Fish contract mycobacteriosis, commonly referred to as piscine mycobacteriosis or fish tuberculosis, across diverse marine and freshwater species, primarily through exposure to contaminated water, sediment, or contact with infected fish. The bacteria can enter the body through the gills, open wounds on the skin, or by ingesting infected material. The disease is caused by several environmental species of Mycobacterium, including M. marinum, M. fortuitum, M. chelonae, and M. salmoniphilum, which can persist in aquatic environments, especially where water quality is poor or fish are stressed.
Mycobacteriosis is most commonly found in aquaculture systems, particularly those with recirculating or high-density setups, where stable water conditions can allow the bacteria to thrive. It is also frequently reported in public aquaria and ornamental fish tanks, where outbreaks of M. marinum are relatively well documented. Wild fish populations can also carry these bacteria, although infections are less often detected due to limited monitoring.
The disease has been reported globally and is particularly prevalent in temperate and tropical waters, where environmental conditions such as water temperature can support bacterial survival and growth. Species affected include a wide range of marine and freshwater fish, including commercially important species like salmonids and groupers, as well as many ornamental fish.
Authored by Nina Sandlund and Lone Madsen, both members of ICES Working Group on Pathology and Diseases of Marine Organisms., Leaflet No. 75 provides authoritative guidance for recognizing, diagnosing, and managing atypical mycobacterial infections.
As mycobacterial infections remain a concern in both intensively farmed and wild fish populations, this leaflet is a proactive tool in disease awareness and prevention, ensuring improved fish health, industry resilience, and public safety.
ICES Id leaflets for diseases and parasites in fish and shellfish
With fish health under pressure from changing environments and shifting disease dynamics, there is a need for clear, practical tools to identify what is going wrong when symptoms appear. Many fish diseases and parasites are difficult to detect or easy to confuse with others. Misidentification can delay action, increase the risk of spread, or result in ineffective treatment. Identification guides help reduce this uncertainty by distilling expert knowledge into clear visuals and straightforward descriptions. These resources support faster and more confident diagnoses, whether they are used on a farm, in the field, or in a lab.
Mycobacteriosis in farmed and wild fish is available to view and download from ICES library.
