How many did you observe like this?

If you didn't put them in a cage, does anyone else have access to the pond and perhaps they did and then released them? The frayed tails look like classic fin wear from being in a fish basket or small holding cage. It would explain the stress and the fungus could be from rough handling of catch and release.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.