Investigating the genetic basis for louse resistance and reproductive success of L. salmonis and C. elongatus in Atlantic salmon
1 Purpose
For salmon lice (Lepeophtheirus salmonis), various semiochemicals have been identified in the fish's surface/mucous layer that allow the lice to recognise a suitable host, whereby different families and subgroups of Atlantic salmon attract lice copepodids differently (i.e. are more resistance or susceptible to infection). However, little is known about this relationship between Atlantic salmon and the generalist louse species, Caligus elongatus. The flow-on effect of resistance in hosts on the reproductive fitness of attached lice is also unknown.
In this experiment, we aim to investigate whether:
1) there is different host susceptibility to C. elongatus in a heterogeneous fish population, that can be correlated with quantity/type of semiochemicals;
2) whether highly resistant or susceptible salmon hosts influence the reproductive success and subsequent infectivity of L. salmonis.
2 Distress
Moderate. Fish will have ranges of infection levels (activity approved in a separate FOTs application) but here will continue until adult females have produced at least their second eggstring. The fish will be infected in Exp 1b and 2 with a moderate-low amount of salmon lice that will not develop into adult stages in the experiment (but will reach the chalimus 2 stage). The fish are PIT-marked before arrival at the experimental facility. PIT tagging is not covered by this application. Mucus will be collected in a gentle way from the fish in the experiment (under full anesthesia).
3 Expected benefit
Potential great value for pest management efforts. Salmon lice are severely obstacles for the sustainability of the aquaculture industry, and lice from fish farms influence population health of wild salmon and sea trout. Identification of potentially new breeding goals for farmed fish with regard to louse resistance (of both L. salmonis and C. elongatus) will be useful for targeted breeding programs.
4 Number of animals, and what kind
Exp 1a - 450 Atlantic salmon including both high and low estimated breeding values.
Exp 1b - 300 Atlantic salmon,
Exp 2 - 1800 Atlantic salmon, from 120 families.
Total animals: 2550 fish. All fish ~130g at experiment start.
5 How to adhere to 3R
Replacement: Not possible as we are investigating a species-specific response and interaction with these parasites. Reduction: The infection success of lice is highly variable and this study has been designed for statistical robustness to define resistance/susceptibility, and potential associated semiochemical profiles. Refinement: Movement and handling of fish will be kept at a minimum, with close monitoring and husbandry throughout the study. Fish will always be anaesthetised during handling, and humane endpoints are in place.
For salmon lice (Lepeophtheirus salmonis), various semiochemicals have been identified in the fish's surface/mucous layer that allow the lice to recognise a suitable host, whereby different families and subgroups of Atlantic salmon attract lice copepodids differently (i.e. are more resistance or susceptible to infection). However, little is known about this relationship between Atlantic salmon and the generalist louse species, Caligus elongatus. The flow-on effect of resistance in hosts on the reproductive fitness of attached lice is also unknown.
In this experiment, we aim to investigate whether:
1) there is different host susceptibility to C. elongatus in a heterogeneous fish population, that can be correlated with quantity/type of semiochemicals;
2) whether highly resistant or susceptible salmon hosts influence the reproductive success and subsequent infectivity of L. salmonis.
2 Distress
Moderate. Fish will have ranges of infection levels (activity approved in a separate FOTs application) but here will continue until adult females have produced at least their second eggstring. The fish will be infected in Exp 1b and 2 with a moderate-low amount of salmon lice that will not develop into adult stages in the experiment (but will reach the chalimus 2 stage). The fish are PIT-marked before arrival at the experimental facility. PIT tagging is not covered by this application. Mucus will be collected in a gentle way from the fish in the experiment (under full anesthesia).
3 Expected benefit
Potential great value for pest management efforts. Salmon lice are severely obstacles for the sustainability of the aquaculture industry, and lice from fish farms influence population health of wild salmon and sea trout. Identification of potentially new breeding goals for farmed fish with regard to louse resistance (of both L. salmonis and C. elongatus) will be useful for targeted breeding programs.
