Cardiomyopathy Syndrome (CMS)

Physical Signs:

• Cardiac Lesions: Inflammation and necrosis of the heart muscle, often visible as white or pale streaks.
• Anemia: Pale gills and organs due to reduced red blood cells.
• Ascites: Accumulation of fluid in the abdominal cavity.
• Exophthalmia: Bulging eyes can be observed in affected fish.

Behavioral Changes:

• Lethargy: Reduced activity and swimming stamina.
• Loss of Appetite: Decreased feeding behavior and subsequent weight loss.
• Abnormal Swimming Patterns: Fish may display erratic or weakened swimming due to cardiac damage 34.

Early Stages: Subtle signs such as reduced feed intake and slight lethargy.

Advanced Stages: More pronounced physical symptoms, including cardiac lesions and anemia, leading to increased mortality if not managed.

Impact on Fish Health: CMS severely compromises heart function, making fish more susceptible to secondary infections and reducing overall vitality 14.

Causative Agent: Piscine myocarditis virus (PMCV).

Transmission Methods:

• Direct Contact: Spread between infected and healthy fish through close proximity.
• Waterborne: The virus can be transmitted through water, potentially spreading from one farm to another 12.

Environmental Factors: Poor water quality, high stocking densities, and stressful conditions can increase susceptibility to CMS.

Farm Management Practices: Ineffective biosecurity measures and lack of routine health monitoring can facilitate the spread of PMCV 13.

Clinical Examination: Observation of physical and behavioral symptoms indicative of CMS.

Laboratory Tests:

• PCR (Polymerase Chain Reaction): Detects PMCV genetic material in fish tissues.
• Histopathology: Microscopic examination of heart tissues to identify characteristic lesions of CMS.
• Immunohistochemistry: Detects viral antigens in tissue samples 245.

Current Treatments: There are no effective antiviral treatments available for CMS. Management focuses on preventing the spread and mitigating the impact through biosecurity measures and supportive care.

Experimental Treatments: Ongoing research into potential antiviral agents and other therapeutic approaches 23.

Biosecurity Protocols:

• Implementing strict quarantine measures for new stock to prevent the introduction of PMCV.
• Regular disinfection of equipment and facilities to minimize the risk of contamination.

Farm Management Practices:

• Reducing stocking densities to decrease the risk of virus transmission.
• Regular health monitoring and early detection programs to identify and manage outbreaks promptly.
• Implementing all-in/all-out stocking practices to reduce the risk of spreading infections 123.

• Norway (1980s): The first identified outbreaks led to significant economic losses and increased regulatory scrutiny.
• Scotland: Ongoing challenges with managing CMS in salmon farming operations.
• Canada: Reports of CMS have prompted industry-wide efforts to improve biosecurity and disease management 1234.

CMS Incidence in Norway:

• CMS is widespread along the entire Norwegian coast 9.
• In 2023, cardiomyopathy syndrome (CMS) was one of the five most common infectious diseases causing mortality in farmed salmon 9.
• CMS is now considered one of the most important problems for the Norwegian aquaculture industry 10.

Geographical Spread:

• CMS affects salmon farms along the entire Norwegian coast 10.
• In 2023, there were large geographical differences in mortality rates across Norway's 13 salmon production areas 6.

Economic Impact:

• CMS most often affects large salmon in their last year at sea, leading to major financial consequences 10.
• In 2023, 62.8 million salmon (16.7%) died in the sea phase of production, the highest recorded mortality rate so far 69.

Treatment & Management:

• Research has confirmed that CMS is a contagious disease that can affect salmon at various life stages, including pre-smolts, post-smolts, and early sea phases 10.
• CMS-sick salmon do not seem able to fight the PMCV infection or get rid of the virus, and heart inflammation does not appear to heal over time 10.
• Heart samples are the best for detecting PMCV-specific RNA in fish with clear CMS changes 10.
• Early detection may be possible through plasma from blood samples and tissue samples from the central kidney 10.

• CMS is a growing problem for salmon farmers in Scotland 10.