en Biology & physiology Biology & physiology پژوهشي Orginal research papers <p>A study was carried out to evaluate the probiotic activity of <em>Bacillus subtilis </em>G1 isolated from fermented pickles in growth performance and disease resistance of <em>Hemibagrus nemurus</em> fingerlings at Universiti Putra Malaysia. The probiotic was mixed in feed at doses of 0 (C, control), 3 x 10⁹ (T1) 3 x 10⁷ (T2) and 3 x 10⁵ (T3) cfu g^-1 and fed to the catfish fingerlings for nine weeks. Results showed that catfish fed a diet containing 10⁷ cfu g^-1 <em>B. subtilis</em> G1 had significantly higher percent weight gain (248.69 ± 3.31%), and better food conversion ratio (1.68 ± 0.03), than those of other treatments. Inhibitory activity of the probiotic <em>B. subtilis</em> G1 against fish pathogens <em>Aeromonas hydrophila</em> and <em>Streptococcus agalactiae</em> was evaluated by well diffusion agar method. Inhibition zones measured showed <em>A. hydrophila</em> and <em>S. agalactiae</em> were 16.13 ± 0.91 mm and 17.5 ± 1.84 mm, respectively, indicating strong inhibitory activity against the pathogens<em>. </em>Three weeks after the feeding trial, the fingerlings were challenged with 0.1 ml containing 10⁶ cfu ml^-1 of <em>A. hydrophila</em> by intra-peritoneal injection. After 14 days, the mortality rate of catfish was significantly lower in group T1 (30 ± 5.8%) compared to the control (C) group (56.7 ± 3.3%). The findings of this study proved that administration of <em>B. subtilis</em> G1 can improve growth and disease resistance in catfish.</p> Hemibagrus nemurus, Probiotic, Growth performance, Disease resistance, Aeromonas hydrophila 846 856 http://jifro.ir/browse.php?a_code=A-10-1272-29&slc_lang=en&sid=1 A.A Farhana 100319475328460014769 100319475328460014769 No C.R Saad cheroos@gmail.com 100319475328460014770 100319475328460014770 Yes M.S Kamarudin 100319475328460014771 100319475328460014771 No H.M Daud 100319475328460014772 100319475328460014772 No