Rudd (Scardinius erythrophthalmus)

Synonyms: Cyprinus erythrophthalmus, Scardinius erythrophthalmus erythrophthalmus

Common Names: European rudd, redeye roach, redfin, pearl roach

Description:

Rudd (Scardinius erythrophthalmus) is a deep-bodied fish in the carp and minnow family, native to Europe and western Asia, with brassy-gold sides and bright red fins [1][2]. It was brought to North America through the live-bait and aquarium trades and has spread to waters in about 20 U.S. states, mainly through bait-bucket release [2]. MISIN tracks it because it strips aquatic plants, muddies the water, and breeds with the native golden shiner [2][4].

Identification:

Rudd is a stocky, deep, slab-sided fish with a green-brown back, brassy-gold sides, and a white belly [2]. Its lower fins (the pectoral, pelvic, and anal fins) are a bright reddish-orange, it has a red spot or red edge on the eye, and its mouth turns up with a protruding lower lip [2]. The most reliable way to tell rudd from native minnows is to run a finger along the belly between the pelvic and anal fins: rudd has a keel (a ridge) there that is covered in scales, while the look-alike golden shiner has a keel with no scales [1][2].

Rudd are most likely to be noticed in the warm months, when they feed in weedy shallows and spawn over submerged plants from spring into summer; anglers sometimes catch an unfamiliar red-finned fish and mistake it for a shiner [2]. Watch for the combination of bright red lower fins and a red eye in vegetated lakes and ponds [2].

At-a-glance cues:

1. A scaled keel (ridge) along the belly between the pelvic and anal fins ? native minnows lack a scaled keel [1][2]
2. Bright reddish-orange lower fins and a red spot or edge on the eye [2]
3. Deep, stocky, slab-sided body with brassy-gold sides and an upturned mouth [2]
4. Found in weedy shallows of lakes, ponds, and slow rivers [2]

Habitat:

Rudd is native to Europe and western Asia, from western Europe east to the Caspian and Aral Sea basins [2]. It was introduced to North America in the late 1800s and 1900s through the aquarium trade and especially the live-bait industry, and it is now found in about 20 U.S. states [2].

It lives in lakes, ponds, and slow rivers, favoring warm, weedy shallows down to a few meters deep [2]. Rudd is hardy and tolerates warm, nutrient-rich, and lower-quality water better than many native fish, which helps it take hold once introduced [2].

Reproduction:

Rudd reach new waters almost entirely because of people. The main route is the live-bait trade: rudd have been raised and sold as bait, and they spread when anglers dump unwanted bait, and they also escape from aquaculture ponds and aquariums [2][3]. Because of this, rudd is illegal to use or possess as bait in many places [3].

Once in the water, rudd spawn in spring and summer (about April through August), laying sticky eggs among submerged plants [2]. A major concern is that rudd readily interbreed with the native golden shiner ? an important forage fish ? producing hybrids [2]. Because new populations start from released or escaped fish, the most important step is keeping rudd out of new waters in the first place [2][3].

Impact and Damage:

Rudd is not a health hazard to people; its impact is on the water and the native fish. As it grows, rudd shifts to feeding heavily on aquatic plants, and research shows it grazes selectively on underwater vegetation ? the very plants that native fish and the insects they eat depend on for food and cover [4]. As rudd feed and stir the bottom, they can raise the cloudiness (turbidity) of the water, lowering water quality [2].

Rudd also threaten native fish directly. They readily hybridize with the native golden shiner, a key bait and forage species, which could erode the golden shiner's native genetics over time [2]. Rudd compete with native fish for food, and because they tolerate warm, nutrient-rich, and degraded water better than many natives, they can come to dominate the waters they invade [2].

Similar species:

Rudd is mistaken for several other deep-bodied or golden minnow-family fish.

Golden shiner (Notemigonus crysoleucas) is the closest look-alike and the species rudd hybridizes with ? both are deep-bodied and golden ? but the golden shiner's belly keel has no scales, its eyes and fins are yellow-green rather than red, and it has fewer dorsal fin rays [1][2].

Goldfish (Carassius auratus) can look similar when drab, but it has a deeper, more arched body, lacks the scaled belly keel and bright red lower fins of rudd, and has no red eye spot [2].

Common carp (Cyprinus carpio) shares the heavy carp-family build but grows far larger and has two pairs of barbels (whisker-like feelers) at the mouth, which rudd lacks [2].

Red shiner (Cyprinella lutrensis) also has reddish fins, but it is small and slender with its dorsal fin set near the middle of the back, unlike the deep-bodied rudd [2].

Monitoring and rapid response:

Signs to watch for:

1. Deep, brassy-gold fish with bright reddish-orange lower fins and a red eye spot in weedy lakes, ponds, or slow rivers [2]
2. A minnow-family fish with a scaled keel along the belly between the pelvic and anal fins [1][2]
3. An unfamiliar red-finned "shiner" caught while fishing, especially in the warm months [2]

What you can do:

1. Never use rudd as bait and never release it ? dispose of unwanted bait and any rudd you catch in the trash, not back in the water [3].
2. Learn to tell rudd from the native golden shiner by the scaled belly keel and red eye, so you do not move it by mistake [1][2].
3. Clean, drain, and dry your boat, trailer, livewell, and gear between waterbodies, and never move water or live fish from one lake or river to another [3].
4. Report any rudd you find, especially in a new lake or river, so agencies can respond quickly [3].
5. Removing rudd from open, connected waters is an agency-led effort and there is no easy way to eradicate an established population ? which is why prevention matters most [2][3].

When to call a professional:

1. Rudd found in a lake, river, or any water connected to other waterbodies, where it cannot be contained [2][3]
2. Any control that would involve netting at scale, draining, or pesticide use, which are agency-led and usually require permits [3]
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Integrated Taxonomic Information System (ITIS). Scardinius erythrophthalmus (Linnaeus, 1758) ? TSN 163613. itis.gov
2. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Scardinius erythrophthalmus (rudd) ? Species Profile. nas.er.usgs.gov
3. Minnesota Department of Natural Resources. Rudd (Scardinius erythrophthalmus). dnr.state.mn.us
4. Kapuscinski KL, Farrell JM, Stehman SV, Boyer GL, Fernando DD, Teece MA, Tschaplinski TJ (2014). "Selective herbivory by an invasive cyprinid, the rudd Scardinius erythrophthalmus." Freshwater Biology 59(11):2315?2327. semanticscholar.org

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