Polypterus bichir

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Polypterus bichir, the Nile bichir, is a fish which lives in the Nile and some of its tributaries in Africa. It is a dark grayish color on the top, with a dark vertical marking and bands on the flank. This marking is more prominent on juveniles, and fades as the fish grows.

Contents

Nile bichir
Nile bichir.png
Polypterus bichir bichir
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Polypteriformes
Family: Polypteridae
Genus: Polypterus
Species:
P. bichir
Binomial name
Polypterus bichir
Lacépède, 1803
Subspecies
Polypterus bichir Map.jpg
Synonyms [1] [2]
  • Polypterus niloticusShaw 1804
  • Polypterus lapradeiSteindachner 1869

Species description

Polypterus bichir, the Nile bichir, is a fish which lives in the Nile and some of its tributaries in Africa. It is a dark grayish color on the top, with a dark vertical marking and bands on its elongated flank. This marking is more prominent on juveniles, and fades as the fish grows. The Nile bichir is characterized by 5-18 dorsal finlets made up of a dorsal spine and connected dorsal ray. This is noted in the etymology of this species name where Polypterus can be traced back to the Greek words meaning ‘many’ and ‘wing’, noting the dorsal finlets. The fish itself is elongated in an anguilliform body plan, with flexible movement. [3] Their swimming style itself mimics eels, with powerful sweeps of its long tail and free movement of the head from side-to-side, otherwise known as an undulatory motion. The bichir's pectoral fins, meanwhile, operate to keep the fish balanced through this process. [4]

Descriptive Guide of Polypterus traits and markings Polypterus Marking Guide.png
Descriptive Guide of Polypterus traits and markings

Nile bichirs are often regarded as ancestral ‘primitive’ fish due to their unique morphology that is usually found only in ancestral actinopterygian fish. Along with the dorsal finlets and coloring, the bichir is known for possessing ‘armor-like’ ganoid scales, true lungs, holoblastic egg development, sexually dimorphic anal fins, and spiracles. In captivity, bichir larvae and juveniles initially show fast growth up to a certain, species-specific, size but subsequently growth rates slow down once they reach maturity. P. bichir can grow as large as 750mm length wise from the tip of the snout to the end of the caudal peduncle, not including their caudal fin.

Photo of Bichir Dorsal finlets, the spine and ray can be seen connected. Bichir Dorsal Finlets- up close.png
Photo of Bichir Dorsal finlets, the spine and ray can be seen connected.

Polypterus Bichir Species Specific Traits

Sample of Tubercle variation in its organization within the same Bichir scale Tubercle variation sample from Coelho Research.png
Sample of Tubercle variation in its organization within the same Bichir scale          

Bichir are composed of 13 recognized species that are often hard to distinguish from one another due to similarity in their general appearance. Nile bichirs are known for being one of the ‘larger body morphs’ for bichir species; their size, higher number of dorsal finlets, wider heads and lower jaw placement are identifying characteristics used to differentiate Nile bichir from other bichir species. However, these identifying characteristics are often hard to distinguish, especially jaw placement, as juvenile Nile bichir jaws are still found higher in a terminal position of the head, which can lead to mislabeling of specimens, and has in the past. [3] Other methods of differentiating bichir species were to compare the tubercle, enamel-like ganoin with small bumps found on their ganoid scales, density, distance, and organization. It was theorized that these ‘ornamentations’ of the ganoid scales might be consistent within a species and differ from others. These scales make up most fossil records for Polypterus species as they preserve well and therefore can be easily studied. However, tubercle organization in the studied specimens varied greatly within the same species, across different regions of the body and even within the same scales. This study de-based former classification tools used by researchers for identification of bichir species. [5]

Data Sample indicating the main time periods of diversification for Polypteridae versus other groups. Diversification of Polypteridae over time.png
Data Sample indicating the main time periods of diversification for Polypteridae versus other groups.

