actually, 50, i heard, IS possible, but only with very very frequent water changes, and it should only be attempted by skilled proffesionals. I read in a magazine some guy, mike wickham, stuff 50 cardinal tetras, 25 kuhli loaches, and another half dozen assorted fish in a twenty gallon.
four years later, all were perfectly fine. it did note, however, *Mike wickham is an extremely skilled pro and retailer and we do not recommend stocking tanks this highly*