Invasion History

First Non-native North American Tidal Record: 1995
First Non-native West Coast Tidal Record: 1995
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Palaemon modestus (Siberian Prawn) is native to eastern Asia, from the Amur River Basin, Russia, through southern China. It is usually restricted to fresh and oligohaline waters (0-4 PSU) in Asia, and occurs in large rivers, lakes, and reservoirs (Kwon and Uno 1968; Holthuis 1980; Emmett et al. 2002; Guo et al. 2005). This species has been introduced to the Western Coast of North America and is found in parts of Washington, Oregon and California.

North American Invasion History:

Invasion History on the West Coast:

Palaemon modestus was first found in North America in the tidal portion of the lower Columbia River near Goble, Oregon in September, 1995 (Emmett et al. 2002). Since 1995, this shrimp has become abundant in the Columbia River, from Bonneville Dam, at the head of tide, past Portland to Miller Sands, 38 km from the river mouth (Emmett et al. 2002). Most captures of P. modestus have been in fresh water. In 2005, P. modestus was collected in the Snake River near Lower Granite Lake Dam, in Washington State (Haskell et al. 2006;  USGS Nonindigenous Aquatic Species Program 2009). In 1997, it was collected in the Umpqua River drainage, on the central coast of Oregon, and is established there (USGS Nonindigenous Aquatic Species Program 2009).

In 2001, P. modestus was first collected in the San Francisco estuary at Stockton, California, Sacramento River (USGS Nonindigenous Aquatic Species Program 2007). Its population grew rapidly. By 2005, it ranged from Wards Landing (Colusa County) on the Sacramento River, south to Mud Slough (Merced County) on the San Joaquin River, and downstream to Suisun, Grizzly, and Honker bays to Carquinez Strait, and infrequently in San Pablo Bay (Hieb 2007). In San Fancisco Bay, P. modestus has colonized brackish waters, reaching mesohaline salinities. In fresh-oligohaline parts of the Delta, it has become the dominant shrimp, largely replacing Palaemon macrodactylus, the Oriental Shrimp (Hieb 2007).


Palaemon modestus is a caridean shrimp. Infraorder characteristics include chelae (movable claws) on the first two pairs of walking legs, and a third thoracic segment overlapping the second segment. This shrimp has a translucent body, a long toothed rostrum and large chelae on the second pereiopods (walking legs). The rostrum is as long as, or shorter than, the carapace. The elevated basal crest is longer than the slender distal part. The carpus (wrist) of the second pereiopod is as long as, or slightly longer than, the chelae (claw). The rostrum is unarmed on the anterior half of the dorsal margin. The eggs measure 0.96-1.01 × 1.20-1.32 mm (Emmett et al. 2002; Guo et al. 2005). Palaemon modestus can be distinguished from P. carinicauda by the smaller chelae (claws) of the second pereiopod in P. modestus, and by two distal spines projecting beyond the tip of the median telson (tail) process. Palaemon carinicauda has small setae which do not go beyond the median telson process (Kubo 1942, cited by Emmett et al. 2002), and has strongly developed ridges (carinae, keels) on the dorsal midline of the four posterior segments of the abdomen (Wicksten et al. 1997; Guo et al. 2005).

A recent revision of the genus Palaemon and its relatives has moved the shrimps of the genus Exopalaemon back into the genus Palaemon (de Grave and Ashelby 2013).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Eucarida
Order:   Decapoda
Suborder:   Pleocyemata
Infraorder:   Caridea
Family:   Palaemonidae
Genus:   Palaemon
Species:   modestus


Leander czerniavskyi (Brashnikov, 1907)
Leander czerniavskyi lacustris (Brashnikov, 1907)
Leander modestus (Heller, 1862)
Leander modestus sibirica (Brashnikov, 1907)
Palaemon modestus (Sowerby, 1925)
Exopalaemon modestus (Holthuis, 1950)
Palaemon modestus (de Grave and Ashelby, 2013)

Potentially Misidentified Species

Palaemon carinicauda
Introduced, known from two specimens.

Palaemon kadiakenisis
Mississippi Grass Shrimp =Palaemonetes kadiakiensis, native to Interior Basin of North America, introduced to the Sacramento-San Joaquin Delta

Palaemon macrodactylus
Oriental Prawn, NW Pacific native, introduced to East and West coasts of North America

Syncaris pacifica
Native freshwater shrimp found in central California, two dorsal teeth, six ventral teeth on rostrum (Emmett et al. 2002; Brown and Hieb 2014).