Nile bichirs are often regarded as ancestral ‘primitive’ fish due to their unique morphology that is usually found only in ancestral fish. Along with the dorsal finlets and coloring, the bichir is known for possessing ‘armor-like’ ganoid scales, true lungs, holoblastic egg development, sexually dimorphic anal fins, and spiracles. [3] This is because polypterid were one of the earliest diverging groups from where they nest under the class Actinopterygii. Polypteridae, the family classification of Nile bichir, are thought to have diversified differently from other ray-finned fishes, with most diversification taking place in the Late Cretaceous period before declining in a ‘Boom and Bust’ style. [6]

Distribution

Map depicting the regional distribution of Nile bichir in Africa. The Key lists the symbols and their associated meanings of validity of the records. Bichir Distribution Map.png
Map depicting the regional distribution of Nile bichir in Africa. The Key lists the symbols and their associated meanings of validity of the records.

The Nile bichir is one of the more highly distributed species across Africa, ranging from the Nile River to the Congo Basin to West African countries like Senegal. [3] P. Bichir live in the deeper depressions of muddy riverbeds, sometimes considered a bottom-living fish, bichir are still active swimmers and travel mostly at night in search of food. [4]

Biology

Most of the features found in bichir are adaptations to both fish and invertebrate predators found in the swamps and rivers of tropical Africa the fish reside in. Ganoid scales and dorsal spines act as defensive measures for bichir to protect themselves from predators. Ganoid scales are hard, bony scales that act as ‘armor’ for the fish, comprising three layers of scales. [7] Ganoid scales are usually rhomboidal in shape and connect through a ‘peg and socket’ joint. They are the scales that arose in the class, Actinopterygii and are often found in primitive fossils of actinopterygians as well as Chondrostean. Ganoid scales are modified cosmoid scales with the cosmine replaced with dentine and the surface vitrodentine replaced with ganoine. Ganoine, which cover the Ganoid scales, are made up of an inorganic bone salt that has calcified into noncellular material. It is considered analogous to teeth enamel in vertebrae (Helfman et al, 2009).

Respiration

Bichirs are also known to possess spiracles, maxillary (upper jaw) bones fused to the skull and a set of true lungs. [7] The lungs of Bichirs are paired, well-developed, and vascularized to allow atmospheric air to regularly be taken in for respiration. Air uptake can occur in two different ways, through the mouth or the spiracles. [3] In poorly oxygenated waters, bichir are obligate air-breathers, and without access to the surface can drown. [8] Juvenile bichirs have external gills, which sometimes can persist for a long time into maturity in different species of bichir. [3] It is believed that the common ancestors of Nile bichir, sarcopterygians and actinopterygians, already possessed lungs, but as polypterid are believed to be the earliest diverging group of actinopterygians, they display many ancestrally associated traits, like these lungs. Polypterus have a similar molecular mechanism of lung development to tetrapods, suggesting that there is a common ancestor to both major ancestral fish lineages, sarcopterygians and actinopterygians that developed evolution for air breathing. The presence of lungs in ancestral fish also points out that the evolution of lungs did not come with the terrestrialization of vertebrates and can further shed understanding on ancestral osteichthyan traits with further research. [9]

Diet

Nile bichirs are often found hunting prey in the vegetated shallow beds of the water bodies it inhabits, using suction-feeding. Suction Feeding- the process of rapid oral cavity expansion to draw prey into its mouth, is often found in ancestral Osteichthyes fishes like bichirs. Most fish often use protrusible jaws to achieve this mechanism, but the bichir is unique in that they lack these protrusible jaws and instead have a relatively simplified mechanism of achieving this feeding method. Instead, they generate their feeding strike power from their body flexibility coordinated with various muscular and skeletal structure movements to create a vacuum, suction force, that draws the prey in. [10] Nile bichir can project cartilaginous-supported labial folds to form a funnel to further aid in this suction feeding mechanism. [3] Bichirs stomachs are adapted to swallow prey whole, the gastric muscles working in tandem to compress the dangerous spines found on their prey, preventing their stomach pouch from being torn. [4] Among these vegetated shallow beds, P. bichir often hunt for aquatic and terrestrial invertebrates, fish and amphibians, with the size of prey depending on the size of their mouths but can eat fish up to half their size. Nile bichirs rely heavily on their sense of smell to achieve this as they navigate the swamps, rivers and lakes they live in.

