POPULATION STRUCTURE OF MALAYSIAN PRAWNS, Macrobrachium rosenbergii (DE MAN), REARED IN EARTHEN PONDS IN SOUTH CAROLINA, 1974-19761

Population structures of Malaysian prawns, Macrobrachium rosenbergii, reared in earthen ponds in South Carolina are presented and various pond management strategies discussed. Sex ratios were generally biased toward females and overall, the total biomass of females was 20.6% greater than the total biomass of males. Mean sizes of males and females at harvest were usually similar (within one gram); however, their respective population structures showed distinct and characteristic differences. In general, females exhibited unimodal approximately normal distributions over a relatively narrow size range whereas the male populations exhibited markedly skewed, bi- or multimodal distributions over a comparatively broad size range. The size distributions of prawns produced in the 15 grow-out studies were influenced by prawn size at stocking, stocking density, and duration of grow-out (4 to 6 months). Of these, initial prawn size was clearly the most important factor controlling size distribution. Stocking juveniles resulted in shifting the prawn biomass at harvest into the larger size classes and the lower the stocking density or longer the rearing period, the more pronounced was this shift in biomass distribution. In contrast, regardless of density (8.4–20.1 m-2) and grow-out time (137–181 days), the stocking of postlarvae resulted in 46 to 96% of the harvested biomass being contained in the small (<15.0 g), less valuable size category. Although stocking juveniles results in a more valued crop, the cost of producing these juveniles may offset much of this economic gain. Our data suggest that an alternative stocking strategy which consists of stocking a mixture of postlarvae and juveniles may in fact result in a greater net return. Pilot-scale demonstrations coupled with economic analyses are needed to test this pond stocking strategy.