Pike

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Pike
Senegalese pike (Polypterus senegalus)

Senegalese pike ( Polypterus senegalus )

Systematics
Sub-stem : Vertebrates (vertebrata)
Superclass : Jaw mouths (Gnathostomata)
Class : Ray fins (Actinopterygii)
Subclass : Cladistia
Order : Polypteriformes
Family : Pike
Scientific name of the  subclass
Cladistia
Cope , 1871
Scientific name of the  order
Polypteriformes
Bleeker , 1859
Scientific name of the  family
Polypteridae
Bonaparte , 1838

The Flösselhechte (Polypteridae, Polypteriformes, from ancient Greek πολύ polý , German 'much' and πτερόν pterón , wing ', fin'), also known as the Flössler fish or simply Flössler , are a family and order of the bony fish (Osteichthyes). Since they are morphologically very different from all other bony fish, they are placed in their own subclass, the cladistia . The family consists of two genera, the actual Flösselhechten ( Polypterus ) and the monotypical genus Erpetoichthys , to which only the Flösselheal ( Erpetoichthys calabaricus ) belongs. For European science, pike were discovered during Napoleon's Egyptian campaign by Étienne Geoffroy Saint-Hilaire , who accompanied the troops as a scientist from 1798 to 1801.

Some species of pike are kept as unusual aquarium fish. For evolutionary biologists and paleontologists, the fish group is important because it can serve as a living pattern for the morphology of the original bony fish.

distribution

Pike are found only in fresh waters in tropical Africa. The raft eel lives in estuaries from Nigeria to the Republic of the Congo and can also tolerate light brackish water . The distribution area of the flossed pike begins south of the Sahara , only in the Nile the Nile flossed pike ( Polypterus bichir ) occurs further north to Egypt . In the south, the distribution area ends with the southern border of the Congo Basin and no longer reaches the Zambezi river basin . In East Africa, pike can still be found in Lake Victoria , Lake Turkana , Lake Tanganyika and Lake Rukwas , but no longer in Lake Malawi and in rivers flowing to the Indian Ocean .

features

This historical drawing of a pike from 1878 clearly shows the ganoid scale armor and the eponymous pike on the back.

Flössler grow to be 23.5 centimeters to one meter long. Their shape is elongated, eel-like or snake-like in the raft eel. It is named after the dorsal fin consisting of 5 to 18 individual, one behind the other arranged pinnulae. The front of each of the rafts is supported by a two-pointed fin spine with a sharp edge on the side, which is anchored in a pterygiophore (pterygiophore) that sits obliquely in the musculature via a hole in its front base . On the back of the fin spine there are diagonally seated lepidotriches consisting of bone scales that have grown together and support a small fin membrane. The rafts can be raised and laid down by one muscle at a time. Lateral flexors for the rafts are missing. In the anal fin located far back, directly in front of the caudal fin , however, they are present and necessary for mating when the males turn them sideways to the genital opening of the females, fold them and thus form an insemination pocket.

The axillary skeleton of the polypterids is well developed. They have ossified vertebral bodies that are concave on both sides, upwardly directed neural processes (supraneuralia), ribs and, in addition, “upper” ribs directed dorsally (towards the back), which are connected to the scales along the lateral line in a joint pit each.

Body armor

The body of the pike is covered by rhombus-shaped ganoid scales running in oblique rows , which form a closed armor and correspond to the exoskeleton of the original bony fish ( plesiomorphism ). The scales are connected to one another by processes and joint pits and form scale half-rings on the right and left side of the body, which are connected to one another by closing scales on the midline of the back and abdomen. The successive scale rings can be pushed over. Underneath the ganoid scales there may still be individual odontodes or odontodes connected to form ridges , to which the scales ultimately go back. The collagen fibers of the skin below the scales mirror the arrangement of the ganoid scales in their crossed course. The body armor is used for protection, but restricts the possibility of body curvature in the anguilliform swimming style of the raft eel. The locomotion is therefore similar to that of the wrasse (Labridae) predominantly by means of the pectoral fins (i.e. labriform), however, due to their greater complexity, it is much more "elegant".

