Spiny and Fishhook Waterfleas
(Bythotrephes longimanus and Cercopagis pengoi)
Spiny Waterfleas and the Fishhook Waterflea are small aquatic predators that were likely introduced to North America through ballast water from ocean-going ships. Native to Eurasia, the two species of zooplankton were first observed in Lake Ontario, the Spiny Waterflea in 1982 and the Fishhook Waterflea in 1998. Spiny Waterfleas prefer large, deep, clear, oligotrophic (poor in nutrients but rich in oxygen) lakes where they migrate vertically from deeper waters during the day to surface waters at night; they collects on fishing lines, downrigger cables and nets as jelly-like masses. Fishhook Waterfleas prefer the upper, warmer layer in deep, open lakes but are able to tolerate a wide range of temperatures; they collect on fishing lines as cotton-like masses.
Reproducing by asexual and sexual means, both species can multiply very quickly. They can spread to inland water bodies when egg-laden females are caught in fishing equipment. Their eggs can survive winter on lake bottoms and be transported long distances on boats or equipment in moist conditions.
Spiny Waterfleas are found in the Great Lakes, with very high densities in Lake Erie, moderate to high in Lake Huron, low in southern Lake Michigan and offshore areas of Lake Superior and very low in Lake Ontario, and in more than 100 inland lakes across Ontario. The species has also been observed in Manitoba and Minnesota. Fishhook Waterfleas are found in Lake Erie, Lake Ontario and Lake Michigan.
How can you help?