Common carp Cyprinus carpio

Common carp is a benthic cyprinid that evolved in the Caspian Sea and spread to the Black and Aral basins, east into mainland Asia and west as far as the Danube, was then introduced throughout the world, and is the mainstay of European and Asian pond aquaculture, with FAO FishStat recording 4,195,230 tonnes farmed in 2024. It is large and long-lived, though sources differ on how large: FishBase gives 129 cm and 40.1 kg against a USGS maximum of 122 cm, with a maximum reported age of 38 years, first maturity at 25 to 36 cm, and females laying more than a million eggs in a season. It tolerates 3 to 35 degrees C and pH 6.5 to 9.0 but spawns best between 18 and 22 degrees C, feeds at dusk and dawn on benthic organisms and plant material using two pairs of barbels and grinding pharyngeal teeth, and takes the bottom niche in Chinese polyculture ponds. Clinically it is defined by koi herpesvirus disease, a notifiable alloherpesvirus infection killing 80 to 100 per cent of naive stock when water sits between 16 and 25 degrees C, with gill mottling and necrosis and no treatment; survivors must be treated as latent carriers. The same virus makes the ornamental koi trade a biosecurity problem as much as a husbandry one.