30 JUNE 2015 • WORLD AQUACULTURE • WWW.WAS.ORG Improving FCR also lessens waste loads in culture systems, resulting in a smaller waste load in effluents. Organic carbon and nitrogen in feed are a source of oxygen demand. Organisms using organic carbon for food require oxygen in respiration to oxidize the organic matter and release the energy contained in it. Nitrogen in feed is a source of oxygen demand because the fraction not converted to biomass of the culture species is released into the water as ammonia that is oxidized by nitrifying bacteria to nitrate, consuming dissolved oxygen. The oxygen demand of feed can be calculated with an equation presented by Boyd (2009). The oxygen demand declines by 120 kg/t for each 0.1-unit improvement in FCR. The amount of nitrogenous waste would decline by 5.1 kg/t for each 0.1-unit reduction in FCR and phosphorus in waste will decline 1.2 kg/t for each 0.1-unit reduction in FCR. In ponds, much of the nitrogen and phosphorus not recovered in biomass is assimilated by natural processes. However, in cages and in raceways without waste removal, all of the non-recovered nitrogen and phosphorus is discharged to the receiving water body. The benefits of a lower FCR in reducing waste load are considerable in those cases. Reducing discharge from ponds is beneficial because it allows greater time for natural processes to assimilate waste. Water exchange in ponds lessens the retention time of water and increases the amount of waste discharged. Mechanical aeration is used in ponds to increase dissolved oxygen supply. This is important for maintaining adequate oxygen for respiration of the culture species, but it is equally important for supplying oxygen for microbial decomposition of organic matter and oxidation of ammonia to nitrate by nitrifying bacteria. Conclusion In retrospect, much of the controversy about aquaculture and its negative environmental impacts that began nearly 25 years ago was fueled by a paucity of information. There were no definitive data on the efficiency of resource use or the negative impacts of aquaculture. The anti-aquaculture side clung to the images of the worst impacts observed, while the pro-aquaculture side countered with the best-case scenarios from research studies or well-managed farms. Unfortunately, to a great extent, this situation still exists; there are few instances where sufficient data are available at the farm level to reveal the range and normal efficiencies of resource use for different species, culture methods and regions. Without such information it is impossible to set target efficiency levels that are both economically feasible and ecologically meaningful. Thus, we believe that the WWF initiative to develop databases to gather and share such information through open-source mechanisms will be invaluable in efforts to advance responsible aquaculture. Notes Claude E. Boyd, School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, Alabama 36849 Aaron A. McNevin and Jason W. Clay, World Wildlife Fund, Washington, DC 20037 Literature Cited Boyd, C.E. 2005. Measuring water flow. Global Aquaculture Advocate 8(5):76-77. Boyd, C.E. 2009. Estimating mechanical aeration requirement in shrimp ponds from oxygen demand of feed. Pages 230234 In: C. L. Browdy and D. E. Jory, editors. The rising tide, proceedings of the special session on suitable shrimp sarming. World Aquaculture Society, Baton Rouge, Louisiana, USA. Boyd, C.E. and A.A. McNevin. 2010. An early assessment of the effectiveness of aquaculture certification and standards. Report to RESOLVE, Washington, D.C., USA. Boyd, C.E. and A.A. McNevin. 2015. Aquaculture, resource use, and the environment. Wiley-Blackwell, New York, New York, USA. Boyd, C.E., J. Queiroz and A. McNevin. 2013. Perspectives on the responsible aquaculture movement. World Aquaculture 44:14-21. Boyd, C.E., C.S. Tucker, A. McNevin, K. Bostick and J. Clay. 2007. Indicators of resource use efficiency and environmental performance in fish and crustacean aquaculture. Reviews in Fisheries Science 15:327-360. Chumnanka, N., C.E. Boyd, R. Viriyatum and S. Tunkijjanukij. 2015. Bottom soil characteristics, survival and production of shrimp in low-salinity, inland ponds in Alabama and Florida (USA). Journal of Soils and Sediments 15:671-682. Clay, J.W. 2004. World Agriculture and the Environment. Island Press, Washington, D.C., USA. Clay, J.W. 2008. The role of better management practices in environmental management. Pages 55-72 In: C.S. Tucker and J.A. Hargreaves, editors. Environmental Best Management Practices for Aquaculture. Wiley-Blackwell, Hoboken, NJ, USA. 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