u/Mental-Possession-33

I noticed this fish had been more lethargic in the past week but I just thought the winter must’ve been hard on him (in Ohio). I’ve always battled high nitrates in this pond so there has been some spikes but no apparent illness or death. The scales at the back end on both sides were missing I think or the fish is at least discolored. The net is never off the skimmer is covered. I’m not sure if it may have been a falling rock the koi are pretty big and get really crazy sometimes. I was hoping someone could dispel my worries that it is a bacterial infection or other illness that is transferable to the other fish. For reference they all seem very active no missing scales.