Bacteria & water moulds
Columnaris: a bacterial lookalike for fungus
Columnaris is associated with Flavobacterium bacteria. Surface lesions can be mistaken for fungal growth.
Why appearance can mislead
Skin, mouth, fins or gills may be affected. Cotton-like or pale areas do not tell you which organism is responsible.
Ask for confirmation
A professional may use microscopy, culture and the pattern of lesions to investigate. The treatment for a bacterial infection can differ from a water-mould treatment.
While arranging help
Record progression with photographs and test the water. Do not automatically raise temperature or combine antibacterial and antifungal products.
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.