I'm sorry--I lost this fish 2 days ago. I lost 4 plecos in total. I still had several that had the parasite on their gill plates. I have since treated with API Super Ich Clear & salt. In 3 days, it is all gone. There is a fellow I am talking to via PM with the exact same problem.

Is that as a bath or treating the entire tank? Do I need to move the Knife fish?

There are several pics of the most affected fish & another, where it is starting on his gill plate (that's where it seems to start 1st). I wonder if that's affecting their breathing--killing them at the end? Here is a recent pic after a full treatment of Kanaplex/salt. As you can see, it's not ...

I can have my vet make a slide of it but neither of us know what we're looking at!

The marks keep moving around his body. The ones that were in the 1st pic are gone on the left side of his body but there are more elsewhere. I am also starting to see a few spots on other plecos now.

3 days post treatment, Kanaplex/salt. The one on his right eye is completely gone! http://img.photobucket.com/albums/v345/Pufferpunk/Other%20Fish/Sickpleco3_zpsa133d459.jpg Looks better??? Here's the other affected fish. Weird, that it attacks the gill plates 1st... http://img.photobucket.com/albums ...

I have been treating with salt & Kanaplex. I believe the fish looks better today, as do some of the others. Of course, he wouldn't come out of the plant for me to take a pic. I'll keep trying to coax him. Maybe some algae wafers will help.

Sure does! Looks like pieces of cauliflower. If viral, how to treat?

I've been in the hobby 40 years & have never seen this before. I'm being told fungal but I'm thinking parasite. It's killed 3 of my plecos so far & is spreading to the others (about 20 in there). I've treated with metro & prazi--no luck. Started treating last night with salt & Kanamycin sulfate ...