Invasion History

First Non-native North American Tidal Record: 2002
First Non-native West Coast Tidal Record: 2002
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Crangonyx pseudogracilis is a freshwater amphipod native to eastern North America. It was described from Ontario by Bousfield (1958). Its range extends through the Great Lakes and Mississippi Basins, and Atlantic watersheds at least as far south as the Missouri and the Delaware Rivers (Bousfield 1958; Bousfield 1973). The southern extent of its native range is obscured by possible confusion with the very similar C. floridanus, which may be synonymous (Sytsma et al. 2004). Crangonyx pseudogracilis has been introduced to tidal freshwater portions of the Columbia River estuary, where it was found in the vicinity of Portland in 2002 (Systma et al. 2004). It has also been reported from creeks in San Luis Obispo County, California, in the watershed of Morro Bay (Bottoroff et al. 2003, cited by Graening et al. 2012), but has not been reported from the estuary yet.

Crangonyx pseudogracilis has also invaded Europe, initially, as a food for pond and lake fishes, in England in 1936, and spreading through fresh waters in Ireland and northern continental Europe, including the Netherlands, Belgium, Germany (Pinkster et al. 1992; Wouters 2002; Gollasch and Nehring 2006), and Portugal (Grabowski et al. 2012). Likely vectors in Europe include fish-stocking, recreational boats, ornamental aquatic plants, and canals.

North American Invasion History:

Invasion History on the West Coast:

The date of first collection of Crangonyx pseudogracilis is uncertain, because of taxonomic confusion in this genus (Cordell, in Sytsma et al. 2004). In 2002, it was collected in several sites along the fresh, tidal Columbia River, from Longview, Washington to Portland, Oregon (Sytsma et al. 2004). In 2000-2003, C. pseudogracilis was collected in California in Stenner and Brizzolara Creeks, in San Luis Opisbo, tributaries of Morro Bay (Bottoroff et al. 2003, cited by Graening et al. 2012). However, this amphipod has not yet been reported from the estuary. There are records from the Truckee River, California-Nevada and Arizona (Graening et al. 2012), but morphological and genetic studies are desirable to determine the identity and invasion history of these populations.

Invasion History Elsewhere in the World:

Crangonyx pseudogracilis was intentionally introduced to southern England in 1936, as a food for pond and lake fishes, and dispersed as far north as Yorkshire, by 1975, when it was also first collected in Ireland. In 1979, it was collected in the Netherlands, in Groningen Province, and spread widely though the Rhine delta (Pinkster et al. 1992). It is now widespread in freshwaters of Belgium (Wouters 2002) and Germany (Gollasch and Nehring 2006). It occurs occasionally in the brackish harbor of Ghent, Belgium (Boets et al. 2011). In 2011, it was collected for the first time in a freshwater stream in Portugal (Grabowski et al. 2012). In Northern Ireland, predation by other Gammarus species (G. pulex, G. duebeni, G. tigrinus, in descending order of predation rate), limited the distribution of the smaller C. pseudogracilis (MacNeil et al. 2003).


The body of Crangonyx pseudogracilis is moderately compressed and smooth, lacking spines on the urosome segments. Coxal plates 1-4 are deep and lined with short setae, with Coxa 4 being larger, having a slightly convex posterior edge, with a rounded ventro-posterior corner. The head is small, with a rounded anterior lobe and lacking a ventral antennal sinus. The eyes are medium-sized and oval. Antenna 1 is 2X longer than Antenna 2, and bears a 2-segment accessory flagellum, characteristic of the Crangonyctidae.

Gnathopod 1 is smaller than gnathopod 2, but both are subchelate, with the dactyl (segment 7) folding against the propodus (segment 6). Both gnathopds are larger and more robust in males than females. In females, the propodus and carpus (segment 5) are roughly equal, but in males, the propodus of both gnathopods is more than 2X as long as the carpus. The palms of both gnathopods are lined with many spines, which are larger in the male than in the female. Pereiopod 6 is the longest. The posterior ventral corners of the abdominal plates (pleons) end in blunt angles. Uropods 1 and 2 are biramous, with the rami roughly equal, while Uropod 3 has the inner ramus reduced to a scale-like structure. In males, the outer ramus of Uropod 2 is lined with small, comb-like spines. Males have a maximum length of 6.5 mm; females reach 10 mm. Description based on: Hynes 1955; Holsinger 1972, Bousfield 1973, and Chapman 2007.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Crangonyctidae
Genus:   Crangonyx
Species:   pseudogracilis


?Crangonyx gracilis (Forbes, 1876)
Eucrangonyx gracilis ( Kunkel, 1918)
Melita parvimana (Holmes, 1905)

Potentially Misidentified Species

Crangonyx floridanus
These species might be synonymous (Sytsma et al. 2004)



Crangonyx pseudogracilis is a free-living, freshwater amphipod. Sexes are separate, the young are brooded, and development is direct (Bousfield 1973). In the laboratory, C. pseudogracilis breeds at 5 to 25C, and the egg development time decreased from 66 to 7 days over that temperature range (Sutcliffe and Carrick 1981). In an English river, breeding took place year-round and the monthly average number of eggs per female varied from 25 to 54 (Hynes 1955).

