Mossberg 500 Chokes

I just purchased a new Mossberg #50588 12GA Shotgun (500A Series). It has the heat shield, 8 shot capaticy, pistol grip, etc..

I recently bought a new Hogue stock for the gun as pistol grip was fun for just blasting away, but it got my wrists sore pretty quick, and I could not aim very well at all. I need to get a choke for the shotgun so the spread is not so severe at long ranges. I looked at the barrel and it is not threaded. So how am I susposed to install a choke? Is this shotgun even able to accept chokes?

Any info would be appreciated.
Thanks,