I'm very sorry, and this makes me nervous to say considering I can't see the fish, and I am not an expert, but there are several threads on proper euthanasia on this board. I know that if you put a bit of vodka in the water, that will knock him out, then you put him in the freezer. He will just go to sleep. I'm so sorry but he is likely in pain and euthanasia is probably the kindest thing to do.