Lice control on fish farms

- a Concerted Action under the European Union FAIR (aquaculture) research programme

Abstracts

Session 1: Management of sea lice on salmon farms

REGULATIONS - MINIMUM MEASURES TO CONTROL SEA LICE IN NORWEGIAN FISH FARMS

Inger Eithun

Norwegian Animal Health Authority, P.O. Box 8147, Dep. 0033, Oslo, Norway.

Sea lice have been recognised as a health problem in Norwegian fish farms for many years. The situation in fish farms has improved, but during the last few years the incidence of sea lice has been recognised as a serious threat to migrating stocks of smolt from Norwegian rivers. In 1997, the Norwegian Animal Health Authorities established a national program for the control of sea lice in co-operation with the Directorate of Fisheries, Directorate of Nature Management, fish farmers organisation and private fish health services.

The national program for the control of sea lice has emphasised three important measures: * routines for counting sea lice in all fish farms; * routines for medical treatments, with emphasis on the period before migration of smolt and co-ordination; and * use of cleaner fish as a supplement to medical treatment.

As a part of the program, regulations made by the Norwegian Animal Health Authorities have entered into force since 1998. The purpose of these regulations is to lay down minimum measures to reduce the incidence of sea lice. These include minimum measures in all fish farms at sea as follows: (1) Mandatory counting, recording and reporting on the incidence of sea lice (2) Mandatory delousing when maximum limits of sea lice are demonstrated and (3) Administrative fines when regulations are violated. These regulations have caused a great deal of discussion, but have also contributed to a larger focus on the control of sea lice. Regulations and experiences from implementation and enforcement will be presented.

PUBLIC MANAGEMENT OF THE SALMON LOUSE PROBLEM IN NORWAY: WHERE ARE WE HEADING?

Peter Andreas Heuch & Tor Atle Mo

National Veterinary Institute, Fish Health Section, PO Box 8156 Dep., N-0033 Oslo, Norway.

Salmon lice (Lepeophtheirus salmonis Krøyer) have caused disease problems in farmed Atlantic salmon (Salmo salar L.) since the mid 1970’s in Norway. Adverse effects of salmon lice on wild stocks of salmon and sea trout (Salmo truttae L.) were first reported in 1993. The apparently increasing problems for the wild stocks, and the fact that salmon farmers continued to take considerable losses due to lice despite novel chemical treatments, made the Norwegian Research Council in 1994 propose a National committee, with members from all implicated parties, to lay down a strategy for the control of salmon lice in farms. The recommendations put forward in 1997 included compulsory monitoring in farms, collection of data on wild stock infection, and the introduction of state regulations of maximum levels of lice/fish. The lice monitoring and limits in farms came into operation in 1998. Generally, the farms should not have more than 2 adult female lice/fish in the spring, but can have up to 5 adult females later in the summer and autumn.

In this paper we present a model of salmon louse egg production in Norway, and show that the public management strategy is critically dependant on the yearly increase in salmon production. This is because the infection pressure is the product of the number of fish in the system, and the average number of lice per fish. Due to the much larger number of farmed than wild salmonids, it is highly likely that lice originating from farmed salmon infect wild stock. Estimated tolerance limits for wild salmonids vary widely, and the louse egg production in farms required to decimate wild populations is not known. Two possible points as limits for total lice egg production are investigated. From these we estimate the lice/fish limits on farms that would have to be obeyed if these two general limits were to be upheld. We conclude that the salmon louse problem cannot be solved by a steady decrease in the number of lice/ fish, as the increase in salmon production within a few years will cancel out the effect. Furthermore, the limit number of lice per fish is inversely proportional to the number of fish that will have to be examined to ensure that the farm is within the set limits. Low numbers of lice/fish will therefore be impractical to verify.

INTEGRATED LICE MANAGEMENT IN MID-NORWAY

Per Andersen1 & Per Gunnar Kvenseth2

1 Department of Fisheries, 7770 Flatanger, Norway.

2 KPMG Management Consulting as - Centre for Aquaculture and Fisheries, Sandviksboder 5, N-5035 Bergen,

Norway.

