Spiny Water Flea

(Bythotrephes cederstroemi)

Spiny water fleas entered the Great Lakes in ship ballast water from Europe, arriving in the 1980s. With translucent bodies, only about ¼ to ½ inches in length, individual water fleas may go unnoticed. However, the species tend to gather in masses on fishing lines and downrigger cables, so anglers may be the first to discover a new infestation.

Other names for this animal include:

  • Common names: Spiny Water Flea
  • Scientific names: Bythotrephes cederstroemi

Ecological threat:

  • Spiny and fishhook water fleas are predators - they eat smaller zooplankton (planktonic animals), including Daphnia. This puts them in direct competition with juvenile fish for food.
  • Young fish have trouble eating these water fleas due to their long, spiny tails.
  • The spiny and fishhook water fleas produce rapidly through parthenogenesis, commonly known as asexual reproduction, which means that no males are required and populations can explode in number.
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