Forsøksdyr: Euthanasia of Zebrafish


Godkjenningsdato 01.07.2020

Godkjenningsperiode 27.09.2019-26.09.2024

The research group uses zebrafish as a model to investigate chemosensory computations, functional
development of the brain, and neural circuits mechanisms underlying neurological disease. A number of lines of genetically modified and wild-type zebrafish lines are bred and maintained in the zebrafish facility at the institute.
In the management of such a colony, humane killing of zebrafish will be necessary, either to prevent
overpopulation, to reduce lines that are no longer of scientific interest, to remove individuals that are getting old or to remove individuals with signs of disease or injury so that the health of the colony is maintained. The current regulation lists a number of methods approved for euthanasia of fish. These methods are not always useful for tropical fish with the size of zebrafish. In addition, there are scientific publications that present evidence that the use of ice water (below 4 °C) is a quicker, less stressful and more humane euthanasia method for zebrafish. In this application we apply for permission to use ice water as a method for humane euthanasia of zebrafish.
Tropical fish are not able to compensate for sudden transitions to low-temperature water. When zebrafish are placed in ice water (2 – 4 °C), hypothermal shock is induced and the fish lose consciousness within a few (0 – 5) seconds. For comparison, an overdose with an anesthetic agent in the water appears to be more stressful and the process lasts longer. This is supported by several scientific publications.
As of today, the group has 159 zebrafish lines that are housed and maintained in the zebrafish facility. It is estimated that up to 40 000 fish may need to be euthanized during a 4-year period which is the duration of this application.
Regarding the 3Rs:
Replacement: Some of the experimental activities will take place on brain samples that have been removed from animals post-mortem. In these cases, living animals will not be needed for the experiments. However, it will be necessary to euthanize animals to be able to take the brain samples.
Reduction: Reduction will take place through a continuous evaluation of what fish lines that are of interest and how many individuals that are needed from each line. The breeding will be adjusted according to this to prevent too many excess fish.
Refinement: The zebrafish will be housed in a state-of-the-art housing system for zebrafish. Each tank has an individual continuous supply of water and the housing system will automatically test the water quality and adjust the water quality if needed. Important water parameters are automatically controlled, and electronic alarms are sent to each group member in case there is something wrong with the system. The fish are housed in stable groups and they are checked every day and food is supplied three times per day. During one of the daily feedings, the fish are given live artemia which is an enrichment to their environment. For the euthanasia procedure, we avoid stress in the fish before the fish is transferred to ice water.