Overview

Comprehensive Description

Biology

Occurs close to the bottom where it probes for food with the long snout. Territorial and usually aggressive towards members of its own species. This behavior has been shown to involve electric organ discharge (EOD) activity (Ref. 10011). Feeds mostly at night on worms and insects (Ref. 7020), probably aided by electro-sensory inputs (Ref. 10011). Electroreceptors are distributed over the entire head, the dorsal and ventral regions of the body, but absent from the side and the caudal peduncle where the electric organ is located (Ref. 10011). Sex-related EOD characteristics in this species has been demonstrated in the laboratory with freshly imported samples during the breeding season; such EOD dimorphism changed with time in captivity (Ref. 10764; 10766). Lead nitrate in water significantly increased EOD rate and selectively altered the EOD waveform of this species (Ref. 10469). Dubbed a `hearing specialist' having auditory abilities in the range of 100-2500 Hz, with `best frequencies' between 300 and 600 Hz (Ref. 10830). Aquarium keeping: in groups of 5 or more individuals; minimum aquarium size 150 cm; not recommended for home aquariums (Ref. 51539).
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General Description

Body is moderately deep, about 25-28% SL, with the greatest depth slightly anterior to the origin of the anal fin. The length of the head 20-25% SL, its depth, 66-75% of its length. Dorsal profile convex, descending in a straight line toward the head. Snout, 40% HL. Lower jaw with a cylindrical to tapering dermal appendix which is as long or longer than the snout; teeth small, notched, 3-5 in upper 5-6 in lower. Mouth small and terminal. Nostrils close together, about one eye diameter anterior to forward margin of eye. Eye, small, its diameter about 12% of length of head. Dorsal fin base length about 20-21% SL, with 27-29 rays. Dorsal fin originates above the 10th anal ray. Anal fin base about 27-28 % SL with 34-36 rays. Predorsal distance about 62 % SL; pre-anal distance about 56% SL. Caudal peduncle length about 3.3 times its depth, about 17% SL. 8 circumpeduncular scales. Scales along the lateral line, 63-70. Caudal fin covered with scales, deeply forked. Coloration: black brown with two distinct bands in the shape of parentheses “()” running from origin of dorsal to the origin of the anal fins. The light color of these bands fades in larger specimens.

This is the best-known species of mormyrid due to its popularity in the international aquarium fish trade where it is known as the "elephantnose fish."

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Distribution

Range Description

This species is known from Nigeria to Central African Republic, and south to Angola and Zambia

Central Africa: Gnathonemus petersii is known from throughout the Congo River basin. In the Lower Guinea region, it is known from the Cross Mungo, Wouri, Lokoundjé, and Lower Sanaga Rivers.

Western Africa: It is found in the Lower Niger, Ogun, Cross basin and This species is known from upper Chari basin.
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Africa: Niger to Congo River basins (Ref. 3203).
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Among the most widespread mormyrid species. Such a large distribution suggests revisionary work may uncover multiple species. In Lower Guinea found in the Cross, Mungo, Wouri, Lokoundjé, and Lower Sanaga Rivers. Elsewhere widely distributed throughout central Africa from the Niger Delta to the Congo River basin. The holotype is from Old Calabar, at the mouth of the Calabar and Cross Rivers. See FishBase for museum records and localities.

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Western and central Africa.
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Physical Description

Morphology

Dorsal spines (total): 0; Dorsal soft rays (total): 25 - 31; Analspines: 0; Analsoft rays: 32 - 36
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Size

Maximum size: 350 mm SL
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Max. size

35.0 cm SL (male/unsexed; (Ref. 2915))
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Maximum size: 350 mm SL.

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Gnathonemus petersii is a demersal species that occurs close to the bottom where it probes for food with the long snout. Territorial and usually aggressive towards members of its own species. This behaviour has been shown to involve electric organ discharge (EOD) activity (Møller 1995). Feeds mostly at night on worms and insects (Mills and Vevers 1989), probably aided by electro-sensory inputs (Møller 1995). The electroreceptors are distributed over the entire head, the dorsal and ventral regions of the body, but absent from the side and the caudal peduncle where the electric organ is located (Møller 1995). Sex-related EOD characteristics in this species has been demonstrated in the laboratory with freshly imported samples during the breeding season; such EOD dimorphism changed with time in captivity (Landsman 1993, 1995). Lead nitrate in water significantly increased EOD rate and selectively altered the EOD waveform of this species (Prabhakar and Landsman 1994). Dubbed a `hearing specialist' having auditory abilities in the range of 100-2500 Hz, with `best frequencies' between 300 and 600 Hz (McCormick and Popper 1984).