Reproduction

In nature, spawning normally occurs in densely vegetated areas, often flooding plains. Bichir often reach sexual maturity within a year, and their eggs are relatively large, and adhesive with a single micropyle. Yet, what really begins the spawning process is the sexually dimorphic anal fins that male and female Nile bichir possess. These unique anal fins are associated with a unique mating behavior, which uses sexually dimorphic anal fins as a part of courtship. [3] These anal fins are copulatory organs, with the male fins being ‘wider and rounded’ and the females described as ‘pointed and narrow’. Male polypteridae anal fins are ‘blown-up’ to form a cup-shaped organ and copulatory chamber. The process begins when, as the male swims alongside a female P. bichir, it will direct its anal fin, folded up like a gutter towards the vent of the female, fertilizing the eggs as they are released. This complex process is theorized to be a product of necessity to ensure all sperm released are successful as male bichir gonads are significantly smaller than females. [11]

Conservation Status

Currently, the Nile bichir is listed as Least Concerned based on the January 2020 reassessment of the IUCN Red list. [12] Regardless, Nile bichir are still highly impacted by human activities like fishing and habitat alteration. Yet due to the limited knowledge on bichir, it is hard to determine if their populations are indeed stable or declining. [3] In Egypt, the subspecies Polypterus bichir bichir is considered regionally extinct due to a variety of impacts placed on the species and its environment, often from habitat use and human impacts. The main major threats to freshwater fish of North Africa, where the Nile River flows through, include groundwater extraction and water pollution, as well as natural disasters such as drought and temperature extremes. Harvesting fish, while also impactful to local populations affects these fish to a lesser extent. [13]

Related Research Articles

<span class="mw-page-title-main">Actinopterygii</span> Class of ray-finned bony fishes

Actinopterygii, members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia, as opposed to the bulkier, fleshy lobed fins of the sister class Sarcopterygii. Resembling folding fans, the actinopterygian fins can easily change shape and wetted area, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton.

<span class="mw-page-title-main">Bichir</span> Family of archaic-looking ray-finned fishes

Bichirs and the reedfish comprise Polypteridae, a family of archaic ray-finned fishes and the only family in the order Polypteriformes.

<span class="mw-page-title-main">Actinopteri</span> Group of fishes

Actinopteri is the sister group of Cladistia (bichirs) in the class Actinopterygii.

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

The reedfish, ropefish, or snakefish, Erpetoichthys calabaricus, is a species of fish in the family Polypteridae alongside the bichirs. It is the only member of the genus Erpetoichthys. It is native to fresh and brackish waters in West and Central Africa. The reedfish possesses a pair of lungs in addition to gills, allowing it to survive in very oxygen-poor water. It is threatened by habitat loss through palm oil plantations, other agriculture, deforestation, and urban development.

<i>Polypterus senegalus</i> Species of fish

Polypterus senegalus, commonly known as the Senegal bichir, gray bichir or Cuvier's bichir, is an African species of ray-finned fish in the bichir family, Polypteridae. It is a typical example of polypterid fishes, as most of its defining physical features are common across the genus, such as its ancient, lungfish- or arowana-like appearance, the ability to breathe atmospheric oxygen, and its armor-like scales. These factors have influenced the species' popularity in captivity, and it is commonly kept by aquarists and other hobbyists.

<i>Polypterus</i> Genus of fishes

Polypterus is a genus of freshwater fish in the bichir family (Polypteridae) of order Polypteriformes. The type species is the Nile bichir. Fish in this genus live in various areas in Africa. Polypterus is the only known vertebrate to have lungs, but no trachea.

