The effect of oral administration of lactic acid bacteria isolated from kefir on intestinal microbiota, growth performance and survival in juvenile rainbow trout, Oncorhynchus mykiss

Lactic acid bacteria (LAB) are used in the aquaculture industry to improve growth indices and nutrition efficiency of farmed fish. Kefir is a natural probiotic that largely consists of these microorganisms. This study aimed to isolate LAB strains from kefir grains and investigate their effects on the intestinal microbiota and growth indices of juvenile rainbow trout. Based on the results, one isolate was identified as Lactobacillus faraginis (LF) and other one as En terococcus durans (ED), both were gram positive, non-hemolytic, catalase and oxidase negative. Both strains showed resistance to acidic environments and gastric juice and were able to grow against bile salts i.e. the hydrophobicity potential of both strains was evaluated above 50%. The results showed that both strains had appropriate and acceptable probiotic properties. A total of 480 juvenile fish with were randomly divided into eight groups viz. Control (basal diet), LF1 and LF2 receiving diets supplemented with L. faraginis at  10 7 and 10 8 cfu/g, respectively, ED1 and ED2 diets supplemented with E. durans at 10 7 and 10 8 cfu/g, respectively, Bactocell group receiving a diet supplemented with commercial probiotic Bactocell PA-10 (10 10 cfu/g), combined treatments LF1+ED1 (5×10 6 cfu/g) and LF2+ED2 (5×10 7 cfu/g). The strains were prepared in the form of lyophilized powder and added to the basal diet as supplements. Sampling was performed after 0, 30, 15, and 45 days feeding with the diets. In the in vivo investigation, the highest LAB colony counts were obtained for the ED2, Bactocell, LF2+ED2 and LF2 groups, respectively. The highest BWI, SGR, DWG, PER, and CF, and the lowest FCR were observed in the LF2+ED2, Bactocell, ED2, and LF2 groups, respectively. On the other hand, the LF2+ED2, Bactocell and LF2 treatments also had the highest survival rate. Apparently, the use of the tested LAB strains as probiotic in high doses (LF2, ED2) and in combination (LF2+ED2) could improve growth indices, the intestinal LAB population and survival rate in juvenile rainbow trout.