Sunbleak
Leucaspius delineatus
The sunbleak is a small, silvery freshwater fish that prefers stagnant or slow-moving waters with abundant vegetation. It is characterized by an incomplete lateral line and a superior mouth, which is perfectly adapted for feeding at the water surface. The species is notable for its interesting brood care behavior, where males guard and clean the eggs attached to aquatic plants.
Details
Identification
Incomplete lateral line (only on the first 7-12 scales), superior mouth, silvery-blue longitudinal stripe on the posterior part of the body.
Social behavior
Distinct schooling fish, usually found in groups within the upper water layers.
Diet
Zooplankton, small insects (surface food), insect larvae, and occasionally algae.
Hunting strategy
Active searching of the water surface and open water for microorganisms.
Spawning substrate
Submerged aquatic plants, roots, or branches where eggs are deposited in bands.
Overwintering
Retreats to deeper, frost-free zones at the bottom of the water body and reduces activity.
Ecology
Ecological role
Important prey for predatory fish and water birds; contributes to the control of mosquito populations.
Natural predators
Pike, European perch, kingfisher, grey heron, little grebe.
Competitor species
Topmouth gudgeon (invasive), bleak, other small cyprinids.
Ecosystem service
Biological control of mosquitoes by consuming their larvae.
Threats
Loss of small water bodies through drainage, shoreline engineering, and the spread of invasive species like the topmouth gudgeon.
Scientific profile
Morphology & ID
Coloration
Back brownish-greenish, sides silvery shiny with a characteristic bluish longitudinal stripe on the posterior part of the body.
Distinguishing features
Very short, incomplete lateral line (only covers 7-12 scales); steeply upward-directed mouth; scales detach easily.
Confusion species
Bleak (Alburnus alburnus - has complete lateral line), Stone Moroko (Pseudorasbora parva - has dark longitudinal band and different scale structure).
Sexual dimorphism
Males develop fine spawning rash on the head during breeding season; females possess a urogenital papilla.
Habitat
Fish region
Lentic waters (stagnophilous), Bream region
Preferred zone
Pelagial and littoral (near-surface)
Flow preference
Lentic (standing waters, oxbow lakes, ponds)
Substrate preference
Vegetation-rich shore zones, submerged vegetation, root networks.
Oxygen requirement
Moderate to low; can tolerate low oxygen concentrations in weed-choked small water bodies for short periods.
Migration
Migration behaviour
No distinct migrations; sedentary within the water system.
Reproduction
Spawning substrate
Phytophilous; eggs are laid in strings on aquatic plants, roots, or floating objects.
Larval phase
After hatching, larvae initially hang from vegetation; after yolk sac absorption, they transition to a planktivorous lifestyle.
Parental care
Male guards the clutch, defends the territory, and fans fresh water to the eggs.
Diet
Feeding type
Omnivorous with a focus on zooplankton and surface insects.
Diet juvenile
Phytoplankton, small zooplankton (rotifers).
Diet adult
Zooplankton (cladocerans, copepods), insect larvae, surface insects (midges, aphids).
Feeding strategy
Active hunter in the open water zone and at the water surface.
Schooling
Strongly developed schooling behavior, especially in open water.
Ecological role
Role in food web
Important consumer of zooplankton; serves as a significant prey fish species for larger predatory fish and water birds.
Natural predators
Northern pike, European perch, Kingfisher, Grey heron, Little grebe.
Competitor species
Bleak (food competition), Stone Moroko (food and habitat).
Parasites
Posthodiplostomum cuticola (black spot disease), various Monogenea.
Bioindicator function
Indicator for small, vegetation-rich water bodies with low fishing pressure and intact shore structures.
Fisheries & legal
Fishing regulation
Protected year-round in many federal states or subject to minimum sizes/closed seasons according to state fishery regulations.
Closed season
Often year-round (e.g., in NRW, Hesse), otherwise varies regionally.
Economic use
No economic importance as a food fish; occasionally used as bait fish or ornamental fish for garden ponds.
Protection & threats
Main threats
Loss of small water bodies (filling, drainage), eutrophication, invasive species (Stone Moroko), intensive fishery use of ponds.
Population trend
Declining in intensively used agricultural landscapes; stable in protected areas.
Conservation measures
Preservation and creation of small water bodies, avoidance of fish stocking in amphibian ponds, protection of riparian vegetation.