Mormyridae
Encyclopedia
The family Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are freshwater fish in the order Osteoglossiformes
native to Africa
. It is by far the largest family in the order with around 200 species. Members of the family are popular, if challenging, aquarium
species. These fish are also known for having large brain size and unusually high intelligence.
They are not to be confused with the Australian ghost shark
(Callorhinchus milii) which is sometimes referred to as the "elephantfish", but is better known as the elephant shark in the scientific community.
(part of the brain) is greatly enlarged, giving them a brain to body size ratio similar to that of humans. This is likely to be related to the interpretation of bio-electrical signals. Secondly, the semicircular canals in the inner ear have an unusual structure and are associated with a gas-filled bladder entirely separate from the main swim bladder.
Some species possess modifications of the mouthparts to facilitate feeding upon small invertebrate
s buried in muddy substrates. The shape and structure of these leads to the popular name of "elephant nosed fish" for those species with particularly prominent mouth extensions. The extensions to the mouthparts usually consist of a fleshy elongation attached to the lower jaw. They are flexible, and equipped with touch, and possibly taste, sensors.
Among those members of the family lacking extended mouthparts, the body shape and general morphology of the fishes has led to some being known among aquarists by the name of "baby whale", despite the fact that true whale
s are mammal
s. Other "mormyrid mammalian misnomers" include the term "dolphin fishes", in reference to certain members of the Genus Mormyrops.
s that allow the fishes to sense their environment in turbid waters where vision is impaired by suspended matter. The generation of these electric fields and their use in providing the fishes with additional sensory input from the environment is the subject of considerable scientific research, as is research into communication between and within species.
Electric discharges are most often pulsatile, with Gymnarchus niloticus
being an exception to this rule, discharging its electric organ
near approximately 500 Hz
, giving it a near-sinusoidal like discharge. The electric organ is developmentally related to muscle
, as in Gymnotiform electric fish, as well as in electric rays and skates. There is a surprising degree of convergent evolution
between the South American Gymnotiforms and the African Mormyridae, particularly in the sensory apparatus for detecting and processing electrical signals involved in electrolocation and electrocommunication.
and Petrocephalinae. The latter has only a single genus:
Family Mormyridae
Osteoglossiformes
Osteoglossiformes is a relatively primitive order of ray-finned fish that contains two sub-orders, the Osteoglossoidei and the Notopteroidei. All of the living species inhabit freshwater...
native to Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. It is by far the largest family in the order with around 200 species. Members of the family are popular, if challenging, aquarium
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
species. These fish are also known for having large brain size and unusually high intelligence.
They are not to be confused with the Australian ghost shark
Australian ghost shark
The elephant shark, Callorhinchus milii, is a cartilaginous fish belonging to the subclass Holocephali . Sharks, rays and skates are the other members of the cartilaginous fish group and are grouped under the subclass Elasmobranchii...
(Callorhinchus milii) which is sometimes referred to as the "elephantfish", but is better known as the elephant shark in the scientific community.
Description and biology
The elephantfishes are a diverse family, with a wide range of different sizes and shapes. The smallest are just 5 centimetres (2 in) in adult length, while the largest reach up to 1.5 metres (4.9 ft). They do, however, have a number of unique features in common. Firstly, the cerebellumCerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
(part of the brain) is greatly enlarged, giving them a brain to body size ratio similar to that of humans. This is likely to be related to the interpretation of bio-electrical signals. Secondly, the semicircular canals in the inner ear have an unusual structure and are associated with a gas-filled bladder entirely separate from the main swim bladder.
Some species possess modifications of the mouthparts to facilitate feeding upon small invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s buried in muddy substrates. The shape and structure of these leads to the popular name of "elephant nosed fish" for those species with particularly prominent mouth extensions. The extensions to the mouthparts usually consist of a fleshy elongation attached to the lower jaw. They are flexible, and equipped with touch, and possibly taste, sensors.
Among those members of the family lacking extended mouthparts, the body shape and general morphology of the fishes has led to some being known among aquarists by the name of "baby whale", despite the fact that true whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s are mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. Other "mormyrid mammalian misnomers" include the term "dolphin fishes", in reference to certain members of the Genus Mormyrops.
Electric fields
Elephantfishes are notable for their ability to generate weak electric fieldElectric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
s that allow the fishes to sense their environment in turbid waters where vision is impaired by suspended matter. The generation of these electric fields and their use in providing the fishes with additional sensory input from the environment is the subject of considerable scientific research, as is research into communication between and within species.
Electric discharges are most often pulsatile, with Gymnarchus niloticus
Gymnarchus niloticus
Gymnarchus niloticus – commonly known as the aba, aba aba, frankfish, freshwater rat-tail or African knifefish – is an electric fish, and the only species in the genus Gymnarchus and the family Gymnarchidae within the order Osteoglossiformes...
being an exception to this rule, discharging its electric organ
Electric organ
In biology, the electric organ is an organ common to all electric fish used for the purposes of creating an electric field. The electric organ is derived from modified nerve or muscle tissue...
near approximately 500 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, giving it a near-sinusoidal like discharge. The electric organ is developmentally related to muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
, as in Gymnotiform electric fish, as well as in electric rays and skates. There is a surprising degree of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
between the South American Gymnotiforms and the African Mormyridae, particularly in the sensory apparatus for detecting and processing electrical signals involved in electrolocation and electrocommunication.
