Fungal Infections in Aquarium Fish

Fungal infections are common secondary issues in aquariums. Unlike Ich, true fungal infections rarely attack healthy, uninjured fish. They typically take hold when a fish's slime coat is damaged due to injury, poor water quality, or a parasitic infection. The most common culprit is the genus Saprolegnia.

Causes

Fungus spores are omnipresent in aquarium water but are generally harmless to healthy fish. Infection occurs when:

• Physical Injury: Nips from other fish, handling damage, or scraping against sharp decor.
• Poor Water Quality: High levels of ammonia or nitrite weaken the fish's slime coat.
• Low Water Temperature: Many fungal strains thrive in cooler water where the fish's immune system might be slower.
• Existing Disease: Bacterial or parasitic infections can leave open wounds vulnerable to fungus.

Symptoms

• Cotton-like Growths: The most distinct sign is white or greyish, fluffy, cotton-wool-like growths on the skin, fins, or mouth.
• Discoloration: The affected area may look pale or white before the fuzz appears.
• Loss of Appetite: Fish may stop eating.
• Lethargy: Fish may hover near the bottom or surface.

Fungal vs. Bacterial (Columnaris)

It is crucial to distinguish true fungus from Columnaris (Cotton Mouth), which is a bacterial infection.

• Fungus: Looks like fluffy cotton wool; usually grows on dead tissue or wounds; grows relatively slowly.
• Columnaris: often looks flatter, like moldy bread or a white saddle on the back; can erode the mouth quickly; spreads very rapidly.

Treatment

1. Correct the Underlying Cause

Since fungus is often secondary, check your water parameters immediately. Perform a water change to improve water quality. If the fish is being bullied, separate it.

2. Anti-Fungal Medication

Treatments specifically designed for fungus are widely available.

• Methylene Blue: Highly effective for fungal infections and safe for most fish. Ideally used in a quarantine tank / bath as it can damage biological filtration and stain silicone.
• Malachite Green: Often found in ''Ich'' cures but is also effective against fungus.
• Pimafix: A natural remedy containing Bay West Indies oil, suitable for mild infections.

3. Salt Bath

For mild cases, a salt bath can help strip away the fungus and promote slime coat regeneration.

• Mix aquarium salt in a separate bucket of tank water (approx. 1 tablespoon per gallon).
• Bathe the fish for 15-30 minutes, watching closely for signs of distress.

Prevention

• Keep water clean: Regular water changes and filter maintenance are your best defense.
• Avoid aggression: Choose compatible tank mates to prevent injuries.
• Handle with care: If you must catch a fish, use a soft net and avoid touching their slime coat.