Silver carp
Hypophthalmichthys molitrix
The silver carp is a large cyprinid fish characterized by a laterally compressed body and very small scales. A distinctive feature is the low-set eyes located below the midline of the head. It possesses specialized gill rakers that function like a sponge to filter phytoplankton from the water column. In many regions outside its native range, it is considered an invasive species due to its rapid reproduction and significant impact on aquatic ecosystems.
Details
Identification
Eyes positioned below the midline of the head, silvery coloration, tiny scales, sharp abdominal keel extending from the throat to the vent.
Social behavior
Schooling fish; often forms large groups in the upper water layers and exhibits synchronous jumping behavior when disturbed by noise (e.g., motors).
Diet
Specialized filter feeder that feeds almost exclusively on phytoplankton (algae and cyanobacteria).
Hunting strategy
Passive filtration of the water column while swimming using specialized gill structures.
Spawning substrate
Pelagic; eggs are released into the open water of large rivers and must be kept in suspension by the current.
Overwintering
Overwinters in deep, calm river sections or lake basins with significantly reduced metabolic activity.
Ecology
Ecological role
Primary consumer; regulates phytoplankton populations but competes heavily with native species (fish larvae, mussels) for food resources.
Natural predators
Juveniles are preyed upon by predatory fish (pike, catfish) and birds; adults have almost no natural predators.
Competitor species
Bighead carp, native planktivorous fish species, and large unionid mussels.
Ecosystem service
Used in biomanipulation for algae control and as a significant protein source in global aquaculture.
Threats
Threatened in its native range by dam construction and overfishing; globally managed as an invasive species in many areas.
Scientific profile
Morphology & ID
Coloration
Silvery shimmering sides, the back is dark grey to olive-green, and the belly is whitish-silver.
Distinguishing features
Characteristic are the very low-set eyes, positioned below the midline of the head. Gill rakers are fused into a sponge-like filtering apparatus. A sharp ventral keel extends from the throat to the anus.
Confusion species
Bighead Carp (Hypophthalmichthys nobilis) β which features dark mottling and a ventral keel that only extends from the pelvic fins to the anus.
Sexual dimorphism
Males develop rough, saw-like structures on the upper surface of the pectoral fin rays during the spawning season.
Habitat
Fish region
Bream zone (Potamon)
Preferred zone
Pelagic zone (open water near the surface)
Flow preference
Lentic to weakly lotic; prefers standing or very slow-flowing waters such as oxbow lakes and reservoirs.
Substrate preference
Fine sediments and mud in resting and feeding areas; however, high-flow river sections are required for reproduction.
Oxygen requirement
Low; the species is very tolerant of low dissolved oxygen levels (down to approx. 3 mg/L).
Migration
Migration behaviour
Distinct upstream spawning migration into main river channels during rising water levels.
Reproduction
Spawning substrate
Pelagic; eggs are semi-pelagic and must drift in the current to avoid sinking to the bottom and suffocating.
Larval phase
After hatching, larvae drift passively into calm shoreline areas or floodplains for further development.
Parental care
None
Diet
Feeding type
Phytoplanktivorous (specialized filter feeder)
Diet juvenile
Initially zooplankton, transitioning to phytoplankton as they grow.
Diet adult
Exclusively phytoplankton (diatoms, green algae, cyanobacteria), strained through the gill filter.
Feeding strategy
Active and passive filtration of microalgae from the water column.
Schooling
Strong schooling behavior, often forms large groups in open water.
Ecological role
Role in food web
Primary consumer; can alter the base of the food web through massive plankton consumption and displace native species.
Natural predators
In Europe, adults have almost no predators; juveniles are preyed upon by pike, zander, and catfish.
Competitor species
All native planktivorous fish species (e.g., coregonids, juveniles of almost all species).
Parasites
Lernaea cyprinacea (anchor worm), various gill flukes (Dactylogyrus spp.).
Bioindicator function
Indicator of high nutrient loading (eutrophication); often used for biomanipulation.
Fisheries & legal
Fishing regulation
In Germany, usually no closed season or minimum size as it is classified as an invasive species; removal often mandatory.
Closed season
None
Economic use
One of the most important food fish in aquaculture worldwide (especially China); locally used in Europe for algae control.
Protection & threats
Main threats
In native range: River regulation (dams prevent migration) and overfishing. In Europe: No threat.
Population trend
Decreasing in natural range; stable to increasing as an invasive species.
Conservation measures
Protection of natural spawning rivers in East Asia; in Europe management to limit populations.