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Spiny waterflea (Bythotrephes longimanus)

Spiny waterflea Common Names: Eurasian spiny waterflea

Description: Likely introduced in ballast water; discovered in Lake Ontario in 1982; spread to all Great Lakes and some inland lakes.

Identification: Tiny (1/2 in.) and translucent with a long, sharply barbed tail spine; dark eyespot is prominent; large numbers form clumps (with black spots) that look/feel like gelatin or wet cotton.

Habitat: Native to northern Europe. Prefer deep lakes, reservoirs, shallow water, large rivers and oxbows.

Reproduction: Can produce both by parthenogenetic (cloning) and gamogenetic (sexual) reproduction. Parthenogenetic reproduction occurs throughout the whole life cycle, while gamogenesis occurs at the end of a growing season and results in the formation of resting eggs capable of surviving unfavourable conditions.

Impact and Damage: Spiny waterfleas collect on fishing gear, especially lines and downrigger cables, lowering the quality of recreational fishing and charter trips. It jams the first eyelet of fishing rods, often resulting in the loss of a hooked fish. It also clumps can damage the drag on some reels and disrupts food web of the aquatic ecosystem.

Similar species: Fishhook waterflea (Cercopagis pengoi).

Monitoring and rapid response: Spread by angling and boating gear contaminated with adults carrying eggs. Bait and bait water should not be transported to other water bodies. Remove gelatinous blobs or cotton-like material from gear and examine lines at swivel, lure and down-rigger connections as well as nets and anchor ropes. Rinse 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:

Spiny waterflea

Scientific Name:

Bythotrephes longimanus


(Water flea)