Is this the one your talking about?Since you don't already have the Oscar, I would recommend a different fish for your 75 gallon. Oscar's get really bulky and up to 15", a little big for a 75.
I would recommend a tetracanthus. They are more aggressive than the Oscar, stay a bit smaller, and have very nice patterns. A big male would definitely fill up a 75 gallon with a catfish.
Nandopsis tetracanthus)