it means green terror but sometimes they hit 12 inch... what about a smaller piranha if they are legal in your state? could do some rare convicts like hrp or pinks, could do a dwarf flowerhorn, 5 star general aka hemichromis elongatus or frempongi, red jewel cichlid breeding groups are impressive if you get some really red ones. what about a leopard ctenopoma or nandus nandus both really cool mini predators. erm thats all i can suggest for active fish, obv there are lots of catfish if thats your thing, might get away with a fresh water barracuda they are cool. green spotted puffers are also awesome but you will need to add salt once it grows to make it brackish, easy to do compared to marine so no biggie.