Fish Mouth Types and Their Uses

Location, Diet, and Feeding Method Vary by Mouth Type

Fish mouths come in a variety of sizes, shapes, and orientations, each of which tells a great deal about what and where the fish eats, as well as something about its behavior. Predatory fish generally have the largest mouths, often sporting large, sharp teeth. Some species have mouths that can be extended, allowing the fish to lengthen its effective reach to catch tasty morsels of food as it swims. Other species have specialized mouthparts that allow them to rasp algae off rocks and branches. And additional varieties have mouths with teeth in the back, nearly in their throat. These pharyngeal teeth assist in grasping and swallowing prey.

Most fish mouths fall into one of three general types:

  • Superior, or sometimes called supra-terminal, mouths are upturned.
  • Terminal mouths point straight forward and are the most common mouth type.
  • Inferior, or sub-terminal, mouths are turned downward. The inferior mouth type is often found in bottom-dwelling species, such as the catfish family.
  • 01 of 07

    Superior Mouth

    Deep sea Hatchet fish {Sternoptychidae} Atlantic ocean
    David Shale/Nature Picture Library/Getty Images

    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.

  • 02 of 07

    Terminal Mouth

    Giant Gourami in aquarium. Osphronemus goramy
    Diane Shapiro/Photolibrary/Getty Images

    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.

  • 03 of 07

    Inferior Mouth

    Close-up of catfish
    PhotoAlto/Jerome Gorin/Getty Images

    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 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.

  • 04 of 07

    Protrusible Mouth

    Gourami Fish kissing
    Jerry Yulsman/Photodisc/Getty Images

    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 actually create a vacuum when they open their mouths, thus sucking in their prey. Various species of fish may use a protrusible mouth on the fly 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, the kissing gourami uses its protrusible mouth to defend territory. Although it may appear to be kissing, it is actually a combative move to show its opponent who owns that space.

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

    Continue to 5 of 7 below.
  • 05 of 07

    Sucker Mouth

    Sailfin Pleco fish (Glytoperichthys gibbiceps) close up of mouth studio shot against white background
    Martin Harvey/Photolibrary/Getty Images

    Sucker mouths are a common feature in fish with inferior mouths. Catfish, such as the popular pleco, use a sucker mouth to rasp algae off driftwood or rocks. Some species use a sucker moth to help them combat currents. By attaching itself to a 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.

  • 06 of 07

    Elongated Mouth

    Dunkers Garfish
    Daniela Dirscherl/Waterframe/Getty Images

    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 have 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 the ​​wrasse family

  • 07 of 07

    Beak Mouth

    Hawaii, Maui, Spotted Porcupinefish (Diodon hystrix) swims along the ocean floor.
    Dave Fleetham/Design Pics/Getty Images

    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 varieties, possess a beak type mouth. Saltwater parrotfish, octopus, and squid also possess a beak.