This study was carried out to study the effect of Fructooligosaccharide (FOS) as a source of prebiotic, commercial dry yeast (Saccharomycescerevisiae) as a source of probiotic and their combination in different level as a source of symbiotic. The experiment was conducted in the fish laboratory of Animal Production Department, Faculty of Agricultural Sciences of Sulaimani University, Sulaimani, Kurdistan Region, Iraq. The trials lasted for three months after an adaptation period of 21 days.120 common carp fingerlings with an average weight of 20 ±2 gm, were used to test the effect of different levels of the FOS, yeast and their combination. In T1 fish were fed a diet with 2.5 g/kg FOS, While in T2, fish were fed a diet 2.5 g/kg yeast, T3 represents the third treatment, in which fish were fed on a diet 5 g/kg FOS, While, in T4 fish were fed a diet 5 g/kg yeast, and T5 2.5 g/kg FOS : 2.5 g/kg yeast , T6 was 5 g/kg FOS : 5 g/kg yeast, the T7 2.5 g/kg FOS : 5 g/kg yeast, while T8 5 g/kg FOS : 2.5 g/kg yeast. Each treatments in three replicates in which five fingerlings common carp were stocked in plastic tanks, which fed the experimental diets twice daily. Blood parameters of tested fish showed significant differences in WBC (109cells/l) differ significantly 234.850 for the fifth treatment and 230.500 for T8; Significant differences were in granulocytes count was 74.800 in T3 while the lymphocytes differ among treatments 15.500, for T8, Monocytes differ significantly was 34.150 in T5. Platelets were 34.000 in the first treatment and 38.000 in T2.
