Koi with Cloudy Eyes and "Bubbles": Parasite Alert

Large koi has chronically cloudy eyes; now shows bubble-like growths over eyes. Eats and swims normally. No other symptoms.

Likely Cause: Diplostomum spathaceum (Eye Fluke)

This trematode parasite migrates through skin to the eye lens, causing cloudiness and cataract-like bubbles. Other parasites (Ichthyophthirius, Myxobolus) can also affect eyes.

Treatment Reality

• Praziquantel kills adult flukes in the gut but does not reverse eye damage.
• Once the lens is parasitized, vision loss is permanent.
• Prevention: Snail control (intermediate host), quarantine new fish, maintain water quality.

Since the fish eats and behaves normally, it can live years with impaired vision. Focus on protecting other fish. Treat the pond with praziquantel per label if flukes are confirmed.