Forsøksdyr: Genetic markers for assessment of gill health during net cleaning

Godkjenningsdato 06.07.2020

Godkjenningsperiode 01.08.2020-31.12.2021

1 Purpose
The aim of the experiment is to identify the presence of harmful biofouling organisms in the gills of salmon via genetic markers, and to develop a non-destructive sampling method for identification of impacts on gill health. Mucus will be sampled from the inside of the gill operculum of anaesthetised fish, thus avoiding he risk of damage to the gills. Sampling will be conducted in connection to net cleaning activities at two farm sites.

2 Distress
The experiment will induce short-term discomfort in fish connected to crowding and transfer to a holding tank where they will be anaesthetised or euthanised

3 Expected benefit
By developing a non-destructive sampling method for analysis of exposure to potentially harmful biofouling organisms, the project will contribute to reducing the need for destructive sampling in some gill health assessments. Furthermore, the project results will be used to demonstrate impacts of net cleaning on fish health and thus support the development of more sustainable biofouling management strategies for the Norwegian salmon farming industry.

4 Animals
In total, 180 Atlantic salmon (Salmo salar) will be sampled, of which 120 will be euthanised and 60 will be subject to capture and anaesthetics before being released.

5 3R
Replacement: The experiments must be carried out using live fish as the interaction between fish gills and biofouling organisms released during net cleaning cannot be realistically simulated using dead animals or tissue samples due to both technical and physiological constraints.
There are currently no alternative methods available for the investigation of gill health other than histological analysis or identification of genetic markers of pathogens in gill swab samples. While visual gill scoring may be used to identify e.g. stages of specific diseases, it cannot provide detailed information on gill pathology. Moreover, it also requires handling/sedation of fish.

Reduction: The number of replicate fish to be sampled in the experiment were calculated using a power analysis based on data from a pilot experiment and experience from laboratory trials, and aim to achieve a trade-off between robust experimental design and the minimal use, handling, and euthanasia of fish. Where possible, the experiment will be conducted in connection with ongoing farm activities that include anaesthesia of fish (e.g. lice counting or gill scoring) and thus allow sampling in order to minimise stress to the cultured fish.

Refinement: The planned experimental methods (crowding, capture using a knotless dip net, anaesthesia, handling) are routine operations that will be handled by experienced farm personnel and typically have little negative impact on the fish. By swabbing the gill operculum instead of the gills, we expect to avoid any impact exceeding the stress related to capture and transfer to an anaesthetic bath. To avoid potentially confounding impacts on fish health it is a priority for the research team to monitor and ensure fish welfare throughout the experiment.
Thus, the project will actively contribute to reduce the use of destructive sampling in fish farming and associated research by developing new and refined methods for the analysis of gill health.