I had an Oscar for over 10 years. He got to be about 1ft in lenght and porbably at least 2-2.5 lbs. Those jokers are thick old brutes.

If you think Oscar are mean, you ought to try snakeheads, Mayan's (Red Devils), or green terrors. Mayans and Green terrors, both cichlids, are the two nastiest fish I've ever kept. Mean little buggers that'll have an entire tank full of mean fish cowering in a corner of the tank. Never had a snakehead, though I saw many pass through the pet stores I worked at. The managuense is pretty brutal too. They've even got small canine teeth. I forget what they call them in Florida, but they've populated too. All are meaner than the meanest Oscar I ever had.
My Oscars weren't as much biters as they were smashers. They'd pound and beat any other fish against the side of the tank until their opponant was dead. They're pretty smart and easily trainable. I had my last one trained to jump half out of the water to snatch a goldfish from my hand. My redneck version of Sea World. He'd wag his tail like a dog when you walked by his tank, hoping you'd throw him a scrap. By far my favorite fish to keep.