Thankfully, I don't have a lot of experience with this one, but I'll tell you what I know. Because the presumed pathogen is an encysted Myxosporidian there is no treatment that will kill the parasite without killing the fish. The best thing you can do is maintain good oxygen levels & low ammonia levels and wait it out. Usually the disease symptoms dissipate over time with low mortality rates.

I would not treat the pond because this can further stress fish that are already stressed, and I would be very careful fertilizing because if you do it wrong you can raise ammonia levels and lower oxygen levels...exactly what you don't want to have happen.

This info could be out-dated (learned about it around 1990)...let me know if someone has current info on this.

Mike Robinson
Keystone Hatcheries