Lungfish
Lungfish
African And South American Lungfish
Bony fish are divided into two major groups: rayfinned and lobe-finned fish. The lobe-finned fish are further subdivided into two orders: the lungfish, or Dipnoi, and the lobe-finned fish, or Crossopterygii. Although crossopterygian fish are the group that is thought to be close to the ancestors of the land vertebrates, lungfish also display many of these characteristics. In the early stages of development, lungfish resemble a frog like amphibian, providing evidence of close association with land forms. However, despite the critical presence of lungs, other features, such as the fusion of the teeth into bony plates, and the solid union of the jaw with the skull (which does not occur in early amphibians) make such a direct link with amphibians unlikely.
Lungfish have changed little over the past 400 million years, and so might be regarded as living fossils. Three living genera of lungfish are recognized today: Neoceratodus in the Mary and Burnett Rivers of southeast Queensland, Australia; Lepidosiren in the Parana´ and Amazon River systems of South America; and Protopterus in sub-Saharan Africa ranging from the Nile in Sudan southward to Senegal in West Africa to the Zambezi River system in southern Africa.
African And South American Lungfish
African and South American lungfish can easily be distinguished by their appearance, but they also share many similar characters. In fact, some zoogeographers have used the close link between these two lungfishes to provide supporting evidence of an early land connection between South America and Africa. Lungfish are eel-like, with a long, narrow, tubular body and small scales well embedded in the body of the fish. Both the pectoral and pelvic fins of lungfish are elongated and somewhat threadlike. In Lepidosiren the pelvic fins are modified to function as accessory respiratory organs, with feathery margins receiving an increased blood supply—they function like a pair of gills. The primary respiratory organs of Lepidosiren are a pair of lungs with a single opening on the floor of the mouth. These lungs have furrowed walls and receive a full supply of blood. The young of both species have long, feathery, external gills located behind the head which are lost in the South American lungfish at 1.6 in (4 cm) in length, and at 5.9 in (15 cm) in the African lungfish. Both South American and African species reach a length of 3.3-6.6 ft (1-2 m).
When lungfish are in water, they breathe air by rising to the surface and sticking the tips of their nasal opening and mouth out of the water, so as to empty their lungs and take in fresh air. In most fish, the nostrils are pouchlike. However, the jaw construction of the lungfish is modified so that there is an opening from the nasal sac to the inside of the mouth. This internal nostril allows the fish to breathe air at the surface without opening its mouth and swallowing water. Because lungfish breathe by lungs instead of gills, air is essential for their survival; if lungfish are forced to remain underwater, they will drown.
Lungfish live in areas with temporary water bodies, such as shallow swamps, the stagnant
backwaters of river courses, and small creeks. These areas are prone to dry out during the dry season. As the water recedes, lungfish burrow into the mud, forming a hollow at the end of the tunnel. The lungfish curl up, tail over head, keeping the nostrils clear of dust and dirt, and secrete a mucous cocoon. Air enters the burrow through a small hole at the top of the dried mud. Lungfish are able to remain in a period of aestivation (dormancy) for the duration of the dry season and have been known to survive as long as four years, although usually a year is all that is necessary. During the aestivation period, lungfish experience a drop in their metabolism and obtain adequate nutrition from the stored fat in their tail.
Breeding takes place in the wet season following the reestablishment of the water bodies they inhabit. The male of the South American lungfish guards the eggs during the period of incubation and hatching.
Australian Lungfish
The Australian lungfish is the most primitive of the modern lungfish and has changed little over the past several million years. The body is long, slim, and has very large scales, and broad, flipper-like pectoral and pelvic fins. A dorsal fin is lacking. The tail of the Australian lungfish is most unusual, and consists of a rim of fin material around the rear end of the body.
