I have 3 freshwater barracuda (Ctenelucius Hujeta) in my 55gal and they're awesome fish. They're always out in the open, never hiding, and when they eat live food they strike so fast it's a blur. The only thing is that they're all silver so they don't add any color to the tank if that's what you're looking for. My 55 gal is gettting a little tight for them now that they've grown a bit but I think a 75 gal with three of them would probably work out great.