Crangonyx pseudogracilis tolerates a wide range of temperature, tolerating ice covered waters and temperatures at least as high as 25C (Bousfield 1958; Sutcliffe and Carrick 1981). It can tolerate somewhat brackish water, but the upper salinity tolerance is not known (Bousfield 1973; Pinkster et al. 1992). Habitats include rivers, ponds, and lakes, preferring areas that are turbid, weedy, and warm in summer (Bousfield 1958; Bousfield 1973). Crangonyx pseudogracilis is probably omnivorous, like many free-living gammarids, feeding on algae, detritus, and occasionally on invertebrates and carrion (Barnes 1983). Amphipods in culture were fed on shoots of the water plants Elodea, Callitriche, and decaying elm leaves (Sutcliffe and Carrick 1981). Fish and other gammarid amphipods are probably the most frequent predators of C. pseudogracilis. In European waters, 3 species of Gammarus all preyed on C. pseudogracilis (Dick 1996).


Detritus, algae, benthic invertebrates


fishes, insects, amphipods


Gammarus spp.

Trophic Status:




General HabitatNontidal FreshwaterNone
General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatCoarse Woody DebrisNone
General HabitatSwampNone
General HabitatTidal Fresh MarshNone
General HabitatUnstructured BottomNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)4Based on geographical range
Minimum Salinity (‰)0This is a freshwater species.
Minimum Reproductive Temperature5Experimental, lowest tested (Sutcliffe and Carrick 1981)
Maximum Reproductive Temperature25Experimental,highest tested (Sutcliffe and Carrick 1981)
Minimum Length (mm)3Males, 6 mm for females (Hynes 1955, England)
Maximum Length (mm)10Adult females (Bousfield 1973, New England); 5 mm for males (Hynes 1955, England)
Broad Temperature RangeNoneCold temperate
Broad Salinity RangeNoneNontidal Limnetic-Oligohaline

General Impacts

Impacts of introduced populations of Crangonyx pseudogracilis have not been reported in North America. In European waters, this amphipod has spread rapidly, and often colonizes marginal pools, polluted waters, and other habitats not used by native amphipods (Pinkster et al. 1992; Piscart et al. 2007). It is smaller than several native and introduced gammarids in Europe, and is prone to predation by them (Dick et al. 1996). However, because of its high fecundity and rapid growth, its appearance in Portugal is considered a threat to several regional endemic species (Grabowski et al. 2012).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
GL-I Lakes Huron, Superior and Michigan 0 Native Estab
GL-II Lake Erie 0 Native Estab
P260 Columbia River 2002 Def Estab
GL-III Lake Ontario 0 Native Estab
M060 Hudson River/Raritan Bay 0 Native Estab
M090 Delaware Bay 0 Native Estab
M040 Long Island Sound 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Bilger, Michael D.; Riva-Murray, Karen;Wall, Gretchen L. (2005) <missing title>, U. S. Geological Survey, Reston, VA. Pp. <missing location>

Boets, Pieter; Lock, Koen; Goethals, Peter L. M. (2011) Using long-term monitoring to investigate the changes in species composition in the harbour of Ghent (Belgium), Hydrobiologia 663: 155-166

Bommerlund, Julie; Baars, Jan-Robert; Schrøder-Nielsen, Audun; Brys. Rein; Mauvisseau, Christophe; Hugo J.; de Boer, Christophe; Mauvisseau, Quentin (2023) eDNA-based detection as an early warning tool for detecting established and emerging invasive amphipods, BioInvasions Records 12: Published online

Bousfield, E.L. (1958) Freshwater amphipod crustaceans of glaciated North Amerca., Canadian Field-Naturalist 72(2): 55-113

Bousfield, E.L. (1973) <missing title>, Comstock Publishing Associates, Ithaca, NY. Pp. <missing location>

Chapman, John W. (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California Press, Berkeley CA. Pp. 545-611

Dick, J. T. A., Nelson, N., Bishop, J. D. D. (1997) Introduction experiments with Gammarus spp. (Crustacea: Amphipoda) in the Isle of Man (British Isles), 1949-1995, Journal of Zoology, London 242: 209-216

