Invasive Alien Species in Northern Ireland

Pomphorhynchus laevis, fish parasite

Pomphorhynchus laevis (Müller, 1776)
Pomphorhynchus laevis belongs to a group of animals called the Acanthocephala which are a group of parasitic worms found in all classes of vertebrates, especially fish and birds. The chief diagnostic feature of the group is the presence of a retractable proboscis armed with hooks from which the common name ‘spiny headed’ worm is derived. An intermediate host, usually an aquatic arthropod, is needed in the completion of the worms life cycle. It was first recorded in rainbow trout and eels in Northern Ireland in 1999 and its mode of introduction is believed to be similar to that found elsewhere and is linked to the trade in live fish. Heavy worm burdens may pose a threat to the health of the fish host and as such P. laevis is considered a fish pathogen.
Live specimens of P. laevis are orange in colour and the unsegmented worms are found attached to the wall of the posterior region of the alimentary tract of a variety of freshwater fish. Preserved or frozen specimens are white. With separate sexes, females are nearly always larger than males. Individual worms range in length from 4–25mm and under the microscope the most distinguishing feature of this worm is the presence of a long armored proboscis containing 13–20 longitudinal rows of hooks, each row with 8-13 hooks. Attached to the base of the proboscis is a proboscis bulb used to help anchor the worm to the gut wall of the host.
Country of origin
United Kingdom.
Current distribution
P. laevis has a localized and discontinuous distribution throughout Britain and Ireland, which has been attributed to postglacial events, movements of infected fish for stocking purposes and to biological factors. Widespread in southern Ireland this worm is only common in the catchments of the Rivers Severn, Thames and Hampshire Avon/Dorset Stour in mainland Britain.
Location in Ireland
P. laevis is widely distributed throughout southern Ireland but has only been recorded from two locations in Northern Ireland in 1999; Movanagher Fish Farm, County Antrim and Kesh Bay, Lower Lough Erne, County Fermanagh (Evans et al., 2001).
Life cycle
The female worm releases eggs inside the host which are shed with host faeces. Eggs hatch after a few hours to produce a larval stage called an acanthor (larval worm encased within a complex shell). This is the only free living stage in the acanthocephalan life cycle and becomes infective when ingested by the appropriate arthropod host, Gammarus duebeni in the case of P. laevis. The intermediate host is then ingested by the final fish host and the adult worm is ‘activated’ into its final mature phase by the presence of digestive enzymes in the host gut.
Wildlife and habitat impacts
In Britain and Ireland P. laevis is an intestinal parasite of freshwater fish and is normally found in the posterior intestine of its fish host where it often penetrates the intestinal wall. The damaging effects of this, combined with high worm burdens in commercially valuable salmonids, means that P. laevis is categorized as a potential fish pathogen. Movement of fish infected with P. laevis is therefore controlled by the Salmon and Freshwater Fisheries Act 1975 and Diseases of Fish Act 1983.
Human impacts
This parasite poses no direct threat to human health as its final host is a fish. However, it does pose a threat to the economic value of the commercially valuable salmonid fisheries that become infected with it, given its potential effects as a serious fish pathogen.
Key vectors
The introduction of this species has always been associated with the movement/trade in live fish particularly cyprinids and salmonids and may be spreading due to the increasing popularity of ‘put and take’ fisheries. Its arrival in Northern Ireland is also believed to have been attributable to the movement of live fish, possibly from the south of Ireland (Evans et al., 2001).
What you can do as an individual
Few people are involved in the commercial movement of fish so it is unlikely that people in general will be involved in spreading this parasite. Legislation exists in Northern Ireland to prevent the movement of fish without prior approval (DCALNI Inland Fisheries Branch – Fish Moving Permit) and because P. laevis is categorized as a potential fish pathogen, movement of infected fish is controlled by the Salmon and Freshwater Fisheries Act 1975 and Diseases of Fish Act 1983.
Advice to specific groups relevant to this species
Anglers and Fish Farmers:
As outlined above, the movment of any fish species including cyprinids and salmonids is regulated and legislation exists in Northern Ireland to prevent the movement of fish without prior approval (DCALNI Inland Fisheries Branch – Fish Moving Permit). Specific veterinary health certificates must also be obtained when moving fish from areas known to be infected with this worm. Permission should always be sought before moving any fish to different waterbodies.
Management measures
The only management measures in place to prevent the spread of P. laevis are those outlined above. No biological or pharmaceutical anthelminthic controls exist for this parasite in the wild.
Management groups
No formal groups exist.
Further information
Evans, D.W., Matthews, M.A. and McClintock, C.A. (2001). First record of Pomphorynchus laevis (Acanthocephala) in fishes from Northern Ireland. Journal of Fish Biology 59: 166-168.
Smyth, J. D. (1985). Introduction to Animal Parasitology. Hodder and Stoughton, London.
Text written by:
Dr Derek Evans