Pectoral fins

  • Shoulder girdle and pectoral fin skeleton of Polypterus bichir

  • Polypterus weeksii , with splayed pectoral fins sitting on muscular stalks

The pectoral fins of Flössler (Brachiopterygien) are fan-shaped to sit on muscular short stalks and thus are similar to the Australian lung fish ( Neoceratodus forsteri ) and the Quastenflosser (Coelacanthiformes), what used to speculation of a membership or close relationship of the Flössler with the Fleischflossern (Sarcopterygii ) led. The internal structure, both in terms of the skeleton and the muscles, is completely different, however, it is also very different from that of other ray fins. The skeleton of the pectoral fin stalk consists of three ossified pterygialia, located towards the body, of which the outer ones are rod-shaped and include a middle, plate-shaped one. The three elements converge towards the body to form a single joint head that articulates on the shoulder girdle (scapulocoracoid) and enables great mobility. Towards the outside they widen in a fan-shaped manner and two rows of radials, of which the inner ones are rod-shaped, the ones directed outwards, are spherical. The spherical radials are encompassed by the base of the pectoral fin rays.

skull

The skull of the Flössler is massive and forms a completely closed dermatocranium . The roof of the skull consists of large, paired bone plates. Special features are the firm connection of the maxillary with the preopercular , the appearance of the quadratojugale , an additional bone in the "cheek region", and a parasphenoid that is shifted far back and surrounds the aortic canal . Above the gill cover region there is a flexible zone with a series of small bones, two of which, the spiracularia, lie in the closure fold of the large injection hole and can be actively moved. Pike have to breathe atmospheric air and ingest it through their mouths or through the injection holes; stale air is released through the gill openings. The Branchiostegal rays are missing on the lower side of the gill region . Instead, it is protected by paired throat-bone plates (gularia). At the front there is a flexible, muscular floor of the mouth, which is important for breathing air and catching prey with suction. The jaw margins and the front palate area are covered with conical, pointed and backward-curved fangs. On the ectopterygoid, a bone lying further back in the "roof of the palate" and on the praearticulare, a lower jaw bone, there are truncated conical teeth. The biting force of the Flössler is high. Only four gill arches are formed in the gill skeleton of the Flössler, the last, incomplete gill arch is covered with tooth plates, which serve to transport the ingested food into the esophagus. The (paired) fifth arch, the pharyngealia inferiora of all other ray fins, is missing here.

lung

Flösselhechte have a primitive pair of lungs with two lungs of different length, which are more likely to be referred to as lung sacs . The left lung sac is significantly shorter, which, analogous to the snakes , is due to a lack of space. In some species, the longer right lung sac can extend beyond the anal opening within the body cavity. Both in Polypterus and in Erpetoichthys the diameter of both lung sacs is the same, in the latter the diameter of both lung sacs is significantly smaller due to the slim shape of the fish. The lung sacs are very simply built, translucent and not chambered. They only have longitudinal furrows that are densely packed with specialized cells. The lungs of the pike emerge embryonically from an abdominal ( ventral ) diverticulum of the foregut and remain connected to the digestive tract via the so-called ductus pneumaticus , so that the animals breathe in and out via the esophagus rather than the trachea. The majority of the lungs, however, lie on the back ( dorsal ) of the digestive tract.

In addition to its function as a respiratory organ, the lungs also have a swim bladder function and allow the fish to float in the water with just a few strokes of the fin.

Sense organs

Pike are macrosmats that orientate themselves largely through their sense of smell . Their tubular nostrils (tentacles) lead to a greatly enlarged and complexly constructed olfactory epithelium , which can reach a surface of 3200 mm² and among fish is only comparable to that of eels. Head movements that are reminiscent of targeted “sniffing” are a behavior that is often observed. The sense of smell is important for finding food and reproductive behavior. There are three side lines on the fuselage sunk into pits in the shed. As usual, the lateral line organ on the skull is enclosed in bony canals, except for short dimple lines, which only open to the outside through pores. There are also fields on the skull for electrical orientation .

