Common rudd
Scardinius erythrophthalmus
The common rudd is a gregarious freshwater fish that prefers standing or slow-moving waters with dense aquatic vegetation. It is distinguished by its deep-bodied profile, golden scales, and characteristic bright red fins. A key identification feature is its upturned mouth, which highlights its specialized feeding habits at the water surface. In the ecosystem, it serves a vital role as a consumer of macrophytes and as a primary prey source for larger predatory fish.
Details
Identification
Upturned mouth, dorsal fin origin significantly behind the pelvic fin base, belly edge between pelvic and anal fins is keeled and scaled.
Social behavior
Shoaling fish that forms large groups in shoreline vegetation, especially during its juvenile phase.
Diet
Omnivorous with an unusually high proportion of aquatic plants and algae for a cyprinid; also feeds on surface insects, insect larvae, and plankton.
Hunting strategy
Active foraging within the vegetation zone and scanning the water surface for insects.
Spawning substrate
Phytophilous; deposits eggs on aquatic plants such as reeds, pondweeds, or milfoil.
Overwintering
Retires to deeper, low-flow water layers and reduces its metabolic rate.
Ecology
Ecological role
Important primary consumer of macrophytes and a significant prey base for predatory fish like pike and perch.
Natural predators
Northern pike, European perch, Zander, Grey heron, Great cormorant, and European otter.
Competitor species
Roach, Common bream, Bleak.
Ecosystem service
Regulation of macrophyte growth and part of the food chain for economically relevant predatory fish species.
Threats
Destruction of reed belts, shore stabilization, excessive removal of aquatic weeds, and heavy eutrophication.
Scientific profile
Morphology & ID
Coloration
Back is olive-green to brownish; sides are brassy to golden; belly is silvery-white. Fins (especially pelvic, anal, and caudal) are bright red.
Distinguishing features
Superior mouth (upturned); dorsal fin origin is positioned clearly behind the base of the pelvic fins; the belly between the pelvic and anal fins is keeled and covered with scales (unlike the Roach).
Confusion species
Roach (Rutilus rutilus) - distinguished by terminal mouth and eye color (Roach often has a red spot in the iris); Ide (Leuciscus idus).
Sexual dimorphism
Males develop fine nuptial tubercles (spawning rash) on the head and the anterior part of the back during the breeding season.
Habitat
Fish region
Bream zone
Preferred zone
Littoral zone of stagnant or very slow-moving waters with dense submerged vegetation.
Flow preference
Limnophilic (prefers stagnant waters)
Substrate preference
Muddy to sandy substrate with extensive macrophyte vegetation.
Oxygen requirement
Moderate; tolerant of temporary oxygen depletion, frequently found in eutrophic waters.
Migration
Migration behaviour
Short-distance migrations between summer habitats (shallow, vegetated shores) and wintering grounds (deeper water zones).
Reproduction
Spawning substrate
Phytophilic; eggs are deposited on aquatic plants (e.g., Myriophyllum, Potamogeton).
Larval phase
After hatching, larvae attach themselves to aquatic plants using adhesive glands until the yolk sac is absorbed.
Parental care
None; eggs are left unattended after spawning.
Diet
Feeding type
Omnivorous with a strong tendency towards herbivory (one of the few primarily herbivorous fish in Central Europe).
Diet juvenile
Zooplankton (cladocerans, copepods) and small insect larvae.
Diet adult
Aquatic plants (macrophytes like Elodea, Potamogeton), algae, terrestrial insects (surface feeding), snails, and small crustaceans.
Feeding strategy
Surface feeding (terrestrial insects) and grazing on submerged aquatic vegetation.
Schooling
Gregarious; forms large schools, especially during the juvenile stage.
Ecological role
Role in food web
Important consumer of primary producers (macrophytes) and prey fish for predators like Pike and Zander.
Natural predators
Northern Pike (Esox lucius), European Perch (Perca fluviatilis), Zander (Sander lucioperca), Cormorant, Grey Heron.
Competitor species
Roach (Rutilus rutilus) β competition for habitat and food, though Rudd is more strictly tied to vegetation.
Parasites
Posthodiplostomum cuticola (Black spot disease), various tapeworms (Ligula intestinalis).
Bioindicator function
Indicator for structurally rich, plant-dense standing waters; sensitive to the loss of macrophyte beds.
Fisheries & legal
Fishing regulation
Regulated by law in most German federal states; often subject to minimum size limits and closed seasons.
Closed season
Varies regionally, often from March 15th to May 31st.
Economic use
Low economic importance as a food fish (many bones); popular as bait fish and in recreational angling.
Protection & threats
Main threats
Loss of spawning habitats due to bank stabilization, removal of aquatic vegetation, eutrophication and subsequent loss of macrophytes.
Population trend
Stable; widespread and common in suitable habitats.
Conservation measures
Protection and restoration of reed zones and submerged vegetation; avoidance of chemical or mechanical weed control.