''Cercopagis pengoi'', or the fishhook waterflea, is a species of

planktonic Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...

cladoceran

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s that is native in the brackish fringes of the

Black Sea The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bound ...

and the

Caspian Sea The Caspian Sea is the world's largest inland body of water, described as the List of lakes by area, world's largest lake and usually referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, ...

. In recent decades it has spread as an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

to some freshwater waterways and reservoirs of Eastern Europe and to the brackish

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

. Further it was introduced in ballast water to the Great Lakes of North America and a number of adjacent lakes, and has become a pest classified among the 100 worst invasive species of the world. ''Cercopagis pengoi'' is a predatory cladoceran and thus a competitor to other planktivorous

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s and smaller fishes. On the other hand, it has provided a new food source for planktivorous fishes. It is also a nuisance to fisheries as it tends to clog nets and fishing gear.Birnbaum, C. (2006)
''Cercopagis pengoi''
. NOBANIS – Invasive Alien Species Fact Sheet.

Description

The length of ''Cercopagis pengoi'' body is 1–3 mm, but with the tail included they range from 6–13 mm. The size varies with location, the largest are found in the

(average body size 2.0 mm) and smallest in

Lake Ontario Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York (state), New York. The Canada–United Sta ...

(average size 1.4 mm).Global Invasive Species Database (2018) Species profile: Cercopagis pengoi. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=118 on 05-05-2018. The English name refers to the three pairs of barbs and a characteristic loop at the end of the tail.

Ecology

''Cercopagis pengoi'' is eurythermal and euryhaline, being able to tolerate a wide range of temperature and salinity. It is a pelagic species, found in a higher abundance further from the shore and from the bottom. It is a generalist feeder which preys on various species in both micro- and mesozooplankton (i.e. cladocerans,

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

rotifer The rotifers (, from Latin 'wheel' and 'bearing'), sometimes called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic Coelom#Pseudocoelomates, pseudocoelomate animals. They were first describ ...

s). The size of prey ranges from its own body size to seventeen times smaller. Prey is captured using thoracopods I, then retained by thoracopods II-IV, and crushed by its cuticle by mandibles, finally C. pengoi sucks the prey body contents. Fishhook waterfleas reproduce asexually during the summer, which produces a quick rise in population.Benson, A., E. Maynard, D. Raikow, J. Larson, T.H. Makled, and A. Fusaro,2018, ''Cercopagis pengoi'': U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=163, Revision Date: 6/4/2013, Access Date: 3/28/2018 When conditions are inhospitable, ''C. pengoi'' will undergo sexual reproduction, producing resting eggs that can over-winter and repopulate the lake quickly in the spring. Resting eggs can withstand desiccation (extreme dryness), freeze-drying, and ingestion by fish.

Invasive species

''Cercopagis pengoi'' was brought to the American

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...

in ship ballast water from the

. It has been documented in Lake Ontario (1998), Lake Erie (2002), Lake Huron (2002), Lake Michigan (1999), the Finger Lakes of New York (Canandaigua, Cayuga, Keuka, Cross, Otisco, Owasco, and Seneca lakes, and the NYCDEP Pepacton Reservoir (2024). The species is transported in the live wells, bait water, and ropes of recreational fishing and boating. ''C. pengoi''’s wide tolerance levels and ability to reproduce both sexually and asexually makes it a very successful invader. Asexual reproduction allows for rapid population growth, and then resting eggs which are produced sexually can stick to boats and fishing gear and dispersed into new bodies of water. In the Baltic and in the Great Lakes, planktivorous fish and mysids are reported to prey on ''C. pengoi'', implying that it has become a new food source. ''C. pengoi'' directly competes with native zooplanktivores like alewife and rainbow smelt. Furthermore, ''C. pengoi'' have a long spine which deters planktivorous fish from consuming them. These factors cause disruption in the lower trophic levels of the Great Lakes food web which can eventually trickle up the food chain to cause problems with fish stock through a trophic cascade.

Control strategies

There is no known method of eradication or control for invasive ''Cercopagis pengoi''. Containing the spread to new areas is the only form of management. Stricter ballast water regulations and awareness would prevent the spread. The ''C. pengoi'' invasion of the Great Lakes occurred after the United States passed a regulation requiring ships exchange freshwater ballast water with ocean water to kill off potential invaders.Ricciardi, A., and H. J. MacIsaac. 2000. Recent mass invasion of the North American Great Lakes by Ponto-Caspian species . TREE vol. 15, no. 2 This means that either the resting eggs remain viable even after boats switch out their ballast water in the ocean or the required ballast water regulations are not being followed. Locally ''C. pengoi'' spread can be limited by only releasing bait or bait water into the water body where the bait was originally collected. Boat owners should wash their boats and equipment with high pressure and hot water (above 40 °C) to limit the spread of adult ''C. pengoi''. Alternatively boats and equipment should be allowed to dry for at least five days before moving to another body of water.Crosier, D. M., and D. P.Molloy. UNDATED. Cercopagis pengoi - Fishhook Waterflea. Aquatic Nuisance Species Research Program.

References

{{Taxonbar, from=Q2709805 Cladocera Freshwater crustaceans of North America Freshwater crustaceans of Europe Crustaceans described in 1891 Invasive animal species in North America