Way of life

Floating raft eel

Flösselhechte mainly live in weedy bank areas of stagnant and slowly flowing water and, during floods, in the flood zones. During the day, they rest on the bottom of the water to search for food at dusk and at night. They approach the prey unnoticed with their pectoral fins, then suddenly snap and swallow it whole. They eat insect larvae , worms, crustaceans , small fish and amphibians , among other things . Pike can also survive in waters with a low oxygen content and survive the drying up of their living waters buried in the mud for some time.

With the strong fin bases of their pectoral fins, pike are able to "walk" outside the water. They put their fins on alternately while they rotate the front body around each of the attached fin by more than 90 °, resulting in a kind of meandering walk that is somewhat similar to that of salamanders and lizards. It is assumed that similarly the ancestors of the land vertebrates in the Devonian moved on dry land (see below ).

As parasites of bichirs include monogenea (monogenean) and nematodes known (Nematoda).

Reproduction

Young fish with tufted outer gills

The reproductive behavior has been researched through aquarium and laborious field observations. In courtship, the partners swim close to each other, chase each other or the male nudges the resting female and brushes it with his swollen anal fin. Air jumps should also occur.

The eggs are relatively large (2.5 mm Ø), rich in yolks and surrounded by a sticky vitelline membrane with adhesive villi . The hatching yolk sac larvae are poorly developed and hang on water plants with the help of a secretion from an adhesive gland. However, if they are disturbed, they are able to flee. The more developed larvae, capable of active feeding, have outer gill tufts protruding from the gill cover and resemble the larvae of the tailed amphibians and lungfish . They lead a hidden life in the vegetation and on the ground. The outer gills are retained for a long time, even in juvenile fish.

Systematics and evolution

External system

The Flösselhechte (Polypteridae) are the only family of the order Polypteriformes. They are a very primitive group of bony fish. Plesiomorphic features are the injection hole and the spiral casing . The systematic position of the Polypteriformes was controversial for a long time. Because of their fleshy pectoral fin stalks, they were often classified among the meat fins (Sarcopterygii) or the paraphyletic "Crossopterygii" ( Actinistia  + Rhipidistia ). Even in 2004, a group of Italian scientists came after a comparison of fragments of mitochondria - and core - DNA to the conclusion that the Polypteriformes among the Fleischflossern and the recent sister group of lungfish (Dipnoi) are, a view that can not prevail could.

For a long time the order was and is in rather conservative systematics until today, together with the sturgeon-like (Acipenseriformes) and a number of extinct bony fish groups that lived from the Devonian to the Lower Jurassic , assigned to the subclass of the cartilaginous organoids (Chondrostei).

In the modern systematics determined with the help of cladistic methods, they form a separate subclass within the class of ray fins (Actinopterygii), the cladistia , the sister group of all other recent ray fins.

The systematic position is illustrated by the following cladogram :

  Bony fish  

 Meatfin (Sarcopterygii), including terrestrial vertebrates (Tetrapoda)


  Ray fins  
  Cladistia  

 Flösselhechte (Polypteriformes)


   

 Actinopteri (all modern bony fish)




Template: Klade / Maintenance / Style

The Scanilepiformes , an extinct bony fish order from the Triassic , possibly form the sister group of the pike.

Internal system

Relationships within the Polypteridae according to Suzuki et al. 2010.
  Polypteridae  

 Erpetoichthys calabaricus


  Polypterus  

 P. retropinnis


   


 P. congicus


   

 P. ansorgii


   

 P. finisheri


   

 P. bichir





   


 P. mokelembembe


   

 P. ornatipinnis


   

 P. weeksii




   


 P. teugelsi


   

 P. palmas



   

 P. senegalus


   

 P. delhezi


   

 P. polli









Template: Klade / Maintenance / Style

Today 14 species are recognized, 13 of which are assigned to the genus Polypterus and one is placed in the monotypic genus Erpetoichthys . The latter, the flössel eel , differs from the actual Flösselhechten ( Polypterus ) in the lack of ventral fins and the relatively much slimmer body.

