Growth performance and disease resistance towards Aeromonas hydrophila in Hemibagrus nemurus (Valenciennes, ۱۸۴۰) fingerlings through probiotic feeding

A study was carried out to evaluate the probiotic activity of Bacillus subtilis G۱ isolated from fermented pickles in growth performance and disease resistance of Hemibagrus nemurus fingerlings at Universiti Putra Malaysia. The probiotic was mixed in feed at doses of ۰ (C, control), ۳ x ۱۰۹ (T۱) ۳ x ۱۰۷ (T۲) and ۳ x ۱۰۵ (T۳) cfu g-۱ and fed to the catfish fingerlings for nine weeks. Results showed that catfish fed a diet containing ۱۰۷ cfu g-۱ B. subtilis G۱ had significantly higher percent weight gain (۲۴۸.۶۹ ± ۳.۳۱%), and better food conversion ratio (۱.۶۸ ± ۰.۰۳), than those of other treatments. Inhibitory activity of the probiotic B. subtilis G۱ against fish pathogens Aeromonas hydrophila and Streptococcus agalactiae was evaluated by well diffusion agar method. Inhibition zones measured showed A. hydrophila and S. agalactiae were ۱۶.۱۳ ± ۰.۹۱ mm and ۱۷.۵ ± ۱.۸۴ mm, respectively, indicating strong inhibitory activity against the pathogens. Three weeks after the feeding trial, the fingerlings were challenged with ۰.۱ ml containing ۱۰۶ cfu ml-۱ of A. hydrophila by intra-peritoneal injection. After ۱۴ days, the mortality rate of catfish was significantly lower in group T۱ (۳۰ ± ۵.۸%) compared to the control (C) group (۵۶.۷ ± ۳.۳%). The findings of this study proved that administration of B. subtilis G۱ can improve growth and disease resistance in catfish.