<span class="mw-page-title-main">Holostei</span> Group of bony fish

Holostei is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by the single living genus, Amia with two species, the bowfins, as well as the Ginglymodi, the sole living representatives being the gars (Lepisosteidae), represented by seven living species in two genera. The earliest members of the clade, which are putative "semionotiforms" such as Acentrophorus and Archaeolepidotus, are known from the Middle to Late Permian and are among the earliest known neopterygians.

<i>Polypterus bichir lapradei</i> Subspecies of fish

Polypterus bichir lapradei is a subspecies of freshwater fish in the family Polypteridae. P. bichir lapradei are demersal, primitive, and popular with experienced aquarists.

<i>Polypterus ornatipinnis</i> Species of fish

Polypterus ornatipinnis, the ornate bichir, is a bony fish of the family Polypteridae found in Lake Tanganyika and the Congo River basin in Central and East Africa. It is known from the Central African Republic, the Democratic Republic of the Congo, and Tanzania.

<span class="mw-page-title-main">Shortnose gar</span> Species of fish

The shortnose gar is a primitive freshwater fish of the family Lepisosteidae. It is native to the United States where its range includes the Mississippi and Missouri River basins, ranging from Montana to the west and the Ohio River to the east, southwards to the Gulf Coast. It inhabits calm waters in large rivers and their backwaters, as well as oxbow lakes and large pools. It is a long, slender fish, brown or olive green above and whitish below. It typically grows to about 60 cm (24 in) and is armored by rows of interlocking, rhomboidal ganoid scales.

<span class="mw-page-title-main">Barred bichir</span> Species of fish

The barred bichir, armoured bichir, bandback bichir, or banded bichir is a species of fish belonging to the class Actinopterygii, or the ray-finned fish, which constitute an order of the class of the bony fish. an elongated fish found in the Congo River, specifically in the upper and middle portions. This species is one of the more commonly available in commercial pet stores.

<span class="mw-page-title-main">Cladistia</span> Clade of ray-finned fishes

Cladistia is a clade of bony fishes whose only living members are the bichirs of tropical Africa. Their major synapomorphies are a heterocercal tail in which the dorsal fin has independent rays, and a posteriorly elongated parasphenoid.

<i>Polypterus endlicherii</i> Species of fish

Polypterus endlicherii, the saddled bichir, is one of the largest species of the Polypterus genus of freshwater fish.

<i>Polypterus congicus</i> Species of fish

Polypterus congicus, the Congo bichir, is a species of bichir with a maximum recorded size of 970 millimetres (38 in). The colour also varies from yellowish brown to grey, darker in the top, paler in the ventral area. It has a pattern of around 8 irregular vertical bands along the flanks of the fish, that do not extend completely onto the ventral surface. The lower jaw is prominent, much like Polypterus endlicherii. The male has a wider and thicker anal fin. These fish are commonly sold as pets.

<i>Polypterus palmas</i> Species of fish

Polypterus palmas, also called the shortfin or marbled bichir, is a fish in the family Polypteridae found in freshwater environments throughout West Africa.

<span class="mw-page-title-main">West African bichir</span> Species of fish

The West African bichir or retropinnis bichir, is a freshwater fish in the family Polypteridae, is found in the central Congo River basin and Ogooué River in Africa. It is a long, slender fish that grows to a maximum length of about 34 cm (13 in).

<i>Polypterus teugelsi</i> Species of fish

Polypterus teugelsi is a species of carnivorous, nocturnal bichir that lives in the Cross River drainage basin in the country of Cameroon. P. teugelsi was described in 2004 by Ralf Britz.

<i>Polypterus mokelembembe</i> Species of fish

Polypterus mokelembembe is a species of the fish genus Polypterus, found in the central basin of the Congo River. It was once considered a morph of the closely related Polypterus retropinnis, but was given species status in 2006 with a description that reclassified both fishes. Because of the recency of the species' description and the fact that P. mokelembembe is the paralectotype of P. retropinnis, they are often mistaken for one another in the aquarium trade.

<i>Polypterus polli</i> Species of fish

Polypterus polli, Poll's bichir, is a species of bichir from the Malebo Pool and the lower and central basins of the Congo River. It was named in honor of Belgian ichthyologist Max Poll.