A new study based on mitochondrial DNA data shows that Polypterus retropinnis is the sister species to all other species in the genus Polypterus .

Fossil record

The oldest fossils , which are assigned to the pike, come from the lowest Upper Cretaceous ( Cenomanium ) of Africa. Most of them are isolated fin spines. They come from the Wadi Milk Formation in Sudan , the Bahariya Formation in northern Egypt and the Kem Kem Beds in Morocco and can be assigned to 17 species, which fall into 9 genera. In addition to Polypterus (3 species), these are the genera †  Bartschichthys (2), †  Bawitius (1), †  Inbecetemia (2), †  Nagaia (1), †  Saharichthys (1), †  Sainthilairia (4), †  Serenoichthys (1 ) and †  Sudania (2). Bawitius is only known for a single dentate ectopterygoid and a few scales. This ectopterygoid, however, is about five times larger than today's pike and must have belonged to a very large individual.

Finds from the Upper Cretaceous ( Coniacium - Santonium ) come from the Ullemmeden Basin in Niger . From there, six of the genera listed above are known, which are also only preserved in fragments. In Africa, only Polypterus occurs in even younger layers . A special find comes from the "Anthracotheriiden-layers" (late Miocene ) of Chad : The holotype of the species Polypterus faraou is in fact a complete and therefore the most complete specimen of a fossil pike that has been discovered to date. The raft eel, on the other hand, is entirely without fossil records.

Outside of Africa, flintfish fossils have so far only been found in South America. The genera †  Dagetella and †  Latinopollia come from the El Molino and Santa Lucia Formations of the Maastrichtian and Palaeocene of Bolivia . Latinopollia is also known from a locality in Brazil. Post-Paleocene occurrences have not yet been discovered. These circumstances suggest that white pike colonized fresh waters in large parts of the large southern continent of Gondwana even before the Cretaceous period. After the opening and widening of the South Atlantic, the African populations were separated from the South American ones. Whilst pike were completely extinct in South America in the early Cenozoic, they have survived in Africa to this day.

Pike as a possible recent analogue for the ancestors of the terrestrial vertebrates

Flössel pike are the "most primitive" of all recent ray fins. They have numerous original features that were also present in the long-extinct fish-like flesh flippers of the Devonian , from which the earliest four-legged vertebrates and thus ultimately all modern land vertebrates (Tetrapoda), including humans, emerged (see →  Landgang ). These features include the lung-swim-bladder organ, which is suitable for oxygen uptake from the air, and, in contrast to the more recent lung fish, pectoral fins, which are used for movement on land. In addition, it is assumed that the environmental variability of the formation of the phenotype during individual development, the so-called developmental plasticity , is similar in the pike fish to that of the fish-like meat fins of the Devonian.

In an eight-month trial with juvenile Senegalese pike ( Polypterus senegalus ), it was determined for the first time in 2014 how the body develops when they are completely denied the opportunity to go into the water. It was found that the experimental animals, which were initially no more than 70 days old, did not simply survive. Instead, they were doing well in the new, albeit ideally designed, environment and, due to the lack of buoyancy, they showed a series of physical adaptations over time. The changes affected both the muscles and the bone structure, especially in the pectoral fins and shoulder girdle. In addition, the test individuals were able to “walk” significantly better on dry land than the individuals in the control group, which was mostly kept in the water.

This allows conclusions to be drawn as to how the evolution of largely fully aquatic fish-like flesh fins, such as Eusthenopteron , via less fish-like representatives, so-called "fish apods", such as Tiktaalik , to animals with real legs instead of fins, such as Ichthyostega , around 400 million years ago Could have started. The experiment shows how both the anatomy and the behavior of animals with suitable physical conditions are plasticized to a certain extent in response to corresponding environmental changes. 400 million years ago, genetic mutations could initially have fixed changes based on phenotypic plasticity in the affected population via selection. The evolutionary sequence would therefore not be: random genetic mutation → natural selection → adaptation in the population, but the other way around: change in environmental conditions → permanent, not yet genetically hereditary phenotypic adaptation → genetic fixation ( genetic assimilation ) of phenotypic adaptation through random mutations.

