Ruffe
Gymnocephalus cernuus
The ruffe is a small, primarily bottom-dwelling freshwater fish belonging to the perch family (Percidae). It features a robust body and a large head covered with slime-producing sensory pores. Its coloration is typically olive-brown with irregular dark spots on the sides and fins. A distinctive feature is the continuous dorsal fin with sharp spines in the anterior section. It inhabits stagnant and slow-moving waters, as well as the brackish waters of the Baltic Sea.
Details
Identification
Fused dorsal fin (spiny and soft rays connected), large sensory pores on the head, slimy skin, dark spotting on the fin rays.
Social behavior
Gregarious species often found in large schools near the bottom.
Diet
Opportunistic carnivore feeding on zooplankton, chironomid larvae, amphipods, worms, and occasionally fish eggs.
Hunting strategy
Uses its highly sensitive lateral line system to locate prey on the water bottom even in total darkness or turbid conditions.
Spawning substrate
Gravel, stones, aquatic plants, or submerged roots.
Overwintering
Retreats to deeper, frost-free, and low-flow water zones during winter.
Ecology
Ecological role
Important consumer of benthic organisms and significant prey for larger predatory fish such as zander and pike.
Natural predators
Zander, northern pike, European perch, eel, and piscivorous birds such as cormorants and herons.
Competitor species
European perch (Perca fluviatilis) and bream (Abramis brama) due to similar feeding habitats.
Ecosystem service
Contributes to nutrient cycling in the sediment and serves as a food source for commercially valuable predatory fish species.
Threats
Water pollution, habitat loss due to river engineering, and competition from invasive goby species.
Scientific profile
Morphology & ID
Coloration
Olive-brown to grayish with irregular dark spots on the body and fins; belly whitish to yellowish.
Distinguishing features
Fused dorsal fins without a notch (anterior spiny, posterior soft-rayed), large sensory pits on the head (lateral line system), very slimy skin, and large, glassy eyes.
Confusion species
European perch (Perca fluviatilis), Zander (Sander lucioperca), Danube ruffe (Gymnocephalus baloni), Schraetzer (Gymnocephalus schraetser).
Sexual dimorphism
Minimal; females appear more robust during the spawning season and often live longer than males.
Habitat
Fish region
Bream zone, Ruffe-Flounder zone (estuaries).
Preferred zone
Benthic (bottom-dwelling).
Flow preference
Stagnophilous to weakly rheophilous (limnophilous).
Substrate preference
Sand, mud, fine gravel, clay.
Oxygen requirement
Moderate; tolerant of temporary hypoxia and eutrophication, but more sensitive than many cyprinids.
Migration
Migration behaviour
Short-distance migrations within river systems or lakes between feeding grounds and spawning sites.
Reproduction
Spawning substrate
Phytolithophilous (plants, stones, roots, sand).
Larval phase
Brief pelagic stage after hatching, followed by a rapid transition to a benthic lifestyle.
Parental care
None.
Diet
Feeding type
Benthivorous (bottom feeder).
Diet juvenile
Zooplankton (rotifers, cladocerans, copepods).
Diet adult
Macrozoobenthos (chironomid larvae, amphipods, small mollusks), occasionally fish eggs.
Feeding strategy
Crepuscular hunter, uses highly sensitive lateral line system to locate prey in turbid water or at night.
Schooling
Gregarious, often forms large schools on the water bottom.
Ecological role
Role in food web
Secondary consumer; important prey for zander, northern pike, and cormorants.
Natural predators
Zander, northern pike, European perch, eel, cormorant, goosander.
Competitor species
European perch, bream, roach, invasive gobies (e.g., round goby).
Parasites
Common host for trematodes (e.g., Diplostomum) and acanthocephalans.
Bioindicator function
Indicator for mesotrophic to eutrophic water conditions; indicates eutrophication.
Fisheries & legal
Fishing regulation
In most German federal states, no closed season or minimum size; often viewed as a food competitor for more valuable fish species.
Closed season
None
Economic use
Low; formerly valued for soup ('ruffe soup'), today mostly bycatch or bait fish.
Protection & threats
Main threats
River engineering, loss of shallow-water spawning habitats, invasive species (food competition from gobies).
Population trend
Stable; declining in some areas due to competition with invasive Ponto-Caspian gobies.
Conservation measures
Preservation of natural shoreline structures, restoration of shallow water zones, and connectivity of water systems.