Fungal Infection

About Fungal Infection

Names: Fungus, Fish Fungus
Disease Type: True fungal infection
Cause/Organism: Saprolegnia and Achlya mold species


A fungal infection usually starts as growth on decaying matter in the aquarium. It attacks fish with a poor slime coat or eggs that have died after being laid. It will also attack lesions left by other injuries. Fish who develop fungus are already in a vulnerable state, the result of other serious health problems or attacks such as parasites, a physical injury or a bacterial infection. Poor water conditions and drastic temperature changes can also play a part in this disease.


White, brown or gray cotton-like growths on the scales, skin or fins of freshwater or brackish water fish.


  • Quarantine the aquarium.
  • Add aquarium salt, 1 tablespoon per 5 gallons
  • Remove activated carbon
  • Treat with Mardel Maracyn® Oxy for up to five days, following label instructions

Mardel Maracyn® Oxy is the treatment of choice. It should be used according to the recommended dosage. Parashield is an herbal alternative that contains natural oils and extracts that have been proven effective against fungal and bacterial infections.

As with any treatment, activated carbon should be removed from the filter as it will remove the drugs from the water.

Please note that many bacterial infections are misdiagnosed as fungal, so if unsure, it is recommended to treat for both types of infection.


  • Maintain high water quality
  • Provide fish with a nutritionally balanced diet
  • Add ParaShield whenever adding new fish to the aquarium to prevent fungal outbreaks.

Fungus is easily prevented. Avoid injuries to your fish by minimizing handling and not mixing specimens that might damage one another. Water quality should be monitored carefully and kept high by performing regular maintenance and water changes. The cleaner the aquarium, the less problematic fungus is likely to be.

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