Characiformes

Characiformes Fossil range: Early Cretaceous - Recent
Hyphessobrycon bentosi
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Characiformes
Families
Acestrorhynchidae Alestiidae Anostomidae Characidae Chilodontidae Citharinidae Crenuchidae Ctenoluciidae Curimatidae Cynodontidae Distichodontidae Erythrinidae Gasteropelecidae Hemiodontidae Hepsetidae Lebiasinidae Parodontidae Prochilodontidae Salminopsidae † Serrasalmidae Sorbinicharacidae †

Characiformes is a diverse order of ray-finned fish, comprising the characins and their allies and with all extant species found in freshwater habitats. Characiformes is a large assemblage of about 2,000 species, including the well-known piranhas and tetras. Extant characiforms are found exclusively in freshwater environments in Africa and the Americas. The largest family is Characidae, the characins.

many very colorful and some silvery, and many, particularly tetras, popular as aquarium fishes. Some are important food fishes (Brycon sp.).

Overview and description

Characiformes belong to the Actinopterygii, a major taxonomic class (or subclass) of fish, known as the "ray-finned fishes," within with 96 of all fish species are placed. Characiformes further belong to the superorder Ostariohysi, and within that the series Otophysi. Members of Otophysimainly are distinguished by the presence of a Weberian apparatus, a series of bony parts connecting the swim bladder and inner ear (Nelson 2006). Other orders in the series Otophysi are Cyriniformes (carps), Siluriformes (catfishes), and Gymnotiformes (American knifefishes).

Characiformes is a large assemblage of species that are poorly known and with much morphological diversity (Nelson 2006). Nelson (2006) recognizes 18 families, 270 genera, and at least 1674 species; however, there has been much taxonomic revision with various subfamilies being raised to the level of families, and so forth.

Superficially, the Characiformes somewhat resemble their carp relatives of the order Cypriniformes. One noticeable difference is the presence of a small fleshy adipose fin between the dorsal fin and tail. The presence of well-developed teeth within the mouth is also often present as most (though not all species) are carnivorous. However, there are exceptions to both of these. Barbels are always absent and the body is almost always covered in well-defined scales. (The characid tetra Gymnocharacinus bergii lacks and adipose fin and scales are almost totally lacking in adults.) The upper jaw of characiformes usually is not truly protractile. A pelvic fin is present, with 5 to 12 rays, and the anal fin is short to moderately long, with fewer than 45 rays (Nelson 2006; Agbayani 2005).

The largest size is 1.4 meters 4.5 feet), reached in Hydrocynus goliath of the Congo, while the smallest size is about 13 millimeters (0.5 inches). Many members are under 3 centimeters (about 1 inch) in length (Nelson 2006).

Distribution

Characins are most diverse in the Neotropics, where they are found in tropical lakes and rivers throughout most of South America, Central America, and central Africa. At least 209 species of characins are found in Africa, including the distichodontids, the citharinids, the alestiids, and the monotypic Hepsetidae, Hepsetus odoe. The rest of the characins originate from the Americas.

Taxonomy

Characiformes is part of a series called Otophysi within the superorder Ostariophysi. Otophysi contains four other orders, Cypriniformes, Siluriformes, and Gymnotiformes. Characiformes forms a group known as Characaphysi with Siluriformes and Gymnotiformes. Characiformes is the sister group to the orders Siluriformes and Gymnotiformes, though this has been debated in light of recent molecular evidence.

Originally the characins were all grouped within a single family, the Characidae, which was included in the Cypriniformes.^{[citation needed]} Since then about 15 different families have been separated out. However, classification varies somewhat, and it appears the circumscribed Characidae are still polyphyletic.^{[citation needed]} Currently, there are eighteen families, about 270 genera, and at least 1674 species. The suborder Citharinoidei, which contains the families Distichodontidae and Citharinidae, is considered the sister group to the rest of the characins, suborder Characoidei.

The taxonomy of the Characidae remains unsettled, including some authorities moving many former members of the family into their own related but distinct families. The pencilfishes of the genus Nannostomus are a typical example, having now been moved into the Lebiasinidae. Likewise, assorted predatory characins belonging to Hoplias and Hoplerythrinus have now been moved into the Erythrinidae, and the sabre-toothed fishes of the genus Hydrolycus have been moved into the Cynodontidae. The subfamily Alestiinae was promoted by some to the family level (Alestiidae) and the subfamilies Crenuchinae and Characidiinae were moved to the family Crenuchidae (Nelson 2006). Other fish families that were formerly classified as members of the Characidae, but which were moved into separate families of their own during recent taxonomic revisions (post-1994) include Acestrorhynchidae, Anostomidae, Chilodontidae, Citharinidae, Ctenoluciidae, Curimatidae, Distichodontidae, Gasteropelecidae, Hemiodontidae, Hepsetidae, Parodontidae, and Prochilodontidae.

The larger piranhas have historically been placed in the Characidae, but some authorities place them in their own related family, the Serrasalmidae. This reassignment has yet to enjoy universal acceptance, but is gaining in popularity among taxonomists working with these fishes. Given the current state of flux of the Characidae, a number of other changes will doubtless take place, reassigning once-familiar species to other families. Indeed, the entire phylogeny of the Ostariophysans (fishes possessing a Weberian apparatus) has yet to be conclusively settled, and until that phylogeny is settled, the opportunity for yet more upheavals within the taxonomy of the Characoid fishes is considerable.

Evolution

The oldest characiform is Satanichthys of the early Cretaceous (Albian stage) of Brazil. While all extant species are freshwater, this species was probably either brackish or marine. Many other fossils are also known. Characiformes likely first diversified during the Cretaceous period, though fossils are poorly known. During the Cretaceous period, the rift between South America and Africa would be forming; this may explain the contrast in diversity between the two continents. Their low diversity in Africa may explain why some primitive fish families and Cypriniformes coexist with them while they are absent in South America, where these fish may have been driven extinct. The characiforms had not spread into Africa soon enough to also reach the land bridge between Africa and Asia. The earliest they could have spread into Central America was the late Miocene.

Relationship to humans

A few characins become quite large, and are important as food or game. Most, however, are small shoaling fish. Many species known as tetras are popular in aquaria thanks to their bright colors, general hardiness, and tolerance towards other fish in community tanks.

References

ISBN links support NWE through referral fees

Agbayani, E.. 2005. Characiformes. FishBase. Ed. Ranier Froese and Daniel Pauly. Feb 2007 version. FishBase

• Nelson, J. S. 2006. Fishes of the World, 4th edition. Hoboken, NJ: John Wiley & Sons. ISBN 0471250317.

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