The spiny water flea is a predacious zooplankton species and a member of the group of organisms known as crustaceans. Shrimp, crayfish, and lobster also belong to this group and the spiny water flea is a relative of another Great Lakes invader - the fishhook water flea. Introduced to North America from the ballast waters of Eurasian ships in 1982, the spiny water flea has spread throughout all the Great Lakes and more than 60 inland lakes in Ontario.

Characteristics

Spiny water flea prey on small organisms called zooplankton and can consume up to 20 per day. The spiny water flea is about 1 to 1.5 cm ( .4 - .6 in ) long. As its common name suggests, it has a long tail spine with barb-like projections. The head has a large black eye and a pair of swimming antennae. Also present are a pair of mandibles, or jaws used to pierce and shred its prey. The animals possess four pairs of legs; the first, longer pair are used for catching prey, whereas the other pairs of limbs are designed for grasping prey while they are being consumed.

Spiny water flea is parthenogenetic which means that it can reproduce asexually and sexually. When conditions are ideal, female spiny water fleas reproduce asexually to produce identical female offspring. Females can produce from one to ten eggs asexually that are able to develop into new females every two weeks. In situations of environmental stress (i.e. low water temperatures, not enough food, etc.), females produce males and mate to produce "resting eggs", which can remain dormant over long periods of time--over winter and even out of water for a period of time--then hatch when environmental conditions improve. Reproductive females carry their offspring on their backs in a balloon-like brood pouch, which can be filled with either developing embryos or resting eggs. Life span varies from several days to a few weeks.

Spiny water fleas are more common in deep, cool lakes, however, they do live in warmer lakes where surface water temperatures can exceed 25° C. Although the spiny water flea can swim up and down in the water column to avoid predators, it relies on current to carry it any great distance.

Distribution

It is believed that the spiny water flea first arrived in North America in the ballast water of Eurasian ships. The first recorded occurrence of the spiny water flea in North America was in Lake Ontario in 1982, and by 1987 it was present in all of the Great Lakes. This crustacean's known range in Ontario now includes over 120 inland lakes and waterways. If the proper precautions are not taken, spiny water fleas can be further spread unknowingly by boaters and anglers.

 Download the Spiny Water Flea distribution map

Impact

The spiny water flea feeds on small animal life called zooplankton. When populations of this invader are high, zooplankton consumption can be significant. Compared to native zooplankton species, it eats up to three times as much food. Unfortunately, this prey is also the preferred food of native predatory zooplankton and native species of juvenile fish, resulting in direct competition. Research on the impact of the spiny water flea has shown changes in both the abundance and the diversity of zooplankton species. However, it is still too early to determine if spiny water flea will alter our aquatic ecosystems to the detriment of fish populations.

Fish will feed on spiny water fleas. However, for fish smaller than 10 cm ( 3.9 in ) long, the tail spine of the spiny water flea gets caught in the throat and the organism is literally coughed out. To date, scientists have not observed a decline in the number of small fish due to the fish's inability to feed on spiny water flea and competition with it for food. However, over time, the possibility of an impact on fish populations is possible.

Spiny water fleas can become entangled in fishing lines and downrigger cables. When the cable is pulled from the water, the spiny water fleas attached to the cable look like straight pins. You may see them raise and lower their tails as they cling to the line.

Prevention

Presently, the best defence against the spiny water flea is to prevent its transfer to new waterbodies. Spiny water flea eggs and adults can get into bilge water, bait buckets, livewells and coat fishing lines when boating or fishing in infested waters. Please take the following precautions to prevent the spread of spiny water flea and other invading species to new waterbodies:

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); or
• 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 spiny water flea in an area not shown on the distribution map.

Spiny 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 in ballast water discharge.