Sounds like an aeromonas bacteria. If it is isolated I wouldn't worry too much and let it go it's course as there is nothing you can really do.

It's apparently stress medidated as most diseases are. It could be caused by spawning stress if it is spawning time, or if it is before spawning rapidly changing water temps can stress fish.

Were any of these fish caught and released in the fall or winter? If so, that may have caused your problem. Bass and bluegill if handled in under 50 degree F. water in the fall or winter can develop fungus etc. on areas of hook wounds or where they are handled later in the spring when the water warms up the bacteria and fungus explode in growth. In cold water warmwater fish have compromised immune systems and can have problems later.

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