However, this scenario contradicts the previous knowledge about the course of the shore leave of the vertebrates, according to which legs and toes should have arisen before the transition to a terrestrial way of life.

Use and endangerment

The raft eel and some species of the real raspberry are caught and imported into wealthy countries as aquarium fish. They are not too difficult to keep in large aquariums, but they rarely show up during the day and can be predatory towards smaller roommates. The aquariums should be well hidden and not too strongly lit. The jeweled pike is regularly reared in the Aquazoo in Düsseldorf.

According to the IUCN, the species in the genus Polypterus are not endangered. Insufficient data are available for Polypterus teugelsi . However, the raft eel is considered to be at low risk. Its coastal habitat is increasingly being destroyed by the cultivation of oil palms .

swell

literature

Individual evidence

  1. ↑ a b c d e f Lecointre & Guyader: Biosystematics. 2005 (see literature ), pp. 443-444.
  2. ↑ a b c d e Bartsch: Cladistia. 2004 (see literature ), p. 230.
  3. ↑ Bartsch: Cladistia. 2004 (see literature ), p. 229.
  4. ^ Ralf Britz, G. David Johnson: On the homology of the posteriormost gill arch in polypterids (Cladistia, Actinopterygii). Zoological Journal of the Linnean Society. Vol. 138, No. 4, 2003, pp. 495-503, doi : 10.1046 / j.1096-3642.2003.t01-1-00067.x (alternative full text access : Smithsonian Libraries ).
  5. ↑ a b c Jeffrey B. Graham: Air-Breathing Fishes: Evolution, Diversity, and Adaptation. Academic Press, San Diego (CA) • London 1997, ISBN 0-12-294860-2 , pp. 73 ff.
  6. ↑ A. Lechleuthner, U. Schumacher, RD Negele, U. Welsch: Lungs of Polypterus and Erpetoichthys. Journal of Morphology. Vol. 201, No. 2, 1989, pp. 161-178, doi : 10.1002 / jmor.1052010206 .
  7. ↑ Bartsch: Cladistia. 2004 (see literature ), p. 231.
  8. ^ Fiedler: Textbook of Special Zoology. 1991 (see literature ), p. 258.
  9. ↑ a b Sterba: Freshwater fish of the world. 1990 (see literature ), pp. 22-23.
  10. ↑ a b c d e Emily M. Standen, Trina Y. Du, Hans CE Larsson: Developmental plasticity and the origin of tetrapods. Nature. Vol. 513, 2014, pp. 54-58, doi : 10.1038 / nature13708 ; see also: Noah Baker: How fish can learn to walk - Land-raised bichirs provide insight into evolutionary pressures facing first vertebrates to live on land. Nature Video of August 27, 2014 (commentary in English).
  11. ↑ Iva Přikrylová, Iveta Matějusová, Naďa Musilová, Milan Gelnar Philip D. Harris: A New Gyrodactylid (monogenean) Genus on Gray Bichir, Polypterus senegalus (Polypteridae) from Senegal (West Africa). The Journal of Parasitology. Vol. 95, No. 3, 2009, pp. 555-560, doi : 10.1645 / GE-1652.1 (alternative full-text access : University of Nebraska - Lincoln , complete booklet).
  12. ↑ Eva Řehulková, Vlastimil Barus, Milan Gelnar: Two remarkable nematodes from the African reedfish Erpetoichthys calabaricus (Polypteriformes: Polypteridae). Helminthologia. Vol. 42, No. 3, 2005, pp. 149–153 ( PDF 2 MB).
  13. ↑ a b Peter Ax: The system of Metazoa III. A textbook on phylogenetic systematics. Spectrum Akademischer Verlag, Heidelberg • Berlin 2001, ISBN 3-8274-1179-3 , pp. 181-183.
