Abstract:The probiotic has various beneficial effects on fish such as improvements in nutrition, immunity and balance of intestinal micro-ecology. The combination of multiple probiotics is thought to be even more beneficial than single probiotic. Lactobacillus, Bacillus and yeast are the most widely used probiotic species in aquaculture. The effects of lactobacillus combined with bacillus have been extensively studied, whereas little is known about the combined effects of bacillus and yeast. In this study we investigated the effects of the compound preparation fermented by bacillus and yeast on the growth performance, digestive enzyme activities and the nonspecific immune indices of Atlantic salmon (Salmo salar). Four hundred and twenty Atlantic salmons with an average body weight of (180±28) g were randomly designated into 4 groups including one control group and three test groups. In each group there were 3 replicates of 35 fish. The control group was fed with the basal diet and test groups were fed with basal diet complemented with 1%, 3% or 5% complex-probiotic-preparation (BSCP) for 42 days. Compared to the control group, there was a higher weight gain and a lower feed conversion ratio and mortality (P<0.05) in the test groups. The digestibility of protein rose along with the increase of BSCP. In the 5% group, there was a difference in protein digestibility (P<0.05) and a reduction in lipid digestibility (P<0.05). BSCP up-regulated the digestive enzyme activities in varied degrees, except that it down-regulated the liver lipase activity in the 5% group (P<0.05). The liver immune indices were improved in test groups, however in the serum, BSCP induced little change except for the decrease of SOD activity in the 3% and 5% groups (P<0.05). The results indicated that the BSCP could improve the growth performance of Atlantic salmon, enhance the activities of some digestive enzymes and protein digestibility, and promote the nonspecific immunity to some extent. The optimal dietary level of BSCP was determined to be 3%.
