Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a variety of different animals, most notably Darwin's frog

Darwin's Frog

Darwin's Frog is a frog native to the forest streams of Argentina and Chile. It was first described by French Zoologist André Marie Constant Duméril and his assistant Gabriel Bibron, and is named after Charles Darwin who discovered it in Chile during his world voyage on the HMS Beagle.The most...

, fishes are by far the most diverse mouthbrooders. Mouthbrooding has evolved independently in several different families of fish.

Mouthbrooding behaviour

Paternal mouthbrooders are species where the male looks after the eggs. Paternal mouthbrooders include the arowana

Arowana

Arowanas are freshwater bony fish of the family Osteoglossidae, also known as bonytongues. In this family of fishes, the head is bony and the elongate body is covered by large, heavy scales, with a mosaic pattern of canals. The dorsal and the anal fins have soft rays and are long based, while the...

, the mouthbrooding betta Betta pugnax, and sea catfish such as Ariopsis felis. Among cichlids, paternal mouthbrooding is relatively rare, but is found among some of the tilapiines

Tilapia

Tilapia , is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the...

, most notably the black-chin tilapia Sarotherodon melanotheron.

In the case of the maternal mouthbrooders, the female takes the eggs. Maternal mouthbrooders are found among both African and South American cichlids. African examples are the haplochromines, such as the mbuna

Mbuna

Mbuna is the common name for a large group of African cichlids from Lake Malawi. The name mbuna means "rockfish" in the language of the Tonga people of Malawi...

 and the dwarf mouthbrooders Pseudocrenilabrus multicolor, and some of the tilapiines, such as Oreochromis mossambicus

Oreochromis mossambicus

The Mozambique tilapia, Oreochromis mossambicus, is a tilapiine cichlid fish native to southern Africa. It is a popular fish for aquaculture...

and Oreochromis niloticus

Oreochromis niloticus

The Nile Tilapia, Oreochromis niloticus is a relatively large cichlid fish, which is native to Africa from Egypt south to East and Central Africa, and as far west as Gambia. It is also native to Israel, and numerous introduced populations exist outside its natural range.It is also commercially...

. The South American maternal mouthbrooders are all members of the Geophaginae

Geophaginae

Geophaginae is a subfamily of cichlid fishes from South America, where they are found as far west as the Andes and as far south as northern Argentina...

 subfamily (commonly known as "eartheaters" on account of their substrate-sifting feeding mode) such as Gymnogeophagus balzanii and Geophagus steindachneri

Geophagus steindachneri

Redhump eartheater is a South American Eartheater Cichlid of the genus Geophagus. It is sometimes referred to by one of two invalid junior synonyms, Geophagus hondae or Geophagus magdalena.-Location:...

.

Biparental mouthbrooding occurs where both parents take some of the eggs. This is relatively rare, but is found among the cichlid genera Asprotilapia and Xenotilapia, and a single catfish, Phyllonemus typus.

Typically, after courtship, the male fertilises the eggs and then collects them in his mouth, holding onto them until they hatch. During this time he cannot feed. Among the maternal mouthbrooding cichlids, it is quite common (e.g., among the mbuna) for the male to fertilise the eggs only once they are in the female's mouth. Some cichlids are able to feed while mouthbrooding the eggs, but invariably they feed less often than they would otherwise do, and after mouthbrooding one batch of eggs, all mouthbrooding fish will be underweight and requiring a period of time to feed and make good the depletion of their energy reserves.

In all cases, the eggs are protected until they hatch and the fry become free swimming. Only in some cases does the parent extend protection to mobile juveniles. Among the cichlids and arowanas, extension of brood care to the fry is common, and they have behavioural cues to tell fry swimming and feeding away from the parent that danger is approaching and that they should return to their parent's mouth. By caring for their offspring in this way, mouthbrooding fish are able to produce smaller numbers of offspring with a higher chance of survival than species that offer no broodcare.

Aquaculture

Some commercially important fish are mouthbrooders, most notably among the tilapiines and arowana

Arowana

Arowanas are freshwater bony fish of the family Osteoglossidae, also known as bonytongues. In this family of fishes, the head is bony and the elongate body is covered by large, heavy scales, with a mosaic pattern of canals. The dorsal and the anal fins have soft rays and are long based, while the...

s. Fry harvesting, getting the brooding fish to open its mouth and release the fry, is important if the fry are to be reared artificially. In the case of endangered species, such as Asian arowana

Asian arowana

The Asian arowana comprises several varieties of freshwater fish in the genus Scleropages. Some sources differentiate these varieties into multiple species, while others consider the different strains to belong to a single species, Scleropages formosus...

, harvesting may be supervised by an official who will certify that the fish farm is a genuine producer of captive-bred fish.

Brood parasites

Some fish have evolved to exploit the mouthbrooding behaviour of other species. Synodontis multipunctatus

Synodontis multipunctatus

Synodontis multipunctata, also known as the cuckoo catfish, cuckoo squeaker, or multipunk, is a small catfish from Lake Tanganyika, one of the lakes in the Great Rift Valley system in Africa...

, also known as the cuckoo catfish, combines mouthbrooding with the behavior of a brood parasite

Brood parasite

Brood parasites are organisms that use the strategy of brood parasitism, a kind of kleptoparasitism found among birds, fish or insects, involving the manipulation and use of host individuals either of the same or different species to raise the young of the brood-parasite...

: it will eat the host mouthbrooder's eggs, while spawning and simultaneously laying and fertilizing its own eggs. The mouthbrooder (typically a cichlid) will incubate the cuckoo catfish young, the catfish eggs hatch earlier than the cichlid's eggs, and eat the as-yet unhatched cichlid eggs before being set free.

Families of mouthbrooding fish

Families of fish known to include mouthbrooding species include:

• Apogonidae
  Apogonidae
  Cardinalfishes are a family, Apogonidae, of ray-finned fishes. They are found in the Atlantic, Indian, and Pacific oceans, they are chiefly marine, but some species are found in brackish water...
  
   (cardinalfish): All paternal mouthbrooders
• Ariidae
  Ariidae
  The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
  
   (sea catfish): All paternal mouthbrooders
• Bagridae
  Bagridae
  Bagridae are a family of catfish that originate from Africa and Asia from Japan to Borneo. These fish are commonly known as naked catfishes or bagrid catfishes.Large Bagrids are important as food fish. Some species are kept as aquarium fishes....
  
   (Bagrid catfish): One species of biparental mouthbrooders
• Cichlidae (cichlids): Numerous species are mouthbrooders, of these most are maternal mouthbrooders. Occasional paternal mouthbrooding e.g. Sarotherodon melanotheron, infrequently biparental mouthbrooders e.g. eretmodine cichlids.
• Luciocephalidae
  Luciocephalidae
  Luciocephalus pulcher is an endangered species of fish. As the prey is swallowed, the extended jaw is folded back into place. The fish is restricted locally to a few forest streams....
  
   (pikeheads): All paternal mouthbrooders
• Cyclopteridae (lumpfish): A few species are paternal mouthbrooders
• Opistognathidae
  Opistognathidae
  Opistognathidae , commonly referred to as jawfishes, are classified within Order Perciformes, Suborder Percoidei. They are found throughout shallow reef areas of the Atlantic and Pacific Oceans, and the Gulf of Mexico.Physically similar to blennies, jawfish are generally smaller-sized fish with an...
  
   (jawfishes): All paternal mouthbrooders
• Osphronemidae (gouramis): A few species are paternal mouthbrooders
• Osteoglossidae (arowanas): All paternal mouthbrooders