Determining mortality thresholds of newly-smoltified Atlantic salmon with salmon lice infections
The aim of this experiment is to determine the threshold of mortality risk caused by salmon lice in newly-smoltified Atlantic salmon. We will mimic the out-migration stage of salmon from the Etne river, using fish from wild Etne parents. Salmon will undergo smoltification followed by exposure to lice copepodids, then swim their migration distance. We will monitor fish closely for up to 30 days post-infection, and if individuals become moribund, they will be euthanised and their infection intensity recorded. The mortality risk associated with infection will be described using infection intensity (lice per gram), lice stage, and days post-infection. For a proportion of surviving fish, aerobic scope and swimming performance will be investigated, to determine the impact of infection history on swimming ability.
Experimental fish will experience some distress, mainly associated with infection. Fish will undergo smoltification (a normal stage in their life-history), then exposure to infective copepodids, then a swimming exercise where they will swim the migration distance (60km) in a swim tunnel at a speed within the range of observations from field studies. The 'migration' swimming stage is not expected to be distressing for the fish as the distance and speed is calculated from field observations, however we aim to have the infection levels ranging from very low to lethal, in order to quantify the intensity and/or lice stage that results in the highest risk of mortality for the fish. The swimming performance challenge is expected to be mildly distressing, as speeds that fish are exposed to are within their capability and no stressors will be applied during the protocol.
The traffic light system will become operational in 2019, and will have significant impacts on the aquaculture industry. One basis for the framework is the risk assessment of wild salmonids based on the lethal threshold of lice infections - 100% mortality risk is assumed for infection levels of >0.3 lice/g, 50% risk for 0.2-0.3 lice/g, 20% risk for 0.1-0.2 lice/g, and 0% risk for levels <0.1 lice/g. No study has focused exclusively on this threshold in relation to risk for wild salmonids, and thus this experiment aims to have a robust experimental design that can address this question to a better standard than previous lab trials.
600 Atlantic salmon (wild parents from the Etne river) will be split among 4 treatment groups and a control, whereby groups will experience increasing levels of infection pressure. Three replicate tanks per group will be used, however the analysis will focus on the infection intensity (lice/g) rather than the original infection pressure. After lice have reached the adult stage for 7 days, 150 of the 600 fish (of varying infection levels) will be tested for swimming performance, and Ucrit calculated to determine the physiological impact of infection on swimming ability.
The 3Rs: Replacement: Not possible as we are investigating a species-specific response and mortality risk. Reduction: The infection success of lice is highly variable and this study has been designed for statistical robustness to define mortality risk with a level of preciseness. Refinement: Movement and handling of fish will be kept at a minimum, with close monitoring and husbandry during periods of moribund-risk.
Experimental fish will experience some distress, mainly associated with infection. Fish will undergo smoltification (a normal stage in their life-history), then exposure to infective copepodids, then a swimming exercise where they will swim the migration distance (60km) in a swim tunnel at a speed within the range of observations from field studies. The 'migration' swimming stage is not expected to be distressing for the fish as the distance and speed is calculated from field observations, however we aim to have the infection levels ranging from very low to lethal, in order to quantify the intensity and/or lice stage that results in the highest risk of mortality for the fish. The swimming performance challenge is expected to be mildly distressing, as speeds that fish are exposed to are within their capability and no stressors will be applied during the protocol.
The traffic light system will become operational in 2019, and will have significant impacts on the aquaculture industry. One basis for the framework is the risk assessment of wild salmonids based on the lethal threshold of lice infections - 100% mortality risk is assumed for infection levels of >0.3 lice/g, 50% risk for 0.2-0.3 lice/g, 20% risk for 0.1-0.2 lice/g, and 0% risk for levels <0.1 lice/g. No study has focused exclusively on this threshold in relation to risk for wild salmonids, and thus this experiment aims to have a robust experimental design that can address this question to a better standard than previous lab trials.
600 Atlantic salmon (wild parents from the Etne river) will be split among 4 treatment groups and a control, whereby groups will experience increasing levels of infection pressure. Three replicate tanks per group will be used, however the analysis will focus on the infection intensity (lice/g) rather than the original infection pressure. After lice have reached the adult stage for 7 days, 150 of the 600 fish (of varying infection levels) will be tested for swimming performance, and Ucrit calculated to determine the physiological impact of infection on swimming ability.
The 3Rs: Replacement: Not possible as we are investigating a species-specific response and mortality risk. Reduction: The infection success of lice is highly variable and this study has been designed for statistical robustness to define mortality risk with a level of preciseness. Refinement: Movement and handling of fish will be kept at a minimum, with close monitoring and husbandry during periods of moribund-risk.
Etterevaluering
Forsøket er betydelig belastende.
Begrunnelse for etterevalueringen
Forsøket skulle bestemme grenseverdier for å dø av lakselusinfeksjon hos nylig smoltifisert laks. Dette skulle gjøres ved å etterligne det en utvandrende laksesmolt utsettes for under migrasjonsprosessen fra elv til sjø og hav.. Forsøket ble utført i henhold til godkjenningen og skaffet viktig kunnskap om forholdet mellom lakselus og ville laksestammer. Forsøkets formål ble derfor oppnådd.
Det ble brukt 600 laks og av disse døde 154 av lakselusinfeksjon, eller ble avlivet fordi de nådde humane endepunkter. Disse fiskene opplevde betydelig belastning. Resten av forsøksfiskene opplevde lett eller moderat belastning.
Å jobbe med en obligat parasitt og finne grenseverdier for parasittantall på vertsfiskene vil uvilkårlig kreve bruk av forsøksfisk der noen vil oppleve betydelig belastning. I dette forsøket var forsøksprotokoll, prosedyrevalg og antall forsøksdyr nødvendig og hensiktsmessig, men på bakgrunn av forsøkets resultater bør fremtidige forsøk, der man ikke fokuserer på virkningen av alvorlige infeksjoner, ikke ha infeksjonsnivåer over en viss grense for fisk på denne størrelsen. Dataene fra forsøket er ikke ferdig analyserte, men foreløpige resultater kan tyde på en grense rundt 0,6 mobile lus pr. gram vertsfisk.
Det ble brukt 600 laks og av disse døde 154 av lakselusinfeksjon, eller ble avlivet fordi de nådde humane endepunkter. Disse fiskene opplevde betydelig belastning. Resten av forsøksfiskene opplevde lett eller moderat belastning.
Å jobbe med en obligat parasitt og finne grenseverdier for parasittantall på vertsfiskene vil uvilkårlig kreve bruk av forsøksfisk der noen vil oppleve betydelig belastning. I dette forsøket var forsøksprotokoll, prosedyrevalg og antall forsøksdyr nødvendig og hensiktsmessig, men på bakgrunn av forsøkets resultater bør fremtidige forsøk, der man ikke fokuserer på virkningen av alvorlige infeksjoner, ikke ha infeksjonsnivåer over en viss grense for fisk på denne størrelsen. Dataene fra forsøket er ikke ferdig analyserte, men foreløpige resultater kan tyde på en grense rundt 0,6 mobile lus pr. gram vertsfisk.