Invasion History

First Non-native North American Tidal Record: 1992
First Non-native West Coast Tidal Record: 1992
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

The mysid Orientomysis aspera is native to coastal waters of Japan, Korea, and northern China. It is characteristic of eutrophic estuaries (Modlin and Orsi 1997; Fukuoka and Murano 2005). In one Japanese estuary, the Chikugo River, it occurred at salinities above 10 PSU (Suzuki et al. 2009).

North American Invasion History:

Invasion History on the West Coast:

In 1992, Orientomysis aspera was collected from the western end of Suisun Bay, where it generally occurs downstream of the introduced mysid Hyperacanthomysis longirostris. It is generally less abundant than H. longirostris, but occurs over a wider range of salinity (0-30 PSU) and is most abundant at 20-28 PSU (Cohen and Carlton 1995; Modlin and Orsi 1997; Baxter and Hieb 2006; Mecum et al. 2006). It has been collected regularly, in small numbers, from October to May in China Camp marsh, San Pablo Bay (Dean et al. 2005).


Mysids are small, shrimplike crustaceans, with a cape-like carapace which covers the head and thorax, but which is not attached to the last four thoracic segments. A pair of spherical statocysts is located at the base of the inner uropods. Adult females have a ventral brood pouch (Barnes 1983; Modlin 2007).

Orientomysis aspera has a slender, elongated body. The anterior edge of the carapace is produced into a blunt, triangular rostrum, with keel and struts at the base. The posterior margin of the carapace has a curved indentation, exposing somites 7 and 8. The eyes are stalked and prominent. The abdominal segments are smooth, without furrows or folds. The distal tip of the antennal scale is rounded. In the male, a penis is located near the basipod of the 7th thoracic leg, and is 2.4X as long as wide. The exopods and endopods of the uropods are blade-like, with the lateral margin slightly concave. The endopods each have a single spine between statocysts and the margin. The telson is roughly triangular, but with an undulating edge, 2.3 X as long as the greatest width. The lateral margin of telson is completely armed with long spines, in the distal half, interspersed with minute spines. The four terminal spines are narrow at the midpoint, and bulging near the base and tip. Adults are up to 13.5 mm in length. Description based on: Modlin and Orsi 1997; Fukuoka and Murano 2005; Mecum 2006; and Modlin, in Carlton 2007.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Mysidacea
Suborder:   Mysida
Family:   Mysidae
Genus:   Orientomysis
Species:   aspera


Acanthomysis aspera (Ii, 1964)
Orientomysis aspera (Fukuoaka & Murano, 2005)

Potentially Misidentified Species

Hyperacanthomysis longirostris
Previously known as Acanthomysis bowmani, abundant in upper San Francisco estuary

Orientomysis hwanhaiensis
Also introduced to San Francisco Bay, most common at 20-28 PSU.



Mysids are small, shrimplike crustaceans, which tend to divide their time between epibenthic habitats and the plankton, sometimes migrating diurnally, or else making brief swims between benthic habitats. Males have a pair of penes located at the junction of the thorax and abdomen, and modified pleopods used for the transfer of spermatophores. In O. aspera this is pleopod 4. Adult females have a brood pouch, and give birth to juveniles, resembling miniature adults (Barnes 1983; Bowman and Orsi 1993; Modlin, in Carlton 2007).

Orientomysis aspera is most abundant in polyhaline salinities in Japanese estuaries and San Francisco Bay, but occasionally occurs in fresh or nearly fresh waters in the upper San Francisco estuary (Mecum 2006; Dean et al. 2005; Suzuki et al. 2009). Mysids may be epibenthic feeders, suspension feeders, predators, or omnivores (Barnes 1983). Specific information on feeding of O. aspera is not available, but it is probably an omnivorous feeder.


