Management strategies associating batch-graded and size-graded postlarvae can reduce heterogeneous individual growth inMacrobrachium rosenbergii(de Man)

Abstract

Two sets of adaptive trials were performed to determine the effects of size grading and batch grading on size heterogeneity in cultured Macrobrachium rosenbergii raised in the Coconut Garden channels of Kuttanad, Southern India. In the first set of trials, postlarvae were batch graded on the basis of their hatching order, segregated and grown separately as first-hatched and second-hatched groups. In the second set of trials, postlarvae were size graded as jumpers and laggards and were grown in separate channels. The average weight attained by prawns after 10 months of culture was highest for jumpers (83.11 g) and lowest for the prawns from the first-hatched group (43.76 g). The percentage of males was highest in the population of jumpers (58.23%). Highest production was recorded in the channel stocked with postlarvae from the second-hatched group (103.4 kg ha−1) and lowest production was obtained from the first-hatched group (63.74 kg ha−1). The proportions of undesirable small males were highest among laggards and the first-hatched group: 24.8% and 15.1% respectively. The level of heterozygosity within morphotypes was also high in these groups. Jumpers attained good growth by the end of culture but, because of their low survival rate, this approach was not economically feasible. However, higher production and survival in the second-hatched group improved economic viability. Thus, for better results, stocking with later-hatched groups would be more appropriate than stocking with the first-hatched group.