large catfish in 55

That was a joke... ;) If you're serious about getting it you'd have to talk to someone with connections. I don' think you'd ever see one in any lfs's in the US...

How bout a chaca chaca. Its one of the ugliest things you'll ever see. But hey...

http://www.scotcat.com/factsheets/chaca_chaca.htm

or you could go with a shovelnose...tiger, gold, lima. As far as I know lima grow to be the smallest.
 
If you want something particularly nasty, you could try a mystus wyckii. (aka black devil catfish or crystal eye catfish)

or

an Asian Redtail Catfish
Hemibagrus wyckioides


Both are supposed to be increadibly aggressive. They might even kill the wolffish.
 
my favorite are the red tail, the tiger shovelnose there is one more but i'm not sure if you are ready for him and lucky for me i just located a local source to pretty much obtain any type of catfish that i am looking for now it's just a matter of obtaining the tanks to hold them, good thing i have a opened unfinished basement!!!!!!
 
AquariaCentral.com