<span class="mw-page-title-main">Spiracle (vertebrates)</span> Inspirational organ of most cartilaginous fish

Spiracles are openings on the surface of some animals, which usually lead to respiratory systems.

References

  1. ↑ Froese, R.; Pauly, D. (2017). "Polypteridae". FishBase . Retrieved 18 May 2017.
  2. ↑ Van Der Laan, Richard; Eschmeyer, William N.; Fricke, Ronald (11 November 2014). "Family-group names of Recent fishes". Zootaxa. 3882 (1): 1–230. doi: 10.11646/zootaxa.3882.1.1 . PMID   25543675.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 Moritz, Timo; Britz, Ralf (2019-07-23). Revision of the extant Polypteridae (Actinopterygii: Cladistia). DE: Verlag Dr. Friedrich Pfeil. doi:10.23788/ief-1094.
  4. 1 2 3 Harrington, N. R. (1899). "The Life Habits of Polypterus". The American Naturalist. 33 (393): 721–728. doi:10.1086/277415. JSTOR   2454356.
  5. 1 2 Coelho, Marcos Vinícius; Cupello, Camila; Brito, Paulo M.; Otero, Olga (July 2024). "Taxonomical use of scale ornamentation: Challenges by intraspecific and intra-individual variations in four adult specimens of Polypterus bichir". Journal of Fish Biology. 105 (1): 129–140. doi:10.1111/jfb.15752. ISSN   0022-1112. PMID   38651306.
  6. 1 2 Near, Thomas J.; Dornburg, Alex; Tokita, Masayoshi; Suzuki, Dai; Brandley, Matthew C.; Friedman, Matt (2014-01-02). "Boom and Bust: Ancient and Recent Diversification in Bichirs (Polypteridae: Actinopterygii), A Relictual Lineage of Ray-Finned Fishes". Evolution. 68 (4): 1014–1026. doi:10.1111/evo.12323. ISSN   0014-3820. PMID   24274466.
  7. 1 2 Moyle, Peter B. (2004). Fishes : an introduction to ichthyology. Joseph J. Cech, Jr.—5th ed. p. cm.
  8. ↑ Sidlauskas, Brian L.; Chakrabarty, Prosanta (September 2010). "The Diversity of Fishes: Biology, Evolution and Ecology". Copeia. 2010 (3) (2nd ed.): 527–529. doi:10.1643/ot-10-040.1. ISSN   0045-8511.
  9. ↑ Tatsumi, Norifumi; Kobayashi, Ritsuko; Yano, Tohru; Noda, Masatsugu; Fujimura, Koji; Okada, Norihiro; Okabe, Masataka (2016-07-28). "Molecular developmental mechanism in polypterid fish provides insight into the origin of vertebrate lungs". Scientific Reports. 6 (1): 30580. Bibcode:2016NatSR...630580T. doi:10.1038/srep30580. ISSN   2045-2322. PMC   4964569 . PMID   27466206.
  10. ↑ Whitlow, Katrina R.; Ross, Callum F.; Gidmark, Nicholas J.; Laurence-Chasen, J. D.; Westneat, Mark W. (2022-02-01). "Suction feeding biomechanics of Polypterus bichir : investigating linkage mechanisms and the contributions of cranial kinesis to oral cavity volume change". Journal of Experimental Biology. 225 (3). doi:10.1242/jeb.243283. ISSN   0022-0949. PMID   35019979.
  11. ↑ Holden, M. J. (1971). "Significance of sexual dimorphism of the anal fin in Polypteridae". Nature. 232 (5306): 135–136. Bibcode:1971Natur.232..135H. doi:10.1038/232135b0. PMID   16062871.
  12. ↑ "The IUCN Red List of Threatened Species- Polypterus Bichir". IUCN Red List. 2020. Retrieved November 4, 2024.
  13. ↑ Garcia, N. "The status and distribution of freshwater biodiversity in Northern Africa". IUCN, Cambridge, UK & Gland, Switzerland, 141 Pp.


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