I had two Bala's (male/female)that would do a "dance" and go through the motions but never breed . I might have a vid somewhere, I'll check . A friend had goldfish breed in a small(350 gal) pond .
There was already a thread on breeding bala sharks. It has been done a couple of times, but it would be way too difficult for a regular aquarist, and would require a huge tank and huge balas. They do do "the bala dance", but they don't breed.