Totally 75 common carp and 100 big head fishes were caught by using net from fish farms in Mashhad, northeast of Iran. In laboratory skin, eye and fin of fishes were inspected by stereomicroscope and in second phase direct smears are prepared from probable lesions. Gills were dissected and its filaments were placed in petri dishes and fixed by Glycerin. In total 50 parasites (consist 19 protozoa and 31 metazoa) were recorded from fishes. The parasites represented in Protozoa (Ichthyophthirius multifiliis and Trichodina sp.) and Monogenea) Dactylogyrus spp.) and Copepoda (Lernea cyprinacea). During this study, infection with Dactylogyrus spp. was recorded on fish in all months. Mean intensity of Dactylogyrus spp. varied significantly among the seasons (P < 0.05). The maximum mean intensity was recorded in winter. Also infection with Lernea cyprinicea in spring was significantly higher than other seasons (P < 0.05). The results of this study together with the previously recorded prevalence of parasitic infection in fishes support that infection to external parasites (both protozoa and metazoa) is widespread cause for losses in fish farms of Iran.
Keywords: Cyprinus carpio; External parasite; Hypophthalmichthys nobilis.