If that's him in your avatar, that's a beautiful fish, ermizam.
You're right in believing that a 50 breeder is big enough for now (36x18x18), but keep a close eye on him. At some point you will have to move to at least a 120, (48x24x24), better still a 150 (60x24x24), or best of all, a 180 (72x24x24). It's very important for this size fish that the tank be at least 2 feet top to bottom and back to front. They need to have a comfortable amount of water under them and they need to have at least their own body length in which to turn around.
If you can't do that, well, at least you are in its native range, so you could release it into the wild or set up an outdoor pond.