Koi

The koi is a domesticated and selectively bred form of carp, with ancestor species likely including the Eurasian carp (or Cyprinus carpio) and the Amur carp (or Cyprinus rubrofuscus). Wild carp inhabit slow-moving rivers, lakes, floodplains and ponds with soft, muddy bottoms and abundant vegetation, their native range extending across the temperate regions of Eurasia. Koi have emerged in Japan and are now widely distributed around the world as ornamental fish. Koi are best known for their striking colours and patterns ranging from white, red, orange, yellow and black, while wild carp species are usually olive-brown, greenish or yellowish with a paler underside and sometimes reddish fins. All carp have elongated, robust bodies with large scales, and distinctive barbels at the corners of the mouth. Adult koi and common carp typically reach standard lengths of 60cm to 90cm and weigh between 6kg and 15kg, though some exceptional individuals can exceed lengths of 1m and weights upwards of 30kg. Females tend to be larger and heavier than males on average.

Koi are domesticated and widely distributed. However, their wild ancestors face various conservation issues. Both Eurasian and Amur carp are of Least Concern, but their native freshwater habitats are threatened by degradation due to river regulation, dam construction, pollution and wetland drainage in many places. This reduces available spawning and feeding grounds. Paradoxically, the Eurasian carp is also one of the 100 worst invasive species worldwide - it has been introduced to every continent except Antarctica, and their bottom-feeding behaviours and strong appetite damage native aquatic vegetation and outcompete native fish. There are efforts to mitigate both challenges. In native carp habitats, measures include wetland restoration, improvement of water quality and regulation, and limiting fishing pressure to protect spawning grounds. In areas with invasive carp, population control via monitoring, removal programmes and public education to prevent releases of ornamental fish are in place. Together, both strategies aim to protect habitats and species in their respective native environments.