until about 6 inches, but the 2 6 inchers I had were unhappy in a 12" wide tank. THey are not huge fish but they need room.
They were very nervous when kept in a small tank, didn't eat that much, didn't swim around much.
When I moved them to a 150 they were completely different fish. Active, hungry, not nervous at all.
They are very fast fish, they need a lot of room.