Dang that sucks Punkymom,
You've a hard choice to make...... I don't envy you.
If I was you I'd set that 55 gal
up real quick and quarantine him, no need to wory about cycling, just do daily PWC
"IF" I really wanted to save that Oscar (and I would), I'd break out a small needle and 100% cotton thread and put his lip back in place with just one or two stitches, then light salt with Mela and Pimafix.
Net'em out, wrap'em in a sopping wet towel and proceed quickly, just make quick simple knots.
No sign of aggression at all? From anyone? Hmmmmmm...
The larger oscar could've tried lip-locking him, got too excited and ripped it off, especially if he's alot bigger.
Jack Dempsies are very controversial as tankmates for Oscars, they are much more aggressive than typical Oscars and if he was trying to stake out territory?........
Just how big is the injured Oscar and how big are his tankmates?