en Parasitic Diseases Parasitic Diseases پژوهشي Original research papers <div style="text-align: justify;">The parasites that normally cause fish disease under farming condition possess a direct life cycle with no need to intermediate hosts for dissemination. The ensuing infection can therefore spread rapidly inducing more damaging lesions in the external parts of host especially the gills. In this study, in order to isolate and identify foreign parasites of phytophagous fish in Guilan province, 4 farms were selected by cluster method from Silver Carp breeding farms around Rasht and 16 pieces of fish in 6 stages for 6 months from April to September 2020. The fish transported live to fish health lab, underwent individual clinical observation of their skin, fins and gills with at least 10 moist extended samples prepared for each part. &nbsp;Isolation and morphometric identification of samples were carried out via microscopic examinations.&nbsp;The collected data were statistically analysed using Excel version 2010 and SPSS 20 software. All the diagrams and table contents representing the intended parameters including frequency and the means were processed by Chi-square critical value of percentage 5. The results of the study showed a similar infestation outbreak of &nbsp;<em>L</em>. <em>Trichodina </em>on the fish fins and gills with no significant difference (P>0.05). <em>Dactyl gyrus spp</em> was more prevalent in fish gills and fins than on skin (P<0.05) but the prevalence rate of<em> Dactylogyrus spp,</em> <em>chilodonellosis</em>, cryptobia and <em>Ichthyophthirius</em> on the gills of phytophagous breeders were more than the rest of examined areas showing a significant difference with that of skin and gills (P<0.05).</div> Hypophthalmichthys molitrix, Fish breeders, external parasites, Guilan 1 9 http://ijaah.ir/browse.php?a_code=A-10-232-4&slc_lang=en&sid=1 M Rahanandeh Rahanandeh1340@gmail.com 10031947532846002731 10031947532846002731 Yes Guilan Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Rasht, Iran B Tizkar btizkar@areeo.ac.ir 10031947532846002732 10031947532846002732 No Guilan Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Rasht, Iran