That shark looking thing is probably a member of the Labeos, which include redtail "sharks" and black sharks and so on. They are really Cyprinids and related to minnows and carps. They probably will leave the livebearers alone in the 29. But they are very territorial towards similar fish, so just keep him. Give him a chemical free flowerpot on its side or with a piece missing. He may make himself at home in such a place. (Or not, they just will not read the books!)

Usually blue gouramis are ok, but they do get pretty big and can be a little pushy around guppies. (And, as you surely guessed, they just love baby guppies.) You could get even, spawn the blue gouramis or Trichogaster trichopterus. The couple 100 TINY baby gouramis would be just loved by the guppies. ;)