The etymology of the genus name derives from a combination of the Greekprefix πολυ-, poly- (many) and the root word πτερον, pteron (wing or fin) – "many fins".
Recoil aspiration
In shallow water, Polypterus inhales primarily through its spiracle (blowhole). Exhalation is powered by muscles in the torso. During exhalation, the bony scales in the upper chest become indented. When the muscles are relaxed, the bony scales spring back into position, generating negative pressure within the torso, resulting in a rapid intake of air through the spiracle. The air is nearly sufficient to fill the lungs. This is followed by one cycle of buccal (mouth) pumping, which "tops off" the lungs, with the surplus air from the buccal pumping process discharged through the pharynx. According to one hypothesis, Devoniantetrapods may have inhaled in this way.[1][2][3]
Discovery
Polypterus was discovered, described, and named in 1802 by Étienne Geoffroy Saint-Hilaire. Naturalists were initially unsure whether to regard it as a fish or an amphibian, and if it were to be classified as a fish, it was unclear whether it ought to be regarded as an Actinopterygian, Chondrichthyan, or Sarcopterygian.[4] Around the time following its initial discovery, some entertained the idea of Polypterus as a living fossil representing the "missing link" between fishes and tetrapods, illustrating a transitional form at the midpoint between finned and limbed vertebrates.[4]
In 1861, Thomas Huxley created the order Crossopterygii to house animals, fossil and living, that possessed lungs and fleshy pectoral fins with lobes. He placed Polypterus and Calamoichthys within this order, allocating them to a new tribe, Polypterini, which he created especially for them. The weight of Huxley's authority allowed this allocation to last in textbooks and lectures long after it had been disproved.[4]
In the 1870s and 1880s, Francis Balfour and his students had shown that embryology could help to answer questions about the evolution of species. No one had studied the embryology of Polypterus. Someone who could do this might prove the "missing link" theory and be greatly honoured, but it could be a dangerous quest. The only breeding Polypterus specimens were in swampy parts of African rivers. Africa was a turbulent place and swamps were rich breeding grounds for mosquitoes carrying malaria.[4]
Two men, Nathan Harrington and John Samuel Budgett, attempted to answer this question by making repeated expeditions to Africa. Harrington failed on his first attempt in 1898 and died early on his second in 1899 before he could reach his destination. Budgett failed in 1898/9, 1900, and 1902. He finally succeeded in 1903, but died of blackwater fever shortly after his return to England. He left excellent samples and drawings, but his only writing was a diary. Consequently, his results on Polypterus were written up and published by his friend John Graham Kerr.[4][5]
Much later, in 1946, Romer confirmed this view, but he also wrote, "The weight of Huxley's [1861] opinion is a heavy one, and even today many a text continues to cite Polypterus as a crossopterygian and it is so described in many a classroom, although students of fish evolution have realized the falsity of this position for many years. ... Polypterus ... is not a crossopterygian, but an actinopterygian, and hence can tell us nothing about crossopterygian anatomy and embryology."[7]
Hall (2001), relying on Patterson (1982) and Noack et al. (1996), writes, "Phylogenetic analyses using both morphological and molecular data affirm Polypterus as a living stem actinopterygian." Research is ongoing. Most of the conclusions drawn by Kerr from Budgett's specimens have been confirmed, but many questions remain.[4]
Polypterus has rarely been bred in captivity. The first success was that of Polypterus senegalus by Arnoult in 1964, a species spawned repeatedly since (see Hartl, 1981; Bartsch and Gemballa, 1992; Bartsch et al., 1997 and Schugardt, 1997).
Shortly after Arnoult's success, a second species, Polypterus ornatipinnis, was spawned by Armbrust for the first time (1966 and 1973) and bred subsequently by Azuma in 1986; Wolf, 1992; Bartsch and Britz, 1996. The third species successfully spawned in captivity was Polypterus endlicheri by Azuma in 1995.
Zoo Basel have been successful in breeding Polypterus in captivity. In December 2005, several eggs were laid, and at the beginning of 2006, six young hatched. Within two months, they reached 10cm (about 4in).[8]
In 2014 researchers at McGill University (published in the journal Nature) turned to Polypterus to help show what might have happened when fish first attempted to walk out of the water. The team of researchers raised juvenile Polypterus on land for nearly a year, with the aim of revealing how these 'terrestrialized' fish looked and moved differently.[9][10]
Actinopterygii, members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia, as opposed to the bulkier, fleshy lobed fins of the sister class Sarcopterygii. Resembling folding fans, the actinopterygian fins can easily change shape and wetted area, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton.
Bichirs and the reedfish comprise Polypteridae, a family of archaic ray-finned fishes and the only family in the order Polypteriformes.
The reedfish, ropefish, or snakefish, Erpetoichthys calabaricus, is a species of fish in the family Polypteridae alongside the bichirs. It is the only member of the genus Erpetoichthys. It is native to fresh and brackish waters in West and Central Africa. The reedfish possesses a pair of lungs in addition to gills, allowing it to survive in very oxygen-poor water. It is threatened by habitat loss through palm oil plantations, other agriculture, deforestation, and urban development.
