The sailfin tetra (''Crenuchus spilurus''), also known as the mojarita, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

belonging to the South American darter family,

Crenuchidae The Crenuchidae, or crenuchids, are a family of freshwater fish of the order Characiformes. The 11 genera include about 115 species, though several species are undescribed. These fish are relatively small (usually under in standard length) and ...

. It is found in the

Amazon Amazon most often refers to: * Amazon River, in South America * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon (company), an American multinational technology company * Amazons, a tribe of female warriors in Greek myth ...

and

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers approximately 1 million km2, with 65% of it in Venezuela and 35% in Colombia. It is the List of rivers by discharge, f ...

Basins, as well as various river Basins in

the Guianas The Guianas, also spelled Guyanas or Guayanas, are a geographical region in north-eastern South America. Strictly, the term refers to the three Guianas: Guyana, Suriname, and French Guiana, formerly British, Dutch, and French Guiana respectiv ...

. It is the only member of the

monospecific genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

, ''Crenuchus'', one of two genera within the subfamily

Crenuchinae The Crenuchidae, or crenuchids, are a family of freshwater fish of the order Characiformes. The 11 genera include about 115 species, though several species are undescribed. These fish are relatively small (usually under in standard length) and ...

Taxonomy

The sailfin tetra was first formally described in 1863 by the German-born British

ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 35,800 species of fish had been described as of March 2 ...

Albert Günther Albert Karl Ludwig Gotthilf Günther , also Albert Charles Lewis Gotthilf Günther (3October 18301February 1914), was a German-born British zoologist, ichthyologist, and herpetologist. Günther is ranked the second-most productive reptile tax ...

with its type locality given as the

Essequibo River The Essequibo River (; originally called by Alonso de Ojeda; ) is the largest river in Guyana, and the largest river between the Orinoco and Amazon River, Amazon. Rising in the Acarai Mountains near the Brazil–Guyana border, the Essequibo flows ...

in Guyana. When he described this species, Günther proposed the new monospecific genus ''Crenuchus''. This taxon is classified within the subfamily Crenuchinae of the family Crenuchidae in the suborder

Characoidei Characiformes is an order of Actinopterygii, ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.; Buckup P.A ...

of the

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Characiformes Characiformes is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.; Buckup P.A.: "Relationsh ...

, the characins and related fishes.

Etymology

The sailfin tetra is the only species in the genus ''Crenuchus'', this name is a combination of ''crena'', a

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word meaning "notch", and ''nucha'',

Medieval Latin Medieval Latin was the form of Literary Latin used in Roman Catholic Church, Roman Catholic Western Europe during the Middle Ages. It was also the administrative language in the former Western Roman Empire, Roman Provinces of Mauretania, Numidi ...

for the

nape The nape is the back of the neck. In technical anatomical/medical terminology, the nape is also called the nucha (from the Medieval Latin rendering of the Arabic , ). The corresponding adjective is ''nuchal'', as in the term ''nuchal rigidity'' ...

. Günther did not explain why he chose this name, nor is it obvious,, although it may be an allusion to the slight indentation on the nape developed by breeding males. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''spilurus'' is a compound of the Greek ''spilos'', which means "mark" or "spot", and ''oura'', meaning tail, a referenceto the circular black spot on the distal end of the

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

Distribution and habitat

The sailfin tetra has a wide distribution in northern South America in the catchments of the

and Amazon Rivers in Brazil, Colombia. Ecuador. Peru and Venezuela, as well as in the coastal rivers of Guyana, Suriname and

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

. It occurs in small streams with a slow current and in intermittent pools along the sides of streams. This species is found in environments with complex structures, frequently being found in assoaciation with leaf litter.

Ecology and behavior

The sailfin tetra, as a tiny species, is unlikely to participate in active dispersal across long distances. This is clear from its absence in the main channel of huge rivers. Active migration in open areas, particularly in a predator-rich environment like the Amazon basin, presents unique obstacles for small, non-schooling fish. The species makes specific use of the rhythmic oscillations of the dorsal fin to control its movements precisely, stressing its close relationship with complex structures. Unlike most members of the Characiformes group, the sailfin tetra does not swim much and prefers to stay near stream margin structures. As a hard substrate spawner with larvae that sink to the substrate, passive larval dispersal is reduced, implying a preference for

philopatry Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives ...

. This behavior stands in stark contrast to the majority of the order's species, which are either spread spawners or have minimal site selection for spawning.

Utilization

The sailfin tetra is found in the

aquarium An aquarium (: aquariums or aquaria) is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. fishkeeping, Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquati ...

trade, but the collection of specimens from the wild is not thought to be a threat to the populations of this species.

References

{{Taxonbar, from=Q1412384 Crenuchinae Tetras of Brazil Freshwater fish of Colombia Freshwater fish of Peru Fish of the Amazon basin Taxa named by Albert Günther