I used to keep Snakeheads. They are the raptors of the fish world.
I had two that were about a foot and a half long- and I would feed them about 4 DOZEN large minnows at a time. They would fly through the tank, slashing and scarfing in a cloud of scales that made the tank look like one of those little things you turn upside-down to look like it is snowing.
SCARY fish.
One ate the other, then he ate himself.
I am not kidding.
He got long enough that he saw his own tail when turning around in the tank, he managed to get ahold of it and shredded it to pieces and then died from the infection.
He had once survived a full day OUTSIDE the tank when he was about a foot long, covered in carpet fuzz after an apparent suicide attempt (or perhaps he was after the cat). I put him back in the tank (carefully!) and he immediately ate a minnow, even with fuzz encrusting him!
They have a lung, and can survive out of water for a short time- and live in the nastiest water with no problem.
I think they will be the last animal alive on earth, at least until they eat themselves.