50 Indian J. Fish., 62(4) : 50-57, 2015 Benthic nutrient luxes inluenced by the common carp Cyprinus carpio in pond polyculture with special reference to nitriication, denitriication and nitrate ammoniication DASEN ZHONG, FANG WANG, SHUANGLIN DONG AND SACHIN ONKAR KHAIRNAR * The Key Laboratory of Mariculture, Ministry of Education, Fisheries College, Ocean University of China Qingdao – 266 003, People’s Republic of China * ICAR-Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar - 752 104, Odisha, India e-mail: wangfang249@163.com ABSTRACT Cyprinus carpio is an important species in pond aquaculture as it can effect bioturbation of sediments which might inluence benthic luxes and biogeochemical processes at the sediment-water interface. In this study, the inluence of common carp Cyprinus carpio on nutrient luxes, speciically nitriication, denitriication and nitrate ammoniication rates at the sediment-water interface in pond polyculture was investigated through ield experiments and ex situ incubation. C. carpio enhanced the sediment oxygen consumption (SOC) from April to September (except in July). The ish did not inluence the NH 4 + -N lux, but promoted NO x - -N (NO 2 - -N and NO 3 - -N) release from the sediment to the water from May to September and it also promoted soluble reactive phosphorus (SRP) release from July to September. Nitriication, denitriication and nitrate ammoniication were also signiicantly promoted by C. carpio. The results suggest that C. carpio can plays a very important role in the migration and transformation of nitrogen and phosphorus at sediment-water interface which could also help nitrogen removal in pond water . Keywords: Cyprinus carpio, Denitriication, Nitrate ammoniication, Nitriication, Nutrient luxes, Polyculture, Pond aquaculture, Sediment-water interface Introduction Pond culture is the most important aquaculture practice in China since thousands of years and the production has touched 1.94 million t (National Bureau of Statistics, 2012). Pond aquaculture plays an important role especially in the integrated polyculture sector, which has become the main mode of pond aquaculture in China. Polyculture incorporating different ish species is a means of species diversiication, whcih can also lead to improvement of the aquaculture environment and ecology (Soto, 2009). Cyprinus carpio is a popular carp species used in pond polyculture (Naylor et al., 2000). The sediment-water interface is where, the most signiicant variations in physical, chemical and biological characteristics takes place and has an important role in material transport and exchange in natural water bodies (Nixon, 1986). The migration and transformation of nutrients at the sediment-water interface affect the budget and circulation dynamics of nutrients (Thibodeau et al., 2010) and is also related to the eutrophication in water bodies (Hou et al., 2013). Inorganic nitrogen (NH 4 + -N, NO 3 - -N, and NO 2 - -N) and soluble reactive phosphorus (SRP) are the prime limiting nutrients in water and these are also the key factors responsible for the quality of aquaculture waters (Paerl, 2009; Xu et al., 2010). The main processes in the migration and transformation of nitrogen and phosphate at sediment-water interface are the diffusion of nitrogen and phosphate across sediments and the overlying water as well as nitriication, denitriication and nitrate ammoniication mediated by microorganisms. These processes can directly decide the budget of nitrogen and phosphate in aquaculture water and inally affect the water quality (Eyre et al., 2011). Macrobenthic organisms are important components at sediment-water interface as these can change sediment grain size, porosity, permeability and other physical properties by digging, feeding, respiration, excretion and other activities and also change the original biological and chemical properties of sediment which affect the migration and transformation of nutrients at sediment-water interface (Meysman et al., 2006). There are few reports on the effects of bioturbation on the migration and transformation of nitrogen and phosphate at sediment- water interface, especially due to Apostichopus japonicus (Zheng et al., 2009), Ruditapes philippinarum (Nizzoli et al., 2006), Neohelice granulata (Fanjul et al., 2011) and