Brown ghost knifefish

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Brown ghost knifefish
Brownghostknifefish.jpg
Endangered
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gymnotiformes
Family: Apteronotidae
Genus: Apteronotus
Species:
A. leptorhynchus
Binomial name
Apteronotus leptorhynchus
(M. M. Ellis, 1912)
Synonyms
  • Sternarchus leptorhynchusEllis 1912

The brown ghost knifefish (Apteronotus leptorhynchus) is a species of weakly electric knifefish in the family Apteronotidae. The brown ghost knifefish is the only vertebrate proven to have negligible brain aging thus far. [1] As such, they are extensively researched as a model species for neurological and developmental studies. In the wild, A. leptorhynchus is understudied known only to inhabit deep channels of large, lowland rivers, specifically the Essequibo River drainage in Guyana, where it is active nocturnally and seeks vegetated retreat sites during the day. [2] They are listed as an endangered species by the ICUN. [3]

Contents

Taxonomy

Apteronotus leptorhynchus is a ray-finned fish belonging to the Neotropical knifefish order Gymnotiformes. Brown ghost knifefish are within the Apteronotidae family, which are distinguished from other Gymnotiforms by the presence of a caudal tail. [4]

Phylogenetic tree of the family Apteronotidae with the genus Apteronotus highlighted Brownghostknifefishtree.jpg
Phylogenetic tree of the family Apteronotidae with the genus Apteronotus highlighted

The clade to which A. leptorhynchus belongs, historically named A. leptorhynchus and thought to be monophyletic, was recently split into nine separate species native to tropical South America. All species within this clade are similar in morphology and osteology, likely due to extreme morphological convergence within similarly structured riparian habitats. [2] The remaining species of Apteronotus leptorhynchus was redefined to a genetically and geographically isolated population inhabiting the Essequibo River and its drainage basin. [4]

Description

The ribbon-like anal fin of the brown ghost knifefish (Apteronotus leptorhynchus) extends along the ventral side and aids in locomotion Brownghostknifefish2.jpg
The ribbon-like anal fin of the brown ghost knifefish (Apteronotus leptorhynchus) extends along the ventral side and aids in locomotion

As a member of the family Apteronotidae, brown ghost knifefish are laterally compressed and sport a long, posteriorly tapered body form. They lack pelvic and dorsal fins, yet retain a pointed pectoral fin and a greatly reduced caudal tail, an identifying trait of Apteronotids among the Gymnotiforms. [4]  Brown ghost knifefish possess an elongated, ribbon-like anal fin which extends along the majority of its ventral side. This fin comprises around one hundred and fifty fin rays and is utilized as the species’ main source of locomotion. [5] Among teleost fishes, this species has relatively restricted gill openings. Brown ghost knifefish have a laterally compressed head, a terminal mouth, and small, laterally located eyes covered by a thin membrane. The urogenital papilla and anus are located beneath the head, posterior to the eyes. [4] Generally, they possess 17–18 pectoral-fin rays, 151–156 anal-fin rays, 17–21 caudal-fin rays, 78–82 scales along the lateral line, 18 precaudal vertebrae, and 78–81 total vertebrae. [4] Among collected individuals, brown ghost knifefish range in total length between 93.1 and 260.0 mm. Tail length ranges from 13.0 to 20.7 mm. Head length ranges from 15.0 to 46.7 mm. [4]

Dentary bone of the brown ghost knifefish; the posterior teeth are twice the size of the anterior teeth Brownghostknifefishteeth.jpg
Dentary bone of the brown ghost knifefish; the posterior teeth are twice the size of the anterior teeth

Brown ghost knifefish can be distinguished from other genera within the family Apteronotidae based on a multitude of distinct synapomorphies. Brown ghost knifefish can be identified externally by the pale median stripe running longitudinally from the chin through the dorsal half of the fish. [4] Their teeth are also distinct in that the posterior teeth of the dentary bone are twice the size of the anterior teeth. [4] Less conspicuous identifiers of brown ghost knifefish include the notable elongation and anterior positioning of some cranial bones, including the anguloarticular, endopterygoid, and quadrate bones. [4]