Classification
There are about 200 species of elephantfish, grouped into two subfamilies, MormyrinaeMormyrinae
The subfamily Mormyrinae contains all but one of the genera of the African freshwater fish family Mormyridae in the order Osteoglossiformes. They live in muddy water...
and Petrocephalinae. The latter has only a single genus:
Family Mormyridae
- Subfamily MormyrinaeMormyrinaeThe subfamily Mormyrinae contains all but one of the genera of the African freshwater fish family Mormyridae in the order Osteoglossiformes. They live in muddy water...
- Boulengeromyrus Taverne & Géry, 1968
- BrienomyrusBrienomyrusBrienomyrus is a genus of elephantfish in the family Mormyridae.- Species :* Brienomyrus adustus * Brienomyrus brachyistius * Brienomyrus kingsleyae...
Taverne, 1971 - CampylomormyrusCampylomormyrusCampylomormyrus is a genus of elephantfish in the family Mormyridae.- Species :* Campylomormyrus alces * Campylomormyrus bredoi * Campylomormyrus cassaicus...
BleekerPieter BleekerPieter Bleeker was a Dutch medical doctor and ichthyologist, famous for his work on the fishes of East Asia – Atlas Ichthyologique des Orientales Neerlandaises – which was published 1862–1877....
, 1874 - Cyphomyrus Pappenheim, 1906
- Genyomyrus Boulenger, 1898
- GnathonemusGnathonemusGnathonemus is a genus of elephantfish in the family Mormyridae.- Species :* Gnathonemus barbatus Poll, 1967* Gnathonemus echidnorhynchus Pellegrin, 1924...
Gill, 1863 - Heteromormyrus Steindachner, 1866
- HippopotamyrusHippopotamyrusHippopotamyrus is a genus of elephantfish in the family Mormyridae.- Species :* Hippopotamyrus aelsbroecki * Hippopotamyrus ansorgii * Hippopotamyrus castor Pappenheim, 1906...
Pappenheim, 1906 - Hyperopisus Gill, 1862
- Isichthys Gill, 1863
- Ivindomyrus Taverne & Géry, 1975
- MarcuseniusMarcuseniusMarcusenius is a genus of fish in the Mormyridae family.- Species :* Marcusenius abadii * Marcusenius altisambesi Kramer, P. H...
Gill, 1862 - MormyropsMormyropsMormyrops is a genus of weakly electric fish in the family Mormyridae. They are characterized by an elongate head measuring twice as long as high, and no teeth on the palate or the tongue.-Species:...
J. P. MüllerJohannes Peter MüllerJohannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...
, 1843 - MormyrusMormyrusMormyrus is a genus of fish in the Mormyridae family.- Species :* Mormyrus bernhardi Pellegrin, 1926 * Mormyrus caballus Boulenger, 1898** Mormyrus caballus asinus Boulenger, 1915...
Linnaeus, 1758 - MyomyrusMyomyrusMyomyrus is a genus of elephantfish in the family Mormyridae.- Species :* Myomyrus macrodon Boulenger, 1898* Myomyrus macrops Boulenger, 1914* Myomyrus pharao...
BoulengerGeorge Albert BoulengerGeorge Albert Boulenger FRS was a Belgian-British zoologist who identified over 2000 new animal species, chiefly fish, reptiles and amphibians.-Life:...
, 1898 - OxymormyrusOxymormyrusOxymormyrus is a small genus of elephantfish in the family Mormyridae.- Species :* Oxymormyrus boulengeri * Oxymormyrus zanclirostris...
BleekerPieter BleekerPieter Bleeker was a Dutch medical doctor and ichthyologist, famous for his work on the fishes of East Asia – Atlas Ichthyologique des Orientales Neerlandaises – which was published 1862–1877....
, 1874 - ParamormyropsParamormyropsParamormyrops is a genus of elephantfish in the family Mormyridae.- Species :* Paramormyrops batesii * Paramormyrops curvifrons...
Taverne, Thys van den audenaerde& Heymer, 1977 - PollimyrusPollimyrusPollimyrus is a genus of fish in the Mormyridae family.- Species :* Pollimyrus adspersus * Pollimyrus brevis * Pollimyrus castelnaui...
Taverne, 1971 - StomatorhinusStomatorhinusStomatorhinus is a small genus of elephantfish in the family Mormyridae.- Species :* Stomatorhinus ater Pellegrin, 1924* Stomatorhinus corneti Boulenger, 1899* Stomatorhinus fuliginosus Poll, 1941...
BoulengerGeorge Albert BoulengerGeorge Albert Boulenger FRS was a Belgian-British zoologist who identified over 2000 new animal species, chiefly fish, reptiles and amphibians.-Life:...
, 1898
- Subfamily Petrocephalinae
- PetrocephalusPetrocephalusPetrocephalus is a genus of elephantfish in the family Mormyridae, being the only genus in the sub-family Petrocephalinae. These fish are native to Africa.- Species :* Petrocephalus ansorgii Boulenger, 1903...
Marcusen, 1854
- Petrocephalus