The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Cyclops strenuus
Cyclops strenuus
(a copepod)
Native Transplant

Copyright Info
Cyclops strenuus Fischer, 1851

Common name: a copepod

Taxonomy: available through www.itis.govITIS logo

Identification: Adults of this copepod species are yellow to brown colored. The caudal ramus of females, which displays no dorsal ridge in the Great Lakes, is 5–7 times longer than it is wide and exhibits a hair-covered inner surface. There is a lateral seta located at 73–87% of the distance from the base to the tip of the caudal ramus in females. In the same sex, the 5th leg displays two separate segments and the distal segment is less than 2 times as long as it is wide. Females’ antennules consist of 17 segments (Einsle 1989; Hudson et al. 1998).

Size: In Canada and Alaska, female C. strenuus are around 1.5 to 1.8 mm long and males are around 1.15 to 1.45 mm long (Reed and McIntyre 1995).

Native Range: Cyclops strenuus is a circumboreal species native to Europe, Alaska, the Yukon, and the Northwest Territories. There have also been reports from Asia which are not yet confirmed. There is a possibility that populations in the upper Great Lakes drainage are native relicts (Reed and McIntyre 1995; Hudson et al. 1998; Tackx et al. 2004; J. W. Reid and P. L. Hudson, unpublished data).

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Cyclops strenuus are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI197519751St. Marys

Table last updated 7/20/2024

† Populations may not be currently present.

Ecology: Cyclops strenuus is capable of producing a resting stage that becomes dormant in the sediments at the 4th or 5th copepodid stage, the pre-fertilized adult female stage, or the fertilized adult female stage. There is no encystment and if fertilized females become dormant, sperm can survive for around 7 months. The diapause period can occur in autumn, winter, or summer. In some permanent waters, C. strenuus can reproduce all year or may produce one or two generations that can undergo diapause.

Cyclops strenuus occurs in all kinds of environments, including ephemeral and permanent waters, subterranean waters, and sphagnum moors (Egmork 1955; Bothar and Oertel 1973; Pesce and Fabrizi 1979; Sarvala 1979; Maier 1990b; Nass and Nilssen 1991a; Frisch 2001, 2002).  Cyclops strenuus is typically found in freshwater and sometimes at very low salinities. It can occur in waters with high pH, even slightly over 10. It can survive temperatures of around 0–25ºC, but is particularly abundant at the warmer temperatures. Naupliar mortality increases at lower temperatures.

In one unusual Norwegian population, reproduction can occur at 0–3ºC in an oligotrophic lake. In reproducing females, the number of eggs per sac is around 31–66 (Elgmork and Halvorsen 1976; Maier 1990a; Hansen et al. 1991; Nass and Nilssen 1991a; Frisch 2001; Tackx et al. 2004).            

Cyclops strenuus is a host to many different parasites in its native range, some of which include the cestodes Triaenophorus crassus and Diphylobothrium spp.; the eel tapeworm Bothriocephalus claviceps; the eel swimbladder nematodes Anguillicola crassus, A. globiceps, and A. novaezelandiae; the tapeworms  Proteocephalus torulosus and P. neglectus; the acanthocephalid worm Pallisentis nagpurensis; and the helminth Traienophorus nodulosus (Sysoev 1982; George and Nadakal 1983; Scholz 1991, 1993, 1997; Moravec et al. 1994a, b; Nagasawa et al. 1994; Dorucu 1999; Pulkkinen et al. 2000).            

Cyclops strenuus is a common prey species for perch, Perca fluviatilis, in its native range. Cyclops strenuus itself is a carnivorous species and preys on ciliates, cladocerans, copepod nauplia, and rotifer nauplia. In Lake Glubokoye, in the former USSR, this species’ presence, along with that of the predator Leptodora kindtii, is negatively correlated with diversity and evenness of the prey community it utilizes. Algae are frequently found in the intestine of this species (Gilyarov 1976, 1977; Brabrand et al. 1983; Rossi et al. 1984; Treasurer 1992).

Means of Introduction: Unclear. Cyclops strenuus could have been introduced in ballast water, transferred with stocking programs, released with bait, discharged from live well water, transferred with recreational gear, transferred with waterfowl, or it may have dispersed via the Long Lac-Ogoki diversion project that connects the Hudson’s Bay drainage to Lake Superior (Hudson et al. 1998; Grigorovich et al. 2003; Holeck et al. 2004; Duggan et al. 2005).

