Nile pike

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Nile pike
Gnathonemus petersii (above) & Campylomormyrus tamandua

Gnathonemus petersii (above) & Campylomormyrus tamandua

Systematics
Subclass : Neuflosser (Neopterygii)
Subclass : Real bony fish (Teleostei)
Overcohort : Osteoglossomorpha (Osteoglossomorpha)
Order : Bony tongues (Osteoglossiformes)
Subordination : Knifefish-like (Notopteroidei)
Family : Nile pike
Scientific name
Mormyridae
Bonaparte , 1832

The Nilhechte (Mormyridae) are a family of African freshwater fish . In German they are also called elephant fish , proboscis fish or tapir fish , depending on the shape of their mouth and snout .

distribution

Distribution area

The range of these fish includes all of Africa south of the Sahara , but without the Capensis , as well as the Nile . The species-poor genera have smaller distribution areas. Hyperopisus , Genyomyrus and Myomyrus occur only in the Congo river basin , Paramormyrops only in Cameroon , Isichthys in West Africa with the exception of the Congo and Hyperopisus lives in the area between Senegal and the Nile. Of the more species-rich genera, Stomatorhinus is restricted to the Congo and Ogooué river basins . In 1909 Boulenger gave 47 endemic species for the Congo , 14 for West Africa north of the Congo region, eight for the Congo region and other West African rivers, seven for the Nile, six living from the Nile via Lake Chad , the Niger to Senegal and two in Lake Victoria . To date, over 100 species have been found in the Congo Basin. The Mormyrids represent 16.2% of all fish species in the Congo and in some regions over 65% of the fish biomass.

features

The members of this family are, depending on the species, 5.2 centimeters to 1.20 meters long. The caudal peduncle is narrow, the caudal fin always forked. The dorsal fin has 12 to 91 fin rays , the anal fin 20 to 70. They sit far back on the body and are often symmetrically opposite each other. Mormyrids have 37 to 64 vertebrae .

The body shape, the relation between the size of the dorsal and anal fin, the shape of the mouth and snout of the Nile pike are extremely variable. In many (the "elephant fish") the snout is very elongated and bent downwards (genus Gnathonemus ), with a terminal mouth or with an elongated lower jaw. Others have a rounded head and a lower mouth (genus Marcusenius ). Species that feed from the bottom of the water often have a goatee that those who eat in the open water lack. The eyes are small, the skin thick, smooth and slimy, the color is inconspicuous, mostly dark gray, black or brownish. Of all bony fish, the Nile pike have the largest brain. In contrast to mammals , however, it is not the cerebrum that is enlarged here, but the cerebellum that extends far forward and covers the cerebrum. Nile pike have a clear ability to learn and a pronounced play instinct. As the only group of fish, the Mormyrids turn on their backs to rub and move back and forth. The sexes of some species can be distinguished by the curve of the body profile line in the area of ​​the anal fin.

Electrical orientation

In the area of ​​the tail stalk, many species have four weak electrical organs , which are used for orientation in murky, muddy waters as well as for territorial delimitation. The electrical organ is located near the tail and is composed of many so-called electrocytes , which are phylogenetically derived from muscle cells . The electrocytes are innervated caudally . As a result of the charge reversal, the simultaneous activation of the electrocytes connected in series creates an electric field first on the caudal and then on the rostral membrane of the electrocytes. With the help of the electrical dipole field generated in this way , the fish can perceive objects or living beings whose conductivity differs from that of the surrounding fresh water and which are located near their bodies. To do this, they have special electroreceptors that sit particularly close to the head of the fish and perceive changes in the density of field lines on the body surface.

Diverse, species-specific vocabulary of electrical communication favors the formation of a large variety of species.

Electrical orientation is also important when searching for food in the animals' home waters, which are often cloudy or dark due to dissolved humic acids . Scientists have found evidence that the Egyptian pike brain senses various electrical fields, such as colors. The fish can thus differentiate between different prey animals based on their "electrical colors".

Way of life

Mormyrids mostly inhabit muddy and cloudy waters and are crepuscular. Most of them are intolerant loners. Only a few live socially. They feed mainly on small animals. The reproduction is only insufficiently known. Some species are supposed to build nests, others dig pits in the sandy soil for spawning . The courtship is supposed to begin with the rainy season , which leads to a rise in the water level and a fall in the conductivity and pH value . Pollimyrus builds floating nests out of plant material. During courtship, the fish make sounds and create specific electrical discharge patterns. After laying eggs, the male chases the female away and guards the nest. The larvae swim free after about 18 days.