There are few inconspicuous, yet observable, traits that distinguish A. leptorhynchus from other members of the Apteronotus genus. Among Apteronotus, the number and morphology of the infraorbital ossifications is variable. A. leptorhynchus is distinct in the tubular form of its fifth infraorbital. [4]

When preserved in alcohol, the body and head of brown ghost knifefish are light to dark brown in coloration. The anal and pectoral fins are dark brown and encircled by translucent membrane bands. The caudal fin is encircled by a pale band at the base and is dark brown posteriorly. A prominent pale band runs laterally along the dorsal midsection of the body. [4]

Geographic distribution

Brown ghost knifefish inhabit the Essequibo River and its drainage basin Essequibo rivermap.png
Brown ghost knifefish inhabit the Essequibo River and its drainage basin

The brown ghost knifefish is endemic to the Essequibo River and its drainage basin in Guyana. [2] Historically, this fish was thought to inhabit broad regions of northern South America, including the Pacific and Caribbean drainages of Colombia, Venezuela, and Peru. These populations were either misidentified or now belong to newly described, distinct species. [4]

Ecology and habitat preference

Within the Essequibo River and its drainage basin, brown ghost knifefish prefer deep channels where limited light can reach. They are active nocturnally and move from deep waters to the shore during dark hours. During the day, they seek refuge among roots and under logs to avoid diurnal predators. [6] Intraspecific competition among shelter sites is determined by dominance hierarchies. These hierarchies are influenced by the size and electric signal intensity of males. Males take shelter alone while female fish group together within retreat sites. [6] [7]

Electric organ discharges (EOD) are frequently produced by brown ghost knifefish, serving a variety of functions including prey capture, navigation, and social dominance. [8] Six distinct signal types have been observed, the most common being short, low frequency "chirps". [9] Chirp production is dependent on the close proximity between individual brown ghost knifefish. [8] [9] Individuals relay an "echo" signal in response to these hardly detectable chirps, indicating a substantially high sensitivity to electrocommunication within this species. [10] Signals increase in frequency as individuals approach or are approached by a focal target. [11] EODs do not seem to incur a significant metabolic costs when in oxygen-abundant conditions. In hypoxic environments however, brown ghost knifefish reduce the amplitude of EODs to maintain a healthy metabolic rate. [12]

Frequency-time chart and oscillogram of a brown ghost knifefish's "chirp" signal Brownghostknifefishchirp.jpg
Frequency-time chart and oscillogram of a brown ghost knifefish's "chirp" signal

Electrocommunication appears to serve different functions between male and female brown ghost knifefish. Among males, electric signals are intense and pronounced, utilized to establish social dominance and access to higher quality resources. [8] [9] During contact between males, aggressive signals characterized as abrupt frequency rises are sent to battle over dominance . Even amongst females, short rises in electric signals serve an aggressive intrasexual function. Long rises, conversely, serve an intersexual role and act as an advertisement of reproductive condition or status towards potential mates. [13]

Diet

Based on diet analysis of closely related and morphologically similar species, brown ghost knifefish likely feed on benthic invertebrates, shrimp, and small fish. [14]

Use in research

Due to their capacity to produce electric signals and their unique lack of brain senescence, brown ghost knifefish are heavily researched in the fields of electrocommunication neuroethology. [1] [15] [16] Many research projects focused on the use of electric signals in this species have shed light on their natural behaviors and the functions of electric communication in similarly electric species. [7] [9] [12] [13] This species has been extensively studied to understand cellular, molecular, and morphological mechanisms underlying adult neurogenesis and neuronal regeneration in both the brain and the spinal cord. [15] [16] Researchers aim to determine the specific genetic and osteological components that prevent brain senescence in this species. However, a complete genome of this fish has yet to be sequenced.

