| Summary: | Sphyrion lumpi is a marine ectoparasitic copepod that has a significant negative impact on fisheries of redfish, Sebastes spp. in the North Atlantic as it reduces the commercial value of the fillets. Long-term data of infestation by S. lumpi and abnormalities in Sebastes mentella, in Icelandic waters were analyzed in this study. Five categories of external abnormalities were applied; black spots, red spots, mixed spots, remnants or lesions caused by S. lumpi and the parasite itself. Infestation intensity of the copepod was not found to be related to redfish condition (K). During the period, the prevalence of S. lumpi infections declined from 25% in 1995 to 9% in 2013. Significant differences in infestations were found between female and male fish and the shallow pelagic and deep pelagic stock. These results show the host response of S. lumpi infections and give a good overall view of trends in S. lumpi infestation, which could be a contributing factor towards defining S. mentella population stock structure. Microparasites in the field of icthyoparasitology are generally limited to Myxozoa (Kingdom Animalia, Phylum Cnidaria), Protozoa (Kingdom Protista) and Microsporidia (Kingdom Fungi). The microparasitic fauna of Sebastes spp. in Icelandic waters was mapped in this study. All major organs were examined thoroughly with a stereoscope and/or a compound microscope. Histopathological examinations were carried out with regards to parasitic infections in order to determine the exact site of the infection. DNA was extracted from myxozoans from the gallbladder and apicomplexans from the intestines and the urinary bladder. The parasites’ DNA was amplified with PCR and sequenced. Six different parasite species were identified, two myxosporeans and four apicomplexans. Results identified the myxosporean species to be Myxidium bergense and Ceratomyxa adeli. The apicomlexan species are not fully identified but are thought to be previously undescribed. Accurate identification awaits further study.
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