Systems
  • Freshwater
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Environment

demersal; freshwater; pH range: 6.0 - 8.0; dH range: 5 - 19
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small to large rivers

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Trophic Strategy

Occurs close to the bottom where it probes for food with the long snout. Territorial and usually aggressive towards members of its own species. This behavior has been shown to involve electric organ discharge (EOD) activity. Feeds mostly at night on worms and insects, probably aided by electrosensory inputs.
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Diseases and Parasites

Turbidity of the Skin (Freshwater fish). Parasitic infestations (protozoa, worms, etc.)
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Sporozoa-infections, other. Parasitic infestations (protozoa, worms, etc.)
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Sporozoa-infection (Myxobolus sp.). Parasitic infestations (protozoa, worms, etc.)
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Sporozoa Infection (Hennegya sp.). Parasitic infestations (protozoa, worms, etc.)
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Nematode Infection (general). Parasitic infestations (protozoa, worms, etc.)
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Dactylogyrus Gill Flukes Disease. Parasitic infestations (protozoa, worms, etc.)
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Bacterial Infections (general). Bacterial diseases
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Aeromonosis. Bacterial diseases
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Life History and Behavior

Behavior

Electric Organ Discharge

In the laboratory, EODs of G. petersii are often sexually dimorphic, with the male EOD longer in duration than that of the female. The EOD has three phases: an initial head negative phase which is visible only after amplifying the vertical axis of the display, followed by a head-positive then head-negative phase. The duration of the EOD is approximately 300 to 500 µs. The presence of an initial head-negative phase to the waveform is characteristic of an electric organ with electrocytes which have penetrating stalks.

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Chin used to hunt: elephantnose fish
 

The long chin of the elephantnose fish navigates and detects prey using sensors that pick up distortions in the fish's electric field.

         
  "The elephantnose fish, which finds its way at night using an electrical version of sonar, has sharp enough senses to assess the shape and size of objects in its tank in the dark, researchers have found. The fish can even identify shapes when they are present as simple wire frames rather than solid objects.

The sensing organ of Gnathonemus petersii (which looks, as the name suggests, like an elephant's nose) is actually an elongated chin packed with electrical sensors that detect distortions in the fish's own electric field. As it hunts for food in the pitch darkness of a tropical central African night, the elephantnose fish sweeps its snout over the ground like a person using a metal detector, to navigate around obstacles and locate the larvae it feeds on." (Muers 2007)


 

"Weakly electric fish can serve as model systems for active sensing because they actively emit electric signals into the environment, which they also perceive with more than 2000 electroreceptor organs (mormyromasts) distributed over almost their entire skin surface. In a process called active electrolocation, animals are able to detect and analyse objects in their environment, which allows them to perceive a detailed electrical picture of their surroundings even in complete darkness. The African mormyrid fish Gnathonemus petersii can not only detect nearby objects, but in addition can perceive other properties such as their distance, their complex electrical impedance, and their three-dimensional shape. Because most of the sensory signals the fish perceive during their nightly activity period are self-produced, evolution has shaped and adapted the mechanisms for signal production, signal perception and signal analysis by the brain. Like in many other sensory systems, so-called prereceptor mechanisms exist, which passively improve the sensory signals in such a way that the signal carrier is optimized for the extraction of relevant sensory information. In G. petersii prereceptor mechanisms include properties of the animal’s skin and internal tissue and the shape of the fish’s body. These lead to a specific design of the signal carrier at different skin regions of the fish, preparing them to perform certain detection tasks. Prereceptor mechanisms also ensure that the moveable skin appendix of G. petersii, the ‘Schnauzenorgan’, receives an optimal sensory signal during all stages of its movement.

