Fishhook waterflea
Cercopagis pengoi
The fishhook waterflea (Cercopagis pengoi) is a predatory crustacean belonging to the order Onychopoda. It is characterized by an exceptionally long caudal spine with a terminal hook, which can be several times its body length. Native to the Ponto-Caspian region, it has successfully invaded the Baltic Sea and the North American Great Lakes. In these regions, it competes with larval fish for food and causes significant issues for commercial fishing by clogging nets.
Details
Identification
Extremely long caudal spine with an S-shaped hook at the tip and three pairs of barbs at the base.
Social behavior
Often occurs in extremely high densities, leading to the formation of clumps or 'ropes'.
Diet
Predatory; feeds on smaller zooplankton such as copepods and rotifers.
Hunting strategy
Uses specialized raptorial legs to capture and hold prey.
Spawning substrate
Resting eggs sink to the water body floor into the sediment.
Overwintering
Production of resistant resting eggs that overwinter in the sediment.
Ecology
Ecological role
Alters zooplankton composition and serves as food for planktivorous fish, but disrupts the growth of fish larvae.
Natural predators
Planktivorous fish such as herring, sprat, and perch.
Competitor species
Other predatory water fleas like Leptodora kindtii and planktivorous larval fish.
Threats
None; the species benefits from warming waters and global trade routes.
Scientific profile
Profile
Distinguishing features
Characteristic S-shaped hook at the end of the very long caudal spine (spine up to 10 mm long); a conspicuously large, deep black compound eye dominating the head; three pairs of specialized grasping legs (thoracic appendages).
Reproduction
Cyclical parthenogenesis; under favorable conditions (summer), rapid asexual reproduction occurs; under stress or in autumn, sexual reproduction takes place.
Role in food web
Invasive predator; exerts strong top-down control on native zooplankton and competes directly with fish larvae for food resources.
Protection & threats
Status not on standard scale
Main threats
None known; the species itself is an invasive threat to biodiversity and fisheries (clogging of nets due to the hooked spines).