Lungfish

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This article is about the fish. For the band, see Lungfish (band).

Lungfish
Temporal range: Early Devonian–Recent
Queensland lungfish
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Sarcopterygii
Clade: Rhipidistia
Clade: Dipnomorpha
Ahlberg, 1991
Class: Dipnoi
J. P. Müller, 1844
Living families

Fossil taxa, see text

Lungfish are freshwater vertebrates belonging to the class Dipnoi.[1] Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Lungfish represent the closest living relatives of the tetrapods (which includes living amphibians, reptiles, birds and mammals). The mouths of lungfish typically bear tooth plates, which are used to crush hard shelled organisms.

Today there are only six known species of lungfish, living in Africa, South America, and Australia, though they were formerly globally distributed. The fossil record of the group extends into the Early Devonian, over 410 million years ago. The earliest known members of the group were marine, while almost all post-Carboniferous representatives inhabit freshwater environments.[2]

Etymology

Modern Latin from the Greek δίπνοος (dipnoos) with two breathing structures, from δι- twice and πνοή breathing, breath.

Anatomy and morphology

All lungfish demonstrate an uninterrupted cartilaginous

tetrapods. During the breeding season, the South American lungfish develops a pair of feathery appendages that are actually highly modified pelvic fins. These fins are thought to improve gas exchange around the fish's eggs in its nest.[3]

Through convergent evolution, lungfishes have evolved internal nostrils similar to the tetrapods' choana,[4] and a brain with certain similarities to the Lissamphibian brain (except for the Queensland lungfish, which branched off in its own direction about 277 million years ago and has a brain resembling that of the Latimeria).[5]

The dentition of lungfish is different from that of any other

lepidosireniformes
, these ridges have been modified to form occluding blades.

The modern lungfishes have a number of larval features, which suggest

paedomorphosis. They also demonstrate the largest genome
among the vertebrates.

Modern lungfish all have an elongate body with fleshy, paired

anal
fins of most fishes.

Lungs

Lateral view of lungs of a dissected spotted lungfish (Protopterus dolloi)

Lungfish have a highly specialized

gas bladders,[6] these bladders are usually simple sacs, devoid of complex internal structure. In contrast, the lungs of lungfish are subdivided into numerous smaller air sacs, maximizing the surface area available for gas exchange
.

Most extant lungfish species have two lungs, with the exception of the Australian lungfish, which has only one. The lungs of lungfish are homologous to the lungs of tetrapods. As in tetrapods and bichirs, the lungs extend from the ventral surface of the esophagus and gut.[7][8]

Perfusion of water

Of extant lungfish, only the

conus arteriosus is open, the bypass arterioles of the third and fourth gill arches (which do not actually have gills) are shut, the second, fifth and sixth gill arch arterioles are open, the ductus arteriosus
branching off the sixth arteriole is open, and the pulmonary arteries are closed. As the water passes through the gills, the lungfish uses a buccal pump. Flow through the mouth and gills is unidirectional. Blood flow through the secondary lamellae is countercurrent to the water, maintaining a more constant concentration gradient.

Perfusion of air

When breathing air, the spiral valve of the conus arteriosus closes (minimizing the mixing of oxygenated and deoxygenated blood), the third and fourth gill arches open, the second and fifth gill arches close (minimizing the possible loss of the oxygen obtained in the lungs through the gills), the sixth arteriole's ductus arteriosus is closed, and the pulmonary arteries open. Importantly, during air breathing, the sixth gill is still used in respiration; deoxygenated blood loses some of its carbon dioxide as it passes through the gill before reaching the lung. This is because carbon dioxide is more soluble in water. Air flow through the mouth is tidal, and through the lungs it is bidirectional and observes "uniform pool" diffusion of oxygen.

Ecology and life history

Lungfish are

intestinal spiral valve rather than a true stomach.[9]

African and South American lungfish are capable of surviving seasonal drying out of their habitats by burrowing into mud and

estivating throughout the dry season. Changes in physiology allow it to slow its metabolism to as little as one sixtieth of the normal metabolic rate, and protein waste is converted from ammonia to less-toxic urea
(normally, lungfish excrete nitrogenous waste as ammonia directly into the water).

Burrowing is seen in at least one group of fossil lungfish, the Gnathorhizidae.

