Rudd, Scardinius erythrophthalmus
Rudd, Scardinius erythrophthalmus. Fish caught from within Barry Park, Syracuse, New York, June 2022. Length: 4.8 cm (1.9 inches). Catch, photography and identification courtesy of Aidan Perkins, Long Island, New York.
The Rudd, Scardinius erythrophthalmus, is a member of the Carp and Minnow or Cyprinidae Family, that is also known as the Common Rudd, and in Mexico as escardinio. Globally, there are ten species in the genus Scardinius, with only this specified being found in the freshwater systems of Mexico. The Rudd originated in Europe and was introduced into North American in the late 19th century. They are highly invasive and widely distributed.
The Rudd has a stocky deep compressed body with a forked caudal fin. They are a dark greenish-brown color dorsally with brassy-yellow sides tapering to a whitish belly. The scales are robustly marked. Their anal, pectoral, and pelvic fins are bright reddish-orange, and their caudal and dorsal fins are reddish-brown. Their head is small with a straight to slightly convex dorsal profile with an oblique terminal mouth that has a tip slightly above the middle of their red or gold with red spot eyes. Their anal fin has 3 spines and 8 to 12 rays; their caudal fin has 18 or 19 rays; their dorsal fin has 3 spines and 8 or 9 rays. They have 9 to 12 gill rakers on the first arch. They have a scaled ventral keel. Their lateral line is greatly decurved.
The Rudd is a benthopelagic fish that is found in nutrient-rich lakes, sluggish pools of medium to large rivers and shallow margins of lakes and ponds in freshwater and brackish waters with temperatures between 2oC (36oF) and 22oC (72oF). They reach a maximum of 62 cm (2 feet 0 inches) in length. As of January 1, 2023, the International Game Fish Association world record stood at 1.58 kg (3 lbs 7 oz), with the fish caught from the Ljungan River in Sweden, July 1988. They are often associated with dense growths of submerged aquatic vegetation. They are omnivorous, feeding on zooplankton, aquatic insects, filamentous algae, higher aquatic plants, and occasionally on fish eggs or small fish. Unlike most fish they have the ability to change their diets based on food availability. The adults can consume up to 40% of their body weight in vegetation each day returning as much as 80% as waste releasing nutrients into the water column. In turn they are preyed upon by numerous fish. The Rudd reach sexual maturity in three years. Reproduction occurs from April to August, typically beginning once water temperatures exceed 16°C (61oF). Adhesive pale, yellow eggs are laid among submerged vegetation in warmer, calmer, waters near shore which are then fertilized by the males. The males defend territories during the breeding period. They are prolific with fecundity for each female ranges from 3,500 to 232,000 eggs. They can adapt to unfavorable environmental conditions and are capable of surviving in polluted waters better than many native fish. They are migratory and have life spans of 17 years.
The Rudd can be easily confused with the Golden Shiner, Notemigonus crysoleucas (7 to 9 dorsal rays; 17 to 19 gill rakers on the first arch; ventral keel unscaled; yellow-green eyes; yellow-green fins) and the Red Shiner, Cyprinella lutrensis (dorsal fin inserted mid-body). The Rudd is the only native North American Minnow (Cyprinidae) that has a scaled keel between the anal and pelvic fins.
At present the Rudd population in Mexico is not well documented. The are known to be present within the Valle del Río Grande in northern Tamaulipas and more than likely will quickly become established throughout Mexico.
The Rudd originated in Europe and arrived in North American in the last 1880s. They have been widely transplanted globally and are highly invasive, primarily attributed to bait bucket releases by recreational fishermen, and currently considered to be a Potential Pest as they have caused irreversible damage to indigenous ecosystems. From a conservation perspective the Rudd is currently considered to be of Least Concern with stable widely distributed populations. They are raised by the aquaculture of use as a live bait. In the 1980s the Rudd were heavily marketed as a new, hardy, colorful bait minnow making it a popular bait with anglers targeting Striped Bass, Morone saxatilis. At present they are banned in several of states within the USA. The Rudd are widely used by the aquarium trade as an ornamental fish where they have been genetically bread to produce a popular gold version, the Golden Rudd. The Rudd are also pursued at a nominal level as a game fish and utilized by some cultures as a human food fish. The Rudd is known to hybridize with the Golden Shiner, Notemigonus crysoleucas, with unknown consequences to wild populations of native species.