Fungal Infections on Aquarium Fish

This guide covers fungal infection aquarium fish with practical steps for home aquariums. White fluffy growth on fish or eggs is fungal — it attacks weakened tissue, not healthy scales on pristine water.

For related reading, see community fish compatibility, Dropsy — Causes and Care and Columnaris in Aquarium Fish.

Appearance

Cotton-like white or gray tufts on mouth, fins, eggs, or wounds. Often follows injury, chill, or bacterial lesion.

Fungus is secondary — killing fungus without fixing underlying stress fails long term.

Egg Fungus

Unfertilized or dead eggs grow fuzzy coats that spread if not removed. Pick white eggs from spawns in breeding tanks.

Methylene blue or commercial egg antifungals help some breeders; gentle aeration also limits spread.

Treatment

Salt baths at tolerated concentrations for many freshwater fish. Antifungal medications (phenoxethanol, malachite green combinations where legal) per label.

Remove visible fluff gently with cotton swab in hospital tank before dosing — exposes tissue to medication.

Supporting Recovery

Warm stable temperature in species range speeds healing. Nutritious food and pristine water reduce recurrence.

Isolate until fluff gone plus one week margin — spores persist in mulm.

Prevention

Avoid temperature shocks during water changes. Handle fish minimally with wet hands and soft nets.

Do not add healthy fish to tanks with active fungal outbreaks without quarantine path.