WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2013 33 and productivity of the Amazon river prawn (Macrobrachium amazonicum) reared in integrated rice-prawn systems. The experiment was carried out in the northeastern São Paulo State, Brazil, using plots of 30 m2 each (Fig. 1). Post-larvae of M. amazonicum (Fig. 2) were stocked at three densities: 5 (5RP), 10 (10RP), 20 (20RP) prawns/m2 and a control of rice monoculture (RM). Each treatment had six replicates. No feed was provided because prawns can take advantage of natural food in rice fields. Water quality was monitored at inlet and outlet points. To block entrance of aquatic predators and escape of prawns, nets were fitted on inlet (Fig. 3) and outlet sluice gates (Fig. 4). To facilitate collection of prawns at harvest, trenches of 50 cm depth, taking about 17 percent of each plot area, were excavated near the outlet sluice gates (Figs. 5 and 6). Rice was not planted in this area (Fig. 7). No chemicals were applied to control rice diseases and pests. Weeds were controlled only by manual methods and flooding after weeding. An economic feasibility study simulated the sale of prawns as live bait for sport fishing and economic performance indicators were calculated for rice monoculture (RM) and the integrated riceprawn system (RP). (CONTINUED ON PAGE 34) FIGURE 5. Manual excavation of trenches. FIGURE 6. Completed trenches are located near outlets. FIGURE 7. Trenches in rice fields after flooding. Note that rice was not planted there to facilitate harvest of prawns. FIGURE 8. Harvest of prawns from trenches using an adapted seine. The Amazon river prawn is a native species with wide distribution in South America, from Venezuela to Argentina (Coelho and Ramos-Porto 1985, Pettovello 1996, Bialetzki et al. 1997). It has been widely exploited by artisanal fishers in Brazil (Silva et al. 2002, Marques and Moraes-Valenti 2011) and shows great potential for aquaculture (Kutty et al. 2000, New 2010, Moraes-Valenti and Valenti 2010). Amazon river prawn can be consumed as human food and used as live bait in sport fishing. Where native, there are no risks of escape to the environment. Currently most animals used as bait by fishermen are collected in nature, causing severe negative impacts on natural populations. The farming of baitfish or freshwater prawn can relieve this pressure, conserve natural populations and contribute to economic and social development. Integrated Rice-Prawn Research Project To obtain technical and economic information about rice-prawn culture, the Agência Paulista de Tecnologia dos Agronegócios (APTA), a research agency of the Agricultural Department of São Paulo State, Brazil, designed a study to evaluate the effects of three stocking densities on the growth
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