That reminds me of the snakehead fish. Its highly invasive and eats anything that fits in its mouth. Sometimes they kill something just to kill and not to eat. I saw this video clip on TV where some juvie snakeheads were being kept in a tank and a goldfish was tossed in. One of the snake heads bit the back end off of the fish and let the front have flounder about til it died.
Worst part about them is that they can breathe air and walk on land for a short while so they can effectively "hop" from waterway to waterway.