Status: Established in Great Lakes (U.S. EPA 2008)

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: It is possible that in eastern Lake Superior and St. Marys River C. strenuus  populations are native relics from northern North America (Hudson et al. 1998).

References: (click for full references)

Bothar, A., and N. Oertel. 1973. Zoological examinations in the sphagnum moor of Egerbakta. Opuscula Zoologica (Budapest) 13(1-2): 37-48.

Brabrand, A., B.A. Faafeng, T. Kallqvist, and J.P. Nilssen. 1983. Biological control of undesirable cyanobacteria in culturally eutrophic lakes. Oecologia (Berlin) 60(1): 1-5.

Dorucu, M. 1999. Seasonal variation of pseudphyllidean cestode, Diphyllobothrium spp. infection in Cyclops strenuus abyssorum (Copepoda) in Loch Lomond. Turkish Journal of Zoology 23(1): 85-91.

Duggan, I.C., C.D.A. van Overdijk, S.A. Bailey, P.T. Jenkins, H. Limen, and H.J. MacIsaac. 2005. Invertebrates associated with residual ballast water and sediments of cargo-carrying ships entering the Great Lakes. Canadian Journal of Fisheries and Aquatic Sciences 62: 2463-2474.

Einsle, U.K. 1989. The identification of copepodid instars of some calanoid and cyclopoid copepods of Lake Konstanz, West Germany. Crustaceana (Leiden) 57(1): 79-87.

Elgmork, K. 1955. A resting stage without encystment in the animal cycle of the freshwater copepod Cyclops strenuus strenuus. Ecology 36(4): 739-743.

Elgmork, K., and G. Halvorsen. 1976. Body size of free-living copepods. Oikos 27(1): 27-33.

Frisch, D. 2001. Life cycles of the two freshwater copepods Cyclops strenuus Fischer and Cyclops insignis Claus (Cyclopoida, Copepoda) in an amphibious floodplain habitat. Hydrobiologia 453-454: 285-293.

Frisch, D. 2002. Dormancy, dispersal and the survival of cyclopoid copepods (Cyclopoida, Copepoda) in a lowland floodplain. Freshwater Biology 47(7): 1269-1281.

George, P.V., and A.M. Nadakal. 1983. Encapsulation of the immature juvenile of the acanthocephalid worm Pallisentis nagpurensis in the liver of definitive host Ophiocephalus striatus. Japanese Journal of Parasitology 32(5): 387-392.

Gilyarov, A.M. 1976. Feeding of Cyclops strenuus (Copepoda, Crustacea) in Lake Glubokoye, Moscow, Oblast, USSR during the summer. Zoologicheskii Zhurnal 55(2): 294-296.

Gilyarov, A.M. 1977. Role of predators in the regulation of species diversity of fresh water zoo plankton. Gidrobiologicheskii Zhurnal 13(2): 33-38.

Grigorovich, I.A., R.I. Colautti, E.L. Mills, K. Holeck, A.G. Ballert, and H.J. MacIsaac. 2003. Ballast-mediated animal introductions in the Laurentian Great Lakes: retrospective and prospective analyses. Canadian Journal of Fisheries and Aquatic Sciences 60: 740-756.

Hansen, A.M., J.V. Christensen, and O. Sortkjaer. 1991. Effect of high pH on zooplankton and nutrients in fish-free enclosures. Archiv für Hydrobiologie 123(2): 143-164.

Holeck, K.T., E.L. Mills, H.J. MacIsaac, M.R. Dochoda, R.J. Colautti, and A. Ricciardi. 2004. Bridging troubled waters: biological invasions, transoceanic shipping, and the Laurentian Great Lakes. BioScience 54: 919-929.

Hudson, P.L., J.W. Reid, L.T. Lesko, and J.H. Selgeby. 1998. Cyclopoid and harpacticoid copepods of the Laurentian Great Lakes. Ohio Biological Survey Bulletin New Series 12(2): i-vi + 1-50.

Maier, G. 1990a. The effect of temperature on the development, reproduction, and longevity of two common cyclopoid copepods Eucyclops serrulatus Fischer and Cyclops strenuus Fischer. Hydrobiologia 203(3): 165-176.

Maier, G. 1990b. The life history of two copepods with special reference to Eudiaptomus vulgaris Schmeil, 1898. Crustaceana (Leiden) 59(2): 204-212.

