Working Group on Pathology and Diseases of Marine Organisms (WGPDMO; outputs from 2024 meeting)

The Working Group on Pathology and Diseases of Marine Organisms (WGPDMO) reviews and reports on the health challenges affecting wild and cultured marine species, including finfish, shellfish, and crustaceans, within the ICES area. This report highlights key disease trends based on data from 14 ICES Member Countries. The last hybrid meeting of this group was in 2023, they met online late in 2024. This report summarizes the information presented during the 2023 WGPDMO expert group meeting covering trend data for the calendar years 2021 and 2022 (ToRa) and notes progress on ToRs b to e (2022–2024).

Key findings highlighted in this report include the following:

Farmed Fish:
• Viral infections, such as recurring outbreaks of Infectious Salmon Anaemia Virus (ISAV) in the North Atlantic, continue to pose significant threats.
• In eastern Canada the first reported virulent ISAV with a full, undeleted highly polymorphic region (HPR0) was detected.
• The emergence of Cyclopterus lumpus virus in lumpfish highlights the growing complexity of aquaculture health management.
• Sea lice infestations and complex gill disease remain critical challenges, impacting productivity in salmon farming operations.
• Bacterial pathogens, including Moritella viscosa and Aeromonas salmonicida, have exhibited changing bacterial variants patterns. Bacterial infections are common secondary to delousing, and an increasing problem in Norway and Scotland.

Wild Fish:
• The geographic expansion of "red skin disease" in Atlantic salmon and the reappearance of Eel rhabdovirus in England signal ongoing threats to wild stocks.
• Increasing trends in parasitic infections, such as Anisakis simplex in herring, Contracaecum osculatum in cod and the presence of granulomas in cod livers suggest broader environmental and ecological impacts.
• The increase in observations of Black spot syndrome, a condition of unknown aetiology, resulting in dermal degradation in Rock cook (Centrolabrus exoletus) in Norway and occasional observations in other wrasse species (Goldsinny, corkwing and cuckoo), warrants further investigation.
• Similarly increased observations of granulomas in mackerel, some of which are associated with mycobacterial infection should be investigated to understand implications.

Molluscs and Crustaceans:
• Following its detection in blue mussels in France in 2020, Francisella halioticida has now been described in blue mussels undergoing mortality in the Netherlands. Work to ad- dress increasing concern from this is ongoing.
• Putative infection of European flat oysters in England by a novel herpes-like virus should be the focus of further study.

Recommendations
1. Enhanced Surveillance: Reduction across national budgets for marine surveillance and disease data collection is having an impact on ability to provide information and advice. Regular monitoring and pathogen characterization should be expanded to detect emerging threats promptly.
2. Biosecurity Improvements: Implementing stricter controls on the movement of aquatic species and farmed stock can mitigate the spread of diseases.
3. Research and Development: Increased focus on vaccine development and selective breeding for disease resistance, especially for bacterial and viral pathogens, affecting aquaculture species, is critical.
4. Integrated Management Strategies: Collaboration across ICES countries to develop holistic approaches addressing environmental factors, pathogen management, and species health is highly desirable.

These findings highlight the urgency of addressing disease challenges in marine environments to support sustainable aquaculture and wild stock conservation; underscoring the importance of continued surveillance, biosecurity, and coordinated efforts to address emerging diseases in marine organisms.