Fishhook water flea is a predatory zooplankton. It is a member of a large group of organisms called crustaceans and is a relative of another invader, the spiny water flea. Native to the Caspian, Aral and Azov Seas, they were first discovered by anglers in Lake Ontario in 1998. The most probable means of introduction was via the discharge of ballast water from foreign vessels.

Characteristics

The fishhook water flea grows to approximately 1 cm ( .4 in. ) long including the tail. The tail, often seven times the length of the body, has three tiny barbs and a unique loop at the end of its tail that looks like a fishhook hence its name. It has a single black eye and a large, pointed brood sac. Fishhook water fleas eat tiny, aquatic organisms called zooplankton that are an important food source for some fish (especially juvenile fish) and invertebrates.

Fishhook water flea is parthenogenetic which means that it can reproduce asexually and sexually. In most cases, female fishhook water fleas are dominant in the population, and they reproduce asexually in ideal conditions to produce female offspring. They can produce up to 13 offspring at a time and reproduce numerous times in one season. In situations of environmental stress (i.e. low water temperatures, not enough food, etc.), females will produce male offspring. Females and males mate and produce "resting eggs", which can remain dormant over long periods of time. These resting eggs can withstand extreme environmental conditions such as over-wintering (freezing), ingestion by predators and desiccation (drying-out) and then hatch when environmental conditions improve. The resting eggs can still hatch regardless if the female is dead or alive. The barbed tail enables the female to cling to gear such as ropes, lines, etc., that could easily be transfer to another waterbody. This reproductive strategy can enable a single female, be it dead or alive, to populate an entire lake.

Distribution

Confirmed reports of fishhook water flea have been limited to Lake Ontario, Lake Erie, Lake Michigan and several inland Finger lakes in New York State (Seneca, Cayuga, Otisco, Canandaigua, Owasco and Keuka).

 Download the Fishhook Water Flea distribution map

Impact

It is too early to fully understand the impacts that fishhook water flea will have on the Great Lakes ecosystem. There are concerns that fishhook water flea will compete with young fish and other predatory zooplankton species for food. Competition could result in the decline of certain zooplankton species and young fish populations. This could have far-ranging effects on fish species further up the food chain.

Fishhook water flea may also be difficult for young and small fish to use as a food source because of its long tail spine, as has been the case with the spiny water flea.

Anglers on Lake Ontario report that fishhook water fleas become entangled on fishing lines and downrigger cables to form gobs of fibrous material (these masses look and feel like cotton batten) forcing them to cut their lines because they are unable to reel them in. Charter boat operators have been forced to shut down due to this problem when large numbers of fishhook water flea are present in the water column in late July and early August. The commercial fishing industry has also been affected when fishhook water fleas foul nets.

Prevention

Although fishhook water flea has become established in several parts of Lake Ontario, Lake Erie and Lake Michigan, its spread can be prevented or slowed to other Great Lakes and our inland lakes. Fishhook water flea eggs and adults may be present in bilge water, boat trailers, vegetation, mud and sediments, bait buckets, livewells and coat fishing lines with both eggs and adults in boats and on equipment from infested areas that can then infect other areas. New research shows what you can do to help prevent the spread of fishhook water flea and kill their resting eggs:

Inspect your boat, trailer, boating equipment, fishing tackle and nets and remove any visible plants or animals before leaving any waterbody.

Drain water from motor, live well, bilge and transom wells while on land before leaving the waterbody.

Empty your bait bucket on land before leaving the waterbody. Never release live bait into a waterbody, or release animals from one waterbody into another.

Wash/Dry your fishing tackle, nets, boat and equipment to kill harmful species that were not seen at the boat launch. Some species can survive for several days out of water, so it is important to:

• rinse your boat and equipment with hot tap water (> 50° C); or 
• spray your boat and equipment with high pressure water (250 psi);
• dry your boat and equipment for at least five days, before transporting to another waterbody;

Call the Invading Species Hotline at 1-800-563-7711 if you find fishhook water flea in an area not shown on the distribution map.

Fishhook water flea and dozens of other non-native species, were introduced to the Great Lakes in the ballast water of ocean-going ships. Canadian and U.S. agencies must work together to implement effective regulations for shippers to reduce and eliminate the risk of organisms being introduced by ballast water discharge.