Cyprinodontiformes is an

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

of ray-finned fish, comprising mostly small, freshwater fish. Many popular aquarium fish, such as killifish and live-bearers, are included. They are closely related to the Atheriniformes and are occasionally included with them. A colloquial term for the order as a whole is toothcarps, though they are not actually close relatives of the true

carp Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...

s – the latter belong to the

superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

Ostariophysi Ostariophysi is the second-largest superorder of fish. Members of this superorder are called ostariophysians. This diverse group contains 10,758 species, about 28% of known fish species in the world and 68% of freshwater species, and are present ...

, while the toothcarps are Acanthopterygii. The families of Cyprinodontiformes can be informally divided into three groups based on reproductive strategy: viviparous and ovoviviparous (all species give live birth), and

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

(all species are egg-laying). The live-bearing groups differ in whether the young are carried to term within (ovoviviparous) or without (viviparous) an enclosing eggshell.

Phylogenetically In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

however, one of the two

suborders Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

– the Aplocheiloidei – contains oviparous species exclusively, as do two of the four superfamilies of the other suborder (the

Cyprinodontoidea Pupfish are a group of small killifish belonging to ten genera of the family Cyprinodontidae of ray-finned fish. Pupfish are especially noted for being found in extreme and isolated situations. They are primarily found in North America, South Am ...

and

Valencioidea ''Valencia'' is the only genus in the family Valenciidae. ''Valencia'' is a genus of ray-finned fishes. It is sometimes grouped into the family Cyprinodontidae. Members of this genus are restricted to southern Europe. Species There are curre ...

of the Cyprinodontoidei). Vivipary and ovovivipary have evolved independently from oviparous ancestors, the latter possibly twice.

Description

Some members of this order are notable for inhabiting extreme environments, such as

saline Saline may refer to: * Saline (medicine), a liquid with salt content to match the human body * Saline water, non-medicinal salt water * Saline, a historical term (especially US) for a salt works or saltern Places * Saline, Calvados, a commune in ...

or very warm waters, heavily polluted waters, rain water pools devoid of minerals and made acidic by decaying vegetation, or isolated situations where no other types of fish occur. They are typically carnivores, and often live near the surface, where the oxygen-rich water compensates for environmental disadvantages. Scheel (1968) observed the gut contents were invariably ants, others have reported insects, worms and aquatic crustaceans. Aquarium specimens are invariably seen eating protozoans from the water column and the surfaces of leaves, however these are not apparent as stomach contents. Many members of the family Cyprinodontidae (the pupfishes) eat plant material as well and some have adapted to a diet very high in algae to the point where one, the American Flag Fish, is a renowned algae eater in the aquarium, in spite of belonging to an order of fishes that do not generally consume any plant material. In addition, killifish derive some of the carotenoids and other chemicals required to make their body pigments from pollen grains on the surface of and in the gut of insects they eat from the surface of the water; this can be simulated in culture by the use of special color enhancing foods that contain these compounds. Although the Cyprinodontiformes are a diverse group, most species contained within are small to medium-sized fish, with small mouths, large eyes, a single dorsal fin, and a rounded caudal fin. The largest species is the ''cuatro ojos'' (''

Anableps dowei The Pacific four-eyed fish (''Anableps dowei)'' is a species of four-eyed fish native to the coastal waters on the Pacific side of southern Mexico to Nicaragua. This fish is gregarious and inhabits mangrove swamps, tidal mudflats, and other coas ...

''), which measures in length, while the smallest, the least killifish (''

Heterandria formosa ''Heterandria formosa'' (known as the least killifish, dwarf topminnow, mosqu or midget livebearer) is a species of livebearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and ...

''), is just long as an adult.

Systematics

CYPRINODONTIFORMES * Suborder Aplocheiloidei (all oviparous) ** Family

Aplocheilidae Aplocheilidae, the Asian killifishes or Asian rivulines, is a family of fish in the order Cyprinodontiformes found in Asia. Some authorities use this family-group name, which is well-established, for a single lumped aplocheiloid family as it giv ...

- Asian killifishes ** Family

Nothobranchiidae Nothobranchiidae are a family of bony fishes containing roughly 300 species, also known as African rivulines. They are small killifish, usually measuring about . They are limited to Africa, living in fresh water but being also somewhat salt-tol ...

- African killifishes ** Family Rivulidae - New World killifishes * Suborder Cyprinodontoidei ** Superfamily Funduloidea *** Family

Profundulidae Profundulidae is a family of killifishes. The species of this family are native to Central America and Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is b ...

– Central American killifishes (oviparous) *** Family Goodeidae – splitfins (largely viviparous) *** Family Fundulidae – topminnows and North American killifishes (oviparous) ** Superfamily

(oviparous) *** Family

Valenciidae ''Valencia'' is the only genus in the family Valenciidae. ''Valencia'' is a genus of ray-finned fishes. It is sometimes grouped into the family Cyprinodontidae. Members of this genus are restricted to southern Europe. Species There are curre ...

– Mediterranean killifishes ** Superfamily Cyprinodontoidea (oviparous) *** Family Cyprinodontidae – pupfishes *** Family

Aphaniidae Aphaniidae, the Oriental killifishes, are a family of the order Cyprinodontiformes. The 42 extant species of the family inhabit inland waters, rivers and lagoons. The distribution of these species extends from the entire Mediterranean region t ...

_ Oriental killifishes ** Superfamily

Poecilioidea Poecilioidea is a superfamily of killifish, one of the four superfamilies which make up the suborder Cyprinodontoidei, which is in turn one of the two constituent suborders of the order Cyprinodontiformes. They are found in mainly in the Neotropi ...

*** Family Anablepidae – four-eyed fishes and relatives (largely ovoviviparous) *** Family Poeciliidae – livebearers and relatives (some oviparous, some ovoviviparous) The family Aplocheilidae has been expanded by some authorities to include all the killifishes with three subfamilies, Aplocheilinae, Cynolebiinae and Nothobranchiinae, but this is not the classification adopted in the 5th Edition of ''

Fishes of the World ''Fishes of the World'' by the American ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classification of the ...

''.

References

{{Authority control Extant Oligocene first appearances Ray-finned fish orders