EFFECT OF DIET COMPOSITION ON NILE TILAPIA GROWTH PERFORMANCE AND MICROBIAL COMMUNITY STRUCTURE OF GUT AND REARING WATER

Abstract

Two experiments were performed at the Fish Nutrition Laboratory (FNL), Department of Animal Production, Faculty of Agriculture, Cairo University, Egypt. Each experiment lasted one month using circular plastic tanks (85 L used to 55 L capacity). The first experiment aimed to evaluate the effects of four carbon sources of gradual complexity; glucose, starch, molasses and cellulose on the integrity of biofloc system. Twelve circular plastic tanks were stocked with 10 tilapia fingerlings stocked each with average body weight 9.14 ± 0.06 g. All water quality parameters were within normal limits for tilapia culture. Cellulose treatment showed the highest significant average final body weight and the best FCR. Cellulose recorded the lowest zooplankton count with no significant differences among treatments. Rotifers (Philodina and Lucane bulla sp.) dominated the zooplanktons. In conclusion, cellulose could be an efficient carbon source under BFT system conditions. The second experiment was designed to study the effects of soybean meal protein substitution by sesame meal protein with percentages (0 (control), 25 and 50 %) on the microbial community of Nile tilapia gut and rearing water under biofloc system conditions. Nine circular plastic tanks were used as experimental units for different treatments in triplicate. Each tank was stocked with 10 tilapia fingerlings with average body weight of 18.27 ± 0.1 g. Water quality parameters were within normal limits for tilapia culture and there were no significant differences except for TAN value of fish group fed diet (SM50%) which was significantly the lowest among other treatments. No significant differences were noticed on different rearing water samples regarding microbial count. However, Bacillus and Lactobacillus count decreased non-significantly as a result of increasing sesame meal inclusion in the diet. While Staphylococcus count increased non-significantly in both water and gut samples. The total zooplankton count decreased as the sesame inclusion increased in fish diet. It could be concluded that the sesame addition to diet in high percentage is not recommended in biofloc system. BFT depends on bacterial activity like Bacillus, 25 % of soybean meal protein substitution with sesame meal protein could be less detrimental for BFT system and maintaining the health and immunological benefits for fish.