Moravec, F., D. Di Cave, P. Orecchia, and L. Paggi. 1994a. Experimental observations on the development of Anguillicola crassus (Nematoda: Dracunculoidea) in its definitive host, Anguilla anguilla (Pisces). Folia Parasitologica (Ceske Budejovice) 41(2): 138-148.

Moravec, F., D. Di Cave, P. Orecchia, and L. Paggi. 1994b. Present occurrence of Anguillicola novaezelandiae (Nematoda: Dracunculoidea) in Europe and its development in the intermediate host. Folia Parasitologica (Ceske Budejovice) 41(3): 203-208.

Nagasawa, K., Y.G. Kim, and H. Hirose. 1994. Anguillicola crassus and A. globiceps (Nematoda: Dracunculoidea) parasitic in the swimbladder of eels (Anguilla japonica and A. anguilla) in East Asia: a review. Folia Parasitologica (Ceske Budejovice) 41(2): 127-137.

Naess, T., and J.P. Nilssen. 1991a. Life cycle dynamics of a Cyclops strenuus (Crustacea, Copepoda) population with unusual diapause and reproductive characteristics. Archiv für Hydrobiologie 122(3): 323-334.

Naess, T., and J.P. Nilssen. 1991b. Diapausing fertilized adults, a new pattern of copepod life cycle. Oecologia (Berlin) 86(3): 368-371.

Pesce, G.L., and R. Fabrizi. 1979. Cyclopids from subterranean waters of Abruzzes, Italy. Contribution to the knowledge of the under ground waters fauna in central and southern Italy 7. Crustacea, Copepoda. Natura (Milan) 70(1-2): 55-75.

Pulkkinen, K., A.F. Pasternak, T. Hasu, and E.T. Tellervo. 2000. Effect of Triaenophorus crassus (Cestoda) infection on behavior and susceptibility to predation of the first intermediate host Cyclops strenuus (Copepoda). Journal of Parasitology 86(4): 664-670.

Reed, E.B., and N.E. McIntyre. 1995. Cyclops strenuus (Fischer, 1851) sensu lato in Alaska and Canada, with new records of occurrence. Canadian Journal of Zoology 73: 1699-1711.

Rossi, O., A. Moront, and E. Siri. 1984. The measurement of niche overlap in 8 carnivorous species of lake-dwelling zooplankton. Journal of Biogeography 11(2): 159-169.

Sarvala, J. 1979. Benthic resting periods of pelagic cyclopoids in an oligotrophic lake. Holarctic Ecology 2(2): 88-100.

Scholz, T. 1991. Studies on the development of the cestode Proteocephalus neglectus La Rue, 1911 (Cestoda, Proteocephalidae) under experimental conditions. Folia Parasitologica (Ceske Budejovice) 38(1): 39-55.

Scholz, T. 1993. Development of Proteocephalus torulosus in the intermediate host under experimental conditions. Journal of Helminthology 67(4): 315-324.

Scholz, T. 1997. Life-cycle of Bothriocephalus claviceps, a specific parasite of eels. Journal of Helminthology 71(3): 241-248.

Selgeby, J.H. 1975. Life histories and abundance of crustacean zooplankton in the outlet of Lake Superior, 1971-1972. Journal of the Fisheries Research Board of Canada 32: 461-470.

Sysoev, A.V. 1982. Composition and dynamics of invasion of the 1st intermediate hosts of Triaenophorus nodulosus (Cestoda, Triaenophoridae) under conditions in Karelia, USSR. Helminthologia (Bratislava) 19(4): 249-255.

Tackx, M.L., M.N. de Pauw, R. van Mieghem, F. Azemar, A. Hannouti, S. van Damme, F. Fiers, N. Daro, and P. Meire. 2004. Zooplankton in the Schelde estuary, Belgium and the Netherlands. Spatial and temporal patterns. Journal of Plankton Research 26(2): 133-141.

Treasurer, J.W. 1992. The predator-prey relationship of perch Perca fluviatilis larvae and zooplankton in two Scottish lochs. Environmental Biology of Fishes 35(1): 63-74.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and http://www.epa.gov/ncea.

Author: Kipp, R.M., J. Larson, and A. Fusaro

Revision Date: 9/12/2019

Citation Information:
Kipp, R.M., J. Larson, and A. Fusaro, 2024, Cyclops strenuus Fischer, 1851: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=2711, Revision Date: 9/12/2019, Access Date: 7/20/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [7/20/2024].

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