Bulgarian Journal of Agricultural Science, 16 (No 3) 2010, 266-274 Agricultural Academy WATER QUALITY IN SEMI-INTENSIVE CARP PRODUCTION SYSTEM USING THREE DIFFERENT FEEDS Z. DULIC 1 , G. SUBAKOV-SIMIC 2 , M. CIRIC 1 , R. RELIC 1 , N. LAKIC 1 , M. STANKOVIC 1 and Z. MARKOVIC 1 1 Faculty of Agriculture, University of Belgrade, 11080 Belgrade, Serbia 2 Faculty of Biology, University of Belgrade, 11000 Belgrade, Serbia Abstract DULIC, Z., G. SUBAKOV-SIMIC, M. CIRIC, R. RELIC, N. LAKIC, M. STANKOVIC and Z. MARKOVIC, 2010. Water quality in semi-intensive carp production system using three different feeds. Bulg. J. Agric. Sci., 16: 266-274 In the era of growing demand for sustainable usage of water, all types of aquaculture systems are under reconsideration. Until recently semi-intensive production was concerned to be one of the least polluting. Nowa- days, this fact has been reassessed especially in many countries culturing carp in this way. One of the most significant influences on a fish pond ecosystem in semi-intensive carp production is changing its characteristics by adding low quality supplemental feeding. Therefore, the type of fish feed, its physical and chemical characteris- tics can considerably change the water quality of a fish pond. Aiming to analyze the effect of commonly used feeds (cereals, pelleted and extruded feed) in semi-intensive production on the water quality, an experiment was carried out at three fish ponds during one production season. Even though the results of physical, chemical and biological parameters showed that there were no statistically significant differences in the water quality between fish ponds with different supplemental feed, looking at the overall picture it could be concluded that the pond that had the lowest quality of feed (row cereals), having high organic mater and chlorophyll a during most of the trial period as well as the specific phytoplankton successions including potentially harmful blue-green alga, had conse- quently the lowest water quality. Key words: carp, semi-intensive system, feed, water quality Abbreviations: dH - Water hardness; ISO - International Organization for Standardization; S - Saprobity idex; h - Absolute abundance of individual taxa; s - Individual taxa saprobic value E-mail: zorkad@agrif.bg.ac.rs Introduction In the view of the worldwide increasing demands on sustainable usage of primary resources, such as land and water, and the necessity of applying sustain- able aquaculture practices, there is an urgent need to improve semi-intensive farming systems, especially in the area concerning nutrition of omnivorous fish within such systems. In semi-intensive pond-based farming systems the dietary nutrient requirements of the cul- tured species is largely met through the consumption of natural food organisms produced endogenously 266