Lungfish can be extremely long-lived. A

Sydney Aquarium;[11] at about 95 years old,[10] it was euthanized following a decline in health consistent with old age.[11]

As of 2022, the oldest lungfish, and probably the oldest aquarium fish in the world is "Methuselah", an Australian lungfish 4 feet (1.2 m) long and weighing around 40 pounds (18 kg). Methuselah is believed to be female, unlike its namesake, and is estimated to be over 90 years old.[10]

Evolution

About 420 million years ago, during the Devonian, the last common ancestor of both lungfish and the tetrapods split into two separate evolutionary lineages, with the ancestor of the extant coelacanths diverging a little earlier from a sarcopterygian progenitor.[12] Youngolepis and Diabolepis, dating to 419–417 million years ago, during Early Devonian (Lochkovian), are the currently oldest known lungfish, and show that the lungfishes had adapted to a diet including hard-shelled prey (durophagy) very early in their evolution.[13] The earliest lungfish were marine. Almost all post-Carboniferous lungfish inhabit or inhabited freshwater environments. There were likely at least two transitions amongst lungfish from marine to freshwater habitats. The last common ancestor of all living lungfish likely lived sometime between the Late Carboniferous[2] and the Jurassic.[14] Lungfish remained present in the northern Laurasian landmasses into the Cretaceous period.[15]

Extant lungfish

Extant lungfishes
Family Genus Species
Neoceratodontidae Neoceratodus
Queensland lungfish
Lepidosirenidae
 Lepidosiren South American lungfish
Protopteridae Protopterus Marbled lungfish
Gilled lungfish
West African lungfish
Spotted lungfish
Queensland lungfish

The

higher vertebrate classes were beginning to evolve.[17] Fossils of lungfish belonging to the genus Neoceratodus have been uncovered in northern New South Wales, indicating that the Queensland lungfish has existed in Australia for at least 100 million years, making it a living fossil and one of the oldest living vertebrate genera on the planet.[17][18] It is the most primitive surviving member of the ancient air-breathing lungfish (Dipnoi) lineages.[17][19] The five other freshwater lungfish species, four in Africa and one in South America, are very different morphologically to N. forsteri.[17] The Queensland lungfish can live for several days out of the water if it is kept moist, but will not survive total water depletion, unlike its African counterparts.[16]

South American lungfish

The

pectoral fins are thin and threadlike, while the pelvic fins are somewhat larger, and set far back. The fins are connected to the shoulder by a single bone, which is a marked difference from most fish, whose fins usually have at least four bones at their base; and a marked similarity with nearly all land-dwelling vertebrates.[23] They have the lowest aquatic respiration of all extant lungfish species,[24] and their gills are greatly reduced and essentially non-functional in the adults.[25]

Marbled lungfish

The

base pairs, making it the largest known genome of any vertebrate. The only organisms known to have more base pairs are the protist Polychaos dubium and the flowering plant Paris japonica at 670 billion and 150 billion, respectively.[28]

Gilled lungfish

The

extant lungfish in the world.[31] This lungfish is uniform blue, or slate grey in colour. It has small or inconspicuous black spots, and a pale grey belly.[32]

West African lungfish

The

ventral side is lighter, with great blackish or brownish spots on the body and fins except on its belly.[36] They reach a length of about 100 cm in the wild.[37]

Spotted lungfish

The

aestivate on land by surrounding itself in a layer of dried mucus.[39][40] It can reach a length of up to 130 cm.[38]

Taxonomy

Ceratodus by Heinrich Harder

The relationship of lungfishes to the rest of the bony fish is well understood:

Recent molecular genetic analyses strongly support a sister relationship of lungfishes and tetrapods (Rhipidistia), with coelacanths branching slightly earlier.[41][42]

The relationships among lungfishes are significantly more difficult to resolve. While Devonian lungfish had enough bone in the skull to determine relationships, post-Devonian lungfish are represented entirely by skull roofs and teeth, as the rest of the skull is

monophyletic
.