Polypterus senegalus, commonly known as the Senegal bichir, gray bichir or Cuvier's bichir, is an African species of ray-finned fish in the bichir family, Polypteridae. It is a typical example of polypterid fishes, as most of its defining physical features are common across the genus, such as its ancient, lungfish- or arowana-like appearance, the ability to breathe atmospheric oxygen, and its armor-like scales. These factors have influenced the species' popularity in captivity, and it is commonly kept by aquarists and other hobbyists.
Hans Christian Bjerring is a Danish-Swedish vertebrate paleontologist and comparative anatomist. He has spent his career at the Swedish Museum of Natural History in Stockholm, Sweden, as curator at the Department of Palaeozoology.
Polypterus bichir lapradei is a subspecies of freshwater fish in the family Polypteridae. P. bichir lapradei are demersal, primitive, and popular with experienced aquarists.
Polypterus bichir, the Nile bichir, is a fish which lives in the Nile and some of its tributaries in Africa. It is a dark grayish color on the top, with a dark vertical marking and bands on the flank. This marking is more prominent on juveniles, and fades as the fish grows.
Polypterus ornatipinnis, the ornate bichir, is a bony fish of the family Polypteridae found in Lake Tanganyika and the Congo River basin in Central and East Africa. It is known from the Central African Republic, the Democratic Republic of the Congo, and Tanzania.
The barred bichir, armoured bichir, bandback bichir, or banded bichir is a species of fish belonging to the class Actinopterygii, or the ray-finned fish, which constitute an order of the class of the bony fish. an elongated fish found in the Congo River, specifically in the upper and middle portions. This species is one of the more commonly available in commercial pet stores.
The skull roof or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
Cladistia is a clade of bony fishes whose only living members are the bichirs of tropical Africa. Their major synapomorphies are a heterocercal tail in which the dorsal fin has independent rays, and a posteriorly elongated parasphenoid.
John Samuel Budgett was a British zoologist and embryologist. He spent most of his short career on the genus Polypterus (bichir). This is found in the lakes, river margins, swamps, and floodplains of tropical central and western Africa and the Nile River system. Zoologists at the time wondered whether it was a bony fish, a cartilaginous fish, a lungfish or a primitive amphibian. Forty years after the publication of Darwin’s Origin of Species, zoologists were seeking to map the history of species and this primitive animal was a key part of the map. To find its place there, it was necessary to observe juvenile Polypterus in the wild. It took Budgett four African expeditions but in the end he succeeded in doing so.
Polypterus palmas, also called the shortfin or marbled bichir, is a fish in the family Polypteridae found in freshwater environments throughout West Africa.
The West African bichir or retropinnis bichir, is a freshwater fish in the family Polypteridae, is found in the central Congo River basin and Ogooué River in Africa. It is a long, slender fish that grows to a maximum length of about 34 cm (13 in).
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. Tetrapods are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals. While most species today are terrestrial, little evidence supports the idea that any of the earliest tetrapods could move about on land, as their limbs could not have held their midsections off the ground and the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear. They are areas of active research and debate among palaeontologists at present.
Polypterus teugelsi is a species of carnivorous, nocturnal bichir that lives in the Cross River drainage basin in the country of Cameroon. P. teugelsi was described in 2004 by Ralf Britz.
Polypterus mokelembembe is a species of the fish genus Polypterus, found in the central basin of the Congo River. It was once considered a morph of the closely related Polypterus retropinnis, but was given species status in 2006 with a description that reclassified both fishes. Because of the recency of the species' description and the fact that P. mokelembembe is the paralectotype of P. retropinnis, they are often mistaken for one another in the aquarium trade.
Polypterus polli, Poll's bichir, is a species of bichir from the Malebo Pool and the lower and central basins of the Congo River. It was named in honor of Belgian ichthyologist Max Poll.
Spiracles are openings on the surface of some animals, which usually lead to respiratory systems.
Goodrich, E. S. (1908). On the systematic position of Polypterus. Report of the 77th Meeting of the British Association for the Advancement of Science (1907): 545-546. Quoted by Hall
Hall, B. K. (2001) John Samuel Budgett (1872-1904): In Pursuit of Polypterus, BioScience, Vol. 51, No. 5 (May, 2001), pp.399–407
Kerr, J.G. (1907), The development of Polypterus senegalus Cuv., Pages 195-290 in Kerr, J.G., (ed. 1907), The Work of John Samuel Budgett, Balfour Student of the University of Cambridge: Being a Collection of His Zoological Papers, together with a Biographical Sketch by A . E. Shipley, F.R.S., and Contributions by Richard Assheton, Edward J.Bles, Edward T. Browne, J. Herbert Budgett and J. Graham Kerr. Cambridge (UK): Cambridge University Press.
Noack K, Zardoya R, Meyer A. 1996. The complete mitochondrial DNA sequence of the bichir (Polypterus ornatipinnis), a basal ray-finned fish: Ancient establishment of the consensus vertebrate gene order. Genetics 144:1165-1180, cited by Hall
Patterson C. (1982). Morphology and interrelationships of primitive actinopterygian fishes. American Zoologist 22: 241-260, cited by Hall.
Romer, A S. (1946). The early evolution of fishes, Quarterly Review of Biology 21: 33-69, cited by Hall
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