Effect of autochthonous and commercial probiotic bacteria on growth, persistence, immunity and disease resistance in juvenile and adult Nile tilapiaOreochromis niloticus

Abstract

Probiotics are gaining worldwide acceptance as means to improve growth and health of fish. However, the type of probiotic, dose, duration and mode of the application, age and size of the fish are among the factors involved in determining the efficacy of the applied probiotic. In this study, two trials were conducted to evaluate the effect of feeding three probiotics on growth, feed conversion (FCR) and gross yield (GY) in juvenile (28.3 g) and adult (93.4 g) tilapia compared to a control probiotic-free diet (CON). In the first trial, an autochthonous Bacillus subtilis isolated from the gut of cultured tilapia (TPI), a commercial Lactobacillus acidophilus probiotic (COM1) and a combination of both (MIX1) were tested. In the second trial, the same treatments were tested in adults (101.8 g) only with the replacement of COM1 with another commercial probiotic (COM2) consisting of four bacterial species. Results showed that in juveniles, the MIX1 treatment had the highest (P < 0.05) mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), GY and best FCR, followed by the TPI and the COM1 treatments. Growth in adults was not affected by probiotics and was depressed by COM1. In the second trial, the COM2 treatment had the highest (P < 0.05) MWT, DGR, SGR, GY and best FCR, followed by the MIX2 and the TPI treatments. These results indicate the positive effect of the probiotics on growth and the synergetic effect of mixing more than two bacteria. The TPI had the highest gut colonization and retention after 15 days of withdrawing the probiotics followed by the MIX1 and MIX2 treatments. The COM1 and COM2 showed no proliferation. Generally, probiotics improved the immunity with the TPI causing the highest improvement. Tilapia fed with the TPI, MIX1 and MIX2 bacteria, then challenged by injecting the LD50 dose (104.86 cfu per fish) of the pathogenic Proteus vulgaris bacterium had a higher relative percentage of survival than the COM1, and COM2 treatments. Results obtained in this study indicate the higher potential of the autochthonous probiotic bacteria and the mixture of bacteria in enhancing growth, immunity and disease resistance in tilapia than the commercial products and a tendency of fish size discrepancy in the response to probiotics.