Cyprinids

The Cyprinidae is a diverse family of mainly freshwater fishes belonging to the ostariophysian order Cypriniformes, collectively called cyprinids. They include carps, true minnows, and their relatives. The Cyprinidae is the largest and most diverse fish family and, in general, the largest vertebrate animal family, with about 3,160 species, of which only 1,270 are extant, divided into about 376 genera. The family occurs in Africa, Eurasia, and North America (northern Canada to southern Mexico). Only two species of cyprinids occur in true marine waters, daces (Tribolodon brandtii and T. sachalinensis) from eastern Asia, and a few stray into brackish water only very rarely. More than sixty-two species of cyprinids are known from Arkansas, which represents almost a third of the total fish fauna. Of these, five species have been introduced into state waters, including four species of carps and the goldfish (Carassius auratus).

The earliest known fossil cyprinids in North America occur in Oligocene deposits, 30 to 35 million years ago. When compared to their Eurasian allies, limited fossil evidence suggests that native cyprinids may be of recent origin. Among cyprinids, the oldest record is a Barbin, Parabarbus sp., from the lower Eocene of Kazakhstan. Outside of North America, the earliest cyprinid fossils are from the Eocene from Asia, with the earliest European fossils of Oligocene age. Interestingly, if cyprinids originated in Asia, they may have invaded North America across the Beringia land bridge connection about 32 million years ago while sea levels were lower during the Oligocene.

Cyprinids range from about 12 mm (0.47 in.) to 3 m (9.8 ft.) in length and 300 kg (660 lb.) in weight (giant barb, Catlocarpio siamensis). Two additional very large species that exceed 2 m (6.6 ft.) in length are the mangar (Luciobarbus esocinus) and golden mahseer (Tor putitora). In North America, the largest cyprinid species is the Colorado pikeminnow (Ptychocheilus lucius), which can reach up to 1.8 m (5.9 ft.) in length. The second-smallest known fish (parasitic males of the anglerfish, Photocorynus spiniceps are the smallest) belongs to the Cyprinidae and is Paedocypris progenetica, found in swamps and streams on the Southeast Asian islands of Borneo, Bintan, and Sumatra; it reaches, at most, 10.3 mm (0.41 in.) in length.

Because of the enormous diversity of cyprinids, it is difficult in many cases to resolve their phylogeny in sufficient detail to make assignment more than tentative to subfamilies. Although some distinct lineages obviously exist, the overall systematics and taxonomy of the Cyprinidae remain subject to considerable debate among ichthyologists. A large number of genera are incertae sedis, too ambiguous in their traits and/or too little-studied to permit placement to a particular subfamily with any confidence. However, one important taxonomic character used in determining species of cyprinids is the ability to accurately count anal fin rays.

Morphological characteristics of cyprinids include cycloid scales and nineteen principal caudal fin rays, and all native species have nine or fewer (usually seven to eight) dorsal fin rays. Cyprinids are stomach-less fish without teeth. However, food items are effectively chewed by the well-developed toothed pharyngeal arches and gill rakers. These pharyngeal arches allow the fish to make chewing motions against a chewing plate formed by a bony process of the skull. As they are unique to each species and quite consistent in shape and number within a species, they are used by biologists to aid in identification of difficult species. Strong pharyngeal arches allow fish to hold, tear, and grind ingested food items. Those of the common carp (Cyprinus carpio) are similar to human molars, and those of the ide (Leuciscus idus) are modified to eat hard-shelled mollusks such as snails and bivalves. Most cyprinids feed mainly on invertebrates and vegetation; however, some species, like the asp (Aspius aspius), are predators that specialize in fish. Many species, such as larger common rudd (Scardinius erythrophthalmus), native to the Caspian and Aral sea basins and an invasive Arkansas species, prey on small fish. Some cyprinids, such as the invasive grass carp (Ctenopharyngodon idella), are specialized herbivores; others, such as the common nase (Chondrostoma nasus), eat algae and biofilms, while carps, such as the black carp (Mylopharyngodon piceus), specialize in snails, and some, such as the silver carp (Hypophthalmichthys molitrix), are specialized filter feeders. For this reason, these latter cyprinids are often introduced as a management tool to control various factors in the aquatic environment, such as aquatic vegetation and diseases transmitted by snails. However, they appear to do more harm than good where they have been introduced, particularly when outcompeting native fish species.

