Spirlin
Alburnoides bipunctatus
The Spirlin, also known as the Schneider, is a small freshwater fish that prefers fast-flowing, oxygen-rich streams and rivers. It is characterized by a slender, laterally compressed body and a distinctive dark double row of spots along its lateral line. The species is highly sensitive to water pollution and structural modifications of its habitat. It is typically found in shoals within the main current of the water body.
Details
Identification
Double row of spots along the lateral line, slightly superior mouth, silvery flanks, dark back.
Social behavior
Distinct shoaling behavior; prefers to stay in the middle water layers of the current.
Diet
Insect larvae, small crustaceans, algae, and terrestrial insects fallen onto the water surface.
Hunting strategy
Actively snaps at food drifting in the current or from the water surface.
Spawning substrate
Gravel or stone substrate in shallow, fast-flowing sections (lithophilic).
Overwintering
Retreats to deeper, calmer water areas or pools during winter.
Ecology
Ecological role
Important consumer of macrozoobenthos and significant prey for predatory fish such as the brown trout.
Natural predators
Brown trout, Northern pike, Kingfisher, Cormorant, Goosander.
Competitor species
Other small invertebrate-eating fish species such as Minnow or Gudgeon.
Threats
River engineering, transverse structures (fragmentation of habitat), eutrophication, and sedimentation of spawning gravels.
Scientific profile
Morphology & ID
Coloration
Back olive-green to brownish, flanks silvery, belly whitish. Characterized by a dark longitudinal band accompanied by a double row of black dots along the lateral line.
Distinguishing features
Double row of dots above and below the lateral line (name: bipunctatus); bases of paired fins (pectoral and pelvic) often reddish or orange.
Confusion species
Common bleak (Alburnus alburnus) - which has a longer anal fin and lacks the double row of dots; Common minnow (Phoxinus phoxinus) - has significantly smaller scales.
Sexual dimorphism
Males develop fine nuptial tubercles on the head and scales of the anterior body during the spawning season.
Habitat
Fish region
Trout zone and grayling zone (upper rhithral).
Preferred zone
Pelagic and benthic zones in fast-flowing, shallow river sections.
Flow preference
Strongly rheophilic; prefers turbulent, fast-flowing, and oxygen-rich waters.
Substrate preference
Gravelly to stony substrate (lithophilic).
Oxygen requirement
Very high; the species is considered highly dependent on high oxygen levels.
Migration
Migration behaviour
Short-distance migrant; performs migrations within the river system to find suitable spawning grounds in high-velocity sections.
Reproduction
Spawning substrate
Coarse gravel and stones in strong currents (Lithophilic).
Larval phase
After hatching, larvae initially stay in calm shoreline areas or between stones.
Parental care
No parental care; eggs are deposited in the interstitial spaces of the gravel.
Diet
Feeding type
Insectivorous / Omnivorous.
Diet juvenile
Zooplankton, small insect larvae, and algal periphyton.
Diet adult
Surface insects, caddisfly larvae, mayfly larvae, and small crustaceans.
Feeding strategy
Active hunting in the open current as well as scanning the water surface.
Schooling
Distinct schooling fish, usually staying in groups within the current.
Ecological role
Role in food web
Secondary consumer; serves as an important food source for larger predatory fish such as brown trout.
Natural predators
Brown trout, Northern pike, Great cormorant, Common kingfisher, Goosander.
Competitor species
Other rheophilic species such as common dace (Leuciscus leuciscus) or common minnow (Phoxinus phoxinus).
Parasites
Various trematodes, fish lice (Argulus), and occasionally tapeworms.
Bioindicator function
Good indicator for water quality class I-II and for the structural integrity of rivers (connectivity).
Fisheries & legal
Fishing regulation
Protected year-round in most German federal states (Red List species).
Closed season
Protected year-round.
Economic use
No economic importance; formerly occasionally used as bait fish.
Protection & threats
Main threats
River engineering, barriers (loss of connectivity), siltation of gravel spawning grounds due to fine sediment input, eutrophication.
Population trend
Strongly declining or endangered in many regions of Central Europe due to habitat loss.
Conservation measures
Restoration of longitudinal connectivity, renaturation of rivers, reduction of sediment and nutrient inputs.