Cyprinids belong to the order Cypriniformes, which includes a very high number of species compared to many other orders.  Typically members of this order inhabit freshwater environments, have pelvic fins of abdominal position and generally lack scales on the head. They present only pharyngeal teeth, with none on the jaws or the palate and their upper jaw is usually protractile. Cyprinids have the gas bladder divided into chambers. The family Cyprinidae (in North America the common name is “minnow” and in Europe “carp”) is the most abundant in species not only within the Order but also in the fresh waters worldwide. The majority of the species are native to Eurasia with the highest genetic diversity in China and Southeast Asia. Nowadays, cyprinids have a wide global distribution as a result of their use as ornamental fish, human consumption, sport fishing or as a tool for biological control. The family Cyprinidae includes, among many other species, several “goldfish” (Carassius auratus auratus), carp (Cyprinus carpio), zebra fish (Danio rerio), barbels (Barbus spp.) and “chub” (Squalius spp.). The systematics of this family is very complex, largely due to the high frequency of hybrids. Cyprinids usually have one or two pairs of barbels in the upper jaw, gas bladder divided in two chambers and emarginate caudal fin. They display sexual dimorphism traits not only in colouring, but also through breeding tubercles or pearl organs, in the male. They typically inhabit freshwater environments, the majority are epibenthic in calm waters and mostly gregarious. Continuous farming of these fish has allowed to achieve selection of ornamental varieties aimed for aquariums and ponds. The best known are zebra fish, koi and mirror carps (varieties of the common carp), and the goldfish. The zebra fish is a small fish (~4 cm) originated from the Himalayan streams, a popular ornamental fish due its attractive colour patterns and rusticity. In addition, it is widely used as model organism for studies of vertebrates, developmental biology, toxicology, environmental monitoring, immunology, genetics and oncology. The goldfish was one of the first fish species to become domesticated and is currently one of the most common species in aquariums and ponds, after a variety of colours and shapes (the tent of veil, dragons, telescope, lions) were achieved by selection. Koi carp, a very popular fish in garden ponds, is an ornamental variety of the common carp with no major changes in the body shape but characterized by the variety of colour patterns. The common carp, a native of Northeast Asia, is the world’s earliest farmed fish species, started in ancient China ~200 BC. Carp inhabit lakes, large rivers and streams, where they normally prefer the slow, warm and shallow waters close to the substrate and with aquatic plants. They prefer high salinity and low oxygen concentration, although they show great plasticity to these and other parameters, such as turbidity. Common carp are omnivorous and feed of benthos and their diet includes macrophytes, detritus, algae, molluscs, larval and adult aquatic insects, crustaceans and small fish. Thus carp has been introduced around the world competing in some cases with the native fauna. Its tasty flesh and high nutritional content has made it important species in aquaculture as well as for sport and commercial fishing. The leather and the mirror carps are varieties of the common carp, the first without scales and the second, with a few very large scales on the back and flanks.   In addition, carps have been introduced in different regions to be used in the control of vegetation and eutrophication, as the grass carp and silver carp (phytoplanktophagus), respectively. The cyprinids remain at first place with respect to global aquaculture production, at 25 to 30 million tons a year. Different species attain different ages, sizes, and maximum weight, with records of more than 1.9 m and 45 kg for the common carp in France and an age record attributed to a koi carp in Japan that died at 226 years.

Information and further reading at: Aquaculture and Behavior (2012) Felicity Huntingford, Malcolm Jobling, Sunil Kadri John Wiley & Sons- Science. http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp http://fishlaboratory.com/fish/koi-hanako-longest-living-fish-ever http://www.farnhamanglingsociety.com/species/carp-ghost-koi.php http://www.fao.org/fishery/culturedspecies/Cyprinus_carpio/en