Fishhook Water flea

Fishhook water fleas are part of a group of animals known as crustaceans that include crabs, shrimp and crayfish. However, unlike these other crustaceans, the spiny and fishhook water fleas are small creatures known as zooplankton. The fishhook water flea closely resembles the spiny water flea. The fishhook water flea arrived in the United States via ballast water in ships traveling from Eurasia and was discovered in Lake Ontario in 1998.

Classification in Wisconsin: Prohibited/Restricted

Ecological Threat

• The fishhook water flea is detrimental to Wisconsin water because it alters the ecosystem's composition, structure and function by eating smaller zooplankton, putting them in direct competition with other large zooplankton and juvenile fish for food. Young fish have difficulty swallowing them because of their long tails, meaning that there are small numbers of natural predators that can keep the population manageable.
• Fishhook water fleas can decrease the biodiversity in an ecosystem by consuming and eliminating the native plankton species. This may reduce young fish populations, as they prey upon the same plankton eaten by the fishhook water flea.

Identification

Body: This species has an average translucent body measuring 0.4" (1 cm). The most noticeable part of this species is the black eyes that boldly stand out against the light-colored body. Typically found in clusters of 10+ individuals, the group will resemble wet cotton lumped on fishing lines, ropes, cables and other items in the water.

Similar Species: Spiny water flea

Distribution

See the reported locations of fishhook water fleas in Wisconsin.

Do you know of other populations? Please send us a report. Control

Mechanical: Recreational fishing and boating are the primary means of transport to new waters, so this species is best combated with boater education and steps to prevent their spread. Once in a body of water, the fishhook water flea is almost impossible to eradicate.

Prevention Steps:

• Inspect and remove aquatic plants, animals, and mud from the boat and equipment before leaving the boat launch.
• Drain water from your boat and equipment before leaving the boat launch.
• Throw away unwanted bait in the trash.
• Spray or rinse your boat and equipment with high pressure and hot tap water, especially if moored for over a day, or dry your boat and equipment entirely for at least five days.

Resources

Sources for content:

• USGS Factsheet [exit DNR]