POPULATION PROFILE DEVELOPMENT AND MORPHOTYPIC DIFFERENTIATION IN THE GIANT FRESHWATER PRAWN Macrobrachium rosenbergii (de Man)

Post‐larval populations of Macrobrachium rosenbergii are characterized by a homogenous size distribution curve which changes, with time, to a positively skewed curve, with some individuals demonstrating a higher growth rate than the rest of the population. No morphotypic variation is observed at the post‐larval and juvenile stages, and the ratio of males to females is 1:1, equally distributed along the whole size distribution curve. Both the mean weight and the development of the skewed distribution curve are inversely affected by increasing density. In a mature population, three male morphotypes can be clearly differentiated by claw color, relative size within the population and the ratio of claw length to body length. The Small Male (SM) morphotype is characterized by short clear claws, while the two larger morphotypes are characterized by Orange Claws (OC) and Blue Claws (BC). Their relative occurrence in the population is SM 20–25%, OC 15–25%, and BC 5–10%. No apparent morphotypic variation exists in females and their size distribution is generally homogenous. Increased population density does not change the relative position, nor the relative proportions of the three male morphotypes and the females, however, the degree of skewness of the curve is inversely related to the density.