Working Group on Pathology and Diseases of Marine Organisms (WGPDMO)

The Working Group on Pathology and Diseases of Marine Organisms (WGPDMO) investigates diseases and pathology in wild and farmed finfish, shellfish and crustaceans. This report describes new disease trends in wild and farmed fish and shellfish in the ICES area, based on national reports from fourteen member countries. Notable reports for wild fish included a widening geographic scope of the enigmatic “red skin disease” in wild Atlantic salmon, with reports now from Norway, Scotland and Ireland as well as the Baltic Sea countries where it was origi-nally observed; increased prevalences of Ichthyophonus sp. infection in herring from Iceland and mackerel from Norway, suggesting potentially increased affects of this pathogen on wild fish in the north; and the first detection of eel rhabdovirus (EVEX) in England and Wales since the 1980s. Detection of piscine orthoreovirus (PRV) in exotic pink salmon straying from cultivation in Russian rivers to Norway raised questions about potential disease interactions between pink salmon and farmed Atlantic salmon that deserve further attention. Reports of diseases in farmed fish included the first detections of infectious pancreatic necrosis virus (IPNV, pathogenic genogroup 5 )and Parvicapsula pseudobranchicolain Atlantic salmon from Iceland, increased detection of Pasteurella skyensis in Atlantic salmon in Scotland, and increased detection of furunculosis caused by Aeromonas salmonicidain Atlantic salmon from Ireland. Sea lice parasitism and complex gill disease (CGD) remain highly significant concerns for Atlantic salmon aquaculture, with reports for 2019 noting increasing prevalences and impacts of both. Notable reports of diseases for shellfish included an outbreak of Haplosporidium costale in cultured Pacific oysters in France; mortality caused by Vibrio aestuarianusin cultured Pacific oysters in Scotland and Ireland, with additional and unusual detection of bacteria belonging to the Vibrio splendidus clade in association with Pacific oyster mortality in Ireland; mortality caused by a coccidian parasite in wild bay scallops in the USA; and documented expansions of the distributions of Bonamia ostreae in flat oysters in Scotland and Marteilia refringens in blue mussels in Norway. The group also summarized work on the role of Vibrio pathogens in contributing to mortalities in shellfish aquaculture as well as seafood-associated disease risks in humans, on the contemporary status of oyster pathogen Bonamia ostreae, on complex gill disease in salmon, on emerging health issues affecting wild salmonids of the Baltic region, and on disease considerations related to cleaner-fish use in salmon culture. The group additionally discussed the status and future directions of the ICES Identification Leaflets for Diseases and Parasites of Fish and Shellfish, and priorities for their work from 2021, potentially including health threats to endangered pen shells in the Mediterranean; eel diseases; and a consideration of which host-pathogen systems might be most promising for management through selective breeding. Group members published two new ICES Identification Leaflets for Diseases and Parasites in Fish and Shellfish in 2019 and five new leaflets are planned for completion in 2020.