The Australian lungfish has four big teeth which look as though they have grown together into fan-shaped crushing plates somewhat resembling a rooster’s comb. Prior to the discovery of the first Australian lungfish around 1869, large teeth of this type had only been found in the fossil record. These teeth are an efficient adaptation for shearing and crushing. Neoceratodus is a carnivorous fish, feeding on small mollusks, crustaceans, and other aquatic invertebrates. Its paddle like fins are unsuitable for crawling; however, the lungfish can stand on these appendages, using them like legs underwater. The Australian lungfish has a single lung located above the gut which is slightly less developed than the lungs of the African and South American species.
Also known as the Burnett salmon, the Australian lungfish inhabits rivers that generally remain as permanent watercourses and do not dry out periodically, although the dissolved oxygen content does vary considerably. This lungfish uses its gills more than the other two types of lungfishes and, in well-oxygenated water, does not need to return to the surface for air. However, this species is less tolerant of poor water quality and can efficiently use its lung to breathe fresh air from the atmosphere when necessary. The Australian lungfish does not aestivate in a cocoon of mud like the African lungfish. Instead the Australian lungfish spawns in shallow water in the fall, laying its eggs on water plants. The native Australians call this lungfish dyelleh.
KEY TERMS
Aestivation —A state of dormancy or torpor during the dry season, a period of drought.
Dorsal —Of, toward, on, in, or near the back.
Pectoral —Pertaining to the breast or chest.
Pelvic —Of, in, near, or pertaining to the pelvis; in fish, either of a pair of lateral hind fins; also called the ventral fin.
Zoogeographer —A person making the biological study of the geographical distribution of animals.
Resources
BOOKS
Bemis, W.E., W.W. Burggren, and N.E. Kemp. The Biology and Evolution of Lungfishes. New York: Alan R. Liss, 1987.
Graham, J.B. Air-breathing Fishes. San Diego: Academic Press, 1997.
Nelson, Joseph S. Fishes of the World. 4th ed. New York: John Wiley & Sons, 2006.
Whiteman, Kate. World Encyclopedia of Fish and Shellfish. New York: Lorenz Books, 2000.
Betsy A. Leonard
Lungfish
Lungfish
Bony fish are divided into two major groups: rayfinned and fleshy-finned fish . The fleshy-finned fish are further subdivided into two orders: the lungfish, or Dipnoi, and the lobe-finned fish, or Crossopterygii. Although crossopterygian fish are the group that is thought to be close to the ancestors of the land vertebrates , lungfish also display many of these characteristics. In the early stages of development, lungfish resemble a frog-like amphibian, providing evidence of close association with land forms. However, despite the critical presence of lungs, other features, such as the fusion of the teeth into bony plates, and the solid union of the jaw with the skull (which does not occur in early amphibians ) make such a direct link with amphibians unlikely.
Lungfish have changed little over the past 400 million years, and so might be regarded as living fossils. Three living genera of lungfish are recognized today: Neoceratodus in the Mary and Burnett Rivers of southeast Queensland, Australia ; Lepidosiren in the ParanNBSP and Amazon River systems of South America ; and Protopterus in sub-Saharan Africa ranging from the Nile in Sudan southward to Senegal in West Africa to the Zambezi River system in southern Africa.
African and South American lungfish
African and South American lungfish can easily be distinguished by their appearance, but they also share many similar characters. In fact, some zoogeographers have used the close link between these two lungfishes to provide supporting evidence of an early land connection between South America and Africa. Lungfish are eel-like, with a long, narrow, tubular body and small scales well embedded in the body of the fish. Both the pectoral and pelvic fins of lungfish are elongated and somewhat threadlike. In Lepidosiren the pelvic fins are modified to function as accessory respiratory organs, with feathery margins receiving an increased blood supply—they function like a pair of gills. The primary respiratory organs of Lepidosiren are a pair of lungs with a single opening on the floor of the mouth. These lungs have furrowed walls and receive a full supply of blood. The young of both species have long, feathery, external gills located behind the head which are lost in the South American lungfish at 1.6 in (4 cm) in length, and at 5.9 in (15 cm) in the African lungfish. Both South American and African species reach a length of 3.3-6.6 ft (1-2 m).