The scope of this work has been to reduce problems with lice on farmed salmon, by increasing the fish-farmers consciousness about sealice in the farms. The work was carried out in the communities of Flatanger, Namsos and Fosnes, in mid-Norway. Essential elements of the strategy are frequent lice counting, and use of wrasse on small salmon. Lice control includes special attention during winter-time when the lice-levels are usually low. Depending on the lice-levels one or two chemical treatments were carried out during the cold period. To reduce the chances of re-infection of the farmed salmon, neighbouring farms were treated at the same time. Since this work started in 1991 the level of lice on farmed fish has been documented to decrease, and is now considered under control. The averaged number of gravid female lice has been reduced from 1,4 lice per fish in 1994 to 0,4 lice per fish in 1997.

INTEGRATED LICE MANAGEMENT ON IRISH SALMON FARMS

David Jackson1 & Terence O'Carroll2

1 Marine Institute, Parkmore Business Park, Galway.

2 BIM, PO Box 12, Crofton Road, Dun Laoghaire, Co. Dublin.

On the basis of information gathered in surveys of lice infestation on salmon farms in 1991 and 1992 the Department of Marine put in place a new initiative in salmon farm management. This initiative, termed Single Bay Management has been progressively introduced over the past six years and has resulted in significant and sustained improvements in lice control on farmed fish. Two case studies are presented where the mechanics of integrated lice control strategies and the barriers to its successful implementation are explored. Crucial elements are identified as separation of generations, annual fallowing of sites, strategic application of chemotheraputants, good fish health management and close co-operation between farms. The process of integrating the elements of Single Bay Management into a co-ordinated local aquaculture management system is outlined together with the implications for sea lice control.

DEVELOPMENT OF SEA LICE INTEGRATED MANAGEMENT STRATEGIES IN CANADA

John D. Smith1 & Myron Roth2

1 Pest Management Regulatory Agency, Health Canada, A.L. 6607D1, 2250 Riverside Drive, Ottawa, Ontario, Canada K1A 0K9.

2 Salmon Health Consortium, 75 Albert St. Suite 907, Ottawa, Ontario, Canada K1P 5E7.

The Pest Management Regulatory Agency, Health Canada, in partnership with the Salmon Health Consortium, is currently working with salmon growers, government officials, therapeutant suppliers and researchers to develop the elements of an integrated pest management program for sea lice. The key elements of the program are prevention, monitoring and intervention, which parallel the designs of established integrated pest management programs in agriculture.

To further develop and implement integrated management of sea lice, a series of regional workshops were held with growers and others involved in sea lice management. These workshops identified the measures that are already in place and those that can be taken to further the implementation of regionally-based integrated management strategies. Key issues identified include adequate availability of sites in order to implement preventive measures, principally year class separation and fallowing, availability of a variety of therapeutants, and collaboration among farmers operating in defined hydrographic regions.

A NATIONAL TREATMENT STRATEGY FOR THE CONTROL OF SEA LICE ON SCOTTISH SALMON FARMS

Gordon H. Rae

Scottish Salmon Growers Association, Drummond House, Scott Street, Perth, PHI 5EJ, UK.

Scottish salmon farming industry scientists have demonstrated that the reproductive capacity of female lice is compromised in the Spring, resulting in reduced survival of offspring. Late winter treatments aimed at reducing the number of adult females to the lowest possible level can have significant benefits. Control of sealice at a national or regional level can be improved by salmon farmers adopting a collaborative policy of co-ordinated treatments. The development of a National Treatment Strategy and progress with this initiative will be described.

PRACTICAL EXPERIENCES IN THE USE OF CLEANER-FISH. RESULTS FROM A QUESTIONNAIRE TO NORWEGIAN SALMON FARMS IN 1997 AND 1999

Anne-Mette Kvenseth1 & Per Gunnar Kvenseth2

1 University of Bergen, Department of Fisheries and Marine Biology, High Technology Centre, Pb 7800, N-5020 Bergen, Norway.

