Bacteria & water moulds
Mycobacteriosis in fish
Mycobacterial infections can cause chronic illness. Weight loss or a bent body does not establish the diagnosis.
A laboratory question
Several organisms and noninfectious conditions can cause gradual deterioration. A vet may need tissue tests to confirm the cause and advise on the system.
Protect your skin
Some fish-associated mycobacteria can infect people through damaged skin. Cover cuts, use suitable gloves for wet work and wash hands. Tell a clinician about aquarium or pond exposure if a persistent skin lesion develops.
Avoid spreading the problem
Do not move affected fish to other homes. Ask the vet about long-term management and disinfection rather than trying repeated mixed treatments.
Sources & further reading
Original WakeyKoi wording, informed by the references below. Linked clinical resources explain the evidence and their scope; they have not reviewed or endorsed this website.
Related guides
Educational guidance cannot diagnose an individual fish. Breathing distress, severe injury or unexplained losses need prompt professional assessment.