Do brown trout sometimes gulp air to assist spawning?

I was kick boat fishing at waits lake yesterday and there were lots of brown trout rising and milling around the surface. I could not see any evidence of a hatch not to say that there was not one happening. I caught several trout and when I was releasing them they would burp. I was reading an article about hatcheries using air to expell spawn in steelhead without killing them I'm wondering if the brown trout may have figured out how to do this on their own.
Yeah I don't know could have been emergers I guess. It was really odd I was using a net and handling the fish gently. I have never caught brown trout before maybe it's normal for them to feed heavily during the spawn. I also didn't expect to find them far from shore in deep water. Not like any feeding behavior I've ever seen. From the reading I've been doing trout do gulp air for their swim bladders. I suppose water boatmen or back swimmers or even fry could have been the food that they were after too. In any case it was a lot of fun. Maybe they we're eating so many water boatmen that they accumulated gas in their digestive track.
This is a little known fact, but while many people think rising fish are taking something off the fact they are just coming up to breathe. else do you think they get air.....and sometimes a belch is necessary.