Fishhook Water Flea

Cercopagis pengoi

Learn about the Fishhook Water Flea, including its identifying features, distribution, habitat, spread, similar species, impacts and our response.

On this page

• Identifying features
• Where is the species invasive
• Distribution
• Habitat
• Similar species
• Impacts
  • Ecological impacts
  • Socio-economic impacts
• Response
• Photo gallery
• Related links

Identifying features

• between 0.6 cm and 1.3 cm long
• tail is at a 90 degree angle from the rest of the body, with three spines and a hook-shaped loop at its end, and occupies approximately 80% of the total length
• females have a pointed-shaped bag containing the eggs on their back

If you think you have seen Fishhook Water Flea, report it.

Where is the species invasive

The Fishhook Water Flea was introduced to North America via ballast water released from commercial shipping vessels. It was found for the first time in Lake Ontario in 1998. It can be found in the interior waters of Northeast America, in particular the Great Lakes, the St. Lawrence River, Lake Champlain and, since 2019, the Richelieu River.

Distribution

The Fishhook Water Flea is native to the region of the North Sea and to central Europe and Asia.

Habitat

The Fishhook Water Flea tolerates a wide range of temperatures, salinities and depths, but prefers fresh water with low salinity. It can migrate towards deeper waters during the day and swim closer to the surface at night to avoid predation. Usually, it is found in pelagic zones far from the coast, but it is found closer to shore in the Richelieu River.

Similar species

The Spiny Water Flea and Fishhook Water Flea look similar to some native water flea species, such as Daphnia. However, the drop shape body of the Daphnia only measures up to 0.5 cm and its tail is very short, accounting for only a quarter of the total length.

Daphnia longispina

Spiny Water Flea (bottom) and Fishhook Water Flea (top)

Impacts

Ecological impacts

The Fishhook Water Flea can reproduce sexually or asexually depending on environmental conditions, giving it formidable invasive potential. Introduction of a very small number of individuals, and even of a single female, allows them to establish themselves quickly once introduced in a new water body. Fishhook Water Fleas compete with native species for food and can significantly modify zooplankton communities. Such changes can have detrimental effects that cascade across the food web.

Socio-economics impacts

Fishhook Water Fleas can affect recreational, Indigenous and commercial fisheries by fouling lines and fishing nets, or by directly impacting fish populations through competition with juvenile fish for small plankton.

Response

The Identification Booklet of Freshwater Invasive Species in Quebec from DFO is available to make the detection of Fishhook Water Fleas easier.

There is currently no effective way to eradicate the Fishhook Water Flea. Prevention remains the best way to avoid its spread into new areas. Eggs, juveniles or adults of this species may be found on equipment and boats that have been used in water bodies where this AIS is present. The best way to protect water bodies from this invader is to properly clean, drain and dry boats and other equipment used in nautical and recreational fishing activities. Follow the clean-up steps described on the DFO Aquatic Invasive Species Prevention page. Always check and follow provincial regulations when planning to move water-based craft and equipment.

Photo gallery

Related links

• Spiny Water Flea and Fishhook Water Flea identification photos and characteristics
• Science Advice on “Clean, Drain, Dry and Decontaminate” treatments and protocols to prevent the introduction and spread of aquatic invasive species (PDF, 632 KB)
• Research Document on “Clean, Drain, Dry, and Decontaminate” treatments and protocols to prevent the introduction and spread of aquatic invasive species