Hemimysis anomala



Conservation status

Not Assessed

First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Transport Stowaway

Introduction pathways subclass - 1

Hitchhikers on ship/boat

Introduction pathways - 2

Transport Stowaway

Introduction pathways subclass - 2

Ship/boat ballast water

Invasive score


NAPRA Ireland risk assessed


Species Biology


Small freshwater mysid (family of Crustaceans), has a distinctive orange and transparent appearance, though exact identification requires examination of the tail (Minchin & Boelons, 2010). Specifically "telson is un-notched and bears two prominent posterior-lateral spines" (Minchin & Boelons, 2010).


Field studies have shown that zooplankton diversity and density decline in water bodies, particularly primary producers, after invasion by H. anamola (Iacarella et al., 2015; Penk et al., 2015), and impacts more on native communities, even at lower densities, than the native mysid Mysis salemaa due to having a higher functional response (ability to consume prey at lower prey densities) (Barrios-O'Neill et al., 2014; Penk et al., 2015).


Inland surface waters


It is ovigerous (bearing externally fertilised eggs) producing 2-4 broods in the year, with sexual development occurring after 45 days (Borcherding et al., 2006).

Pathway and vector description

Originally found in Lough Derg (Minchin & Holmes, 2008) it was likely introduced as a hitchhiker in ballast water of leisure craft and dispersed downstream (Minchin & Boelons, 2010). May be facilitated in its spread within Ireland by contaminant water, though unlikely to be able to move overland as it lacks a resting phase that can survive outside of water (Minchin & Boelons, 2010).

Mechanism of impact

Competition, Predation

Broad environment


Habitat description

Inland surface waters

Species group


Native region

Temperate Asia


World distribution(GBIF)

Irish distribution

Established - Localised. Established in the Shannon river basin, (Minchin & Boelons, 2010), it has not been recorded in other river systems to date.

Native distribution

Ponto-Caspian species, native to the drainage basin of the Caspian, Aral and Black Seas.

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2024

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How can you help

Report any sightings to the National Biodiversity Data Centre.

Further information

Ponto-Caspian species introduced into Europe via the Suez Canal are often referred to as 'Lessepsian migrants', after Ferdinand de Lessep, the French diplomat in charge of the construction of the canal.



Barrios-O'Neill, D., Dick, J. T., Ricciardi, A., MacIsaac, H. J., & Emmerson, M. C. (2014). Deep impact: in situ functional responses reveal context-dependent interactions between vertically migrating invasive and native mesopredators and shared prey. Freshwater Biology, 59(10), 2194-2203.

Borcherding, J., Murawski, S., & Arndt, H. (2006). Population ecology, vertical migration and feeding of the Ponto-Caspian invader Hemimysis anomala in a gravel-pit lake connected to the River Rhine. Freshwater Biology, 51(12), 2376-2387.

Iacarella, J. C., Dick, J. T., & Ricciardi, A. (2015). A spatio-temporal contrast of the predatory impact of an invasive Freshwater crustacean. Diversity and Distributions.

Minchin, D., & Holmes, J. M. C. (2008). The Ponto-Caspian mysid, Hemimysis anomala GO Sars 1907 (Crustacea), arrives in Ireland. Aquatic Invasions, 3(2), 257-259.

Minchin, D., & Boelens, R. (2010). Hemimysis anomala is established in the Shannon River Basin District in Ireland. Aquatic Invasions, 5(1), 71-78.

Penk, M., Irvine, K., & Donohue, I. (2015). Ecosystem-level effects of a globally-spreading invertebrate invader are not moderated by a functionally similar native. Journal of Animal Ecology.

CABI Datasheet

DAISIE Factsheet