Forsøksdyr: Development and application of an in vivo disease challenge model to measure susceptibility of Atlantic salmon fry to infection by Flavobacterium psychrophilum.

Godkjenningsdato 27.04.2018

Flavobacterium psychrophilum is a bacterium that causes disease of salmonids in fresh and brackish water known as Rainbow trout fry syndrome (RTFS). The rainbow trout is known to be a particularly susceptible fish species. The bacterium is also reported as a cause of disease in other fish species such as Atlantic salmon. Therefore Atlantic salmon will be used in this project.
Vaccination of fry has so far not yielded satisfactory results, and targeted breeding is considered an effective measure for increased resistance to the bacterium. Genetic mapping to identify groups with favourable genotypes in terms of resistance to disease is an important approach within targeted breeding. In this study, the genetic resilience to Flavobacterium psychrophilum will be tested in 600 families of Atlantic salmon with different genotypes.

This study consists of two parts, to be performed in 2018 and 2019, with 9 trials altogether. Up to a total of 8966 individuals will be used in this project. To minimize the number of fish, safety tests and a dose response test are included in this study.
The 3Rs:
Replacement: It is not possible to replace with another species or to use an in vitro alternative to determine virulence or to test susceptibility.
Reduction: Minimum fish numbers for statistical considerations will be used. A further reduction is not recommended based on the applicant’s prior experiences and ‘best practices’ in animal breeding and genomics; a reduction would lead to a reduction in power, which would limit the downstream utility of the data. Fish numbers have also been discussed with, and approved by husbandry experts to ensure optimal stocking densities for the welfare of this species.
Small numbers of fish will be used in the safety studies, challenge dose and isolate selection and the study will only be taken forward if morbidity is achieved.
Refinement: Fish will be monitored at least twice daily with increased monitoring at critical periods (post challenge and at onset of signs of disease). During critical periods, fish will be checked at least every 12 hours, and more frequently during the working day. The frequency will be increased for the passage test where very high pathogen doses are used.
The fish will be observed for a maximum 3 weeks during the challenge trials and morbidity/mortality recorded. Fish that are moribund will be taken out of the trial and registered as dead in accordance with humane endpoint.

The results will be of scientific and long-term social value. The development of methods to prevent RTFS is urgently required, due to the potential risk of resistance developing towards the antibiotics presently licensed for use in aquaculture. The challenge model will be published and therefore available for further studies on RTFS in Atlantic salmon.