Spiny Waterflea and Fishhook Waterflea
(Bythotrephes cederstroemi and Cercopagis pengoi)
Both waterfleas entered the Great Lakes in ship ballast water from Europe – the spiny waterflea arrived in the 1980’s, followed in the 1990’s by the fishhook water flea. Only about ¼ to ½ inches in length, individual waterfleas may go unnoticed. However, both species tend to gather in masses on fishing lines and downrigger cables, so anglers may be the first to discover a new infestation.
Spiny and fishhook waterfleas 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 waterfleas 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.
Fishing, boating, and other water recreational equipment can transport spiny waterfleas and their eggs to new water bodies. Their resting eggs can survive long after the adults are dead, even under extreme environmental conditions. So care must be taken not to transport water between water bodies and to remove all waterfleas and eggs from equipment.
Spiny water fleas were found in the Gile Flowage (Iron County) in 2003 and Stormy Lake (Vilas County) in 2007. These are the only inland Wisconsin lakes known to contain invasive water fleas. Unfortunately, at this time no effective strategy is available to control the spiny water fleas once they are introduced to lakes.
Anyone who thinks they may have spotted spiny water fleas in other inland Wisconsin lakes is asked to contact their local DNR office or call (608) 266-9270.