When lungfish are in water , they breathe air by rising to the surface and sticking the tips of their nasal opening and mouth out of the water, so as to empty their lungs and take in fresh air. In most fish, the nostrils are pouchlike. However, the jaw construction of the lungfish is modified so that there is an opening from the nasal sac to the inside of the mouth. This internal nostril allows the fish to breathe air at the surface without opening its mouth and swallowing water. Because lungfish breathe by lungs instead of gills, air is essential for their survival; if lungfish are forced to remain underwater, they will drown.
Lungfish live in areas with temporary water bodies, such as shallow swamps, the stagnant backwaters of river courses, and small creeks. These areas are prone to dry out during the dry season. As the water recedes, lungfish burrow into the mud, forming a hollow at the end of the tunnel. The lungfish curl up, tail over head, keeping the nostrils clear of dust and dirt, and secrete a mucous cocoon. Air enters the burrow through a small hole at the top of the dried mud. Lungfish are able to remain in a period of aestivation (dormancy) for the duration of the dry season and have been known to survive as long as four years, although usually a year is all that is necessary. During the aestivation period, lungfish experience a drop in their metabolism and obtain adequate nutrition from the stored fat in their tail. Breeding takes place in the wet season following the reestablishment of the water bodies they inhabit. The male of the South American lungfish guards the eggs during the period of incubation and hatching.
Australian lungfish
The Australian lungfish is the most primitive of the modern lungfish and has changed little over the past several million years. The body is long, slim, and has very large scales, and broad, flipper-like pectoral and pelvic fins. A dorsal fin is lacking. The tail of the Australian lungfish is most unusual, and consists of a rim of fin material around the rear end of the body.
The Australian lungfish has four big teeth which look as though they have grown together into fan-shaped crushing plates somewhat resembling a rooster's comb. Prior to the discovery of the first Australian lungfish around 1869, large teeth of this type had only been found in the fossil record. These teeth are an efficient adaptation for shearing and crushing. Neoceratodus is a carnivorous fish, feeding on small mollusks , crustaceans, and other aquatic invertebrates . Its paddle-like fins are unsuitable for crawling; however, the lungfish can stand on these appendages, using them like legs underwater. The Australian lungfish has a single lung located above the gut which is slightly less developed than the lungs of the African and South American species.
Also known as the Burnett salmon , the Australian lungfish inhabits rivers that generally remain as permanent watercourses and do not dry out periodically, although the dissolved oxygen content does vary considerably. This lungfish uses its gills more than the other two types of lungfishes and, in well-oxygenated water, does not need to return to the surface for air. However, this species is less tolerant of poor water quality and can efficiently use its lung to breathe fresh air from the atmosphere when necessary. The Australian lungfish does not aestivate in a cocoon of mud like the African lungfish. Instead the Australian lungfish spawns in shallow water in the fall, laying its eggs on water plants. The native Australians call this lungfish dyelleh.
Resources
books
Whiteman, Kate. World Encyclopedia of Fish & Shellfish. New York: Lorenz Books, 2000.
Betsy A. Leonard
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Aestivation
—A state of dormancy or torpor during the dry season, a period of drought.
- Dorsal
—Of, toward, on, in, or near the back.
- Pectoral
—Pertaining to the breast or chest.
- Pelvic
—Of, in, near, or pertaining to the pelvis; in fish, either of a pair of lateral hind fins; also called the ventral fin.
- Zoogeographer
—A person making the biological study of the geographical distribution of animals.
Dipnoi
Dipneusti
Dipnoi
lungfish
lung·fish / ˈləngˌfish/ • n. (pl. same or -fishes) an elongated freshwater fish (families Ceratodontidae, Lepidosirenidae, and Protopteridae) with one or two sacs that function as lungs, enabling it to breathe air. It can estivate in mud for long periods to survive drought.