Our largest tank isn't over stocked, never has been. All the fish have plenty of room to swim, lots of places to hide and they all get their fair share of food. Even if some of them do get too large, some of them are capable to go into a pond or get moved into a spare tank we have.
We both know Black Sharks can be aggressive, we've seen it in Red-Finned and Red-Tail Black Sharks, just wasn't sure what fish Black Sharks are more prone to attack. When it does go into our largest tank, it will still be too small to be of threat and so far, no other fish of the Labeo group has beaten the Red-Tail.
As for the advise Lupin gave, it is good and I happen to have alot of respect for him, as does Call Me Elmo.
We do not overstock our tanks, we do not just go out and buy what ever fish we want, stuff them into an overcrowded tank and expect them to be all good and happy like, just because we can. Our fish might be large and some of you might consider our tank too small just because it's in litres, but they're all happy how they are and very comfortable. There hasn't been a fish added to the 185gal/700L tank in roughly six months, if not more.
We've kept fish for four years, mightn't be as long as some of you have kept them for, but we research any fish we don't know about and then decide if we should really get them or not.
The fish are happy and healthy, the tank is free of disease and they get fresh veg and live food once a week.
If we can, we'll post a pic of our largest tank for you to have a look.