The purpose of this study was to determine the effect combined application of dietary Fructooligosaccharid (FOS) and Pediococcus acidilacticiplus Lactococcus lactison some growth preformane, haematological parameters and intestinal microbiota of Rutilus frisii kutum. According to the bacterial growth in in vitro condition and production of volatile fatty acid (VFA), t hree treatments consisting of (Treat1): 0.5% FOS plus 10¹⁰cfu/g Lactococcus lactisand and 10⁷cfu/g Pediococcus acidilactici, (Treat2): 0.5% FOS plus 10¹⁰cfu/g Lactococcus lactisand and 10¹⁰cfu/g Pediococcus acidilactici and (Treat3): 0.5% FOS plus10⁷cfu/g Lactococcus lactisand and 10¹⁰cfu/g Pediococcus acidilactici were used in 400 Kutum fry weighing 0.75±0.02 g obtained from a reproduction fish center, Guilan Province Iran.. Fish were kept in 1000 L water and fed on experimental diet for 60 days. Results showed that growth indices such as final weight (FW) and specific growth rate (SGR) were significantly increased in all treatment groups compared to control one (p<0.05). Also, FCR in all treatments were lower than control one. In treatment 1, final weight (1.67) , SGR (1.34) and FCR (2) were significantly higher than other treatments. The results showed that hematological parameters values in different treatments showed no significant differences (p>0.05). However, immunoglubolin level in treatment 1 (22.33mg/ml ) was significantly higher than other treatments. The total lactic acid bacteria counts in treatment 1 (5.2) and treatment 3 (5) was significantly higher than other treatments (p<0.05). The present findings show that the combined application of probiotics and prebiotics could be a useful tool in the rearing of early stages of Rutilus frisi kutum fry.

Key word: Rutilus frisikutum fry,synbiosis,growth, intestinal microbiot