2 KPMG Management Consulting as - Centre for Aquaculture and Fisheries, Sandviksboder 5, N-5035 Bergen, Norway.

Norway has so far been the leading country in the practical use of cleaner wrasse in commercial salmon farms. In 1997 the number of salmon farms in Norway using cleaner fish solely, or as a supplement to chemical treatments, was estimated to be 300. The practical experience of the farmers when it comes to knowledge about the effect and limitations of wrasse is invaluable. To gain access to this knowledge, a questionnaire was sent out by KPMG to all Norwegian salmon farms in 1997 and 1999. Farmers were asked to estimate the problems with sealice in the locality, the necessity of chemical delousing and the effect of wrasse on lice problems and on net fouling.

In 1997 more than 100 out of 817 salmon farms from all salmon-producing counties, answered the questionnaire. Out of these 22 did not use wrasse, but only two stated that it was because of bad experience. On farms using wrasse for small salmon 38 had very good experience with the effect of wrasse, 7 had good experience and one had poor experience. Of the farms using wrasse for large salmon the numbers were "very good"- 9, "good"- 4 and "poor"-5. In half of the farms using ballan wrasse on large salmon the farmers had registered injuries on the salmon, but most farms had solved this by feeding the ballan in the pen when other food sources (lice and fouling) were scarce. Detailed results from the 1997 and 1999 questionnaire will be presented.

EXPERIENCES WITH BALLAN WRASSE (LABRUS BERGGYLTA A.) USED AS CLEANER-FISH ON LARGE FARMED SALMON IN NORWAY

Per Gunnar Kvenseth1 & Anne-Mette Kvenseth2

1 KPMG Management Consulting as - Centre for Aquaculture and Fisheries, Sandviksboder 5, N-5035 Bergen, Norway.

2 University of Bergen, Department of Fisheries and Marine Biology, High Technology Centre, Pb 7800, N-5020 Bergen, Norway.

This presentation reports the successful use of ballan wrasse (Labrus bergylta) to control infestations of sea lice (Lepeophtheirus salmonis) on Atlantic salmon (Salmo salar) of 3-7 kg size in a commercial salmon farm on the west coast of Norway. Ballan wrasse reduced the number of mobile lice from 60 to 8 per salmon over a three weeks period, while control pens with different combinations of the smaller wrasse species had a similar development in lice populations as pens without cleaner-fish.

Adult lice were never recorded on salmon in the pen with ballan wrasse. Lice content in ballan stomachs increased as lice numbers increased and the lice developed from chalimus to the preadult stage. The mean intensity of lice per stomach was 30. A maximum of 150 adult lice was found in the stomach of one ballan wrasse. Ballan wrasse caused no damage to the salmon.

Experiments feeding 50 live adult lice to ballan in single aquariums showed that seven out of eight ballan ate most of the lice within two hours. These ballan had experience as cleaner-fish.

FACTORS AFFECTING INDIVIDUAL VARIATION IN CLEANING EFFICIENCY OF GOLDSINNY, CTENOLABRUS RUPESTRIS (L.), USED ON A SALMON FARM IN THE WEST OF IRELAND

Sarah J. Varian, S. Deady & Julie M. Fives

Zoology Department, National University of Ireland, Galway.

Facultative cleaning behaviour was observed during commercial cleaner-fish trials on a salmon farm in the west of Ireland, where SCUBA observations and gut contents analysis revealed that only a small proportion (between 10% and 16%) of goldsinny in the cages actually removed sea lice (Lepeophtheirus salmonis Kroyer) from the salmon (Salmo salar L.). Results obtained from experiments in aquaria suggested that differences in the cleaning ability of goldsinny may be related to a personality trait described as the 'feeding confidence' (i.e. an individual's willingness to take risks in order to obtain food), which appears to be inherent in the phenotype of the wrasse. Variation in cleaning ability and 'feeding confidence' of goldsinny was found to be unrelated to sex, size and social dominance, ruling out the possibility of selecting cleaner-fish from wild populations according to external characteristics. However, it appears that certain factors enhancing the 'feeding confidence' of wrasse in aquaria, i.e. hunger, familiarity of environment and a 'stress-free' environment, may be manipulated within salmon cages in order to optimise conditions which lead to a higher rate of cleaning.

