54 March 2009 Discussion Because Colossoma and Piaractus species have intramuscular Y bones (Peralta and Teichert-Coddington 1989), fish farmers should produce fish bigger than 1.2 kg in order to sell them in local markets. The results showed that growth is density dependent in semi-intensive culture without either water exchange or supplemental aeration. If larger commercial sizes are desired, it is advisable not to exceed a maximum carrying capacity of 500-600 g/m2. In conclusion, the stocking density to be used in growout culture should be <0.3 fish/m2. The density of 0.2 fish/m2 proved to be the most suitable one for producing fish that can be marketed in regional or foreign markets and if climatic conditions in the Argentinean subtropical region are taken into account. The technology will allow farmers to get specimens larger than 1.2 kg with a two-summer culture. Notes 1Centro Nacional de Desarrollo Acuícola (CENADAC). 2Dirección de Acuicultura Nación. Paseo Colón 982-Anexo Pesca, Buenos Aires 1063, Argentina. Email: guillegus@arnet.com.ar, lluchi@mecon.gov.ar, dcluis@yahoo.com Acknowledgments The authors wish to thank to Isla-Pe enterprise for grant the pacu stock for research and the Ministry of Economy and Production (Subsecretaría de Pesca y Acuicultura) for financial support to the Aquaculture Division and the staff of CENADAC for their effort and support. References Bernardino, G., A.C.Peret and V.H.Verani. 1998 Biomasa sustentable do Pacu, Piaractus mesopotmicus (Holmberg, 1887) criados em viveros com baixa renovação de agua. Resumos do Aquicultura, Brasil ´98: 261. Recife, Brazil. Boyd, C. 1998. Water and bottom soil quality management in freshwater aquaculture ponds. Annais do Aquaculture I:303-312. Cantelmo, O.A. and J.A. Souza. 1988. Uso de raçoes comerciais na cria do pacu. Bol.Téc.CEPTA 1(1):37-44. Cantelmo, O.A. 1993. Niveis de proteina e energia em dietas para o crescimento do pacu, Piaractus mesopotamicus (Holmberg,1887). Dissertação apresentada para obtenção do titulo do Mestre em Aquicultura , UFSC, 55 p. Hepher, B. 1993. Nutrición de peces comerciales en estanques. Ed. Limusa, México, 405 p. Hintze, J.L. 1998. Number cruncher statistical system (NCSS,2000). Versión 6.0.Graphics Dr.JerryL.Hintze.Kaysvile, Utah, USA. Jacobo, W. M.C.Martinez and F.Revidatti. 1992. Cultivo experimental de pacú, Piaractus mesopotamicus (Holmberg, 1887) en el noroeste de la provincia de Corrientes. Argentina. Revista de Ictiología 1:93-98. Machado-Allison, A. 1980. Estudio sobre las subfamilias Serrasalmidae ( Teleostei, Characidae). Parte 1. Estudio comparado de los juveniles de las cachamas de Venezuela (Géneros Colossoma y Piaractus ). Acta Biológica Venezuélica 11(3):1-101. Peralta, M. and G. Teichert-Coddington. 1989. Producción comparativa de Colossoma macropomum y tilapia nilotica en Panamá. Journal of the World Aquaculture Society 20:236239. Piper, R.I., I. Mc Elwain, L.Orme, J. Mcraren, L. Fowler and J. Leonard. 1986. Fish hatchery management. US Fish and Wildlife Service. Washington, DC. Quirós, R. 1990. The Paraná River basin development and the changes in the lower basin fisheries. Interciencia 15(6):442-451 Roux,J.P and J.A.Bechara. 1998.Engode de pacú (Piaractus mesopotamicus) en sistema semiintensivos en el Norte de la provincia de Santa Fe-Argentina. Revista de Ictiología 6(1-2):65-72. Argentina. Silva, J.W., G. Bernardino, M.J. Silva Nobre da, V.A. Ferrari and J.O. Mendonca. 1997. Cultivo do pacu , Piaractus mesopotamicus (Holmberg, 1887) em duas densidades de estocagem no Nordeste do Brasil. Bol.Téc.CEPTA 10:61-70. Stickney, R. 1994. Principles of Aquaculture. John Wiley & Sons. New York, New York USA. Table 2. Experimental results compared with other authors results on Piaractus mesopotamicus culture Authors Jacobo,W Silva et al. Roux and Bechara, This work 1992 1997 1998 Density (ind/m2) 0.98 0.64 1.0 0..5 1.0 0.8 1.0 0.8 1.0 05 0.3 0.21 Initial weight (g) 3.0 3.0 27.0 33.0 1.0 1.0 1.0 1.0 0.25 0.25 0.25 0.25 Final weight (g) 1,085 846.0 656.0 978.0 880.0 740.0 670.0 649.0 560.2 753.7 953.0 1.374.2 Days of culture 431 431 375 375 350 350 350 350 495 495 4.95 495 Number of ponds 1 1 3 3 1 1 1 1 10 11 8 6 FCR1 1.8 2.79 4.94 4.4 1.9 2.5 2.3 2.5 1.46 1.56 1.75 2.70 SGR2 1.36 1.30 0.86 0.91 0.84 0.82 0.78 0.78 1.56 1.62 1.66 1.74 Production (kg/ha) 10.182 5.032 5,717 4.5828 8.900 5.920 6.700 5.129 6.071 4.170 3.027 2.890 1FCR = Feed conversion ratio 2SGR = Specific growth rate
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