  14. ↑ Lucia Rocco, Domenico Costagliola, Maria Alessandra Morescalchi, Vincenzo Stingo: A molecular approach to systematics of Polypteriformes among Osteichthyes. Italian Journal of Zoology. Vol. 71, No. 4, 2004, pp. 347-351 doi : 10.1080 / 11250000409356594 .
  15. ^ Integrated Taxonomic Information System: Chondrostei.
  16. ^ P. Myers, R. Espinosa, CS Parr, T. Jones, GS Hammond, TA Dewey: Order Polypteriformes. The Animal Diversity Web, 2008.
  17. ^ Nelson: Fishes of the World. 2006 (see literature ), p. 88.
  18. ↑ Bartsch: Cladistia. 2004 (see literature ), p. 228.
  19. ↑ Sam Giles, Guang-Hui Xu, Thomas J. Near, Matt Friedman. Early members of 'living fossil' lineage imply later origin of modern ray-finned fishes. Nature , 2017; DOI: 10.1038 / nature23654
  20. ↑ a b Dai Suzuki, Matthew C. Brandley, Masayoshi Tokita: The mitochondrial phylogeny of an ancient lineage of ray-finned fishes (Polypteridae) with implications for the evolution of body elongation, pelvic fin loss, and craniofacial morphology in Osteichthyes. BMC Evolutionary Biology. Vol. 10, item no. 21, 2010, doi : 10.1186 / 1471-2148-10-21
  21. ^ A b Dai Suzuki, Matthew C. Brandley, Masayoshi Tokita: CORRECTION: The mitochondrial phylogeny of an ancient lineage of ray-finned fishes (Polypteridae) with implications for the evolution of body elongation, pelvic fin loss, and craniofacial morphology in Osteichthyes. BMC Evolutionary Biology. Vol. 10, item no. 209, 2010, doi : 10.1186 / 1471-2148-10-209
  22. ↑ Mireille Gayet, François J. Meunier, Christa Werner: Diversification in Polypteriformes and Special Comparison with the Lepisosteiformes. Paleontology. Vol. 45, No. 2, 2002, pp. 361-376, doi : 10.1111 / 1475-4983.00241 (alternative full text access : ResearchGate ).
  23. ^ A b Barbara S. Grandstaff, Joshua B. Smith, Matthew C. Lamanna, Kenneth J. Lacovara, Medhat Said Abdel-Ghani: Bawitius , called nov., A Giant polypterid (Osteichthyes, Actinopterygii) from the Upper Cretaceous Bahariya Formation of Egypt. Journal of Vertebrate Paleontology. Vol. 32, No. 1, pp. 17-26, doi : 10.1080 / 02724634.2012.626823 .
  24. ↑ O. Otero, A. Likius, P. Vignaud, M. Brunet: A new polypterid fish: Polypterus faraou sp. nov. (Cladistia, Polypteridae) from the Late Miocene, Toros-Menalla, Chad. Zoological Journal of the Linnean Society. Vol. 146, No. 2, 2006, pp. 227-237, doi : 10.1111 / j.1096-3642.2006.00201.x (alternative full text access: ResearchGate ).
  25. ^ Stephanie E. Pierce, Jennifer A. Clack, John R. Hutchinson: Three-dimensional limb joint mobility in the early tetrapod Ichthyostega. Nature. Vol. 486, No. 7404, 2012, pp. 523-526, doi : 10.1038 / nature11124 .
  26. ↑ WE Engelmann: zoo animal husbandry - animals in human care: fish. Verlag Harri Deutsch, Frankfurt am Main 2005, ISBN 3-8171-1352-8 , pp. 242-243.
  27. ↑ Polypterus in the IUCN Red List of Threatened Species 2014.2. Retrieved October 28, 2014 ..
  28. ↑ Polypterus teugelsi in the IUCN Red List of Threatened Species 2014.2. Posted by: T. Moelants, 2009. Retrieved October 28, 2014 ..
  29. ↑ Erpetoichthys calabaricus in the IUCN Red List of Threatened Species 2014.2. Posted by: P. Lalèyè, T. Moelants, BD Olaosebikan, 2009. Retrieved October 28, 2014 ..

Web links

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This version was added to the list of articles worth reading on December 16, 2010 .