PROSPECTS FOR COMBATING PESTICIDE RESISTANCE IN SEALICE: LESSONS FROM INSECT PESTS

Ian Denholm1, Greg Devine2 & Tor Horsberg3

1 IACR-Rothamsted, Harpenden, Herts. AL5 2JQ, UK.

2 Aberdeen University, Tillydrone Avenue, Aberdeen AB9 2TN, UK.

3 Norwegian College of Veterinary Medicine, P.O. Box 8146 Dep., N-0033, Oslo, Norway.

From even a rudimentary knowledge of factors promoting resistance to pesticides and chemotherapeutic agents, the appearance of insecticide resistance in sealice should be seen as no surprise, but rather as an inevitable consequence of management practices in some commercial fish production systems. In many respects, large-scale reliance on chemicals for lice control, coupled with the comparative genetic isolation of sealice populations, renders these systems a marine equivalent of horticultural glasshouses, in which insecticide resistance has historically developed most rapidly and has been particularly challenging to contain. As in conventional agriculture, effective management of resistance in sealice requires considerable effort to reduce and diversify the selection pressure for individual resistance genes. By drawing on parallels with insect pests, this paper will review some "C" 'critical' issues - including the role of pest ecology and genetics, resistance mechanisms and their implications for cross-resistance - pertaining to resistance in sealice, and explore the feasibility and likely effectiveness of possible management options.

THE EFFICACY OF CO-ORDINATED, WINTER TREATMENTS OF FARMED ATLANTIC SALMON, SALMO SALAR L., INFESTED WITH SEA LICE, LEPEOPHTHEIRUS SALMONIS (KRØYER, 1837) (COPEPODA: CALIGIDAE)

Simon Wadsworth1, Jim Treasurer1 & Andrew Grant2

1 Marine Harvest McConnell, Lochailort, Inverness-shire, Scotland. PH38 4LZ.

2 Marine Harvest McConnell, Farms Office, Blar Mhor, Fort William. PH33 7PT.

The epidemiology of Lepeophtheirus salmonis on Atlantic salmon Salmo salar production sites was examined at a number of farms within Loch Sunart during 1994. Intensity of infection was found to be influenced by both management practices and seasonal variations. By instigating a series of co-ordinated, synchronous, strategic treatments throughout the loch system during the winter of 1996, initial chalimus levels during the spring were significantly reduced by 90% (p<0.001). Lice numbers for the rest of the production cycle were significantly lower (p<0.01). In addition there was a reduction in the number of treatments needed, an increase in the interval between treatments, reduced fish mortalities and improvements in fish harvest quality. There was no significant reduction in mean chalimus numbers observed at the control site where treatments were not co-ordinated. The strategic treatments were successfully repeated in the Loch Linnhe system during 1997 and the Loch Sunart system during 1998. The recruitment success of L. salmonis to the copepodid stage was examined during the winter and found to be correlated with reduced temperature.

A CASE STUDY OF REDUCED SENSITIVITY TO DICHLORVOS IN SEA LICE AND STRATEGIES FOR RESISTANCE MANAGEMENT

Myron Roth

Salmon Health Consortium, 75 Albert St. Suite 907, Ottawa, Ontario, Canada K1P 5E7.

The use of dichlorvos is reviewed and presented as a case study in reduced sensitivity to chemotherapeutants. Key factors that most likely contributed to reduced sensitivity identified include: 1) the reliance on chemotherapy in the absence of non-chemotherapeutic control methods; 2) the repeated use of a single chemotherapeutant; 3) the short generation time of sea lice; 4) lack of toxicity of dichlorvos to early developmental stages of lice; and 5) sub-therapeutic dose rates. To ensure the long-term effectiveness of the limited number of available sea lice control products the following resistance management strategies are recommended: 1) chemotherapeutants be used as part of a well defined, documented, integrated pest management strategy that focus on minimising the use of chemotherapeutants; 2) co-ordinated monitoring and treatment efforts between farmers in common hydrographic regions; 3) compound selection that optimises efficacy; 4) treatment rotation; 5) accurate dosing; and 6) routine treatment evaluation and sensitivity testing.