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

planktonic Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

cladocera The Diplostraca or Cladocera, commonly known as water fleas, are a superorder of small crustaceans that feed on microscopic chunks of organic matter (excluding some predatory forms). Over 1000 species have been recognised so far, with many more ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s that is native in the brackish fringes of the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean 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 bounded by Bulgaria, Georgia, Roma ...

and the

Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asia ...

. In recent decades it has spread as an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

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 Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

. Further it was introduced in

ballast water Ballast is used in ships to provide moment to resist the lateral forces on the hull. Insufficiently ballasted boats tend to tip or heel excessively in high winds. Too much heel may result in the vessel capsizing. If a sailing vessel needs to voy ...

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 Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

cladoceran and thus a competitor to other

planktivorous A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton. Planktivorous organisms encompass a range of some of the planet's smallest to largest multicellular animals in both the present day and ...

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

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. The Canada–United States border sp ...

(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.

ns,

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 (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

rotifer The rotifers (, from the Latin , "wheel", and , "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John H ...

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 egg Rest or REST may refer to: Relief from activity * Sleep ** Bed rest * Kneeling * Lying (position) * Sitting * Squatting position Structural support * Structural support ** Rest (cue sports) ** Armrest ** Headrest ** Footrest Arts and entertain ...

s 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 in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...

in ship ballast water from the

. It has been documented in Lake Ontario (1998), Lake Erie (2002), Lake Huron (2002), Lake Michigan (1999), and the

Finger Lakes The Finger Lakes are a group of eleven long, narrow, roughly north–south lakes located south of Lake Ontario in an area called the ''Finger Lakes region'' in New York, in the United States. This region straddles the northern and transitional ...

of New York (Canandaigua, Cayuga, Keuka, Cross, Otisco, Owasco, and Seneca lakes. 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,

fish and

mysid Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in ...

s 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 The rainbow smelt (''Osmerus mordax'') is a North American species of fish of the family Osmeridae. Walleye, trout, and other larger fish prey on these smelt. The rainbow smelt prefer juvenile ciscoes, zooplankton such as calanoid copepods ('' L ...

. 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 Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...

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