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Spiny Water Flea

Alias (scientific name in latin): Bythotrephes (bith-o-TREH-feez) cederstroemi; other aliases: Spiny Tailed Water Flea

Home Land (origination): Great Britain and northern Europe east to the Caspian Sea.

Arrival Date: Discovered in 1984 in Lake Huron. Scientists have hypothesized that the spiny water flea came to North America in the water onboard freighters from European ports, especially the port of St. Petersburg, Russia. North American freighters take products to Europe and return empty. In order to keep the boats stable, the empty freighters take on lots of water in the hold area of the ship. Small organisms, and even fish, are pumped in with the water and can survive the voyage across the ocean. Once ships reach North America, the water is discharged and the organisms are released into the waters here.

Invaded Territory: The water fleas spread to every Great Lake by 1987. They can also be found in some inland lakes in Michigan and southern Ontario.

How to Identify: Spiny water fleas are crustaceans, a relative of the shrimp, lobster, and crayfish. They have a long, sharp, barbed tail spine. They are large zooplankton measuring about 1 centimeter in length and are active from late spring to late fall. Spiny water fleas can rapidly reproduce in summer because adult females can produce young without mating, when water temperatures are just right, at a rate of 10 young every two weeks. They live for several days up to two weeks. In fall, females mate and produce resting eggs which live through the winter.

Disguise (don't be fooled by look-alikes): The spiny water flea looks similar to some harmless zooplankton, so get out your hand lens to look carefully. Our native harmless zooplankton is called water flea or daphnia.

Evidence: Because spiny water fleas eat zooplankton like Daphnia, they compete directly with small fish that also need to eat zooplankton. Research shows that perch aren't growing like they should and some young can't survive because of the lack of food. A decrease in small fish populations could also take away a food source for larger sport fish in Lake Michigan.

Spiny water fleas could be controlled if fish could eat large quantities of them, however, their sharp spine can only be swallowed by larger fish. Smaller fish can't swallow them and can have problems getting a spiny water flea free-meal. Because the fleas don't have many predators, their populations grow rapidly as they continue to eat up much of the zooplankton.

Mode of Transportation: Spiny water flea eggs and adults can get into bilge water, bait buckets, and livewells in boats on the Great Lakes if not monitored closely. Also, fishing lines and downriggers will often be coated with both eggs and adults. They can be carried to a new lake and introduced there if water is dumped out of a boat, bait bucket or livewell that just came from one of the Great Lakes. They can even invade a new place if a spiny water flea-infested fishing line is cast into a new lake.

Help Stop the Alien Invasion!

Teach people about these invaders. Scientists say that the spiny water flea is now a permanent member of the Great Lakes ecosystem. You can help by reporting any sightings of the spiny water flea, or other alien species in inland lakes, to the Wisconsin Department of Natural Resources. Don't let spiny water fleas tag along on your next fishing trip! Check your boat's bilge water, bait buckets, livewells, fishing lines, and downriggers for both eggs and adults before you leave one of the Great Lakes.