4 Number of animals, and what kind
Exp 1a - 450 Atlantic salmon including both high and low estimated breeding values.
Exp 1b - 300 Atlantic salmon,
Exp 2 - 1800 Atlantic salmon, from 120 families.
Total animals: 2550 fish. All fish ~130g at experiment start.
5 How to adhere to 3R
Replacement: Not possible as we are investigating a species-specific response and interaction with these parasites. Reduction: The infection success of lice is highly variable and this study has been designed for statistical robustness to define resistance/susceptibility, and potential associated semiochemical profiles. Refinement: Movement and handling of fish will be kept at a minimum, with close monitoring and husbandry throughout the study. Fish will always be anaesthetised during handling, and humane endpoints are in place.
Etterevaluering
Mattilsynet er forpliktet etter regelverket til å etterevaluere alle forsøk som er betydelig belastende for forsøksdyrene.
Begrunnelse for etterevalueringen
The primary objective of the experiment was achieved, the experimental design was appropriate to achieve the objectives, and the results showed proof-of-concept evidence towards host differential effects on infectivity of lice for the next generation. Marginal differences in fecundity of the lice grown up on the three different experimental groups were found.
The secondary objective relating to C. elongatus was not achieved due to the inability to source enough lice to produce copepodids for an infection challenge.
The experiment has brought forward new information on the fecundity of lice and infectivity of the following generation depending on host infection status. Samples of mucous layer and genetic background information will also be analysed to determine whether those factors influenced the host's susceptibility to infection.
In total 876 fish were used to achieve the experiment objectives, with actual severity as expected. Of these 678 fish were categorized with moderate severity and 198 as mild. However, the researcher has not given information about how many salmon that got wounds due to the lice infestation and the severity of these lesions. Thus, we are not able to assess the severity of harm that the animals were exposed to.
The remaining fish applied for were not used because the secondary experiment with C. elongatus was not carried out (~1600 fish not used)
Procedures generally did not need further refinement, fish had good welfare throughout and severity of the experiment remained as expected. The research group has experience with this type of experiment and always try to adjust to optimise infection and handling procedures. For more robust results, the number of eggstrings harvested for the fecundity study should have been higher, because the infection levels were so low in the group with the lowest lice count. That would require more fish in this group to ensure enough female lice for the next part of the experiment.
Procedures with handling, sedation, and recovery were applied carefully to reduce procedure-related severity, however the moderate severity of the experiment was largely due to the lice infections, and this could not be reduced. The daily surveillance and use of scoring forms at the facility worked satisfactorily.
The secondary objective relating to C. elongatus was not achieved due to the inability to source enough lice to produce copepodids for an infection challenge.
The experiment has brought forward new information on the fecundity of lice and infectivity of the following generation depending on host infection status. Samples of mucous layer and genetic background information will also be analysed to determine whether those factors influenced the host's susceptibility to infection.
In total 876 fish were used to achieve the experiment objectives, with actual severity as expected. Of these 678 fish were categorized with moderate severity and 198 as mild. However, the researcher has not given information about how many salmon that got wounds due to the lice infestation and the severity of these lesions. Thus, we are not able to assess the severity of harm that the animals were exposed to.
The remaining fish applied for were not used because the secondary experiment with C. elongatus was not carried out (~1600 fish not used)
Procedures generally did not need further refinement, fish had good welfare throughout and severity of the experiment remained as expected. The research group has experience with this type of experiment and always try to adjust to optimise infection and handling procedures. For more robust results, the number of eggstrings harvested for the fecundity study should have been higher, because the infection levels were so low in the group with the lowest lice count. That would require more fish in this group to ensure enough female lice for the next part of the experiment.
Procedures with handling, sedation, and recovery were applied carefully to reduce procedure-related severity, however the moderate severity of the experiment was largely due to the lice infections, and this could not be reduced. The daily surveillance and use of scoring forms at the facility worked satisfactorily.