Systematics

External system

The mormyrids among the Knochenzünglerartigen (Osteoglossiformes), a group of very old primitive bony fish, which is common in tropical freshwater worldwide. Together with the Great Niloticus ( Gymnarchus niloticus ), the only species of the monotypic family Gymnarchidae, the Nilhechte form the superfamily Mormyroidea. They differ from greater nil pike, among other things, in their enlarged cerebellum.

Internal system

Petrocephalus simus
Campylomormyrus elephas
Marcusenius moorii
Campylomormyrus phantasticus

There are about 215 species in 20 genera and two subfamilies. The genus Petrocephalus is basal and is the sister genus of all other genera:


Cladogram :

 Mormyroidea  
  Gymnarchidae  

 Great Nilpike ( Gymnarchus )


  Mormyridae  

 Petrocephalinae 


   

 Mormyrinae 




Template: Klade / Maintenance / Style

Aquarium keeping

Some Mormyrids, especially the elephantnose fish, are caught for the purpose of aquarium keeping and imported to Germany. Campylomormyrus cassaicus , Mormyrus rume , Pollimyrus isidori and Petrocephalus bovei have already been bred in captivity. To do this, an artificial rainy season is simulated by increasing the water level and lowering the conductivity and pH value. Pollimyrus isidori was 28 years and 11 months old in the aquarium, Mormyrus kannume was 16 years and 3 months old .

swell

literature

  • Kurt Fiedler: Textbook of Special Zoology, Volume II, Part 2: Fish . Gustav Fischer Verlag Jena, 1991, ISBN 3-334-00339-6
  • Wilhelm Harder : The relationship between electroreceptors, electrical organ, lateral line organs and the nervous system in the Mormyridae (Teleostei, Pisces), Zeitschrift für Comparative Physiologie 59, 1968, pp. 272-318
  • Lavoué, Bigorne, Lecointre & Ágnèset: Phylogenetic Relationships of Mormyrid Electric Fishes (Mormyridae; Teleostei) Inferred from Cytochrome b Sequences. Molecular Phylogenetics and Evolution, No. 1, Jan. 2000 PDF

Individual evidence

  1. ↑ Stiassny, Melanie LJ; Teugels, Guy G .; Hopkins, Carl (2007) (PDF). Poissons d'eaux douces et saumâtres de basse Guinée, ouest de l'Afrique centrale, volume 1 - volume 42 . IRD Editions. pp. 799. ISBN 978-27-0991-620-2 .
  2. ↑ Petru Banaescu: Zoogeography of Fresh Waters . Page 63, AULA, Wiesbaden 1990, ISBN 3-89104-480-1
  3. ↑ Lavoué, Bigorne, Lecointre & Ágnèset (2000)
  4. ^ Joseph S. Nelson: Fishes of the World . John Wiley & Sons, 2006, ISBN 0-471-25031-7
  5. ↑ a b c Günther Sterba : Freshwater fish of the world. 2nd Edition. Urania, Leipzig / Jena / Berlin 1990, ISBN 3-332-00109-4 .
  6. ^ ORF Science - Species-rich through electrical communication
  7. ↑ Martin Gottwald, Neha Singh, André N. Haubrich, Sophia Regett, Gerhard von der Emde. Electric-Color Sensing in Weakly Electric Fish Suggests Color Perception as a Sensory Concept beyond Vision. Current Biology, 2018; DOI: 10.1016 / j.cub.2018.09.036
  8. ↑ a b Peter Bucher: Zoo animal keeping 5. Fish . Pages 254-257 German Harri GmbH, 2005, ISBN 3-8171-1352-8
  9. ^ A b John P. Sullivan, Sebastien Lavoue and Carl D. Hopkins. 2016. Cryptomyrus : A New Genus of Mormyridae (Teleostei, Osteoglossomorpha) with Two New Species from Gabon, West-Central Africa. ZooKeys . 561: 117-150. DOI: 10.3897 / zookeys.561.7137
  10. ↑ Lavoué, S., Sullivan JP, & Hopkins CD (2003): Phylogenetic utility of the first two introns of the S7 ribosomal protein gene in African electric fishes (Mormyroidea: Teleostei) and congruence with other molecular markers. Biological Journal of the Linnean Society. 78, 273-292. PDF
  11. ↑ Sullivan, JP, Lavoué S., & Hopkins CD (2000): Molecular systematics of the African electric fishes (Mormyroidea: Teleostei) and a model for the evolution of their electric organs. Journal of Experimental Biology. 203, 665-683. PDF

Web links

Commons : Mormyridae  - Collection of images, videos and audio files