Hydrocynus vittatus is a big vicious predatory fish. Reputed to grow to over 600mm, although I've never seen one that big. Obviously, they need tank space comensurate with that kind of size though.
The biggest I've seen was probably about 450mm, and was caught with a rod and line at Popa Falls on the Caprivi Strip, Namibia, near the border with Angola. The guy that caught it fought with it for about 15 minutes before landing it. He "killed" it and bought it back to the camp site where he intended to eat it. Left by the tents, he went back to clean it to find it had jumped about 20m and was still going - a real tough cookie. Well dead, cleaned and cooked in foil over a fire, he said it made good eating.