Mormyrinae
Encyclopedia
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. They are often called elephantfish due to a long protrusion below their mouths used to detect buried invertebrate
s that is suggestive of a tusk or trunk (some such as Marcusenius senegalensis gracilis are sometimes called Trunkfish though this term is usually associated with an unrelated group of fish). They can also be called tapirfish.
Fish in this subfamily have a high brain to body mass ratio
due to an expanded cerebellum
(called a gigantocerebellum) used in their electroperception. Linked to this they are notable for holding the zoological record at around 60% as the brains that consume the most energy as a percentage of the body's metabolic rate of any animal. Previous to this discovery, it was the “human brain, which had been thought to hold the record in this respect”.p. 605 The human brain
in comparison uses only 20%.
Mormyrinae is the largest subfamily in the Osteoglossiformes order with around 170 species.
s. However research published in 1996 in the Journal of Experimental Biology
by Göran Nilsson at Uppsala University
found that mormyrinae brains utilize roughly 60% of their body O2 consumption. This is due to the combination of large brain size (3.1% of body mass compared to 2% in humans) and them being ectothermic.
The body energy expenditure of ectothermic animals is about 1/13 of that of endotherms but the energy expenditure of the brains of both ectothermic and endothermic animals are similar. Other high brain percentage (2.6–3.7 % of the body mass) animals exist such as bat
s, swallow
s, crow
s and sparrow
s but these due to their endothermy also have high body energy metabolism. The unusual high brain energy consumption percentage of mormyrinae fish is thus due to them having the unusual combination of a large brain in a low energy consuming body. The actual energy consumption per unit mass of its brain is not in fact particularly high and indeed lower (2.02 mg g1 h1) than that in some other fish such as Salmonidae
(2.20 mg g−1 h−1). In comparison that of rats is 6.02 mg g−1 h−1 and humans 2.61 mg g−1 h−1.Table 1
The oxygen for this in low oxygen conditions
comes from gulping air at the water surface.
s, the part of the brain enlarged in mormyrinae fish is the cerebellum
not the cerebrum and reflecting this is called a gigantocerebellum. This enlarged cerebellum links to their electroreception
. They generate weak electrical fields from specialized electric organ
muscles. To detect these fields from those created by other mormyrinae fish, their prey animals, and how their nearby environment distorts them, their skin contains three types of electroreceptors. The electroperception they enable is used in hunting prey, electrolocation, and communication
(Knollenorgan
s are the specialized electrical detection organs for this function). This electroperception however requires complex information processing
in special neurocircuitry
since it is dependent upon the ability to distinguish between self-generated and other generated electric fields, and their self-created aspects and their environment modification. To enable this specialized information processing, with each self-generated electrical discharge, an efference copy
of it is made for comparison with the detected electric field it creates. The cerebellum plays a key role in processing such efference copy dependent perception. The muddy waters where they live has resulted in such electroperception playing a key role in their survival and this has resulted in their gigantocerebellum.
methods. The classification below comes from FishBase
.
Freshwater fish
Freshwater fish are fish that spend some or all of their lives in freshwater, such as rivers and lakes, with a salinity of less than 0.05%. These environments differ from marine conditions in many ways, the most obvious being the difference in levels of salinity...
family Mormyridae
Mormyridae
The family Mormyridae, sometimes called "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...
in the order Osteoglossiformes
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...
. They live in muddy water. They are often called elephantfish due to a long protrusion below their mouths used to detect buried 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 that is suggestive of a tusk or trunk (some such as Marcusenius senegalensis gracilis are sometimes called Trunkfish though this term is usually associated with an unrelated group of fish). They can also be called tapirfish.
Fish in this subfamily have a high brain to body mass ratio
Brain to body mass ratio
Brain-to-body mass ratio, also known as the brain to body weight ratio, is the ratio of brain weight to body weight, which is hypothesised to be a rough estimate of the intelligence of an animal. A more complex measurement, encephalization quotient, takes into account allometric effects of widely...
due to an expanded cerebellum
Cerebellum
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...
(called a gigantocerebellum) used in their electroperception. Linked to this they are notable for holding the zoological record at around 60% as the brains that consume the most energy as a percentage of the body's metabolic rate of any animal. Previous to this discovery, it was the “human brain, which had been thought to hold the record in this respect”.p. 605 The human brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
in comparison uses only 20%.
Mormyrinae is the largest subfamily in the Osteoglossiformes order with around 170 species.