In recreation

The brown ghost knifefish, along with the closely related black ghost knifefish, are popular aquarium pets and are readily available to purchase within the fish trade. [17]

Threats and Conservation

Because the brown ghost knifefish is not well-studied in its natural habitat, not much is known about the threats that impact its population. As such, it is unclear how this species is responding to most human impacts, such as habitat degradation or climate change. Commercially farmed catfish within the Essequibo River are a prominent predator of this species and represent a growing biotic threat. A. leptorhynchus is currently listed as an endangered species according to the ICUN. [3]

See also

Related Research Articles

<span class="mw-page-title-main">Gymnotiformes</span> Order of bony fishes

The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water, these mostly nocturnal fish are capable of producing electric fields to detect prey, for navigation, communication, and, in the case of the electric eel, attack and defense. A few species are familiar to the aquarium trade, such as the black ghost knifefish, the glass knifefish, and the banded knifefish.

<span class="mw-page-title-main">Ghost knifefish</span> Family of fishes

The ghost knifefishes are a family, Apteronotidae, of ray-finned fishes in the order Gymnotiformes. These fish are native to Panama and South America. They inhabit a wide range of freshwater habitats, but more than half the species in the family are found deep in rivers where there is little or no light.

<span class="mw-page-title-main">Electric fish</span> Fish that can generate electric fields

An electric fish is any fish that can generate electric fields, whether to sense things around them, for defence, or to stun prey. Most fish able to produce shocks are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family (Uranoscopidae). Electric fish, although a small minority of all fishes, include both oceanic and freshwater species, and both cartilaginous and bony fishes.

<span class="mw-page-title-main">Black ghost knifefish</span> Species of fish

The black ghost knifefish is a tropical fish belonging to the ghost knifefish family (Apteronotidae). They originate in freshwater habitats in South America where they range from Venezuela to the Paraguay–Paraná River, including the Amazon Basin. They are popular in aquaria. The fish is all black except for two white rings on its tail, and a white blaze on its nose, which can occasionally extend into a stripe down its back. It moves mainly by undulating a long fin on its underside. It will grow to a length of 45–50 centimetres (18–20 in).

<span class="mw-page-title-main">Electroreception and electrogenesis</span> Biological electricity-related abilities

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 stun prey. The capabilities are found almost exclusively in aquatic or amphibious animals, since water is a much better conductor of electricity than air. In passive electrolocation, objects such as prey are detected by sensing the electric fields they create. In active electrolocation, fish generate a weak electric field and sense the different distortions of that field created by objects that conduct or resist electricity. Active electrolocation is practised by two groups of weakly electric fish, the Gymnotiformes (knifefishes) and the Mormyridae (elephantfishes), and by Gymnarchus niloticus, the African knifefish. An electric fish generates an electric field using an electric organ, modified from muscles in its tail. The field is called weak if it is only enough to detect prey, and strong if it is powerful enough to stun or kill. The field may be in brief pulses, as in the elephantfishes, or a continuous wave, as in the knifefishes. Some strongly electric fish, such as the electric eel, locate prey by generating a weak electric field, and then discharge their electric organs strongly to stun the prey; other strongly electric fish, such as the electric ray, electrolocate passively. The stargazers are unique in being strongly electric but not using electrolocation.

<span class="mw-page-title-main">Banded knifefish</span> Species of fish

The banded knifefish is a species of gymniform knifefish native to a wide range of freshwater habitats in South America. It is the most widespread species of Gymnotus, but it has frequently been confused with several relatives, including some found outside its range like the Central America G. maculosus. The English name "banded knifefish" is sometimes used for the entire genus Gymnotus instead of only the species G. carapo.

<i>Magosternarchus</i> Genus of fishes

Magosternarchus is a genus of weakly electric knifefish in the family Apteronotidae, containing two species. They are endemic to Brazil, occurring in large river channels in the Amazon River basin. Both species are unusual benthic predators that specialize in biting off the tails of other knifefishes, and are characterized by their greatly enlarged jaws and teeth. Recent systematic studies indicate that both species should be included in Sternarchella instead of being placed in their own genus.

