Well, it would definitely do better in a 30g at the minimum, But still, im sure if there was enough swimming space, and the water quality was great, i think you could manage. But IMO
, i would never do it. I think that the tank minimums are there for a reason. If you did ever do this, i would suggest you keep a sharp eye on the thing, and at any detection of stress, i would bring it back, or if you had a bigger tank, put him in that one.