Unique brain percentage of body energy consumption
The range with which the adult brain in all animals regardless of body size consumes energy as a percentage of the body's energy is roughly 2% to 8%. The only exceptions of animal brains using more than 10% (in terms of O2 intake) are a few primates (11–13%) and humanHuman
Humans are the only living species in the Homo genus...
s. However research published in 1996 in the Journal of Experimental Biology
Journal of Experimental Biology
The Journal of Experimental Biology is a peer-reviewed scientific journal in the field of comparative physiology and integrative biology. It is published by The Company of Biologists from editorial offices in Cambridge, United Kingdom.- History :...
by Göran Nilsson at Uppsala University
Uppsala University
Uppsala University is a research university in Uppsala, Sweden, and is the oldest university in Scandinavia, founded in 1477. It consistently ranks among the best universities in Northern Europe in international rankings and is generally considered one of the most prestigious institutions of...
found that mormyrinae brains utilize roughly 60% of their body O2 consumption. This is due to the combination of large brain size (3.1% of body mass compared to 2% in humans) and them being ectothermic.
The body energy expenditure of ectothermic animals is about 1/13 of that of endotherms but the energy expenditure of the brains of both ectothermic and endothermic animals are similar. Other high brain percentage (2.6–3.7 % of the body mass) animals exist such as bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s, swallow
Swallow
The swallows and martins are a group of passerine birds in the family Hirundinidae which are characterised by their adaptation to aerial feeding...
s, crow
Crow
Crows form the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents and several...
s and sparrow
Sparrow
The sparrows are a family of small passerine birds, Passeridae. They are also known as true sparrows, or Old World sparrows, names also used for a genus of the family, Passer...
s but these due to their endothermy also have high body energy metabolism. The unusual high brain energy consumption percentage of mormyrinae fish is thus due to them having the unusual combination of a large brain in a low energy consuming body. The actual energy consumption per unit mass of its brain is not in fact particularly high and indeed lower (2.02 mg g1 h1) than that in some other fish such as Salmonidae
Salmonidae
Salmonidae is a family of ray-finned fish, the only living family currently placed in the order Salmoniformes. It includes salmon, trout, chars, freshwater whitefishes and graylings...
(2.20 mg g−1 h−1). In comparison that of rats is 6.02 mg g−1 h−1 and humans 2.61 mg g−1 h−1.Table 1
The oxygen for this in low oxygen conditions
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
comes from gulping air at the water surface.
Large brains
Unlike mammalMammal
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, the part of the brain enlarged in mormyrinae fish is the cerebellum
Cerebellum
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...
not the cerebrum and reflecting this is called a gigantocerebellum. This enlarged cerebellum links to their electroreception
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
. They generate weak electrical fields from specialized 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...
muscles. To detect these fields from those created by other mormyrinae fish, their prey animals, and how their nearby environment distorts them, their skin contains three types of electroreceptors. The electroperception they enable is used in hunting prey, electrolocation, and communication
Animal communication
Animal communication is any behavior on the part of one animal that has an effect on the current or future behaviour of another animal. The study of animal communication, is sometimes called Zoosemiotics has played an important part in the...
(Knollenorgan
Knollenorgan
Knollenorgan is the name given to an electroreceptor found in the skin of weakly electric fish of the family Mormyridae from Africa. It was first described by V. Franz , a German anatomist who was unaware of its function. They are named after "Knolle", German for "tuberous root" which describes...
s are the specialized electrical detection organs for this function). This electroperception however requires complex information processing
Information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...
in special neurocircuitry
Biological neural network
In neuroscience, a biological neural network describes a population of physically interconnected neurons or a group of disparate neurons whose inputs or signalling targets define a recognizable circuit. Communication between neurons often involves an electrochemical process...
since it is dependent upon the ability to distinguish between self-generated and other generated electric fields, and their self-created aspects and their environment modification. To enable this specialized information processing, with each self-generated electrical discharge, an efference copy
Efference copy
right|thumb|282px|Efference copies are created with our own movement but not those of other people. This is why other people can tickle us but we cannot [[tickle]] ourselves .Efference copy is an internal copy created with a motor command of its predicted movement and its...
of it is made for comparison with the detected electric field it creates. The cerebellum plays a key role in processing such efference copy dependent perception. The muddy waters where they live has resulted in such electroperception playing a key role in their survival and this has resulted in their gigantocerebellum.
Classification
The classification by osteology-based traits of Mormyridae into the two subfamilies of Mormyrinae and Petrocephalinae has been confirmed using molecular phylogenyMolecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
methods. The classification below comes from FishBase
FishBase
FishBase is a comprehensive database of information about fish species . It is the largest and most extensively accessed online database on adult finfish on the web...
.
- 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