When you say dragon fish, do you mean this one?
Dragon Gobies
I have a feeling he'd wind up being attacked and/or eaten by bigger fish. They aren't big enough to stand against the other tough fish you've got. They are good tankmates for fish like mollies...
Clown knife fish grow HUGE -
Clown Knifefish Caught in Florida
Do you think you really have room in the tank for that? here's another -
NAS - Species FactSheet
If you do decide to keep one, keep ONE. They're not friendly, as they mature.
How big was this tank again? You said you got another one now?
See thing is, when keeping aggressive species, you have to pick one or maybe two species, and keep a mostly empty tank otherwise. If you like the arowana, get rid of everyone else and keep it as the only fish in the tank. If you like pacus, keep only pacus. If you like parrots, keep parrots and maybe one other big cichlid and that's it. You just can't have everything. Besides, aggressive fish are territorial. They don't want neighbors.
and your parrot isn't pregnant. Parrots are hybrid cichlids and are generally sterile. They just have deformed backs and look all bulgy and bumpy.