I have a single juvenile five-bar cichlid (Neolamprologus tretocephalus) living alone with 2 Synodontis catfish. They are known to be very aggressive, and I believe that mine may have injured his lower law due to his aggression (he likes to bite at rocks, glass, etc.) At first, it was a small injury, but due to my neglect at realising the issue's severity, the injury started growing white fuzzy stuff all over the lower law, disintegrating it and leaving him barely able to eat. I've been treating him with strong doses of melafix, but the situation has gotten worse and worse over the last few days. Any help would be more than welcome, as I just want to know if there is a chance to save my little buddy. If not, it would be helpful to provide some info of methods of how to humanely euthanise fish. I would only euthanise him if it was the last option though, as he was quite expensive and one of my favorite fish. But I do hate to see him struggling more and more to eat food, and so I just want the best possible choice.
(sorry for the bad image quality)