Fish Fungus: Complete Treatment Guide

**Quick Answer:** Fish fungus appears as white, cotton-like growths on the body, fins, or mouth. Treat by improving water quality, performing 25-30% daily water changes, and using antifungal medications like API Pimafix or Blue Planet Anti-Fungal Remedy. Most fungal infections clear up within 7-10 days with proper treatment, but always address the underlying cause (usually injury or poor water quality) to prevent recurrence.

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What is Fish Fungus?

Fish fungus is a common infection caused by various fungal organisms, most commonly Saprolegnia and Achyla species. These fungi are opportunistic pathogens that typically attack fish that are already stressed, injured, or suffering from another illness. Fungal spores are naturally present in most aquariums but only become problematic when fish are vulnerable.

The characteristic cotton-like or fluffy white to grey growths are actually colonies of fungal hyphae (threads) that grow on the fish's body. Unlike bacterial infections that may develop anywhere, fungal infections almost always start at sites of injury, stress, or previous infection.

Symptoms

White, grey, or slightly beige cotton-like growths on body, fins, or mouth

Fluffy or thread-like appearance to the growths

Growths that start small and expand outward over days

Lethargy and reduced swimming activity

Loss of appetite

Hiding behaviour more than usual

Rubbing or flashing against objects (trying to remove the fungus)

Redness or inflammation around the fungal growth

Secondary bacterial infections developing near fungal sites

Frayed or deteriorating fins if fungus is present there

Causes

Physical injuries or open wounds

Previous bacterial infections that damaged tissue

Poor water quality (high ammonia or nitrite levels)

Stress from improper water parameters or temperature fluctuations

Weakened immune system from poor diet or chronic stress

Handling fish with dry hands or rough nets

Parasitic infections that create entry points for fungus

Fungal spores on new plants, decorations, or fish

Treatment Steps

1. **Test water parameters** - Check ammonia, nitrite, nitrate, pH, and temperature

2. **Perform water changes** - Do 25-30% daily water changes with properly conditioned water

3. **Clean the tank** - Gently vacuum substrate to remove waste and fungal spores

4. **Add antifungal medication** - Use API Pimafix ($12-18 at Petbarn) or Blue Planet Anti-Fungal Remedy ($15-20 at Aquarium Spare Parts Adelaide)

5. **Remove carbon filtration** - Carbon will absorb medication, making it ineffective

6. **Increase water temperature** - Gradually raise to 26-28°C to speed up the fish's metabolism and immune response

7. **Add aquarium salt** - For freshwater fish that tolerate it, add 1 tablespoon per 19 litres (avoid with tetras, catfish, and other salt-sensitive species)

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Prevention

Maintain excellent water quality with 0ppm ammonia and nitrite

Perform regular 25-30% weekly water changes

Use nets and equipment that won't damage fish's protective slime coat

Quarantine new fish for 2-4 weeks before adding to main tank

Disinfect or quarantine new plants and decorations

Feed a varied, high-quality diet to boost immune function

Avoid overcrowding your aquarium

Treat injuries promptly to prevent fungal colonization

When to Worry

If fungal growths continue to spread despite treatment, or if they appear on the gills or cover large portions of the body, more aggressive treatment is needed. Fungal infections that reach the gills can interfere with breathing and quickly become life-threatening. If you notice the fish gasping, showing rapid gill movement, or if the fungus has spread to cover more than 25% of the body, consider using a stronger medication like Seachem ParaGuard ($25-35 at specialist stores in Adelaide) which treats both fungal and bacterial infections. In Adelaide's humid climate, especially during transitional seasons, fungal spores can proliferate more readily, so be extra vigilant with tank maintenance.

Common Questions

**How quickly does fish fungus spread?**

Fungal infections typically start small but can spread noticeably within 24-48 hours if conditions are favorable. Without treatment, they can cover significant portions of the fish within a week.

**Can fish recover from fungus without treatment?**

Minor fungal infections on healthy fish with strong immune systems may occasionally resolve on their own with improved water conditions. However, most cases require medication to prevent spreading and deeper tissue invasion.

**Is fish fungus contagious to other fish?**

Yes, fungal spores can spread to other fish, especially those with injuries or weakened immune systems. While healthy fish can typically resist infection, it's best to treat the entire tank when fungus is detected.

**Can fish fungus infect humans?**

No, the species of fungi that infect fish are not typically harmful to humans. However, it's always good practice to wash your hands after handling aquarium water or equipment.

**How can I tell the difference between fungus and columnaris (cotton wool disease)?**

Fungal infections typically appear fluffy and cotton-like, while columnaris (a bacterial infection sometimes mistaken for fungus) often has a more mucus-like appearance and may have a yellowish tint. Columnaris also tends to spread more rapidly. FinsDoc's AI can help distinguish between these conditions by analyzing photos of your fish.

Still unsure about your fish's condition? Join over 750 Australian aquarists who've used FinsDoc for accurate diagnosis. Upload a photo now at https://finsdoc.com.au and get personalised treatment recommendations for your fish's specific fungal infection.