Hello
No offense, but it sounds like you have done no research, and have no knowledge about this fish, which isn't always a good way to start, and with this in mind, I must ask, does it have tankmates? If so, you won't, very soon. I also hope you have a mega tank for it as he isn't done growing yet.
Now down to business. They are called lungfish for a reason, they .. have lungs, and they breathe atmospheric air. This is why he is gulping air.
As for the "pectoral fin" - Usually they do, sometimes they don't. I have extensive experience, and am here to help if you have more questions. Jude