You should definitely put them back in the lake. Its not normally like one fish gets it and spreads it to others, many lakes have varying degrees of disease outbreaks. Sores like that can be caused by many different parasites, diseases, or stresses. I have seen some fish survive through worse ailments than that in the past. Always worth sending a picture into fish and wildlife though, they may appreciate knowledge of different outbreaks in different lakes.

It is also illegal not to return a sport fish you're not retaining to the water, throwing fish in the bushes is not a good idea. No officer with any knowledge of fish would recommend that. I have witnessed fish with much worse ailments than that make a full recovery, on top of that I've caught a pike missing the top half of its mouth and on another occasion one missing the majority of its gills on one side, both looked pretty healthy and the injuries were not recent (fully healed over). Both were retained for supper as they were legal by only a few inches and i was by chance hungry that day (i like to keep the smallest pike possible and let the big mature spawners go).

Just food for thought.