Argulus (fish louse)

The fish louse Argulus is a highly damaging parasite and one of the greatest disease threats to still water trout fisheries. National Fisheries Services have been trialing a new approach to help control infections of this parasite in stillwaters.

The aim is to provide fishery owners with a cheap, simple and effective way to break the life cycle of the parasite and reduce future disease problems.

Argulus biology

Argulus reproduce by laying eggs in long strings on any hard substrate. Female parasites start laying their eggs in spring when water temperatures rise above 10ºC and will lay through the year until water temperatures drop below 10ºC. Eggs hatch in around 16 days at 20ºC, longer in colder temperatures. During winter many adult parasites will die off and it is mainly egg strings that overwinter, with these egg strings dictating infections the following spring. Argulus is a common parasite of freshwater fish, found in fisheries throughout the UK. Adult lice are flat, round, jelly-like parasites that feed on skin and mucus. Heavy infections can quickly cause irritation, condition loss and death.

Managing Argulus infections

In 2005, the Environment Agency part funded a PhD project in partnership with the trout industry and Stirling University to improve understanding of Argulus infections in still water trout fisheries. This focussed on identifying the risk factors for disease problems and how these could be avoided through fishery management approaches. This work confirmed that a number of fishery management measures, in particular stocking practices, can help reduce the impact of the parasite and, in combination, prevent the build-up of infections.

You can find current approaches for managing Argulus infections in our guidance for fisheries (Argulus: Management in Stillwater Trout Fisheries factsheet), or through your local Environment Agency fishery officer. Please get in touch if you would like this guidance (details below).

Desperate times bring desperate measures

Despite these approaches, Argulus continue to cause serious problems in still water fisheries every year. These measures are not always feasible and in some cases can be more expensive. Similarly, they are primarily focussed on trout fisheries and offer limited value for coarse fisheries, where Argulus can also be problematic.

The scale of this problem has led to some drastic measures in an attempt to control the parasite. These include closing fisheries, culling stock during the summer months, illegal use of chemicals and draining and liming fisheries, sometimes year upon year.

Argulus in trout and other fish

Argulus parasites

An additional difficulty with managing Argulus in fisheries is being able to monitor parasite levels before they become a problem. Counting lice on the fish caught by anglers is important, but can lead to an underestimate of a problem as only the healthier fish tend to get caught. This alone can hinder awareness of how the parasite population is developing through the year.

These challenges have highlighted the need for a simple, cheap and effective solution to break the life cycle of the parasite and help fishery owners to both monitor and reduce lice burdens in still water fisheries. 

Studies on a new approach

From early 2017, Environment Agency staff at National Fisheries Services (NFS) Brampton have been trialling a new approach to break the life cycle of Argulus by harvesting the egg strings of the parasite. These are based on the use of plastic pipes, placed vertically in the margins of fisheries where Argulus can lay their eggs and then be removed easily from the water. Trials suggest that this approach, in combination with other fishery management tools, could provide an effective way to monitor egg laying activity and also kill large numbers of parasites in the process.

Egg strings ArgulusThe principle of artificial egg-laying substrates is not new, but it is hoped that the use of marginal pipes will offer a number of benefits for fisheries. These are widely available, easily installed, simple and quick to manage from the bankside and unobtrusive to angling and boating. Staff at NFS Brampton have developed three different designs for use in different situations, and these are proving effective for use in different fisheries and scenarios.    

Testing fisheries

These trials have shown that through the use of plastic pipes, in combination with other management practices, large numbers of egg strings can be successfully harvested and removed from fisheries with Argulus problems. It also provides a cheap and simple approach that can be applied to any water, allowing easy monitoring of egg string numbers and removal of eggs before they hatch. In some fisheries, over half a million eggs have been removed on each pipe, with a reduction in lice burdens on the resident fish. It is too early to say whether this provides a long term solution for Argulus control, and results are not guaranteed, but we are keen to raise awareness of the work and are supporting trials at more fishery sites this year. 

If you are interested in exploring this approach at your fishery, please contact us so we can offer advice on the best way to proceed. The success of this approach is not guaranteed and will rely on many different factors including the size and characteristics of the fishery, existing egg laying sites and other management practices, so these need to be considered as part of a wider management plan. You may be able to obtain some funding for this initiative through our national Fisheries Improvement Funds. For more information on this please get in touch with us, or contact your local Environment Agency fisheries officer. 

NFS Brampton are here to help with any fish health related query or suspected disease problem. Please get in touch if you would like to discuss any of this further. We're interested to hear of your experiences with this initiative or any ideas of how you think we could improve this for other fisheries. 

Contact National Fisheries Services

National Fisheries Services – Fish Health, Ageing and Species, Environment Agency, Bromholme Lane, Brampton, Huntingdon, PE28 4NE

Call: 02084 745244 or 07825 111723, email: fish.health@environment-agency.gov.uk

Last date edited: 23 August 2018