Most species of trout do have teeth, although depending on the species the teeth may be located in different places. For example, rainbow trout have a mouth that doesn’t go past the back of their eyes and teeth that are located along the roof of their mouth whereas other species of trout have teeth that are located along the base of their tongue (known as hyoid teeth).
When some trout are feeding they often engulf their prey. Sometimes they may follow their moving prey very slowly or their prey may be carried by the current in front of a trout which has happened to open its mouth. When this happens the trout’s gills flare up and the prey is sucked into the fish’s mouth. Here, the prey is then trapped by the tongue against the roof of the mouth as a means to “test” the food and it is then either swallowed or expelled. This process is done very quickly.
To engulf some prey would pose a deadly threat to these fish. For instance, the Freshwater crayfish is equipped with spikes and a spine that would catch in the throat of a trout and result in choking the fish. It is for this reason that the crayfish must be grasped and turned tail first toward the throat and then swallowed. This grasping feeding system is done by the trout using its small, sharp grasping teeth.