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Fishhook waterflea (Cercopagis pengoi)

Fishhook waterflea Common Names: Fish-hook water flea

Description: Reported in Lake Ontario in 1998, likely introduced in ballast water; spread to Lakes Michigan and Erie.

Identification: 1/4 - 5/8 inch; long tail spine ending in a "hook"; prominent dark eyespot; can form clumps (with black spots) that look and feel like gelatin or wet cotton.

Habitat: Native to northern Europe. Prefer brackish to freshwater; deep lakes and shallow water bodies.

Reproduction: Cyclic parthenogen. It reproduces parthenogenically during the summer and gametogenically later in the year. The parthenogenically-produced young develop in a fluid-filled dorsal brood pouch that ruptures to release the young. In late summer and autumn, parthenogenic females produce eggs that develop into males and gametogenic females, which copulate. Gametogenic reproduction results in resting eggs, which are released when the brood pouch ruptures and overwinter in sediment. Sexual females are reproductive only at instars II and II, producing 1-4 eggs, while parthenogenic females produce 1-24 embryos.

Impact and Damage: The fishhook waterflea's "hook" catches on fishing lines and nets, fouling gear and lowering the quality of recreational fishing and charter trips. They can jam the first eyelet of fishing rods, often resulting in the loss of a hooked fish. They also devour plankton, the essential diet of larval native fish. They can also coat commercial fishing nets.

Similar species: Spiny waterflea (Bythotrephes longimanus).

Monitoring and rapid response: Spread by angling and boating equipment; eggs can be transported between lakes in early spring in sediment stuck to anchors and downrigger cables. Bait and bait water should not be transported to other waterbodies. Remove gelatinous blobs or cotton-like material from gear and examin lines at swivel, lure and downrigger connections as well as nets and anchor ropes. Rinsing boat and equipment with hot water (>40 degrees celsius), high pressure spray or drying boat and equipment for at least 5 days before re-entering water.

Credits: The information provided in this factsheet was gathered from the Global Invasive Species Database and from "Invaders of the Great Lakes" produced by Wildlife Forever and the Sea Grant Great Lakes Network.

Individual species images that appear with a number in a black box are courtesy of the network ( photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (

Common Name:

Fishhook waterflea

Scientific Name:

Cercopagis pengoi


(Water flea)