These flukes were very small and nearly transparent. The only reason I found them was because it was on the cornea of the fish and was causing edema (whitening) of the cornea. When I saw this I used a large magnifying glass to look at the eye, and to my surprise I could see a small nearly transparent organism that, under a microscope, I identified as a fluke. A freshwater dip solved the problem, but catching the little sucker was a bi@$#.
While the fluke may not have killled the fish, it would have stressed it to a point where it may have gotten seriously ill.