I have 1 in a 150 @ 9" and I saw a photo of a wild one at almost 3'. I would like to try a group of 5+, thats why I said a pond or 500+ tank, they will need the room.
I finally got mine on some frozen krill and mysis. Only problem is it eats the entire cube(s) so I gotta put in extra for the other fish.
Might get rid of a few fish in my 150 to get 2 more in there.