Fungal Infection
Saprolegnia
Moderate severity
Cotton-wool-like growth on the skin, fins or eyes, usually on already-injured tissue.
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Symptoms
White or grey fuzzy, cotton-wool tufts on the body, fins, mouth or eggs, often where injury or other disease exists.
Causes
Opportunistic fungus colonising damaged tissue, dead eggs or fish stressed by poor water quality.
Treatment
Improve water quality, remove decaying matter, and treat with an antifungal medication. Salt baths help mild external cases. Address the underlying wound or infection.
Prevention
Maintain clean water, remove dead matter promptly, and treat injuries and other diseases before fungus sets in.
FAQ
How do I tell fungus from columnaris?
True fungus is fluffy and tufted on injured spots; columnaris is flatter, spreads fast and is bacterial. When unsure, treat for both.
Can fungus spread to other fish?
Healthy fish usually resist it, but the same poor conditions that triggered it can affect others.
This information is general guidance, not veterinary advice. Consult an aquatic vet for serious cases.