Nice jack, but do be careful... Those things don't just bump and nip like most aquarium fish, they can take chunks out. I've never kept one with any other fish for fear of it simply decimating everyone in the tank.
Don't worry about keeping it in full fresh, they'll grow to their full size potential in freshwater impoundments here in Australia. The only thing is that they won't breed in it. Not really an issue for you.
They're highly intelligent fish with a hell of a personality, so do enjoy. Mine also used to be extremely dextrous when it came to using its teeth. When it came across a live fish too big to swallow in one shot, it'd grab it across the shoulders with its canines and then spin it around to swallow it after it stopped struggling. They also live quite a long time, so you should have a pet for quite a while, hopefully.