Population structure and yield characteristics of a prawn <i>Macrobrachium rosenbergii</i> (de Man) reared in polders under monoculture system

Abstract

Density dependent variation could be noticed in the population structure and yield characteristics of Macrobrachium rosenbergii raised in two polders of Kuttanad under modified commercial extensive monoculture system. Though the initial stocking density was maintained .3./m2 in the two polders, the population density at the time of harvest was 1.44 and 0.55/m2 in polder 1 and 2 respectively and the production worked out to 674 and 532 kg/ha/7 months. Females were dominant in the former (55.5%), while males (90.57U+0025) dominated in the latter. The proportion of male morphotypes changed with density. The percentage of SM and WOC increased at higher density, while the frequency of SOC and t-SOC was more at the lower density. Though OBC appeared as the most predominant morphotype in both the polders, its contribution in the total population was 38.87U+0025 in the latter against 23.22U+0025 in the former. The mean weight attained by males of M. rosenbergii was 109.92 g in polder 2 while it was 56.19 g in polder 1. The dominant weight groups at the lower density were 100-150 g (48.30U+0025) and 150-200 g (27.22U+0025) while the same at higher density were 30-50 g and 50-70 g. In polder 2, 98.25U+0025 of the yield was constituted by 30 g group and therefore marketable while the same in polder 1 was only 91.28%.