Ok, I know I might be a few.... days late to the party and I don't know whom this will ever help, but here goes:
You can breed the Dragonfish in 1.6.4 by making a Salmon-Boneless Hybrid (I chose Salmon 'cause it ain't fussy like the others) or a Salmon-Enderfish Hybrid and breed them with a Enderfish or Boneless fish, respectively.
Eventually you'll get your hard earned reward !!!
It took me a WEEK! to get these PERFECT fish ('cause I'm a bit mental), but as you can see below, it was aaaaall worth it !