Sternarchella schotti is a species of weakly electric knifefish in the family Apteronotidae. This species is endemic to Brazil where it is found in the Amazon River basin, and is sometimes kept in aquaria. The species grows to approximately 20 cm in length, and has a pale pink color in life with brown speckling along the dorsal surface of the head and body. As with many other ghost knifefishes (Apteronotidae) this species is aggressive with other electric fish species (Gymnotiformes), but is often compatible in captivity with species in other orders, such as catfish and angelfish. A recommended diet for S. schotti is frozen or live blood worms and insect larva, and diced meat.

Sternarchogiton nattereri is a species of weakly electric knifefish in the family Apteronotidae. It is native to the Amazon River system and feeds on sponges. Unlike other members of the genus Sternarchogiton, there is pronounced sexual dimorphism in S. nattereri, with reproductively mature males developing strong external teeth on tips of their jaws. These males are so different from the females and juveniles that they were thought to be a different genus and species, the "tooth-lip knifefish" Oedemognathus exodon, for over 40 years.

<i>Orthosternarchus</i> Species of fish

Orthosternarchus tamandua, the tamandua knifefish, is a species of weakly electric knifefish in the family Apteronotidae, native to the deep river channels of the Amazon basin. This species is characterized by its whitish-pink color, long tubular snout, long dorsal appendage, and tiny, bilaterally asymmetrical eyes.

Sternarchogiton porcinum is a species of weakly electric knifefish in the family Apteronotidae. It is native to deep river channels in the Río Huallaga, Río Napo, and Río Amazonas in Peru, and in the Río Orinoco in Venezuela. Many specimens once identified as S. porcinum from the Brazilian Amazon Basin and the Venezuelan Orinoco are now known to be a different species, S. preto.

<i>Tembeassu</i> Species of fish

Tembeassu is a genus of weakly electric knifefish in the family Apteronotidae. It is monotypic, being represented by the single species Tembeassu marauna. This species is known only from three specimens collected from the upper Paraná River, Brazil, in 1965. This fish can be identified by fleshy extensions at the tips of its upper and lower jaws, with the upper extension bearing a patch of extra teeth. The function of these unique structures is unknown, but may relate to feeding. Apparently a specialized inhabitant of deep riverine environments, T. marauna may be endangered by extensive dam construction in the upper Paraná region, if not already extinct.

<i>Apteronotus</i> Genus of fishes

Apteronotus is a genus of weakly electric knifefish in the family Apteronotidae, distinguished by the presence of a tiny tail fin. This genus is restricted to tropical and subtropical South America and Panama where found in a wide range of freshwater habitats. They feed on small animals.

<span class="mw-page-title-main">Jamming avoidance response</span> Behavior performed by weakly electric fish to prevent jamming of their sense of electroreception

The jamming avoidance response is a behavior of some species of weakly electric fish. It occurs when two electric fish with wave discharges meet – if their discharge frequencies are very similar, each fish shifts its discharge frequency to increase the difference between the two. By doing this, both fish prevent jamming of their sense of electroreception.

<span class="mw-page-title-main">Günther K.H. Zupanc</span> German-American neurobiologist (born 1958)

Günther K.H. Zupanc is a German-American neurobiologist, researcher, university teacher, book author, journal editor, and educational reformer. He is a Professor in the Department of Biology at Northeastern University in Boston, Massachusetts.

Sternarchella, the bulldog knifefish, is a genus of ghost knifefishes found at depths of 2–50 m (7–164 ft) in the main channel of large rivers in South America. Most are from the Amazon basin, but S. orthos is found both in the Amazon and Orinoco, S. orinoco is restricted to the Orinoco and S. curvioperculata restricted to the upper Paraná basin. They are often common in their habitat.

<i>Rhamphichthys</i> Genus of fishes

Rhamphichthys(Rhamphos = Greek for beak and Ichthys = Greek for fish) is a genus of fish that includes the South American sand knifefish. These fish are eel shaped with a distinct beak like snout which gave them their name. Like most other knifefish Rhamphichthys species have electrical organs that help them live in the murky waters of South America. Currently there are 10 recognized species of Rhamphichthys, although many changes have been made in their taxonomy since their original discovery.

