• Fish are flashing. Flashing is when a fish swims slowly near the side or bottom of the pond and then quickly swims off by first rubbing it’s side against the pond wall.
• A fish is isolating itself from the other fish.
• One or more fish have stopped eating.
• A fish spends much of the time near the water fall gasping for air.
• Fish are sitting on the bottom of the pond with their fins clamped close to their body or are drifting in the pond with their head pointed upward or downward for several minutes at a time.
• Sores developing on the fishes body or fins.
• Fish are dying.

Proper treatment for parasites depends on which parasite the koi have. If you have access to a microscope, by simply taking a scraping from the fish and examining it under the microscope, you can usually tell exactly which parasites are present and then treat for them accordingly.