ABSTRACT
The effect of diets formula on zooplankton community structure and quality subsequently and tilapia fingerling performance under biofloc system condition was examined using  three isonitrogenous (30% crud protein) and isocaloric (4500 Kcal kg^-1) diets; Control diet (C;  Soybean based diet) 25%  and 50% of soybean protein that were substituted by floc meal  to form  FM₂₅ and FM₅₀ diets, respectively. Protozoa was the most dominant group during the experiments especially ciliated protozoa which was dominated by Centropyxius sp. The control treatment showed the highest number for Centropyxius sp. (285000 org./L) subsequently  the total zooplankton count (325667 org./L) and the best final body weight of tilapia. No significant difference was recorded between control and FM₂₅ regarding tilapia final body weight. Despite the lowest different zooplankton group recorded their lowest numbers was under experimental condition of FM₂₅ treatment, while the highest percentage of oligochaete worms (5.9%) was noticed for such treatment. Significant positive correlation was found between Centropyxius sp. and Asplanchna sp. (r= 0.95, P= 0.004)and ciliate protozoa with oligochaete worms (r=0.85, P=0.03). Rotifer population showed a significant correlation with dietary phosphorus and selenium content (r=0.96, p=0.017). Also, the decreasing of rotifers in control (9.11 %) and 25% substitution biofloc experiment (17.3%) was accompanied with the increasing of tilapia final weight to be 31 and 24 g, respectively. This may attributed to the preference and consuming rotifers by fish. So, we conclude that diets formula affect the zooplankton community structure which subsequently showed their reflection on fish performance. More studies are needed to understand the relation among different zooplankton species as a step to control the biofloc meal quality by manipulating diets formula.