Distocyclus conirostris is a species of glass knifefishes found in the deep waters of the Amazon basin, lower portions of the Potaro River and in major parts of the Rio Orinoco. They are typically relegated to flood basins, flooded forests and main river channels. They have often been found gathering in small groups around vegetation, indicating a social nature. The fish has semi-translucent, glass-like pectoral and anal fins. The main body is a ground-like color with a lighter head. The largest currently recorded specimen is 34.5 cm.

Compsaraia samueli, the pelican knifefish, is a species of apteronotid electric fish from the western Amazon basin of Brazil and Peru. It exhibits pronounced sexual dimorphism in which mature males develop extremely elongated snouts and oral jaws. This phenotype is found in several other apteronotid species and is used in agonistic jaw-locking behaviors between males.

Apteronotus rostratus is a species of apteronotid electric fish. These fish typically exhibit a wide diversity of skull shapes, ranging from highly elongate skulls to highly foreshortened ones, with both types evolving independently multiple times. In Apteronotus rostratus and some others, such as Compsaraia samueli, mature males grow extremely elongated snouts and oral jaws which are used in agonistic interactions with other males. This is an example of sexual weaponry. A study comparing skull shape and jaw-closing performance in males and females of Apteronotus rostratus suggested that males with elongated faces for use in fights did not have lower mechanical advantages, in contrast to the similar species Compsaraia samueli in which males exhibit a trade-off between sexual weaponry and jaw leverage.

