We used to call those riot guns and they were cylinder bore (no choke constriction). That photo does show something at the muzzle whete the barrel is larger. If you unload the gun and look into the muzzle, you may or may not see little notches at the end of the bore, there would be 4 equi-distant. Those are lugs for a choke wrench to unscrew. Most all waterfowl and sporting clays shotguns use choke tubes, and for steel shot you use one step less constriction than for lead.
If you dont see the 4 notches, you have cylinder bore only. Which is good for buckshot and slugs.
Edit: twist adjustable chokes do exist, but are uncommon