Invasion History

First Non-native North American Tidal Record: 2004
First Non-native West Coast Tidal Record: 2004
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

The mysid Neomysis japonica is native to coastal waters and estuaries of the Northwest Pacific, from the South China Sea to the Bohai and Yellow Seas and the east and west coasts of central Japan (Ii 1964). It has been introduced to San Francisco Bay, California (Cohen et al. 2005; Modlin in Carlton 2007) and New South Wales, Australia (Hutchings et al. 1986).

North American Invasion History:

Invasion History on the West Coast:

Neomysis japonica was first definitively identified from the Petaluma River, California, a tributary of San Pablo Bay in 2004 (Cohen et al. 2005; Modlin in Carlton 2007). In 1996, a mysid, then identified as the native N. kadiakensis, appeared in the Sacramento-San Joaquin Delta and Suisun Bay, occurring in low abundances, roughly equal to those of the formerly dominant native N. mercedis. This was probably N. japonica, but characters for separating these species were not known at that time (Baxter and Hieb 2006). Similarly, some or even all of the 'N. kadiakensis' comprising 94-99% of the mysids caught at China Camp, San Pablo Bay in 2002-2005 (Dean et al. 2005) may have been N. japonica. At this time, the range and abundance of N. japonica in the San Francisco estuary is unknown.

Invasion History Elsewhere in the World:

Neomysis japonica was collected and found to be breeding in the Hunter River, New South Wales, Australia (Hutchings et al. 1986; Lowry and Stoddart 2003). Williams et al. (1988) found this mysid in ballast water from Japanese ships in Australian harbors. We have no further information on the occurrence of this animal in Australian waters.


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 in Carlton 2007).

Neomysis japonica has a carapace with its front edge broadly rounded, reaching slightly beyond the base of the antennules and just covering the inner part of the base of the eye-stalks. The posterior edge of the carapace is curved forward, exposing parts of thoracic segments 7 and 8. The eyes are large and about 1 2/3 X as long as broad. The abdominal segments are smooth, without furrows or folds. The antennal scale is 9 X as long as wide, with the apex sharply pointed, with a distal joint comprising about 1/5 of the total length. The 4th pleopod of the male has an elongated exopodite, with the 1st joint 6 X the length of the second. The telson is roughly triangular, about 2 1/2 X as long as its greatest width and lined with about 35-40 small spines, with two larger terminal spines at the tip, flanking a pair of median small spines. The spines are more widely spaced at the proximal end of the telson and more closely spaced. The largest individuals are about 13 mm long (Ii 1964; Modlin in Carlton 2007).

In San Francisco Bay, N. japonica was confused with N. kadiakensis. The latter is characteristic of deeper, more saline bays and inlets, whereas N. japonica is more characteristic of estuaries. Neomysis japonica is likely to co-occur with the native N. mercedis, which was formerly very abundant in upper San Francisco estuary (Ii 1964; 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:   Neomysis
Species:   japonica


Potentially Misidentified Species

Neomysis kadiakensis
Neomysis kadiakensis has an antennal scale 13-14X as long as wide, and a telson 2 1/2X as long as wide, so forming a more narrow triangle (Ii 1964; Modlin, in Carlton 2007).

Neomysis mercedis
See Modlin, in Carlton 2007, p. 492 for distinguishing characteristics of N. japonica.

Neomysis rayi
See Modlin, in Carlton 2007, p. 492 for distinguishing characteristics of N. japonica. This mysid is characteristic of offshore waters and deep inlets.



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 N. americana this is pleopod 5. Adult females have a brood pouch, and give birth to juveniles, resembling miniature adults (Barnes 1983; Modlin, in Carlton 2007).

The abundance and distribution of Neomysis japonica, in San Francisco Bay, is poorly known because of taxonomic confusion with N. kadakiensis. In Japan, it is 'abundant in the brackish water along the Pacific coast of Japan and is also very common in the estuaries and lagoons'( Ii 1964). In the Chikugo River estuary, Japan, it was common between 1 and 10 PSU, but was also common in the outer estuary at 10-20+ PSU (Suzuki et al. 2009). In the Petaluma River, it was collected at 8-10 PSU (Cohen et al. 2005). This mysid is probably most abundant in low-salinity estuarine habitats in the upper San Francisco estuary. Mysids may be epibenthic feeders, suspension feeders, predators, or omnivores (Barnes 1983). Members of the genus Neomysis are omnivorous feeders (Johnson and Allen 2005).


Phytoplankton; Zooplankton


Fishes, decapod shrimps

Trophic Status:




General HabitatUnstructured BottomNone
General HabitatSalt-brackish marshNone
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)8Chikugo River estuary, Japan (Suzuki et al. 2009)
Maximum Temperature (ºC)30Chikugo River estuary, Japan (Suzuki et al. 2009)
Minimum Salinity (‰)1Chikugo River estuary, Japan (Suzuki et al. 2009)
Broad Temperature RangeNoneCold-temperate-Warm temeprate
Broad Salinity RangeNoneOligohaline-Euhaline

General Impacts

The abundance and distribution of Neomysis japonica is poorly known, both on the West Coast of North America and in Australia. In the San Francisco estuary, where it has been confused with the more marine native, N. kadakiensis, competition is likeliest with the estuarine native N. mercedis (Baxter and Heib 2006; Modlin et al. 2012).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-3a None 0 Native Estab
AUS-X None 1983 Def Estab
NWP-2 None 0 Native Estab
P090 San Francisco Bay 2004 Def Estab
NWP-3b None 0 Native Estab
NWP-4b None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 2004 Def Estab
NWP-4a None 0 Native Estab
P093 _CDA_P093 (San Pablo Bay) 2004 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

Carlton, James T. (Ed.) (2007) <missing title>, University of California Press, Berkeley. Pp. <missing location>

Cohen, Andrew N. and 10 authors (2005) <missing title>, San Francisco Estuary Institute, Oakland CA. 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

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

Hutchings, P. (1992) Ballast water introductions of exotic marine organisms into Australia: current status and management options, Marine Pollution Bulletin 25(5-8): 196-199

Hutchings, P., van der Velde, J., Keable, S. (1986) Colonisation of NSW by foreign marine species, Australian Fisheries 45(4): 40-42

Ii, Naoyoshi (1964) Mysidae (Crustacea), Fauna Japonica 1964: 1-610.

Johnson, William S.; Allen, Dennis M. (2005) <missing title>, Johns Hopkins Press, Baltimore. Pp. <missing location>

Jones, Madeline M. (1991) Marine organisms transported in ballast water, Bulletin of Rural Resources 11: 1-48

Lowry, J. K.; Stoddart, H. E. (2003) <missing title>, 19.2B CSIRO Publishing, Canberra, Australia. Pp. <missing location>

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

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

Williams, R. J.; Griffiths, F. B.; van der Wal, E. J.; Kelly, J. (1988) Cargo vessel ballast water as a vector for the transport of non-indigenous marine species, Estuarine, Coastal and Shelf Science 26: 409-420