WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2013 35 These results indicate that the incorporation of prawns into a rice monoculture system was economically feasible at 5 prawns/m2 despite the small size of harvested prawns because of the short production cycle (about 4.5 months) and high mortalities caused by predation and severe temperature oscillations. Future Studies and Perspectives With regard to ecological aspects, some issues should be studied. Freshwater prawns are thought to control some pests of rice (e.g. the weevil Oryzophagus oryzae) but in Brazil there are no studies confirming this hypothesis. Rice productivity in the rice-prawn system was similar to rice monoculture, despite the area being 17 percent smaller because of the trenches. Perhaps the fertilizing effect of ammonia excreted by prawns could explain this, but further experiments must be done to substantiate this mechanism. The low water level of rice fields caused high mortality of prawns from thermal oscillation. Future studies are necessary to minimize this problem. In this case, the economic viability of shelters to provide shade in trenches and increasing water flow or depth of paddy fields are possibilities that should be investigated. Conclusions • Rice-prawn systems are a good option for rice farmers to add value to monoculture. This system is especially recommended for smallholders who do not use chemicals to control pests and diseases; • Only a low level of investment is necessary to implement this system in rice fields and good financial returns can be obtained within a short period of time (less than seven years); • Amazon river prawn can be reared in a rice-prawn system and sold as live bait in the sport fishing market, producing good profits even with low survival rates; • Introducing prawns to rice fields does not degrade effluent quality and sometimes improves it, probably because of recycling of nutrients by prawns. FIGURE 11. Manual harvest of rice. Notes Marcello Villar Boock is scientific researcher at the Agência Paulista de Tecnologia dos Agonegócios (APTA) - Agricultural Department of São Paulo State, Brazil. Helcio L. A. Marques, Helenice P. Barros and Margarete Mallasen are scientific researchers at the Fisheries Institute - APTA - Agricultural Department of São Paulo State, Brazil. Michélle Roberta dos Santos is M.Sc. Student at São Paulo State University - UNESP, SP, Brazil. Patricia Moraes-Valenti is Professor and Researcher at Santo Amaro University - UNISA, São Paulo, SP, Brazil. Acknowledgements To São Paulo Research Foundation (FAPESP) (Pr. 2006/56061-4) for support and CNPq (Proc. 472059/2009-2) for funding part of the study related to this issue; to the Aquaculture Center of São Paulo State University (CAUNESP) for donating and transporting PLs of M. amazonicum. References Bialetzki, A., K. Nakatani, G. Baumgartner and G. Bond-Buckup. 1997. Occurrence of Macrobrachium amazonicum (Heller, 1862) (Decapoda, Palaemonidae) in Leopoldo’s Inlet (Ressaco do Leopoldo), upper Paraná river, Porto Rico, Paraná, Brasil. Revista Brasileira de Zoologia 14:379-390. Coelho, P. A. and M. R. Ramos-Porto. 1985. Camarões de água doce do Brasil: distribuição geográfica. Revista Brasileira de Zoologia 2:405-410. Kutty, M. N., F. Herman and H. L. Menn. 2000. Culture of other prawn species. Pages 393-410 In New, M. B. and W. C. Valenti, editors. Freshwater Prawn Farming: The Farming of Macrobrachium rosenbergii. Blackwell Science Ltd, Oxford, England. Marques, H. L. A. and P. M. C. Moraes-Valenti. 2011.Current status and prospects of farming the giant river prawn (Macrobrachium rosenbergii (De Man 1879) and the Amazon river prawn Macrobrachium amazonicum (Heller 1862) in Brazil. Aquaculture Research 43:984-992. Moraes-Valenti, P. M. C. and W.C. Valenti. 2010. Culture of the Amazon river prawn Macrobrachium amazonicum. Pages 485501 In M. B. New, W. C. Valenti, J. H. Tidwell, L. R. D’Abramo and M.N. Kutty, editors. Freshwater Prawns. Biology and Farming. Wiley-Blackwell, Oxford, England. New, M. B. 2010. History and global status of freshwater prawn farming. In M.B. New, W.C. Valenti, J.H. Tidwell, L. R. D’Abramo and M. N. Kutty, editors. Freshwater Prawns. Biology and Farming. Wiley-Blackwell, Oxford, England. Pettovello A. D. 1996. First record of Macrobrachium amazonicum (Decapoda, Palaemonidae) in Argentina. Crustaceana 69:113-114. Silva, K. C. A., R. A. L. Souza and I. H. A. Cintra. 2002. Espécies de camarões capturadas em áreas estuarinas no município de Vigia - Pará - Brasil. Boletim Técnico Científico do CEPNOR 2:81-96.
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