 

"Another important aspect of active sensing in G. petersii concerns the locomotor strategies during electrolocation. When foraging, the animals adopt a particular position with the body slanted forward bringing the so-called ‘nasal region’ in a position to examine the environment in front of and at the side of the fish. Simultaneously, the Schnauzenorgan performs rhythmic left–right searching movements. When an object of interest is encountered, the Schnauzenorgan is brought in a twitching movement towards the object and is moved over it for further exploration. The densities of electroreceptor organs is extraordinary high at the Schnauzenorgan and, to a lesser extend, at the nasal region. In these so-called foveal regions, the mormyromasts have a different morphology compared to other parts of the electroreceptive skin. Our results on mormyromast density and morphology, prereceptor mechanisms and electric images, central processing of electroreceptive information, and on behavioural strategies of G. petersii lead us to formulate the hypothesis that these fish possess two separate electric foveae, each of which is specialized for certain perceptional tasks." (von der Emde et al. 2007:3082)


  Learn more about this functional adaptation.
  • von der Emde, Gerhard; Steffen Fetz. 2007. Distance, shape and more: recognition of object features during active electrolocation in a weakly electric fish. Journal of Experimental Biology. 210(17): 3082-3095.
  • von der Emde G.; Amey M.; Engelmann J.; Fetz S.; Folde C.; Hollmann M.; Metzen M.; Pusch R. 2008. Active Electrolocation in Gnathonemus petersii: Behaviour, Sensory Performance, and Receptor Systems. Journal of Physiology-Paris. 102(4-6): 279-290.
  • Mary Muers. 2007. 'Seeing' through the chin. news@nature.com [Internet], Accessed August 28, 2007.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Gnathonemus petersii

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 6 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ACTCGCTGATTTTTCTCAACCAATCACAAAGACATCGGCACCCTATACCTAGTGTTCGGGGCCTGAGCCGGAATGGTAGGCACTGCACTA---AGCCTACTCATCCGAGCGGAACTAAACCAACCTGGAGCCCTACTTGGGGAT---GACCAGATTTATAATGTTATCGTCACAGCACACGCCTTCGTAATAATTTTCTTCATGGTAATGCCCATTATGATCGGCGGCTTCGGCAACTGATTAATCCCCCTCATG---CTCGGCGCTCCTGATATAGCATTCCCTCGAATGAACAACATAAGCTTCTGACTCCTGCCTCCATCGTTCCTTCTTCTACTGGCCTCTTCTGGCGTAGAAGCTGGGGTCGGTACGGGGTGAACCGTTTATCCACCGCTAGCCGGTAACCTTGCCCATGCTGGAGCCTCCGTAGACCTA---GCCATTTTCTCCCTTCACCTGGCCGGGGTCTCTTCAATCCTTGGTTCAATTAACTTTATTACCACAATTATCAACATAAAACCCCCAGCAATTTCCCAATACCAAACCCCATTGTTTATTTGAGCCCTGCTAGTAACCACCGTGCTTCTGCTGCTGTCATTACCAGTCTTAGCTGCA---GGAATTACGATATTACTGACAGATCGGAACCTAAACACAACATTCTTTGATCCGGCAGGCGGAGGAGACCCAATCCTCTACCAACACTTATTCTGATTCTTCGGACACCCCGAAGTATATATTCTAATTCTCCCAGGCTTCGGAATAATCTCTCACATTGTCGCCTACTACGCAGGGAAAAAG---GAGCCCTTTGGATACATAGGAATAGTATGAGCAATGATAGCAATCGGCCTTCTAGGGTTCATCGTGTGAGCCCACCACATATTTACAGTAGGAATGGATGTCGACACCCGAGCCTATTTCACATCAGCAACAATAATTATCGCAATTCCAACTGGTGTAAAAGTATTCAGCTGACTC---GCCACCCTATATGGAGGC---TCAATCAAGTGAGAAGCTCCATTCTTATGGGCCCTAGGCTTCATTTTCTTATTCACAGTGGGAGGCCTAACTGGTATTATTCTAGCCAACTCTTCTCTAGACATTGTACTGCACGACACGTACTACGTAGTTGCACACTTCCACTACGTC---CTATCCATAGGAGCCGTATTTGCAATTATGGGGGGATTTGTACACTGATTCCCACTATTCTCCGGGTACACCTTACACAGCACATGAACTAAAATCCACTTTGCTGTGATATTCATTGGAGTAAACCTCACATTCTTCCCACAACACTTCCTAGGGCTAGCAGGAATACCACGA---CGATACTCCGACTACCCAGACGCCTACACC---CTGTGAAACACCGTCTCATCCATTGGATCCCTAATCTCCCTTGTAGCCGTTATCATGTTCCTATTTATCCTTTGAGAAGCCTTCGCCGCCAAACGAGAAGTA---CTATCAGTAGACCTAACTACAACAAAC
-- end --

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Statistics of barcoding coverage: Gnathonemus petersii

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 10
Specimens with Barcodes: 13
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2010

Assessor/s
Awaïss, A., Lalèyè, P. & Moelants, T.

