The common carp is native to southeast Europe, but since ancient times, carp have been highly valued for farming in fishponds as food, and they have been widely introduced all over the world. Carp were possibly first introduced to Ireland in the 1600s, or perhaps earlier, and from the 1950s, carp became popular among coarse anglers in Ireland and were frequently redistributed between angling waters. Today, they are found in large ponds, small lakes and put-and-take fisheries, mostly scattered around south Leinster and north Munster.
Carp can be recognised by their long dorsal fins along their backs and their large, thick-lipped, protruding mouths, which have two pairs of barbels. Carp are often found in small shoals and like to feed on bottom-dwelling invertebrates, often disturbing the sediment and making the water turbid or dirty, thereby having an impact on aquatic plants and other animals that live in habitat where carp are present. Carp are very variable in appearance and occur in several varieties that differ in the size and colour of their scales:
- Common carp are typical fully scaled fish.
- Mirror carp have relatively few large, shiny scales.
- Linear carp have scales only along the lateral line.
- Leather or naked carp have very few scales.
- A lead-coloured variety that appears naked but that is covered with thin, clear scales.
- Koi carp are colourful varieties imported for ornamental ponds.
Carp are famously long-lived fish, and some individuals can survive for decades, with a maximum recorded age of 38 years for wild carp. They are tough, capable of surviving water temperatures from near freezing to 40°C, low oxygen conditions, brackish water and poor water quality. Their eggs, however, require water temperatures more than 18°C for successful reproduction, which probably prevents them from breeding in the wild in Ireland in most years. Indeed, cooler water temperatures is probably also why carp in Ireland tend to grow to smaller sizes than in continental Europe. Nevertheless, their longevity still allows them to reach relatively large sizes in Ireland, and carp are the largest coarse fish that can be caught by anglers in Ireland.
Disease is a threat to carp populations in Ireland. In 2018, a major fish kill occurred when carp edema virus wiped out carp in The Lough in Cork City and nearby Belvelly Lake. Carp are also susceptible to koi herpes virus and spring viraemia of carp.