Fish Mouth Types and Their Uses

Superior Mouth

The superior mouth is oriented upwards, and the lower jaw is longer than the upper jaw. Usually, fish with this type of mouth feed at the surface. They lie in wait for prey to appear above them, then strike suddenly from below.

Many species of fish with a superior mouth feed largely on insects, however, some may feed on other fish that swim near the surface. Some species with a superior mouth have an elongated lower jaw that functions much like a scoop.

Archers, half-beaks, and hatchetfish are all examples of species of aquarium fish that have a superior mouth.

Terminal Mouth

Terminal mouths are located in the middle of the head and point forward. Both jaws are the same length. More fish have this mouth type than any other. Fish having a terminal mouth are generally mid-water feeders; however, they can feed at any location. These species of fish are often omnivores, eating anything that is available. They typically feed on the move, either grabbing bits of food that they pass or preying on other fish that they chase down.

It is quite common for fish with a terminal mouth to also have a protrusible mouth which allows them to thrust the jaw forward when grabbing food. Most fish that feed on other fish have terminal mouths, which are often hinged to allow them to accommodate the action of snatching and swallowing another fish. They may also possess specialized teeth, and in some cases an additional jaw. Moray eels are one type of species that have a pharyngeal jaw placed well back in their throat.

Most barbs, cichlids, gouramis, and tetras have terminal mouths.

Inferior Mouth

Also called a sub-terminal or ventral mouth, the inferior mouth is turned downward. The lower jaw is shorter than the upper jaw, and the jaw will often be protrusible. Fish with inferior mouths are usually bottom feeders and often possess barbels that assist in locating food particles.

Most members of the catfish family have inferior jaws, and many of them also have a sucker mouth as well. The diet of fish with inferior mouths includes algae, invertebrates (such as snails), as well as detritus, and any food that falls to the bottom.

Protrusible Mouth

A protrusible mouth allows a fish to extend its reach when attempting to snatch prey or food particles. This feature can be seen in all mouth types. Fish with a protrusible and hinged terminal mouth can create a vacuum when they open their mouths, thus sucking in their prey. Various species of fish may use a protrusible mouth while chasing down prey, while other species quietly lie in wait for prey to pass by, then rapidly extend the mouth to snatch the hapless victim. 

Some species use this feature to engage in non-feeding activities. For example, kissing gourami uses its protrusible mouth to defend territory against others of the same species. Although it may appear to be kissing the other gourami, it is a combative move to show its opponent who owns that space.

Other species, such as some members of the sucker catfish family, use a protrusible mouth to stay in place by attaching to a rock or other stationary object.

Sucker Mouth

Sucker mouths are a common feature in fish with inferior mouths. Catfish, such as the popular plecostomus (which literally translates to folded mouth), use a sucker mouth to rasp algae off driftwood or rocks. Some species use a sucker mouth to hold on to help them combat currents. By attaching itself to rock via its sucker mouth, it can stay where it wishes, even in a strong current.

These sucker mouths are also protrusible, which allows the fish to extend its reach when sifting through the substrate for food particles. Sucker mouths can also be used when defending territory or quarreling with another fish.

Elongated Mouth

A greatly elongated snout is another kind of mouth adaptation. This type of mouth allows the fish to poke into small crevices and holes to find food. They may also use this mouth to dig through the substrate to reach buried food treasures. Some surface-feeding fish also has an elongated mouth that allows them to scoop insects and food particles from the surface.

Freshwater species with elongated mouths include the halfbeaks, gars, and pencilfish. Saltwater species include the needlefish and fish in the ​​wrasse family.

Beak Mouth

The beak mouth is an interesting, but less common, mouth variation; it's also known as a rostrum. In this design, the mouth consists of two very hard pieces that are hinged and come together in a scissor-like fashion. This allows them to crush hard shells of invertebrates.

Pufferfish, both freshwater and saltwater species, and Saltwater parrotfish possess a beak-type mouth.