Invasive Alien Species in Northern Ireland

Hemimysis anomala, shrimp

Hemimysis anomala G. O. Sars, 1907
Hemimysis anomala is a ‘mysid’, a group of crustaceans characterised by possession of a brooding pouch or ‘marsupium’, within which their embryos develop. Mysids are related to the amphipods (see Gammarus pulex and Dikerogammarus villosus), but mysids are much more ‘shrimp-like’ in appearance. H. anomala can be found in lakes and running waters and can tolerate salty water (up to about half sea water strength). It appears to be most active at night and thus can be overlooked. It prefers to aggregate into swarms, which can be observed at evening time. The species has spread extensively in Europe, reaching England in 2004 and is very likely to spread to Ireland.
Adults reach about 1.3cm in length, females slightly larger than males, look shrimp-like but with a curved body, have long thin antennae and large bulbous eyes. Unlike our native mysids, which are almost transparent, H. anomala is often colourful, ranging from deep red to yellow.
Country of origin
H. anomala comes from the Black and Caspian Seas area.
Current distribution
This species is now found in Russia, Lithuania, Ukraine, Moldova, the Baltic Sea, Poland, Finland, Germany (for example, River Rhine), Holland, Belgium, Scandinavia and most recently England.
Location in Ireland
Whilst not yet found in Ireland, the conditions here would suit its invasion.
Life cycle
Breeding occurs April-October, females carry 18 embryos on average (maximum recorded is 31), usually two generations are produced each year. Young are miniature versions of adults, with no larval stage.
Wildlife and habitat impacts
Surprisingly, this species has received little study of its impacts. We know from Dutch studies that H. anomala is omnivorous, eating algae and small invertebrates, to such an extent that populations of these creatures can decline significantly and almost disappear. Any effects this may have on other organisms, such as fish, has not been investigated.
Human impacts
No human impacts identified as yet.
Key vectors
This species has been deliberately introduced to lakes, such as in the former Soviet Union, for fish food. New canals, such as between the Rivers Danube and Main, have aided its spread from east to west, and the River Rhine (which connects with the River Main) has been a major route of invasion into western Europe. Its spread may also have been aided by shipping, such as through transfer of ballast water among ports.
What you can do as an individual
If you find a mysid, do not immediately assume it is the invader. We have two native species of mysid, but both are transparent as opposed to the striking colours of H. anomala. Mysis relicta lives in Lough Neagh and other Irish lakes, while Neomysis integer is more coastal, although it does come up rivers. If you find a red/yellow mysid in fresh/brackish water, however, this may be H. anomala. Specimens can be sent to the person named below who will have them formally identified.
Advice to specific groups relevant to this species
All users of lakes and rivers should be careful not to spread this species if it arrives here. It is not known how H. anomala reached England, although one site hosts international boating events. Thus, anglers, boating clubs, fish farmers and garden centres with ponds should all watch out for this invader and take steps to avoid spread. At the moment there are no guidelines for control, although filtering water may help.
Management measures
There are no formal measures for control of this species, filtering water may be an option but this needs research.
Management groups
There are no groups specifically for management of this species. However, Dr David Holdich is currently writing a risk assessment for this species, and may be contacted c/o the person detailed below.
Further information
The QUERCUS Biodiversity and Conservation Biology Centre at Queen’s University Belfast has research projects on invasive species in general. There are few scientific articles that go into detail about this particular invader and its impacts. The author has been studying invasive crustaceans for 20 years and can help provide further information.
The invasive Ponto-Caspian mysid, Hemimysis anomala, reaches the UK. David Holdich, Sean Gallagher, Lesley Rippon, Phil Harding and Rachel Stubbington

Text written by:
Dr Jaimie Dick, Reader in Behaviour, Ecology & Environmental Biology, Queen's University Belfast