Phylogeny after Kemp, Cavin & Guinot, 2017[2]

†Diabolepis

†Uranolophus

†Stomiahykus

Cladogram after Brownstein et al. 2023[14]

†Ceratodus

†Gosfordia

†Paraceratodus

†Ptychoceratodus

†Ferganoceratodus

†Mioceratodus

Neoceratodus (Queensland lungfish)

Lepidosiren
(South American lungfish)

Protopterus (African lungfish)


See also

  • Ceratodus
  • Lepidogalaxias salamandroides
  • Polypteridae

References

  1. ^ "ITIS - Report: Dipnoi". www.itis.gov. Retrieved 13 March 2023.
  2. ^
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  4. ^ "Evolution: On the evolution of internal nostrils (choanae)". Science-Week. Archived from the original on 20 March 2012. Retrieved 23 September 2011.
  5. PMID 25427173. 10.1371. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
    .
  6. S2CID 87285937, archived from the original
    (PDF) on 11 June 2010
  7. ^ Wisenden, Brian (2003). "Chapter 24: The Respiratory System – Evolution Atlas". Human Anatomy. Pearson Education, Inc. Archived from the original on 25 November 2010.
  8. ^ Hilber, S.A. (2007). "Gnathostome form & function". Vertebrate Zoology Lab. U. Florida. Lab 2. Archived from the original on 20 July 2011. Retrieved 31 December 2010.
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  10. ^ a b c "Methuselah: Oldest aquarium fish lives in San Francisco and likes belly rubs". The Guardian. 26 January 2022.
  11. ^ a b "Chicago aquarium euthanizes 90 year-old lungfish". Star Tribune. Archived from the original on 7 February 2017. Retrieved 6 February 2017.
  12. ^ Australian lungfish has largest genome of any animal sequenced so far - New Scientist
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  14. ^
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  16. ^ a b Lake, John S. (1978). Australian Freshwater Fishes. Nelson Field Guides. Melbourne: Thomas Nelson Australia Pty. Ltd. p. 12.
  17. ^ a b c d Allen, G.R.; Midgley, S.H.; Allen, M. (2002). Knight, Jan; Bulgin, Wendy (eds.). Field Guide to the Freshwater Fishes of Australia. Perth, W.A.: Western Australia Museum. pp. 54–55.
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  20. ^ Haeckel, Ernst Heinrich Philipp August; Lankester, Edwin Ray; Schmitz, L. Dora (1892). The History of Creation, or, the Development of the Earth and Its Inhabitants by the Action of Natural Causes. D. Appleton. pp. 289, 422. A popular exposition of the doctrine of evolution in general, and of that of Darwin, Goethe, and Lamarck in particular. From the 8th German edition by Ernst Haeckel
  21. ^ Guenther, Konrad (1931). A Naturalist in Brazil. Translated by Miall, Bernard. Houghton Mifflin Company. pp. 275, 399. The record of a year's observation of her flora, her fauna, and her people.
  22. ^ "South American Lungfish". Animal World.
  23. ^ "Your Inner Fish" Neil Shubin, 2008,2009,Vintage, p.33
  24. ^ The differential cardio-respiratory responses to ambient hypoxia and systemic hypoxaemia in the South American lungfish, Lepidosiren paradoxa
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  26. ^ Fishbase.org
  27. ^ Animal-World. "Marbled Lungfish". Animal World.
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  29. ^ EOL.org (Retrieved 19 February 2010.)
  30. ^ Fishbase.org (Retrieved 19 February 2010.)
  31. ^ Primitive Fishes.com Archived 11 December 2008 at the Wayback Machine Retrieved 19 February 2010.
  32. ^ Fishbase.org (Retrieved 25 September 2010.)
  33. ^ EOL.org (Retrieved 13 May 2010.)
  34. ^ Fishbase.org (Retrieved 13 May 2010.)
  35. ^ "Protopterus annectens, West African lungfish : fisheries, aquaculture". FishBase.
  36. ^ "West African Lungfish (Protopterus annectens annectens) - Information on West African Lungfish - Encyclopedia of Life". Encyclopedia of Life.[permanent dead link]
  37. ^ Primitivefishes.com (Retrieved May 13, 2010.) Archived 11 October 2010 at the Wayback Machine
  38. ^ a b Fishbase.org
  39. ^ Brien, P. (1959). Ethologie du Protopterus dolloi(Boulenger) et de ses larves. Signification des sacs pulmonaires des Dipneustes. Ann. Soc. R. Zool. Belg. 89, 9-48.
  40. ^ Poll, M. (1961). Révision systématique et raciation géographique des Protopteridae de l’Afrique centrale. Ann. Mus. R. Afr. Centr. Sér. 8. Sci. Zool. 103, 3-50.
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  42. PMID 28082606
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Further reading

External links

Wikispecies has information related to Dipnoi.
The Wikibook Dichotomous Key has a page on the topic of: Dipnoi