The Cypriniformes are an order of ray-finned fish, including the carps, minnows, loaches and relatives. This order contains 5-6 families, over 320 genera, and more than 3,250 species, with new species being described every few months or so, and new genera being recognized regularly. They are most diverse in southeastern Asia, but are entirely absent from Australia and South America.
The most notable family placed here is the Cyprinidae (carps and minnows) which make up two-thirds of the order's diversity. This is one of the largest families of fish, and is widely distributed across Africa, Eurasia, and North America. Most species are strictly freshwater inhabitants, but a considerable number are found in brackish water, such as roach and bream. At least one species is found in the sea, the Pacific Redfin, Tribolodon brandtii.. Brackish water and marine cyprinids are invariably anadromous, swimming upstream into rivers to spawn. The enigmatic mountain carps are a small group of mountain stream fishes confined to Southeast Asia. Sometimes separated as family Psilorhynchidae, they seem to be specially-adapted Cyprinidae in fact.
The Balitoridae and Gyrinocheilidae are families of mountain stream fishes the feed on algae and small invertebrates. The are found only in tropical and subtropical Asia. While the former are a speciose group, the latter contain only a handful of species. The suckers (Catostomidae) are found in temperate North America and eastern Asia. These large fishes are similar to carps in appearance and ecology. The Cobitidae are common across Eurasia and parts of North Africa. A mid-sized group like the suckers, they are rather similar to catfish in morphology and behaviour, feeding primarily off the substrate and equipped with barbels to help them locate food at night or in murky conditions. The Cobitidae, Balitoridae and Gyrinocheilidae, or more properly the first only, are called loaches, although it seems that the last do not belong to the lineage of "true" loaches but are related to the suckers.
Historically these included all the forms now placed in the superorder Ostariophysi except the catfish, which were placed in the order Siluriformes. Defined thus, the Cypriniformes were paraphyletic, and recently the orders Gonorhynchiformes, Characiformes (characins and allies), and Gymnotiformes (knifefishes and electric eels) have been separated out to form their own monophyletic orders.
The families of Cypriniformes are traditionally divided into two superfamilies. Superfamily Cyprinioidea contains carps and minnows (Cyprinidae) and according to some also the mysterious mountain carps as family Psilorhynchidae. Superfamily Cobitioidea contains hillstream loaches (Balitoridae), suckers (Catostomidae), true loaches (Cobitidae), and sucking loaches (Gyrinocheilidae) in the traditional system.
Catostomoidea is usually treated as a junior synonym of Cobitioidea. But it seems that it would indeed be warranted to split off the Catostomidae and Gyrinocheilidae in a distinct superfamily; the Catostomoidea might actually be closer relatives of carps and minnows than of the "true" loaches. While the Cyprinioidea seem more "primitive" than the loach-like forms, they apparently were successful enough to never completely shift from the original ecological niche of the basal Ostariophysi. Yet from the ecomorphologically conservative main lineage apparently at least two major radiations branched off. These both diversified from the lowlands into torrential river habitat, acquiring similar habitus and adaptations in the process.
Meanwhile, it seems that the mountain carps are highly apomorphic Cyprinidae, perhaps close to true carps (Cyprininae), maybe to danionins. While some details about the phylogenetic structures of this massively diverse family are known – e.g. that Cultrinae and Leuciscinae are rather close relatives and stand apart from Cyprininae – there is no good consensus yet on how the main lineages are interrelated. A systematic list, from the most ancient to the most modern lineages, can thus be given as:
Cypriniformes is thought to have originated in south-east Asia, where the most diversity of this group is found today. The alternative hypothesis is that they began in South America, similar to the other otophysans. If this were the case, they would have spread to Asia through Africa or North America. As the Characiformes began to diversify and spread, they may have outcompeted South American basal cypriniforms in Africa, where more advanced cypriniforms survive and coexist with characiforms.
The earliest fossils are already assignable to the living family Catostomidae; from the Paleocene of Alberta, they are roughly 60 million years old. During the Eocene (55-35 mya), catostomids and cyprinids spread throughout Asia. In the Oligocene, around 30 mya, advanced cyprinids began to outcompete catostomids whereever they were sympatric, causing a decline of the suckers. Cyprinids reached North America and Europe by about the same time, and Africa in the early Miocene (some 23-20 mya). The cypriniforms would have spread to North America through the Bering land bridge, which formed and disappeared again several times during the dozens of million years of cypriniform evolution.
Accidentally or deliberately introduced populations of Common Carp (Cyprinus carpio) and Grass Carp (Ctenopharyngodon idella) are found on all continents except Antarctica. In some cases, these exotic species have a negative impact on the environment. Carp in particular stir up the riverbed reducing the clarity of the water, making it difficult for plants to grow..
Habitat destruction, damming of upland rivers, pollution and in some cases overfishing for food or pet trade have driven some Cypriniformes to the brink of extinction or even beyond. In particular, Cyprinidae of southwestern North America have been severely affected; a considerable number went entirely extinct after settlement by Europeans. For example, in 1900 the Thicktail Chub (Gila crassicauda) was the most common freshwater fish found in California; 70 years later not a single living individual existed anymore.
The well-known Red-tailed Black Shark (Epalzeorhynchos bicolor) from the Mae Klong river of The Bridge on the River Kwai fame possibly only survives in captivity. Ironically, while pollution and other forms of overuse by humans have driven it from its native home, it is bred for the aquarium fish trade by the thousands. The Yarqon Bleak (Acanthobrama telavivensis) from the Yarqon River had to be rescued into captivity from imminent extinction; new populations have apparently been established again successfully from captive stock. Balitoridae and Cobitidae, meanwhile, contain a very large number of species about which essentially nothing is known except how they look like and where they were first found.
Globally extinct Cypriniformes species are: