What is do fish yawn?

Fish do not actually yawn in the same way that humans do. However, fish opening and closing their mouths can sometimes be mistaken for yawning. This behavior is often a way for fish to increase the oxygen flow in their gills, or to adjust their position in the water. It can also be a sign of stress or illness in some species. Overall, fish do not yawn in the way that mammals do, but their mouth movements serve important functions in their underwater environment.