Cynodontinae is a subfamily of tropical

Tropics

The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

n fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 of the order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Characiformes

Characiformes

The Characiformes are an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, there are a few thousand different species, including the well-known piranha and tetras.-Taxonomy:...

. They are characterized by an oblique mouth and very distinct canines. They are not prized as food fish, but are important in subsistence and commercial fisheries

Fishery

Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

. Hydrolycus are game fish

Game fish

Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...

, having been recently added to the International Game Fish Association

International Game Fish Association

The International Game Fish Association is the leading authority on angling pursuits and the keeper of the most current World Record fishing catches by fish categories. Fishermen who are sport fishers are careful to follow their stringent rules for fair play and line requirements in order to...

 in the fly and rod class. Cynodontid fish are also sometimes housed in aquaria

Aquarium

An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

.

Taxonomy

This monophyletic

Monophyly

In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...

 subfamily contains only a few species: three species of Cynodon, four speciecs of Hydrolycus, and one species in the monotypic

Monotypic

In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...

 Rhaphiodon genus, Rhaphiodon vulpinus. These fish have been previously classified within Characidae

Characidae

The Characidae, characids or characins are a family of freshwater subtropical and tropical fish, belonging to the order Characiformes. The name "characins" is the historical one, but scientists today tend to prefer "characids" to reflect their status as a by and large monophyletic group at family...

.

Rhaphiodon and Cynodon are sister groups to each other; these two genera together have a sister group relationship to the genus Hydrolycus.

Distribution and habitat

Cynodontinae species are found throughout the Orinoco and 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...

s, as well as the rivers of the Atlantic slopes of the Guianas. Of the cynodontines, R. vulpinus has the greatest distribution, including the Paraná

Paraná River

The Paraná River is a river in south Central South America, running through Brazil, Paraguay and Argentina for some . It is second in length only to the Amazon River among South American rivers. The name Paraná is an abbreviation of the phrase "para rehe onáva", which comes from the Tupi language...

-Paraguay River

Paraguay River

The Paraguay River is a major river in south central South America, running through Brazil, Bolivia, Paraguay, and Argentina...

 and Uruguay River

Uruguay River

The Uruguay River is a river in South America. It flows from north to south and makes boundary with Brazil, Argentina, and Uruguay, separating some of the Argentine provinces of the Mesopotamia from the other two countries...

 basins. Fossil teeth have been found in the Magdalena River

Magdalena River

The Magdalena River is the principal river of Colombia, flowing northward about through the western half of the country. It takes its name from the biblical figure Mary Magdalene. It is navigable through much of its lower reaches, in spite of the shifting sand bars at the mouth of its delta, as...

 basin and Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

, where cynodontines are not currently found.

These fish live in mid- to surface-water levels in rivers, flooded forests, and lakes.

Appearance and anatomy

Cynodontines are distinguished by their oblique mouth and highly developed pair of dentary canine teeth

Canine tooth

In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...

. These fish can get relatively large; Hydrolycus species can reach 65 centimetres (26 in).

Species

Hydrolycus species here are ordered based on their relationships from the most basal

Basal (phylogenetics)

In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 to the most apomorphic based on sister group relationships when possible. Descriptions and dates based on ITIS

Integrated Taxonomic Information System

The Integrated Taxonomic Information System is a partnership designed to provide consistent and reliable information on the taxonomy of biological species. ITIS was originally formed in 1996 as an interagency group within the U.S...

.

Rhaphiodon Agassiz in Spix and Agassiz, 1829

• Rhaphiodon vulpinus Agassiz in Spix and Agassiz, 1829

Cynodon Agassiz, 1829

• Cynodon gibbus (Agassiz, 1829)
• Cynodon meionactis Géry, Le Bail and Keith, 1999
• Cynodon septenarius Toledo-Piza, 2000

Hydrolycus Müller and Troschel, 1844

• Hydrolycus wallacei Toledo-Piza, Menezes and dos Santos, 1999
• Hydrolycus scomberoides (Cuvier, 1819)
• Hydrolycus armatus (Jardine and Schomburgk in Schomburgk, 1841)
• Hydrolycus tatauaia Toledo-Piza, Menezes and dos Santos, 1999