mmmmmm a 100g, where do we start?
Wow, lets see any birchir is a suitable tank mate, although i would consider bigger is better here, try:
P.Ornatapinnins
P.Palmas Palmas
P.Enderlichi
Those are the daddy birchirs!
Catfish try as ytou said S.lima, but at the moment im in love with the marmaratus catfish (peruno?) I always recommend plecos with oscars, but the choice out there is humongus, and its all down to personal taste on these guys, but remember these guys are lean mean pooping machines, and they sometimes give birchirs and other slow catfish a hard time by sucking on them!
Hujeta garfish are not my first choice in dealing with oscars as they are somewhat small, try any of these guys, if u want more info ask tho
Tropical Gar, atractosteus tropicus
Spotted Gar, lepisosteus oculatus
also my local lfs has some large 7-9" needle fish at £10 each, i'd snap them up but just forked out on an adonis plec!
I have seen oscars kept with uarus before but im not entirely sure this is a safe stocking choice though.......
maybe look into ciger sharks?#
If you can find one a large spiny eel would be ideal such as a tyre track eel, but be wary as most cats would make a spaghetti snack out of it if he was too small!