38 MARCH 2017 • WORLD AQUACULTURE • WWW.WAS.ORG Vandenberg and Moccia 1998, Webster et al. 1995), while positive effects were observed in channel catfish (Mustin and Lovell 1993). Ractopaminne supplementation seems to modulate protein synthesis and metabolic rate in some fish species, inducing a decrease in carcass and muscle fat, and an increase in protein deposition in fish muscle (Mustin and Lovell 1993, Vandenberg and Moccia 1998). Ractopamine exposure induces a shift in muscle cell metabolism by changing the rate of protein turnover, consequently increasing nitrogen retention and diverting the use of non-protein energy to support protein accretion. The effect of these changes on intermediary metabolism has been sparsely studied in fish and even in higher vertebrates. Our results suggest that ractopamine has limited effects on intermediary metabolism of tambaqui and for reducing fat content, which is consistent with the results of carcass traits. However, for a complete picture of the effects of ractopamine on muscle growth of tambaqui and associated metabolism, tissue-specific metabolites should be evaluated. Additionally, ractopamine has transient effects on swine and the response to ractopamine changes after long exposure periods (>14 days) (Adeola et al. 1990). This may have affected our results; however, no studies have been performed with fish to determine the timing of using dietary ractopamine. Ractopamine supplementation at 5 mg/kg has limited effects on increasing protein metabolism and inducing lipolysis in tambaqui by using some indirect serum metabolites. However, the use of 20 mg/kg ractopamine for 30 days induces a slight decrease in visceral fat. Implications for Tambaqui Farming in Goias The growth rate of tambaqui in net cages was high. Juvenile tambaqui had markedly lower growth rates during June and July, which was expected due to low water temperatures associated with the winter season in this region. However, tambaqui clearly showed great compensatory growth in the months that followed, reaching a growth rate of 13 g/day. These values are ten times greater than those of tambaqui subjected to feed deprivation for 28 days under laboratory conditions (Ituassú et al. 2004). The average daily weight gain observed in our study was 1.5 times greater than that reported for tambaqui grown for a similar duration (8 months) and stocking density, but without a prominent winter season (Gomes et al. 2006). The high growth rate observed in our trials may be an effect of differences in genetic groups of tambaqui used in the trials, feed quality, and differences in environmental conditions. Thus, comparing our results with previous studies should be made with care. These results are promising for the farming of tambaqui in Goias, a species that has been traditionally cultured in regions with water temperature greater than 20 C. This was not the case of the water body (Paranaíba River) that we used for the trials. Adaptation of conventional management practices may be required for raising tambaqui in regions with cooler water temperatures. Acknowledgments This research was financially supported by the Brazilian National Council of Technological and Scientific Development - CNPq (Project # 477920/2012-8). We are thankful to João M.C. Alves from Guabi Nutrição Animal for supplying the feed used in the first trial. Notes Igo G. Guimarães*, Curso de Zootecnia, Universidade Federal de Goias, Jatai/GO, Brazil. Thiago M. Faria, Bruno S. M. Mazini, Graciela P. Martins, Cristielle N. Souto. Laboratorio de Pesquisa em Aquicultura, Universidade Federal de Goias, Jatai, GO, Brazil Silvio L. Oliveira, Denise S. Oliveira. Curso de Ciências Biológicas, Universidade Federal de Goias, Jatai/GO, Brazil. * Corresponding author: Igo G. Guimarães, Laboratorio de Pesquisa em Aquicultura, Universidade Federal de Goias, Campus Jatai, PO Box 03, 75801615, Jatai, GO, Brazil. E-mail: igoguimaraes@ufg.br References Adeola, O., E. A. Darko, P. He and L.G. Young. 1990. Manipulation of porcine carcass composition by ractopamine. Journal of Animal Science 68:3633-3641. Bicudo, A., R.Y. Sado and J.E.P. Cyrino. 2012. Growth, body composition and hematology of juvenile pacu (Piaractus mesopotamicus) fed increasing levels of ractopamine. Arquivo Brasileiro de Medicina Veterinária e Zootecnia 64:1335-1342. de Carvalho Gomes, L., E.C. Chagas, H. Martins-Junior, R. Roubach, E.A. Ono and J. N. de Paula Lourenço. 2006. Cage culture of tambaqui (Colossoma macropomum) in a central Amazon floodplain lake. Aquaculture 253:374-384. Devens, M., R. Lazzari, D. Rotilli, L. Pucci, C. Veiverberg and I. Coldebella. 012. Ractopamine in the diet of Hungarian Carp reared in net cages. Arquivo Brasileiro de Medicina Veterinária e Zootecnia 64:1717-1722. TABLE 3. Carcass traits of tambaqui fed ractopamine-supplemented diets for 30 days (DP=dress-out percentage, F=fillet percentage, HIS=hepatosomatic index, VFI=visceral fat index). RAC DP F HSI VFI 0.0 94.2±0.2 42.0±0.5 1.6±0.4 3.7±0.6 2.5 93.8±0.7 41.5±1.8 1.4±0.1 4.0±0.5 5.0 94.3±0.2 40.3±1.4 1.3±0.2 3.7±0.3 10.0 93.8±1.3 39.6±0.4 1.3±0.3 3.7±0.4 20.0 94.2±0.7 41.0±1.0 1.3±0.2 3.2±0.5 Means within column followed by a different superscript were significantly different by SNK multiple range test (p < 0.05).
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