fa fish disease fish disease پژوهشي Orginal research papers <p dir="ltr" style="text-align: justify;">Streptococcosis has been defined as a hemorrhagic septicemia in many fish species especially rainbow trout. This disease causes serious economic losses due to high mortality in fish and the bacteria responsible is also considered as a zoonotic pathogen. The aim of this study was identification of different causative agents of warm water streptococcosis and evaluation of the capsule gene in <em>Lactococcus garvieae</em> isolates collected from rainbow trout in Chaharmahal - Bakhtiari Province, Iran. A total of 430 clinically suspected fish were collected from 43 rainbow trout farms. The samples were analyzed using biochemical methods and multiplex-PCR. The results indicated that samples of 36 fish farms (83.7%) were infected with one of the studied bacteria. The infection by <em>L. garvieae</em> was found to be more than that by other species (30 of 36 farms, 83%). Infection by <em>S. iniae</em> and <em>S. uberis</em> was found in nine and one fish farm, respectively. Presence of virulence genes was studied in <em>L. garvieae</em> isolates by PCR assay. According to the results 34 of 50 isolates (68%) contained the capsule gene. The results revealed high prevalence of virulent<em> L. garvieae</em> in rainbow trout farms which should be considered in preventional policies such as vaccine production and also in public health.&nbsp;</p> Streptococcosis, Virulence gene, Rainbow trout, PCR, Iran 836 845 http://jifro.ir/browse.php?a_code=A-10-1272-200&slc_lang=fa&sid=1 M. Raissy mehdi.raissy@iaushk.ac.ir 100319475328460016155 100319475328460016155 Yes M. Sarshoughi 100319475328460016156 100319475328460016156 No M. Moumeni 100319475328460016157 100319475328460016157 No