My husband noticed this wound on our male guppy today. I have moved him into a quarantine tank and treated it with melafix (that's all I have on hand) and salt to help it heal. Is this a bacterial disease? There has been no aggression in my tank that I have seen which makes me think this is a disease rather than an injury. If so, what do I do? Any ideas on what it could be? I don't want the rest of the tank to be at risk. When I removed him, I also did a 30-40% water change in the main tank and treated it with salt and changed for a new filter.
I have 7 guppies (1 male, 6 female), 4 Cory catfish, 4 Otto catfish, 4 diamond tetra, and 4 amano shrimp. Water parameters are 0 ammonia and nitrite and about 5-10 nitrate. Attachment 1