ENCLOSED PRAWN NURSERY SYSTEMS AND EFFECTS OF STOCKING JUVENILE Macrobrachium rosenbergii IN PONDS 1

In temperate areas the stocking of small juveniles may be required for pond culture of prawns, Macrobrachium rosenbergii , to be economically attractive. Twelve nursery trials were conducted focused primarily on a two‐phase nursery system. In phase I trials, prawns grew from 0.01 g to 0.2‐0.4 g at densities of 1,194‐6,276 prawns/m 2 tank bottom during 67–105 days. Estimated survival rates at densities of 1,194‐1,663/m 2 were comparable after 4, 8, and 12 weeks of culture and averaged 96, 93, and 90%, respectively. At high densities survival rates were substantially lower. in the phase II trials, prawn stocking size varied from 0.09‐0.70 g and density from 538–904/m 2 . Prawns attained a weight of 0.9‐2.1 g during 42–64 days of culture. Estimated survival averaged 91% after 4 weeks and 84% after 8 weeks. One monophasic or continuous phase trial was conducted at a density of 323/m 2 . During this 8‐week trial, prawns grew from 0.05 to 1.64 g and exhibited a survival rate of 92%. The biological and economic effect of stocking larger juveniles (1 and 2 g size) was estimated for seasonal pond production of prawns. when 1 and 2 g prawns were stocked in ponds at a density of 43,100/ha, final prawn size increased 13 and 25%, respectively, and total production increased 111 and 208 kg/ha. At stocking density 64,600/ha, harvest size of prawns increased 17 and 27%, respectively, and production increased 183 and 299 kg/ha. Estimated revenues were increased when the additional cost of producing or purchasing these large juveniles was ≤ $15/1,000 for 1 g animals or ≤ $30/1,000 for 2 g animals.