Unlike most fish species, cyprinids generally increase in abundance in eutrophic lakes. Here, they contribute toward positive feedback, as they are efficient at eating the zooplankton that would otherwise graze on the algae, reducing its abundance. Cyprinids have evolved to occupy a vast array of aquatic sites, where they feed on detritus, algae, aquatic and terrestrial insects, microcrustacea, Asiatic clams, and small fishes. In Eurasia, many cyprinids are detritivores and herbivores.

Hearing is a well-developed special sense in cyprinids because they possess Weberian apparatus or ossicles, which are four anterior specialized vertebral processes that transfer vibrations or motions of the gas bladder to the auditory receptors in the brain. The vertebral processes of the Weberian organ also permit a fish to detect changes in motion of the gas bladder due to atmospheric conditions or depth changes. Cyprinids are also considered physostomes because their pneumatic duct is retained in adult stages, and the fish are able to gulp air to fill the gas bladder, or they can release excess gas to the gut.

In terms of reproduction, males (and occasionally females) of many cyprinids develop nuptial tubercles on their heads (especially stonerollers, Campostoma and hornyhead chubs, Nocomis) and brilliant coloration (red and yellow) during breeding activities in spring and summer months. Spawning is typically random, but several species hollow out well-defined nests in gravel substrates or utilize nests of other fish species. Cyprinids are egg layers and one of the few fishes for which there is little to no parental care, as most parents do not guard their eggs. Some exceptions are bluntnose minnows (Pimephales notatus) and fathead minnows (P. promelas), whose males remain with the eggs, cleaning and guarding them until hatching. However, a few species do build nests and/or guard the eggs. Hornyhead chubs (Nocomis biguttatus) and creek chubs (Semotilus atromaculatus) spawn in pits dug by males that have carried pebbles in their mouths to those pits. The Ozark minnow (Notropis nubilis) and redfin shiner (Lythrurus umbratilis) spawn over the nests of other minnows or in nests of fishes from entirely different families. Interestingly, the bitterlings (Rhodeus spp.) are famous for depositing their eggs in bivalve mollusks, where the young develop until they are able to fend for themselves.

Cyprinids are highly prized food fish that are caught in recreational fishing and have been deliberately stocked in ponds and lakes for many years for this reason. They are also farmed, especially across Eurasia. In land-locked countries in particular, cyprinids are often the major species of fish eaten because they make up the largest part of the biomass in most water types, except for fast-flowing rivers. For example, in Eastern Europe, they are often prepared with traditional methods such as drying and salting. Common carp are popular for angling and fishing because of their size and fighting power when caught.

Several cyprinids have been introduced into waters outside their native ranges to provide biological control for some pest species. The Asian carp (C. carpio) and the grass carp are two species of the most important of these introductions. In some situations, such as in the Asian carp of the Mississippi Basin, they have become an invasive species that competes with native fishes and has the potential to disrupt the environment. In particular, carp can stir up sediment, reducing the clarity of the water, which makes it difficult for plants to grow.

Numerous cyprinids have become important in the aquarium trade and fishpond hobbying, most famously the goldfish, which was bred in China from the Prussian carp (Carassius (auratus) gibelio). It was much fancied by Chinese nobility as early as AD 1150 and first imported into Europe around 1728. In Japan from the eighteenth century onward, carp were bred into the ornamental variety known as koi (colored varieties of Amur Carp [Cyprinus rubrofuscus]). Larger species are bred by the thousands in outdoor ponds, particularly in Southeast Asia, and trade in these aquarium fishes is of considerable commercial importance. One particularly important species is the zebrafish (Danio rerio). It has been used as the standard model species for studying developmental genetics of vertebrates, in particular fish.

