I'm very fond of those little fish. But I will quarantine them and probably deworm them before putting them in with any of my fish. Wild suckermouths have had a pretty rough road from when they were collected, shipped to wholesalers, shipped to the LFS and brought home to an aquarist's tank. Their lot is complicated by the fact that their diet is not usually what all the other fish are getting, so they may be very starved (something we don't see because of their armour.) With all of that stress, it is not surprising that sometimes diseases cut loose or that they catch something already in the tank, but notthreatening the other fishes.

I'm also leary of the "plecos" (often Hypostomus) raised in Florida. They aren't run through quite the same mill as the others, but they are pond raised, as opposed to growing up in a flowing river system and that may expose them to a higher bacterial load. They too should be given special food and attention upon purchase.

Scott L, is of course correct, about isolating that fish ASAP. They can also chill easily. It might be good to watch that fish to see if there is evidence of merely the bacterial infections/ dropsy or worms. Then you know what to worry about in your main tank. :(

If the sick fish shows evidence of worms, please treat your tank. A lot of our mystery deaths probably can be attributed to internal worms. Your call as to whether to change more water, more frequently, or also do a preventative medication of the tank with an antibiotic if the otto has dropsey.