The effect of density of Macrobrachium rosenbergii raised in earthen ponds on their population structure and weight distribution

Abstract

The population structure and weight distribution of Macrobrachium rosenbergii raised in earthen ponds in polyculture with fish were studied. Over 10 000 prawns were grown in 12 ponds stocked with 1, 2, 3 or 4 prawns per m 2. Females were more abundant than males in all of the treatments. The proportions of three different male morphotypes, blue claw, orange claw and small males, changed with density but those of the female morphotypes did not. A detailed analysis of prawn weight distribution (mean, coefficient of variation and skewness) was carried out separately for each sex and for the morphotypes within each sex. Prawn survival was approximately 85%, independent of prawn density. Yield increased and mean prawn size decreased with prawn density. The most profitable density was 2 prawns per m 2. The biological mechanisms controlling variation in sex ratio and morphotype frequency and the social control of growth are discussed.