As disgusting as they appear many fish can tolerate parasites. If your fish are performing well as in feeding well and have good relative weights I believe you'll be O.K. If you eat any of these fish be sure to cook them thoroughly. No sushi!
There is a treatment for intestinal parasites but it's more of a few fish at a time in a quarantine/treatment tank thing and it's only approved for ornamental fish. Not applicable for a pond treatment.