Phytoplankton, Zooplankton


Fishes, decapod shrimps

Trophic Status:




General HabitatUnstructured BottomNone
General HabitatSalt-brackish marshNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Tidal RangeSubtidalNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)0.2Field data for "Acanthomysis sp." (Kimmerer et al. 1998)
Maximum Salinity (‰)20Field data for "Acanthomysis sp." (Kimmerer et al. 1998). However, Orientomysis aspera appeared downstream of Hyperacanthomysis longirostris (=A. bowmani) and may have a higher salinity tolerance and preference (Modlin and Orsi 1997).
Minimum Length (mm)7.2Adult males. Smallest females were 8.5 (Fukuoka and Murano 2005)
Maximum Length (mm)13.6Adult males. Largest females were 11.1 (Fukuoka and Murano 2005)
Broad Temperature RangeNoneCold temeprate-Warm temperate
Broad Salinity RangeNoneTidal Limnetic-Polyhaline

General Impacts

The impacts of Orientomysis aspera in San Francisco Bay are unclear, because its abundance is apparently much lower than that of Hyperacanthomysis longirostris (formerly Acanthomysis bowmani). Both species were frequently lumped in San Francisco Bay literature as 'Acanthomysis sp.'. These two species have replaced the formerly dominant, and larger, native Neomysis mercedis, which was an important food item for juvenile fishes in the upper San Francisco estuary (Feyrer et al. 2003. Winder et al. 2011).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-4a None 0 Native Estab
NWP-4b None 0 Native Estab
NWP-3b None 1936 Native Estab
NWP-3a None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 1992 Def Estab
P090 San Francisco Bay 1992 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


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

Baxter, Randall; Heib, Katherine (2006) Zooplankton Monitoring 2005, IEP Newsletter 19(2): 13-16

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Dean, Amy F.; Bollens, Stephen M.; Simenstad, Charles; Cordell, Jeffery (2005) Marshes as sources or sinks of an estuarine mysid: demographic patterns and tidal flux of Neomysis kadiakensis at China Camp marsh, San Francisco estuary, Estuarine, Coastal and Shelf Science 63: 1-11

Fairey, Russell; Dunn, Roslyn; Sigala, Marco; Oliver, John (2002) Introduced aquatic species in California's coastal waters: Final Report, California Department of Fish and Game, Sacramento. Pp. <missing location>

Feyrer, Frederick; Herbold, Bruce; Matern, Scott A.; Moyle, Peter (2003) Dietary shifts in a stressed fish assemblage: consequences of a bivalve invasion in the San Francisco estuary., Environmental Biology of Fishes 67: 277-288

Fukuoka, Kouki; Murano, Masaaki (2005) A revision of East Asian Acanthomysis (Crustacea: Mysida: Mysidae) and redefinition of Orientomysis, with description of a new species., Journal of Natural History 39(9): 657-708

Huang, Zongguo (Ed.), Junda Lin (Translator) (2001) Marine Species and Their Distributions in China's Seas, Krieger, Malabar, FL. Pp. <missing location>

Mecum, W. Lee (2006) <missing title>, California Department of Fish and Game, Sacramento CA. Pp. 1-6

Modlin, Richard F. (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California, Berkeley CA. Pp. 489-485

Modlin, Richard F.; Orsi, James J. (1997) Acanthomysis bowmani, a new species, and A. aspera Li, Mysidacea newly reported from the Sacramento-San Joaquin Estuary, Califronia (Crustacea: Mysidae), Proceedings of the Biological Society of Washington. 110(3): 439-446

Suzuki, Keita W.; Kasai, Akihide; Isoda,Takane; Nakayama, Kouji; Tanaka, Masaru (2009) Horizontal distribution and population dynamics of the dominant mysid Hyperacanthomysis longirostris along a temperate macrotidal estuary (Chikugo River estuary, Japan), Estuarine, Coastal and Shelf Science 83: 517-528

Winder; Monika; Jassby, Alan D.; Mac Nally, Ralph (2011) Synergies between climate anomalies and hydrological modifications facilitate estuarine biotic invasions, Ecology Letters 14: 749-757