In terms of conservation, habitat destruction and other detrimental environmental causes have reduced several native cyprinids to dangerously low population levels. Indeed, some are already entirely extinct. In particular, the cyprinids of the subfamily Leuciscinae (true minnows) from southwestern North America have been hit hard by pollution and unsustainable water use in the early to mid-twentieth century; most globally extinct cypriniform species are in fact leuciscinid cyprinids from the southwestern United States and northern Mexico.

Some important genera of cyprinids in Arkansas include the following: Campostoma, Cyprinella, Hybognathus, Hybopsis, Luxilus, Lythrurus, Macrhybopsis, Nocomis, Notemigonus, Notropis, Opsopoeodus, Phenocobius, Phoxinus, Pimephales, Pteronotropis, and Semotilus. A great deal of parasites have been reported from cyprinids, including several reports from genera from Arkansas.

For additional information:
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Brown, J. A., Henry W. Robison, and Chris T. McAllister. “Occurrence of the Shoal Chub, Macrhybopsis hyostoma (Cypriniformes: Cyprinidae) in an Unusual Habitat in the Arkansas River System of Arkansas: Could Direct Tributaries be Refugia Allowing Persistence Despite Fragmentation of Instream Habitat?” Journal of the Arkansas Academy of Science 70 (2016): 260‒262. Online at https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2212&context=jaas (accessed September 2, 2020).

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Hoffman, Glenn L. Parasites of North American Freshwater Fishes. 2nd ed. Berkeley: University of California Press, 2009.

Kottelat, Maurice, Ralf Britz, Tan Heok Hui, and Kai-Erik Witte. “Paedocypris, a New Genus of Southeast Asian Cyprinid Fish with a Remarkable Sexual Dimorphism, Comprises the World’s Smallest Vertebrate.” Proceedings of the Royal Society B, The Royal Society 273 (2005): 895–899.

McAllister, Chris T., Michael A. Barger, Thomas J. Fayton, Matthew B. Connior, David A. Neely, and Henry W. Robison. “Acanthocephalan Parasites of Select Fishes (Catostomidae, Centrarchidae, Cyprinidae, Ictaluridae), from the White River Drainage, Arkansas.” Journal of the Arkansas Academy of Science 69 (2015): 132‒134. Online at https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1024&context=jaas (accessed September 2, 2020).

McAllister, Chris T., William F. Font, Thomas J. Fayton, and Henry W. Robison. “Helminth Parasites of Select Cyprinid Fishes from the Red River Drainage of Southeastern Oklahoma.” Proceedings of the Oklahoma Academy of Science 94 (2014): 81‒86.

McAllister, Chris T., Dennis J. Richardson, Michael A. Barger, Thomas J. Fayton, and Henry W. Robison. “Acanthocephala of Arkansas, Including New Host and Geographic Distribution Records from Fishes.” Journal of the Arkansas Academy of Science 70 (2016): 155‒160. Online at https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2196&context=jaas (accessed September 2, 2020).

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Miller, Rudolph J., and Henry W. Robison. Fishes of Oklahoma. Norman: University of Oklahoma Press, 2004.

Page, Larry M., and Brooks M. Burr. Peterson Field Guide to Freshwater Fishes of North America North of Mexico. 2nd ed. Boston: Houghton Mifflin Harcourt, 2011.

Pflieger, William L. The Fishes of Missouri. Jefferson City: Missouri Department of Conservation, 1997.

Robison, Henry W., and Thomas M. Buchanan. Fishes of Arkansas. 2nd ed. Fayetteville: University of Arkansas Press, 2020.

Ross, Stephen. The Inland Fishes of Mississippi. Jackson: University Press of Mississippi, 2001.

Thomas, Chad, Timothy H. Bonner, and Bobby G. Whiteside. Freshwater Fishes of Texas: A Field Guide. College Station: Texas A&M University Press, 2007.

Chris T. McAllister
Eastern Oklahoma State College