I used to keep big tanks too .
I love, love love fish tanks. I cant live with out one in my presence. ..
My suggestion.. if you are looking for an aggressive, live fish eating type 'fish' and not worried about it LOOKING like a shark?
You need a 100 gallon tank to house one well enough.
Fresh water, very aggressive, WILL bite you if it can...... Oscars eat live fish, raw meat.. and are pretty mean looking. Though.. look nothing like a shark.
You can find them in solid colors, patterns, and albino.
very easy to keep. In fact thrive on a semi 'dirty' tank. Meaning.. you dont have to keep it spotless, vacuum it once a week or do a water change more then once a month.. less often if you have a good filter.