Abstract
Mud crab (Scylla paramamosain) is an economically important crustacean species for fisheries and aquaculture industry in China and other Southeast Asian countries. In this study, the sex ratio, morphological dimorphism, and the characteristics of morphological traits between female and male S. paramamosain juveniles at three different pond-culture stages were determined. The sex ratio skewed towards female crablets as growth and development proceeded. Three growth traits exhibited significant differences between sexes when the crablets were at two months of pond-culture stage, however, the number of growth traits with significant differences increased to seven when the crablets were at three and four months of pond-culture stages. Further, significant positive correlations were detected among all the 190 trait-pairs, irrespective of the pond-culture stages of the crablets. Apart from this, the path coefficients and determination coefficients varied between sexes among the three pond-culture stages, suggesting that the growth traits have different effects on body weight (BW) of female and male crablets during different pond-culture stages. The effect of growth traits on BW in both sexes at different pond-culture stages was determined by constructing six multiple regression equations. Analysis of the width-weight relationship revealed that male crablets had positive growth allometry whereas the females had isometric growth. In addition, an obvious sexual dimorphism in cheliped size and abdomen width was observed with growth and development. A discriminant function equation was successfully constructed for sex identification based on morphological indexes, with a high accuracy of 90.4%.