Life History- In caridean shrimps, the copulating pair is usually oriented at right angles to one another, with the genital regions opposing each other. The modified first and second pairs of pleopods are used to transfer a spermatophore to a receptacle between the thoracic legs of the female (Barnes 1983). After mating, female palaemonid shrimps carry broods of fertilized eggs on their abdomen. These hatch into planktonic larvae with feathery appendages, called zoeae. Zoeae of shrimps lack the prominent spines seen in brachyuran crabs, and look quite shrimplike (Johnson and Allen 2005). They go through several molts and metamorphose into postlarvae, which have well-developed walking legs. After a subsequent molt, the body takes on the adult shape.

In Palaemon modestus, larval development is shortened, probably as an adaptation to river environments, where longer planktonic development can cause larvae to be washed out of a favorable environment. There are only two zoeal stages- these are quite large (~4 mm long) and completed in three days. The first postlarval stage is a well-formed juvenile shrimp, with well-developed walking legs and pleopods (swimmerets). Most marine palaemonids have several zoeal stages and longer planktonic development, while some freshwater forms have direct development, with all the zoeal stages occurring inside the egg. Palaemon modestus is at an intermediate stage, with a sharply abbreviated planktonic stage (Kwon and Uno 1968).

Ecology- Palaemon modestus is a widespread freshwater shrimp (Holthuis 1980; Guo et al. 2005), but it does occur in oligohaline waters (Oh et al. 2002; Hieb 2007). In South Korean estuaries, it retreats upstream when salinities rise above 4 PSU (Kwon and Uno 1968).


algae, invertebrates




Palaemon macrodactylus

Trophic Status:




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

Tolerances and Life History Parameters

Minimum Temperature (ºC)4.6Field, Suisun Bay (Brown and Hieb 2014)
Maximum Temperature (ºC)32.1Field (Suisun Bay, Brown and Hieb 2014)
Minimum Salinity (‰)0This is a freshwater species.
Maximum Salinity (‰)23.6Field (Suisun Bay, Brown and Hieb 2014)
Maximum Reproductive Temperature29.5Field, Young-Am Lake, southwestern South Korea (Oh et al. 2002)
Minimum Reproductive Salinity0This is a freshwater species.
Maximum Reproductive Salinity7Reared at 6-7 PSU, but rare above 4 PSU in South Korean rivers (Kwan and Uno 1968).
Minimum Duration3Zoea stages 1 and 2- 1st postlarval stage is a well-formed juvenile shrimp (Kwan and Uno 1968)
Maximum Length (mm)76Emmet et al. 2002
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneNontidal Limnetic-Mesohaline

General Impacts

Palaemon modestus has become abundant in the Columbia River and San Francisco estuaries. Detailed studies of its ecological and economic impacts have not been made. However, in the Sacramento-San Joaquin Delta, its increasing abundance, the decline of other decapod shrimps, and its significance in the diet of Striped Bass (Morone saxatilis) suggest that this species may be altering the Delta's food web. In the Columbia River, there are concerns that through predation or competition, P. modestus may adversely alter the food web for Pacific salmon (Oncorhynchus spp.) (Emmett et al. 2002).

Ecological Impacts

Competition- In fresh-oligohaline parts of the Sacramento-San Joaquin Delta, P. modestus has become the dominant shrimp, largely replacing Palaemon macrodactylus, the Oriental Shrimp (Hieb 2007). 'Since both P. modestus and P. macrodactylus rear in shallow areas with vegetation or other structure, the reduced catch of P. macrodactylus in the upstream portion of its distribution may have resulted from competitive interactions with or predation by P. modestus.' (Hieb 2007).

Food/Prey- Decapod shrimp, mostly P. modestus, were a major food item in the stomachs of juvenile Striped Bass (Morone saxatilis), next in frequency after amphipods (Nobriga and Feyrer 2008).

Regional Impacts

P090San Francisco BayEcological ImpactCompetition
In fresh-oligohaline parts of the Delta, it has become the dominant shrimp, largely replacing Palaemon macrodactylus, the Oriental Shrimp (Hieb 2007). 'Since both P. modestus and P. macrodactylus rear in shallow areas with vegetation or other structure, the reduced catch of P. macrodactylus in the upstream portion of its distribution may have resulted from competitive interactions with or predation by P. modestus.' (Hieb 2007).
P090San Francisco BayEcological ImpactFood/Prey
Decapod shrimp, mostly P. modestus, were a major food item in the stomachs of juvenile Striped Bass (Morone saxatilis), next in frequency after amphipods (Nobriga and Feyrer 2008).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
P260 Columbia River 1995 Def Estab
P090 San Francisco Bay 2000 Def Estab
P180 Umpqua River 1997 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
28256 USGS Nonindigenous Aquatic Species Program 2007 2000 2000-01-01 Sacramento River Def 38.7850 -121.6217


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