fa fish disease fish disease پژوهشي Orginal research papers <p dir="ltr" style="text-align: justify;">Increasing bacterial resistance to commercial antibiotics has led to considering medicinal herb applications. This study aimed to identify chemical composition of essential oil of some native medical herbs and their antibacterial activity against <em>Yersinia ruckeri </em>compared with Enrofloxacin in <em>in vitro</em> experiments. The antibacterial activities of ethanolic extracts and essential oils of <em>Eryngium campestr</em><em>e, </em><em>Pimpinella affinis, </em><em>Mentha piperita, Achillea wilhelmsii </em>and <em>Cuminum cyminum </em>were analyzed by disk diffusion, Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) methods in <em>in vitro</em>. Also, the oil constituents of the mentioned plants were analyzed by gas chromatography. The MIC value of the ethanolic extracts and essential oils were 31.2-500 &micro;g/mL and 15.6-250 &micro;g/mL, respectively, while the MBC of the mentioned extracts and essential oil were 62.4-500 &micro;g/ml and 31.2-250 &micro;g/ml, respectively. The results showed that the <em>C. cyminun</em>, <em>E. campestre</em> and <em>M. piperita </em>could be introduced as more effective antimicrobial candidates to aquaculture industry<em>.&nbsp;</em></p> Antibacterial activity, Chemical composition, Iranian medical herbs, Yersinia ruckeri 1108 1123 http://jifro.ir/browse.php?a_code=A-10-1272-216&slc_lang=fa&sid=1 M. Adel 100319475328460017549 100319475328460017549 No R. Safari 100319475328460017550 100319475328460017550 No A.H. Ghitanchi 100319475328460017551 100319475328460017551 No M.J. Zorriehzahra zorrieh@yahoo.com 100319475328460017552 100319475328460017552 Yes