Pond production characteristics of freshwater prawns Macrobrachium rosenbergii as influenced by the stocking of size-graded populations of juveniles

Abstract

A nursery-reared population of 50-day-old post-larvae of freshwater shrimp ( Macrobrachium rosenbergii) averaging 0.16 ± 0.08 g was divided into three groups. Two groups were size-graded by passive passage through either a 0.64 or a 0.48 cm mesh. Prawns passing through the 0.64 cm mesh proportionately graded into two size groups, 30% upper (0.40 ± 0.13 g) and 70% lower (0.15 ± 0.06 g). Size groups resulting from the 0.48 cm mesh grading were 70% upper (0.21 ± 0.09 g) and 30% lower (0.10 ± 0.03 g). Earthen ponds (0.061–0.073 ha) were stocked at a density of 39530/ha in triplicate with individuals from one of each of the graded or ungraded groups. After a 125- to 138-day growing season, average harvest weight ranged from 24.3 g (ungraded) to 35.4 g (30% upper) and differed significantly among treatments. Growth rates were not significantly different. Samples of prawns removed from each pond were classified into 5 morphotypes: blue claw male (BC), orange claw male + no clawed male (OCNC), small male (SM), berried female + open female (BFOF), and virgin female (VF). Mean harvest weights of the BFOF and OCNC categories in the 30% upper treatment were significantly greater than those for all other treatments. Average yield for the 30% upper and 70% upper treatments (1106 and 884 kg·ha −1, respectively) were significantly greater than that of the ungraded treatment (775 kg·ha −1). Differences in average harvest weight and total yield were achieved through changes in morphotype distributions. Calculated gross revenues in graded populations were 6–73% greater than that of the ungraded population.