For the arapaima vs gator gar discussion, I wanted to add a little fuel to the fire....
Alligator gar LOOK like monsters with all of those visible teeth. But after spending time in the water with both over the years, gators are kinda whimpy compared to an arapaima of the same size. It's been my experience that arapaima are much faster and more aggressive when compared to a gator gar - especially when feeding.
That being said, messing around with adults of either speices is not something I'd suggest for most people. Haha