Dick, Jaimie T. A. (1996) Post-invasion amphipod communities of Lough Neagh, Northern Ireland: Influences of habitat selection and mutual predation., Journal of Animal Ecology 65(6): 756-767

Dobson, Michael (2012) <missing title>, Freshwater Biological Association, Far Sawrey, Ambleside, Cumbria, England. Pp. <missing location>

Gollasch, Stephan; Nehring, Stefan (2006) National checklist for aquatic alien species in Germany., Aquatic Invasions 1(2): 245-269

Grabowski, M.; Rachalewski, M.; Banha, F.; Anastacio, P. (2012) Crangonyx pseudogracilis Bousfield, 1958 – the first alien amphipod crustacean in freshwaters of Iberian Peninsula (Portugal), Knowledge and Management of Aquatic Ecosystems 404(11): published online

Graening, G. O.; Rogers, D. Christopher; Holsinger, John R.; Barr, Cheryl; Bottorff, Richard (2012) Checklist of inland aquatic Amphipoda (Crustacea: Malacostraca) of California, Zootaxa 3544: 1-27

Hautus, Tjeu; Pinkster, Sjouk (1987) Range extension in the period 1985-1986 of the alien amphipods, Gammarus tigrinus, 1939, and Crangonyx pseudogracilis, 1958, in the Netherlands., Bulletin Zoologisch Museum Universiteit van Amsterdam 11(6): <missing location>

Holsinger, J. R. (1972) <missing title>, US Environmental Protection Agency, Washington DC. Pp. 1-89

Hynes, H. B. N. (1955) The reproductive cycle of some British freshwater Gammaridae, Journal of Animal Ecology 24(2): 352-387

Labat, Frédéric; Piscart, Christophe; Fontan, Bruno (2011) First records, pathways and distributions of four new Ponto-Caspian amphipods in France, Limnologica 41: 290-295

MacNeil, Calum, and 5 authors (2003) Parasite-mediated predation between native and invasive amphipods, Proceedings of the Royal Society of London B 270: 1309-1314

MacNeil, Calum; Dick, Jaimie T. A.; Alexander, Mhairi E.; Dodd, Jennifer A.; Ricciardi, Anthony (2013) Predators vs. alien: differential biotic resistance to an invasive species by two resident predators, Neobiota 19: 1-19

Pinkster, Sjouk, Scheepmaker, Maarten, Platvoet, Dirk, Broodbakker, Nico (1992) Drastic changes in the amphipod fauna (Crustacea) of Dutch inland waters during the last 25 years., Bijdragen tot de Dierkunde 61(4): 193-204

Pinkster, Sjouk; Platvoet, Dirk (1983) Further observations on the distribution and biology of two alien amphipods, Gammarus tigrinus, Sexton 1939 and Crangonyx pseudogracilis, Bousfield 1958, in the Netherlands (Crustacea, Amphipoda)., Bulletin Zoologisch Museum Universiteit van Amsterdam 9(17): 154-164.

Piscart, Christophe; Manach, Alain; Copp, Gordon H.; Marmonier, Pierre (2007) Distribution and microhabitats of native and non-native gammarids (Amphipoda, Crustacea) in Brittany, with particular reference to the endangered endemic sub-species Gammarus duebeni celticus., Journal of Biogeography 34: 524-533

Platvoet, Dirk; Pinkster, Sjouk (1985) The present position of the alien amphipods, Gammarus tigrinus and Crangonyx pseudogracilis in the Netherlands, Bulletin Zoologisch Museum Universiteit van Amsterdam 10(16): 125-128

Slothouber Galbreath, Johanna G. M.; Smith, Judith E.; Becnel, James J.; Butlin, Roger K.; Dunn, Alison M. (2010) Reduction in post-invasion genetic diversity in Crangonyx pseudogracilis (Amphipoda: Crustacea): a genetic bottleneck or the work of hitchhiking vertically transmitted microparasites?, Biological Invasions 12: 191-209

Sytsma, Mark D.; Cordell, Jeffrey R.; Chapman, John W.; Draheim, Robyn, C. (2004) <missing title>, Center for Lakes and Reservoirs, Portland State University, Portland OR. Pp. <missing location>

The Conchological Society of Great Britain and Ireland 2022 The Conchological Society of Great Britain and Ireland- Doris pseudoargus.

Wouters, Karel (2002) On the distribution of alien non-marine and estuarine macro-crustaceans in Belgium., Bulletin Van Het Koninklin Instituut Voor Naturwetenschappen, Biologie. 17: 119-129

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