Physical Characteristics
The common rudd has an elegant, elongated body that is more solidly compressed laterally than the roach, especially in the anterior part, giving it a distinctive silhouette. The body is covered with small, shiny scales, silver to golden in color on the flanks, with an olive-green or blue-gray back and silvery-white belly. The most distinctive characteristic is the intense red-orange coloration of the pectoral, ventral, anal, and caudal fins, which contrasts strongly with the silvery body. The eyes are large, with a red or orange iris, an important diagnostic element. The mouth is relatively small, terminal and upturned (superior), adapted for feeding from the water surface and from vegetation. The head is small in relation to the body. The dorsal fin is positioned more posteriorly than in roach, almost directly above the anal fin, which represents an important differentiation criterion. Average dimensions are 15-25 cm in length, but mature specimens can reach 40-50 cm and weights of 2-3 kg, even exceeding these values under optimal conditions. The lateral line has 40-45 scales. Young specimens have a slimmer body, while older adults develop a deeper and broader body.
Habitat & Distribution
The common rudd is a typical species of still or very slow-flowing waters, with a marked preference for areas rich in submerged and emergent vegetation. In the Danube Delta, the preferred habitat includes permanent lakes with dense reed beds, marshes with bulrush and water lilies, secondary channels with abundant vegetation, and confluence areas with very weak current and rich plant cover. The species is closely associated with aquatic plants, spending most of its time in the middle or at the edge of vegetation, where it finds both protection from predators and abundant food. The rudd prefers clear waters with moderate to warm temperatures and is sensitive to pollution, being considered an indicator of water quality. It tolerates temperatures between 2°C and 22°C, with optimum for growth and reproduction between 18-22°C. The species is present throughout the Delta, but the highest densities are found in lakes with well-developed vegetation such as Fortuna, Roșu, Puiu, and the Uzlina complex. In winter, the rudd retreats to deeper areas or remains near reed beds, reducing its activity but without entering complete hibernation. It is a gregarious fish, forming mixed schools with roach and other cyprinids, especially in feeding areas.
Behavior and Feeding
The common rudd is an omnivorous fish with a pronounced preference for food of plant origin, thus differing from many other cyprinids. Its varied diet includes aquatic plants (soft parts of reeds, bulrush, duckweed), filamentous and unicellular algae, aquatic insects and their larvae, zooplankton (cladocerans, copepods), small mollusks, and crustaceans. The feeding mode is characteristic: the rudd feeds predominantly at the water surface or in the upper vegetation layer, using its upturned mouth to capture surface insects, pollen, seeds, and floating plant parts. It is an active fish especially in the early morning and evening, when it emerges from vegetation to feed in more open areas. Social behavior is well developed, with rudd forming numerous schools especially during the juvenile and breeding periods. Large adults may become more solitary, occupying territories in areas with dense vegetation. The species is less active than roach in searching for food on the bottom, preferring the upper layers. In autumn, the rudd intensifies its feeding to accumulate reserves before winter, a period when it becomes more aggressive in capturing available food.
Life Cycle & Reproduction
The common rudd reaches sexual maturity relatively early, at the age of 1-3 years, depending on environmental conditions, with males becoming mature one year earlier than females. Reproduction occurs later than in roach, between early May and the end of June, when water temperature reaches 17-23°C. Fish gather in shallow areas with abundant vegetation, often in the same places each year, forming noisy and active breeding schools. The female lays an impressive number of eggs – between 100,000-200,000 eggs per kilogram of body weight – on submerged aquatic plants, in several stages. The eggs are small (1-1.5 mm), sticky, and yellowish-green in color, adhering firmly to vegetation. Fertilization is external, with males being very active and competitive during the breeding period, developing nuptial tubercles on the head and body. Hatching occurs after 3-10 days, depending on water temperature, with larvae remaining attached to vegetation until absorption of the yolk sac. Fry initially feed on fine zooplankton, gradually moving to insects and plant matter. Growth is relatively rapid in the first year of life, with rudd reaching 5-8 cm. Mortality in the first months is high due to predators and variable environmental conditions.
Conservation Status
The common rudd is classified as "Least Concern" (LC) globally by IUCN, being a common and widespread species throughout most of its range. However, in some regions of Western Europe, including Germany, the species is considered threatened and benefits from legal protection due to population decline caused by loss of aquatic habitats and degradation of water quality. In the Danube Delta, the rudd is still abundant in areas with well-preserved vegetation, but densities have decreased in areas affected by intensive anthropogenic activities. Main threats include eutrophication of waters, which leads to changes in aquatic vegetation composition, chemical and organic pollution, clearing of reed beds for fishery or agricultural developments, and overfishing in some areas. In Romania, the species does not benefit from special protection measures and fishing is permitted without minimum size restrictions, subject to the general prohibition period for reproduction. The rudd is sensitive to habitat changes and can be used as an indicator species for monitoring the health of marsh and lake ecosystems with rich vegetation. Conservation of natural wetlands and aquatic vegetation is essential for maintaining viable rudd populations in the Danube Delta.
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