Reviewer/s
Snoeks, J., Tweddle, D., Getahun, A., Lalèyè, P., Paugy, D., Zaiss, R., Fishar, M.R.A & Brooks, E.

Contributor/s

Justification
This species has a wide distribution, with no known major widespread threats. It is therefore listed as Least Concern. It has also been assessed regionally as Least Concern for central and western Africa.
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Population

Population
No information available.

Population Trend
Unknown
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Threats

Major Threats
None known.
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Least Concern (LC)
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Management

Conservation Actions

Conservation Actions
None known. The taxonomy needs revision.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: subsistence fisheries; aquarium: commercial
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Wikipedia

Peters' elephantnose fish

Two elephantnose fish

Peters' elephantnose fish (Gnathonemus petersii; syn. Gnathonemus brevicaudatus Pellegrin, 1919, Mormyrus petersii Günther, 1862[2]) is an African freshwater elephantfish in the genus Gnathonemus. Other names in English include elephantnose fish, long-nosed elephant fish, and Ubangi mormyrid, after the Ubangi River. As the Latin name petersii confirms it is named after someone called "Peters" (probably Wilhelm Peters), although the apostrophe is often misplaced and the common name given as "Peter's elephantnose fish".

Description[edit]

Illustration (1864), the upper is Peters' elephantnose fish. The lower is Worm-Jawed Mormyrid, (Campylomormyrus tamandua), [Mormyridae], Elephant Nose

Peters' elephantnose fish are native to the rivers of West and Central Africa, in particular the lower Niger River basin, the Ogun River basin and in the upper Chari River. It prefers muddy, slowly moving rivers and pools with cover such as submerged branches. It is a dark brown to black in colour, laterally compressed (averaging 23–25 cm), with a rear dorsal fin and anal fin of the same length. Its caudal or tail fin is forked. It has two stripes on its lower pendicular. Its most striking feature, as its names suggest, is a trunk-like protrusion on the head. This is not actually a nose, but a sensitive extension of the mouth, that it uses for self-defense, communication, navigation, and finding worms and insects to eat. This organ is covered in electroreceptors, as is much of the rest of its body. The elephantnose fish has poor eyesight and uses a weak electric field, which it generates by muscular contractions, to find food, to navigate in dark or turbid waters, and to find a mate. Peters' elephantnose fish live to about 6-10 years, but there are reports of them living even longer.

In the aquarium[edit]

Peters' elephantnose fish is probably the most commonly available Mormyrid in aquarium stores in the USA. In the aquarium (which should be at least 200 liters) it is timid, preferring a heavily planted environment with subdued lighting. Ideally, a pipe or hollow log should be provided. The substrate should ideally be soft sand to allow the fish to sift through it with its delicate extended lip. It feeds on small worms (bloodworms) and aquatic invertebrates such as mosquito larvae, but in the aquarium will usually accept frozen or even flake food. How peaceful an elephantnose fish is can depend on the individual; some are quite aggressive with other species, while others are retiring. They may be kept in a community aquarium with peaceful species who share their water preferences. However, unless kept in an aquarium of over 400 liters, it is unwise to keep more than one elephantnose fish as they can be territorial. The conditions suggested to keep them in an aquarium are as follows: pH of 6.8 to 7.2, water temperature 26 to 28 degrees Celsius, and water of medium hardness. The substrate should always be something that does not irritate the sensitive snout of the fish.

The weak electrical impulses generated by this fish can be made audible by placing two electrodes in the fish tank that are then hooked up to an audio amplifier or a piezoelectric earbud. The elephant nose fish can use its electosensing to detect moving prey and worms in the substrate.

Although the elephant nose fish was once thought to have poor eyesight, it is now known to have good low light vision. Its eyes use a combination of photonic crystals, parabolic mirrors and a clustered arrangement of rods and cones. [3]

See also[edit]

Notes[edit]

References[edit]

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