The subfamily Mormyrinae contains all but one of the genera of the African
freshwater fish
Freshwater fish are those that spend some or all of their lives in fresh water, such as rivers and lakes, with a salinity of less than 1.05%. These environments differ from marine conditions in many ways, especially the difference in levels of ...
family
Mormyridae
The Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are a family of weakly electric freshwater fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order with around 2 ...
in the order
Osteoglossiformes
Osteoglossiformes (Greek: "bony tongues") is a relatively primitive order of ray-finned fish that contains two sub-orders, the Osteoglossoidei and the Notopteroidei. All of at least 245 living species inhabit freshwater. They are found in South ...
. They are often called elephantfish due to a long protrusion below their mouths used to detect buried
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s that is suggestive of a tusk or trunk (some such as ''Marcusenius senegalensis gracilis'' are sometimes called
Trunkfish
Ostraciidae is a family of squared, bony fish belonging to the order Tetraodontiformes, closely related to the pufferfishes and filefishes. Fish in the family are known variously as boxfishes, cofferfishes, cowfishes and trunkfishes. It contains ...
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.
[Bell CC, Szabo T (1986). Electroreception in Mormyrid fish. Central Anatomy. pp. 375–421. In: Bullock TH, Heiligenberg W, (eds.), Electroreception. New York, Wiley ] 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
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ce ...
of any animal.
[Nilsson G (1996]
"Brain and body oxygen requirements of Gnathonemus petersii, a fish with an exceptionally large brain"
''Journal of Experimental Biology'', 199(3): 603-607
Download
/ref> 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
The human brain is the central organ (anatomy), organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the act ...
in comparison uses only 20%.[Mink JW, Blumenschine RJ, Adams DB. (1981). Ratio of central nervous system to body metabolism in vertebrates: its constancy and functional basis. Am J Physiol. 241(3):R203-12. ]
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 human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s. However, research published in 1996 in ''The Journal of Experimental Biology
''Journal of Experimental Biology'' (formerly ''The British 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. ...
'' by Göran Nilsson at Uppsala University
Uppsala University ( sv, Uppsala universitet) is a public research university in Uppsala, Sweden. Founded in 1477, it is the oldest university in Sweden and the Nordic countries still in operation.
The university rose to significance during ...
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
An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life ...
.
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
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...
s, swallow
The swallows, martins, and saw-wings, or Hirundinidae, are a family of passerine songbirds found around the world on all continents, including occasionally in Antarctica. Highly adapted to aerial feeding, they have a distinctive appearance. The ...
s, crow
A crow is a bird of the genus '' Corvus'', or more broadly a synonym for all of ''Corvus''. Crows are generally black in colour. The word "crow" is used as part of the common name of many species. The related term "raven" is not pinned scientifica ...
s and sparrows 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 is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whitefis ...
(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.
Large brains
Unlike mammals, the part of the brain enlarged in mormyrinae fish is the cerebellum not the cerebrum
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb ...
and reflecting this is called a gigantocerebellum.[Nieuwenhuys R. Nicholson, C. (1969). A survey of the general morphology, the fiber connections and the possible functional significance of the gigantocerebellum of mormyrid fishes. pp. 107–134. In Neurobiology of Cerebellar Evolution and Development. (ed. R. Llinás), American Medical Association. ] This enlarged cerebellum links to their electroreception
Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to st ...
. They generate weak electrical field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field f ...
s from specialized electric organ
An electric organ, also known as electronic organ, is an electronic keyboard instrument which was derived from the pump organ, harmonium, pipe organ and theatre organ. Originally designed to imitate their sound, or orchestral sounds, it has sinc ...
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 electroreceptor
Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
s. The electroperception they enable is used in hunting prey, electrolocation
Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
, and communication
Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqui ...
(Knollenorgan
A Knollenorgan is an electroreceptor in the skin of weakly electric fish of the family Mormyridae (Elephantfish) from Africa. The structure was first described by Viktor Franz (1921), a German anatomist unaware of its function. They are named afte ...
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
In physiology, an efference copy or efferent copy is an internal copy of an outflowing ('' efferent''), movement-producing signal generated by an organism's motor system.Jeannerod, Marc (2003): "Action Monitoring and Forward Control of Movements". ...
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
''Petrocephalus'' is a genus of ray-finned fish in the family Mormyridae. All the fish species of this genus are endemic to Africa.
Species
There are currently 46 recognized species in this genus:
* '' Petrocephalus ansorgii'' Boulenger 1903 ( ...
has been confirmed using molecular phylogeny
Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
methods. The classification below comes from FishBase.
* Subfamily Mormyrinae
** '' Boulengeromyrus'' Taverne & Géry
Géry () is a commune in the Meuse department in Grand Est in north-eastern France.
See also
*Communes of the Meuse department
The following is a list of the 499 communes of the Meuse department of France.
The communes cooperate in the fo ...
, 1968
**'' Brevimyrus'' Taverne, 1971
** '' Brienomyrus'' Taverne, 1971
** '' Campylomormyrus'' Bleeker, 1874
** '' Cyphomyrus'' Pappenheim
Pappenheim is a town in the Weißenburg-Gunzenhausen district, in Bavaria, Germany. It is situated on the river Altmühl, 11 km south of Weißenburg in Bayern.
History
Historically, Pappenheim was a statelet within Holy Roman Empire. It ...
, 1906
** '' Genyomyrus'' Boulenger, 1898
** '' Gnathonemus'' Gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
, 1863
** '' Heteromormyrus'' Steindachner, 1866
** '' Hippopotamyrus'' Pappenheim
Pappenheim is a town in the Weißenburg-Gunzenhausen district, in Bavaria, Germany. It is situated on the river Altmühl, 11 km south of Weißenburg in Bayern.
History
Historically, Pappenheim was a statelet within Holy Roman Empire. It ...
, 1906
** '' Hyperopisus'' Gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
, 1862
** '' Isichthys'' Gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
, 1863
** '' Ivindomyrus'' Taverne & Géry
Géry () is a commune in the Meuse department in Grand Est in north-eastern France.
See also
*Communes of the Meuse department
The following is a list of the 499 communes of the Meuse department of France.
The communes cooperate in the fo ...
, 1975
** ''Marcusenius
''Marcusenius'' is a genus of elephantfishes native to Africa. Its members are highly diverse in size, with the smallest species reaching less than and the largest more than .
The genus is named after Johann Marcusen.
Species
There are cur ...
'' Gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
, 1862
** '' Mormyrops'' J. P. Müller, 1843
** ''Mormyrus
''Mormyrus'' is a genus of ray-finned fish in the family Mormyridae.
Species
There are currently 22 recognized species in this genus:
* '' Mormyrus bernhardi'' Pellegrin 1926 (Bernhard's elephant-snout fish)
* '' Mormyrus caballus'' Boul ...
'' Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
, 1758
** '' Myomyrus'' Boulenger, 1898
** '' Oxymormyrus'' Bleeker, 1874
** '' Paramormyrops'' Taverne, Thys van den audenaerde& Heymer, 1977
** '' Pollimyrus'' Taverne, 1971
** '' Stomatorhinus'' Boulenger, 1898
See also
* Medjed (fish)
Medjed was a kind of elephantfish worshipped at Oxyrhynchus (Ὀξύρρυγχος) in ancient Egyptian religion. These fish were believed to have eaten the penis of the god Osiris after his brother Set had dismembered and scattered the god's bo ...
— worshipped elephantfish in Ancient Egypt.
References
{{Taxonbar, from=Q1948267
Mormyridae
Fish of Africa
Ray-finned fish subfamilies