In fishes, a suckermouth is a ventrally-oriented (inferior) mouth adapted for grazing on algae and small organisms that grow on submerged objects.

All Loricariidae

Loricariidae

Loricariidae is the largest family of catfish , with almost 700 species and new species being described each year. Loricariids originate from fresh water habitats of Costa Rica, Panama, and tropical and subtropical South America. These fish are noted for the bony plates covering their bodies and...

 possess a suckermouth as do the cypriniform algae eater

Algae eater

Algae eater is a common name for many bottom-dwelling fish that feed on algae. Algae eaters are important for the fishkeeping hobby and many are commonly kept by hobbyists.Some of the common and most popular freshwater algae eaters include:...

s of the genus Gyrinocheilus

Gyrinocheilus

Gyrinocheilus, also Chinese algae eater or sucking loach, is the single genus in the family Gyrinocheilidae, a family of small Southeast Asian cypriniform fishes that live in fast-flowing freshwater mountain streams...

and other genera. The 'False Siamensis' (Epalzeorhynchus sp. or Garra taeniata) also has this feature. Three genera in Mochokidae

Mochokidae

The Mochokidae are a family of catfishes that are known as the squeakers and upside-down catfish. There are 10 genera and about 188 species of mochokids. All the mochokids are freshwater species originating from Africa....

, Atopochilus

Atopochilus

Atopochilus is a genus of catfishes of the family Mochokidae. It includes seven species.- Species :*Atopochilus chabanaudi*Atopochilus christyi*Atopochilus macrocephalus*Atopochilus mandevillei...

, Chiloglanis

Chiloglanis

Chiloglanis is a genus of catfishes of the family Mochokidae.-Description:Chiloglanis species have modified lips and barbels that form a suckermouth. They also have a naked body. Sexual dimorphism has been reported in Chiloglanis. The adult males of many of these species have elongate anal and...

, and Euchilichthys

Euchilichthys

Euchilichthys is a genus of catfishes of the family Mochokidae. It includes five species, E. astatodon, E. boulengeri, E. dybowskii, E. guentheri, and E. royauxi....

, also possess an oral sucker, formed by the lips and part of the barbels

Barbel (anatomy)

A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...

. The Loricariidae and members of the genus Gyrinocheilus are further adapted by having a special opening on the gill cover so that the fish can breathe without using its mouth.

Additionally many other fish of the order Cypriniformes

Cypriniformes

The Cypriniformes are an order of ray-finned fish, including the carps, minnows, loaches and relatives. This order contains 5-6 families, over 320 genera, and more than 3,250 species, with new species being described every few months or so, and new genera being recognized regularly...

 have developed a sucking ability to a lesser or greater extent:

• the Hillstream loach
  Hillstream loach
  The hillstream loaches or river loaches are a family, the Balitoridae, of small Eurasian fish. Many of the species are popular for aquaria. They have a number of similarities with the Cobitidae, their sibling family of "loaches", such as multiple barbels around the mouth...
  
  es (family Balitoridae) have modified fins to attach themselves to a surface and a ventrally located mouth.
• The sucker fish
  Catostomidae
  Catostomidae is the sucker family of the order Cypriniformes. There are 80 species in this family of freshwater fishes. Catostomidae are found in North America, east central China, and eastern Siberia...
  
   (family Catostomidae
  Catostomidae
  Catostomidae is the sucker family of the order Cypriniformes. There are 80 species in this family of freshwater fishes. Catostomidae are found in North America, east central China, and eastern Siberia...
  
  ) also have a modified mouth.

In general many benthic dwelling or feeding fish will have a suckermouth feature. Many of these fishes originate from fast-moving waters, where the sucker allows the fish to 'stick' itself down without too much difficulty.

Whilst all these fish have a limited sucking ability - they are able to swallow their food - it is not necessarily correct to assume that they can attach themselves to a submerged object by suction - though their behaviour may give that impression - the orientation of their fins and a flow of water can give sufficient downward force to temporarily attach themselves to an object.

See also

• Lamprey
  Lamprey
  Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...
  
   - Uses teeth to attach itself to a host. The sucker-like mouth is generally termed as an "oral disk."
• Remora
  Remora
  The remora , sometimes called a suckerfish or sharksucker, is an elongated, brown fish in the order Perciformes and family Echeneidae...
  
   - Sometimes known as 'suckerfish', remora use a modified dorsal fin to stick onto objects and other animals.
• Leech
  Leech
  Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...
  
  - The anterior portion (not the mouth) of this animal is modified to attach itself to a host.