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Spiny and Fishhook Waterflea

Spiny (Bythotrephes longimanus) and fishhook (Cercopagis pengoi) waterfleas are small predacious crustaceans that threaten aquatic ecosystems and fishing by competing with native fish for food and fouling gear. Both arrived in ships'ballast water from Eurasia. Spiny waterfleas were discovered in Lake Ontario in 1982, then spread to all of the Great Lakes and some inland lakes. Fishhook waterfleas were first discovered in Lake Ontario in 1998, then spread to parts of lakesMichigan, Erie, and the Finger Lakes of NewYork.

Anglers often discover new infestations. Both waterfleas collect in masses on fishing lines and downrigger cables (see cover). These masses can clog the first eyelet of rods, damage a reel's drag system, and prevent fish from being landed. They can spread to inland waters when fishing gear is contaminated with egg-laden females.While females die out of water, under certain conditions they produce eggs that resist drying, remain viable, and can establish a new population. Eradicating established infestations is impossible. Your help to report new sightings and to prevent their spread is vital.

Identify Invasive Waterfleas

Identify Invasive Waterfleas

General Characteristics

  • Difficult to distinguish without magnification, 1/4 - 5/8 in (5-15mm) total length
  • Clumps look and feel like gelatin or cotton batting with tiny black spots
  • Prefer deep lakes, but can establish in shallow waterbodies and rivers
  • Abundant during summer (June-September) depending upon water temperatures

What You Can Do

  • Learn to recognize these waterfleas on fishing gear.
  • Inspect and remove and remove aquatic plants and animals, including gelatinous or cotton batting-like material from lines, especially where they meet a swivel, lure or downrigger ball connection (plucking like a guitar string helps).
  • Drain lake or river water from bilge, livewell, and motor before leaving access.
  • Dispose of unwanted live bait, worms, and fish parts in the trash.
  • Rinse boat and equipment with high pressure, hot water, AND/OR
  • Dry everything for five days or more before reuse.
  • Report new sightings - note exact location; put specimen in a sealed container with rubbing alcohol; and call the Minnesota Sea Grant Program in Duluth, (218) 726-8712, or a Minnesota DNR Invasive Species Specialist (see www.mndnr.gov/invasives/contacts.html), 1-888-MINNDNR or (651) 259-5100.

Know the rules!

Specimens are needed to confirm sightings, but some jurisdictions prohibit possession and transport of invasive aquatic plants and animals. Contact your local natural resource management agency for instructions. Unauthorized introduction of plants, fish, or invertebrates into the wild is illegal. Protect your property and our waters.

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This page last modified on July 26, 2013     © 1996 – 2016 Regents of the University of Minnesota     The University of Minnesota is an equal opportunity educator and employer.
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