Harmful Aquatic Hitchhikers: Crustaceans: Spiny Water Flea and Fishhook Water Flea

What do the spiny and fishhook water fleas look like?

As two of the lesser known hitchhikers, the spiny and fishhook water fleas are part of group of animals known as crustaceans that include crabs, shrimp, crayfish and lobsters. However, unlike these other crustaceans, the spiny and fishhook water fleas are very small creatures known as zooplankton. Every water body contains these microscopic organisms, which play an important role in the food chain.

Both of these creatures can be identified by their unique body shape, which consists of a hard outer shell and long, stout spine that serves a vital protective function. The tail spine is its distinguishing feature that separates these invertebrates from all other free-swimming lake zooplankton. The spine is proportionately long, making up over 70 percent of the animal's total length and it contains from one to four pairs of thorn-like barbs. The head consists primarily of a single, large eye filled with black pigment and a pair of mandibles, or jaws. The animals possess four pairs of legs, the first pair being much longer than the others. Although these water fleas are relatively small, (average length is scarcely more than one centimeter 0.4 inch), they can have as profound an effect on an ecosystem as a larger invader.

Why are these water fleas considered to be a nuisance?

Direct Competition - Research has shown that both water fleas eat smaller zooplankton that an important food item for juvenile fish. And because of their ability to reproduce quickly, this feature enables them to monopolize the food supply.
Ecological Advantages - Although the water fleas can fall prey to fish, their spine seems to frustrate most small fish, which tend to experience great difficulty swallowing the animal. Studies indicate spiny water fleas adversely affect the growth rates and survival of young fish, due to the competition for food and experts believe the fishhook water flea will have the same effect.
Nuisance Buildup - With the growing problem of the water flea infestation, anglers have experienced a nuisance buildup of these creatures on their line as they trolled various lakes. The build up is so heavy that it becomes nearly impossible to fish with any degree of enjoyment.

How do water fleas affect recreational users?

Lake anglers are most likely to encounter water fleas on their fishing lines in clumps of hundreds of individuals. The long spiny tails can become entangled on fishing lines, creating havoc for anglers as the first line guide of their fishing rod becomes clogged. Anglers have reported having to cut their lines because they are unable to reel them in. These masses of individuals look and feel like wet cotton.

Where are these water fleas currently found?

Both hitchhikers come from north-eastern Europe. Confirmed reports have shown the fishhook water flea to be limited to Lake Ontario, Lake Michigan and several inland lakes in New York State; however, it is likely that it and the spiny water flea will spread to the other Great Lakes.

What are these water fleas' potential to spread elsewhere in U.S.?

Since both creatures are very small and are only noticeable when clumping together, there is a significant chance that they will spread to other inland waters.

How can I prevent the spread of these water fleas?

Be vigilant about cleaning all of your equipment.
Clean all downgrigger lines to make sure no clumps of waterfleas are transported.
Clean all monofilament on reels to make sure no waterfleas are being transported on your reels.