References

  1. 1 2 Ilieş, Iulian; Sîrbulescu, Ruxandra F.; Zupanc, Günther K.H. (November 2014). "Indeterminate body growth and lack of gonadal decline in the brown ghost knifefish ( Apteronotus leptorhynchus ), an organism exhibiting negligible brain senescence". Canadian Journal of Zoology. 92 (11): 947–953. Bibcode:2014CaJZ...92..947I. doi:10.1139/cjz-2014-0109. ISSN   0008-4301.
  2. 1 2 3 Bernt, Maxwell J.; Tagliacollo, Victor A.; Albert, James S. (2019-06-01). "Molecular phylogeny of the ghost knifefishes (Gymnotiformes: Apteronotidae)". Molecular Phylogenetics and Evolution. 135: 297–307. Bibcode:2019MolPE.135..297B. doi:10.1016/j.ympev.2019.02.019. ISSN   1055-7903. PMID   30844446.
  3. 1 2 "https://www.iucnredlist.org/".{{cite web}}: External link in |title= (help)[ full citation needed ]
  4. 1 2 3 4 5 6 7 8 9 10 11 12 De Santana, Carlos David; Vari, Richard P. (July 2013). "Brown ghost electric fishes of the Apteronotus leptorhynchus species-group (Ostariophysi, Gymnotiformes); monophyly, major clades, and revision: Apteronotus Leptorhynchus Species-Group". Zoological Journal of the Linnean Society. 168 (3): 564–596. doi:10.1111/zoj.12022.
  5. ↑ Youngerman, Eric D.; Flammang, Brooke E.; Lauder, George V. (2014-10-01). "Locomotion of free-swimming ghost knifefish: anal fin kinematics during four behaviors". Zoology. 117 (5): 337–348. Bibcode:2014Zool..117..337Y. doi:10.1016/j.zool.2014.04.004. ISSN   0944-2006. PMID   25043841.
  6. 1 2 Dunlap, K.; Oliveri, L. (2002-07-01). "Retreat site selection and social organization in captive electric fish, Apteronotus leptorhynchus". Journal of Comparative Physiology A. 188 (6): 469–477. doi:10.1007/s00359-002-0319-5. ISSN   1432-1351. PMID   12122465.
  7. 1 2 Raab, Till; Linhart, Laura; Wurm, Anna; Benda, Jan (2019-07-05). "Dominance in Habitat Preference and Diurnal Explorative Behavior of the Weakly Electric Fish Apteronotus leptorhynchus". Frontiers in Integrative Neuroscience. 13: 21. doi: 10.3389/fnint.2019.00021 . ISSN   1662-5145. PMC   6624740 . PMID   31333424.
  8. 1 2 3 Hupé, Ginette J.; Lewis, John E. (2008-05-15). "Electrocommunication signals in free swimming brown ghost knifefish, Apteronotus leptorhynchus". Journal of Experimental Biology. 211 (10): 1657–1667. Bibcode:2008JExpB.211.1657H. doi:10.1242/jeb.013516. ISSN   1477-9145. PMID   18456893.
  9. 1 2 3 4 Zupanc, G. K. H.; Sîrbulescu, R. F.; Nichols, A.; Ilies, I. (2006-02-01). "Electric interactions through chirping behavior in the weakly electric fish, Apteronotus leptorhynchus". Journal of Comparative Physiology A. 192 (2): 159–173. doi:10.1007/s00359-005-0058-5. ISSN   1432-1351.
  10. ↑ Gama Salgado, José Antonio; Zupanc, Günther K.H. (June 2011). "Echo response to chirping in the weakly electric brown ghost knifefish ( Apteronotus leptorhynchus ): role of frequency and amplitude modulations". Canadian Journal of Zoology. 89 (6): 498–508. Bibcode:2011CaJZ...89..498G. doi:10.1139/z11-014. ISSN   0008-4301.
  11. ↑ Rasnow, B. (1996-03-01). "The effects of simple objects on the electric field of Apteronotus". Journal of Comparative Physiology A. 178 (3): 397–411. doi:10.1007/BF00193977. ISSN   1432-1351.
  12. 1 2 Reardon, Erin E.; Parisi, Alana; Krahe, Rüdiger; Chapman, Lauren J. (2011-12-15). "Energetic constraints on electric signalling in wave-type weakly electric fishes". Journal of Experimental Biology. 214 (24): 4141–4150. Bibcode:2011JExpB.214.4141R. doi:10.1242/jeb.059444. ISSN   1477-9145. PMID   22116756.
  13. 1 2 Tallarovic, S.; Zakon, H. (2002-09-01). "Electrocommunication signals in female brown ghost electric knifefish, Apteronotus leptorhynchus". Journal of Comparative Physiology A. 188 (8): 649–657. doi:10.1007/s00359-002-0344-4. ISSN   1432-1351. PMID   12355241.
  14. ↑ Winemiller, Kirk O.; Adite, Alphonse (1997-06-01). "Convergent evolution of weakly electric fishes from floodplain habitats in Africa and South America". Environmental Biology of Fishes. 49 (2): 175–186. Bibcode:1997EnvBF..49..175W. doi:10.1023/A:1007376826609. ISSN   1573-5133.
  15. 1 2 Heiligenberg, W.; Wong, C. J. H.; Metzner, W.; Keller, C. H. (1996-11-01). "Motor control of the jamming avoidance response of Apteronotus leptorhynchus: evolutionary changes of a behavior and its neuronal substrates". Journal of Comparative Physiology A. 179 (5): 653–674. doi:10.1007/BF00216130. ISSN   1432-1351. PMID   8888577.
  16. 1 2 Sas, E.; Maler, L. (May 1986). "Retinofugal projections in a weakly electric gymnotid fish (Apteronotus leptorhynchus)". Neuroscience. 18 (1): 247–259. doi:10.1016/0306-4522(86)90191-0. ISSN   0306-4522. PMID   2426631.
  17. ↑ Smith, Adam R.; Proffitt, Melissa R.; Ho, Winnie W.; Mullaney, Claire B.; Maldonado-Ocampo, Javier A.; Lovejoy, Nathan R.; Alves-Gomes, José A.; Smith, G. Troy (2016-10-01). "Evolution of electric communication signals in the South American ghost knifefishes (Gymnotiformes: Apteronotidae): A phylogenetic comparative study using a sequence-based phylogeny". Journal of Physiology-Paris. Electric Fish Meeting 2016: Electrosensory and Electromotor Systems. 110 (3, Part B): 302–313. doi:10.1016/j.jphysparis.2016.10.002. ISSN   0928-4257. PMC   5836322 . PMID   27769924.


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