Fishhook water flea

Cercopagis pengoi

FAMILY

Cercopagidae

TAXONOMY

Cercopagis pengoi Ostroumov, 1891, Caspian Sea.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

C. pengoi lacks the ventral (lower surface) portion of the carapace; as a result, its limbs are uncovered and its body is very mobile. The dorsal (upper surface) portion of the carapace remains and protects the brood cavity. The head of this cladoceran is rounded and contains strong mandibles (jaws) that are hardened with chitin. C. pengoi has only four pairs of thoracic legs, which are covered with setae (bristles) and spines. It has a long caudal (tail-like) appendage extending from its abdomen. Females are 0.05–0.08 in (1.2–2 mm) in length, and males are 0.04–0.06 in (1.1–1.4 mm) long; the caudal appendage may be 5–7 times the length of the body.

DISTRIBUTION

Native to the Caspian, Black, Azov, and Aral Seas; introduced to the Baltic Sea and the North American Great Lakes.

HABITAT

Inhabits brackish water as well as freshwater seas, lakes, and reservoirs.

BEHAVIOR

In its native range, this species migrates vertically on a daily basis; it lives at depths of 164–197 ft (50–60 m) during the day and rises to the surface layer at night. Young individuals are not found below 66–98 ft (20–30 m). Strong migration patterns are not observed in the Baltic Sea or Great Lakes.

FEEDING ECOLOGY AND DIET

C. pengoi is a predatory species; it actively catches prey and eats the tissues and soft body parts. Prey items include such other zooplankton as rotifers, copepods, protozoans, and other cladocerans. C. pengoi may be consumed by such larger planktivorous fish as herring and smelt.

REPRODUCTIVE BIOLOGY

C. pengoi reproduces asexually for most of the summer. Sexual reproduction takes place in late autumn.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

The hook on the caudal appendage of C. pengoi often becomes tangled in fishing gear, fouling the equipment. In addition, C.

pengoi competes with fish for food, and high populations of this species may reduce the number of fishes in a water body. Further, the fishhook water flea may intensify the eutrophication (overgrowth of algae resulting from an increased supply of nutrients) of water bodies by eating zooplankton that would normally graze on the algae.