knifegill;2996516; said:Looks to me like an ulceration or deep boil which festered, then finally opened. How deep is it?
Can't be a prolapse. A prolapse is a protruding organ, usually through its own orifice.
Is he behaving loopy, like he's been bleeding at all? If he's acting normal, I'd observe it for a day and see if it is trying to heal. As you know, spiny eels don't medicate well. I'd even be hesitant about salt. Just melafix, pimafix and if it gets any worse, isolate and inspect for parasites. How's his poo?
If it's not parasites and it gets worse, it's probably bacterial, so Maracyn one and two (someone more knowledgeable could probably tell you which to use, to avoid over-medicating).
Sit and stare for awhile to make sure nothing pokes its head out of that hole.
Marycin-Two is meant to treat ulcers and other similar diseases.