Causative agent: Chilodonella cyprini / C. hexasticha — heart-shaped ciliate protozoan
Chilodonella is a ciliate protozoan parasite that poses a particular danger to Australian goldfish and koi keepers, especially during the cooler winter months when the parasite thrives and the fish's immune system is naturally suppressed. The heart-shaped parasite attaches to the skin and gills of fish, causing irritation, excessive mucus production, and in severe cases, death. The bluish or milky patches on the skin are a characteristic visual sign, along with gasping at the surface as the gills become compromised. Unlike many parasites, Chilodonella is highly sensitive to elevated temperatures — raising the water temperature above 25°C can significantly slow its reproduction. In Australian ponds, Chilodonella outbreaks most commonly occur in early spring as fish emerge from their winter torpor in a weakened state. Treatment with salt baths combined with Aquasonic Bactonex or Aquasonic Ichonex is effective when started promptly. Maintaining good water quality and appropriate nutrition throughout winter is the best prevention strategy.
Symptoms
- •Milky or bluish skin patches
- •excess mucus production
- •frayed fins
- •scratching
- •labored breathing
- •loss of appetite
- •listlessness
- •skin ulcers in severe cases
Treatment
- •Salt baths
- •formalin
- •malachite green
- •potassium permanganate
- •methylene blue
- •raise water temperature above 25°C (parasite sensitive to heat)
Australian Medications
- •Aquasonic Bactonex
- •Aquasonic Ichonex
- •Aquasonic Methylene Blue
Commonly Affected Fish
- •Goldfish and koi especially susceptible
- •all coldwater freshwater fish at risk
Important Notes
Thrives in cold water (below 20°C). Common in goldfish in early spring. Raising water temperature is an effective treatment aid.