs are still relatively sparse compared to marine species. Studies of D. pagei have mainly examined population characteristics, such as growth (Mansur et al 2005;Pinheiro & Taddei 2005b;Taddei & Herrera 2010;Davanso et al 2013), sexual maturity (Herrera et al 2013), fecundity (Mansur & Hebling 2002), locomotor activity (Renzulli & Collins 2001), the circadian cycle and feeding habits (Williner & Collins 2002), and the relationship between weight and size (Pinheiro & Taddei 2005a) and juvenile development (Vieira et al 2013). Physiological studies have examined gill physiology (Furriel et al 2010;Granado et al 2010;Firmino et al 2011) and biochemical characteristics (Zanotto & Baptista 2011).…”