Say “ahhh” You can tell a lot about how a fish makes a living by looking at its mouth. The mouths of sturgeon, carp, and suckers point downward; these fish are bottom feeders. Killifish have an underbite and often feed at the surface. Anchovies have a pronounced overbite, and can open their mouths wide to filter plankton. Some fish have sharp teeth that can take bites out of their prey (bluefish) while others simply swallow their meals whole (striped bass). A seahorse’s small, tube-like mouth is perfect for eating tiny invertebrates.