Pariosternarchus amazonensis
Encyclopedia
Pariosternarchus amazonensis is a little-known species
of weakly electric
knifefish
in the family
Apteronotidae, and the only member of its genus
. It is found in the main channel of the Amazon River
in Brazil
and Peru
, likely near the bottom in deep, fast-moving water. This species is characterized by a wide head with a flat bottom, and very large sensory canals along the lower jaw. Like several other knifefishes found in deep river channels, it has reduced eyes, scales, and body pigmentation.
Ichthyological Exploration of Freshwaters; the type specimen is a 12.1 cm (4.8 in) long fish caught near the municipality
of Alvarães
in the Brazilian state of Amazonas. The authors coined for it the new genus Pariosternarchus, from the Greek
pario ("cheek", referring to the wide head), and sternon + archos ("chest" + "rectum", a commonly used name for apteronotids that refers to the anterior position of the urogenital opening
). From morphological
similarities, P. amazonensis is thought to belong to the navajini, an informal taxonomic group of apteronotids adapted to fast-flowing, large rivers, with the genus Sternarchella being its closest relatives.
, along the Rio Solimões in Brazil
from the confluence of the Rio Japurá to the confluence of the Rio Madeira, and near the city of Iquitos
in Peru
. It can be found in deep river channels, flooded beaches, and the mouths of large whitewater
tributaries.
are highly expanded. P. amazonensis is laterally compressed with a short body cavity
. Like other members of its family, it has a long anal fin, a minute caudal fin, no pelvic or dorsal fin
s, and an electroreceptive dorsal appendage that originates about halfway along the back. There are 155–168 anal fin rays, 14–15 pectoral fin rays, and 16–17 caudal fin rays. The scales are large and diamond-shaped, with 6–8 rows above the lateral line
but not reaching the upper surface of the head and body. Virtually unpigment
ed aside from tiny chromatophore
s speckling the bottom of the head and branchiostegal membranes, P. amazonensis is uniformly white-pink with translucent fins. The largest known specimen is 15.2 cm (6 in) long.
for electrolocation and communication like all other gymnotiforms, though its electric organ discharge (EOD) has not been described.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of weakly electric
Electric fish
An electric fish is a fish that can generate electric fields. It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the sea and in freshwater...
knifefish
Gymnotiformes
The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Apteronotidae, and the only member of its genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
. It is found in the main channel of the Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
, likely near the bottom in deep, fast-moving water. This species is characterized by a wide head with a flat bottom, and very large sensory canals along the lower jaw. Like several other knifefishes found in deep river channels, it has reduced eyes, scales, and body pigmentation.
Taxonomy
Ichthyologists James S. Albert and William G.R. Crampton described P. amazonensis in 2006, in the scientific journalScientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Ichthyological Exploration of Freshwaters; the type specimen is a 12.1 cm (4.8 in) long fish caught near the municipality
Municipality
A municipality is essentially an urban administrative division having corporate status and usually powers of self-government. It can also be used to mean the governing body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district...
of Alvarães
Alvarães, Amazonas
Alvarães is a municipality located in the Brazilian state of Amazonas. Its population was 14,369 and its area is 5,912 km²....
in the Brazilian state of Amazonas. The authors coined for it the new genus Pariosternarchus, from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
pario ("cheek", referring to the wide head), and sternon + archos ("chest" + "rectum", a commonly used name for apteronotids that refers to the anterior position of the urogenital opening
Urogenital opening
The urogenital opening is where waste products of the body and reproductive fluids are expelled to the environment outside of the body cavity. In some organisms, including birds and many fish, discharge from the urological, digestive, and reproductive systems empty into a common sac called the...
). From morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
similarities, P. amazonensis is thought to belong to the navajini, an informal taxonomic group of apteronotids adapted to fast-flowing, large rivers, with the genus Sternarchella being its closest relatives.
Distribution and habitat
Pariosternarchus amazonensis occurs in the Amazon RiverAmazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
, along the Rio Solimões in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
from the confluence of the Rio Japurá to the confluence of the Rio Madeira, and near the city of Iquitos
Iquitos
Iquitos is the largest city in the Peruvian rainforest, with a population of 370,962. It is the capital of Loreto Region and Maynas Province.Located on the Amazon River, it is only above sea level, although it is more than from the mouth of the Amazon at Belém on the Atlantic Ocean...
in Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
. It can be found in deep river channels, flooded beaches, and the mouths of large whitewater
Whitewater
Whitewater is formed in a rapid, when a river's gradient increases enough to disturb its laminar flow and create turbulence, i.e. form a bubbly, or aerated and unstable current; the frothy water appears white...
tributaries.
Description
Pariosternarchus amazonensis has a wide head, measuring up to a seventh as wide as long, with a completely flat ventral surface. The mouth is small and slung beneath the moderately long snout; conical teeth are present in both jaws. The sensory canals along the mandibleMandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
are highly expanded. P. amazonensis is laterally compressed with a short body cavity
Body cavity
By the broadest definition, a body cavity is any fluid-filled space in a multicellular organism. However, the term usually refers to the space located between an animal’s outer covering and the outer lining of the gut cavity, where internal organs develop...
. Like other members of its family, it has a long anal fin, a minute caudal fin, no pelvic or dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s, and an electroreceptive dorsal appendage that originates about halfway along the back. There are 155–168 anal fin rays, 14–15 pectoral fin rays, and 16–17 caudal fin rays. The scales are large and diamond-shaped, with 6–8 rows above the lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
but not reaching the upper surface of the head and body. Virtually unpigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
ed aside from tiny chromatophore
Chromatophore
Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...
s speckling the bottom of the head and branchiostegal membranes, P. amazonensis is uniformly white-pink with translucent fins. The largest known specimen is 15.2 cm (6 in) long.
Biology and ecology
The highly compressed form, small eyes, and reduced scales and coloration of P. amazonensis are consistent with living in deep (up to 25 m), fast-moving waters in large rivers. Its broad, flat-bottomed head and small, subterminal mouth suggest that it is a benthic forager. P. amazonensis is presumably capable of producing an electric fieldElectric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
for electrolocation and communication like all other gymnotiforms, though its electric organ discharge (EOD) has not been described.