en Genetics Genetics پژوهشي Orginal research papers <p dir="ltr" style="text-align: justify;">In this research, antagonistic activity of two <em>Bacillus</em> species isolated from digestive tract of marine fish and culture pond of sea cucumber was studied. The inhibitory activity of <em>Bacillus</em> spp. isolates against some common pathogenic bacteria of fish was assessed using the agar diffusion method. The strain of <em>B. subtilis</em> G024 exhibited antimicrobial activity against <em>Vibrio anguillarum</em>, <em>V. harveyi</em>, <em>V. vulnificus</em>, <em>Streptococcus</em> sp. and <em>Staphylococcus aureus</em>; the isolate of <em>B. amyloliquefaciens</em> N004 inhibited growth in <em>V. anguillarum</em>, <em>V. campbellii</em>, <em>V. vulnificus</em>, <em>V. parahamolyticus</em>, <em>Edwardsiella tarda</em>, <em>Streptococcus </em>sp., <em>B.</em> cereus. Scanning electron microscopy (SEM) investigation of indicator bacteria showed that cell morphologies were strongly affected by the cell-free supernatant of the two <em>Bacillus</em> spp. isolates. It is determined that the culture filtrates contained inhibitors against growth of some pathogenic bacteria with different degrees of inhibition, although none of the culture filtrates could inhibit the growth of <em>V. fluvialis</em>, <em>V. alginolyticus</em>, <em>V. splendidus</em>. Based upon these characteristics, both of the antagonistic <em>Bacillus</em> spp. isolates could be the potential probiotics used in the aquaculture production.</p> Bacillus, Antagonistic activity, Scanning electron microscopy, Probiotic, Aquaculture 701 714 http://jifro.ir/browse.php?a_code=A-10-1622-1&slc_lang=en&sid=1 Y. Chen 100319475328460016016 100319475328460016016 Yes J. Li 100319475328460016017 100319475328460016017 No P. Xiao 100319475328460016018 100319475328460016018 No W. Zhu 100319475328460016019 100319475328460016019 No Z. Mo 100319475328460016020 100319475328460016020 No