The rudd (Scardinius erythrophthalmus), is a cyprinid fish (in the minnow family) native to Europe. It is believed that the rudd was originally imported into the United States from Europe as a food and game fish in the early 1900s. Since its introduction, the rudd has been commonly used in aquaculture operations and as bait, contributing to its spread.
Although the rudd prefers to live in stagnant and slow-flowing freshwater with thick vegetation, it can adapt to other environmental conditions, including poor water quality. It is an omnivorous species that lives up to 15 years, with feeding habits shifting as individuals mature; young feed on algae and small invertebrates, while adults feed on aquatic vegetation and insects. This characteristic enables rudd to compete broadly with native species for available resources. Since rudd do not process vegetation effectively, they tend to increase the amount of nutrients in the water as the undigested organic matter is expelled.
Environmental impact: impact caused by the rudd's introduction into the Great Lakes is largely unknown. Aside from general competition with native species for resources, nutrient load increases caused by its incomplete digestive processes may result in localized algal blooms and other changes in water quality. Also, the rudd is capable of breeding with the native golden shiner, resulting in hybrid offspring. It is unclear how this "genetic pollution" will impact subsequent generations of the native fish.