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"Nytt fra HAVBRUK" newsletter no. 2/2009:

Seeking effective stun methods

Using carbon dioxide (CO2) to anaesthetise salmon prior to slaughter will no longer be permitted as of 1 January 2010. Researcher Bjørn Roth of the Nofima research group led a project that studied the advantages and disadvantages of other methods.

"The objective is a humane death for the fish," says Dr Roth. "Effective anaesthesia is important not only as a concern for the well-being of the live salmon, but also for the quality of the slaughtered salmon. Stress results in poor quality and quicker onset of rigor mortis."

The project is profiled in the most recent newsletter from the HAVBRUK programme ("Nytt fra HAVBRUK" no. 2/2009, available in Norwegian only). This issue of the newsletter is focused on sustainability.

Mechanical blow to the head

The ban on CO2 use leaves electrical stunning and percussive blow as alternative methods of anaesthesia, both of which are better than CO2.
"Fish that are properly stunned with a mechanical blow are normally knocked unconscious instantly. But a lot needs to go right for this method to work as it should," cautions Dr Roth. "The fish must be the proper size and enter the machine as designed, and then the blow must strike accurately. If not, the fish may only be paralysed and could regain consciousness before dying."

Electrical stunning

Using electrical current stuns the fish quickly, but does it work quickly enough?
"It used to be common to apply very low voltage [less than 50 volts], but that is not sufficient. By increasing to 110 volts it is possible to anaesthetise an individual fish within half a second. The disadvantage is that extended exposure to electrical stimulation to ensure lasting anaesthetic effect also leads to earlier onset of rigor mortis than with the percussive stun."

Cold fish

Before either of these methods is applied, pre-anaesthetic cooling is used to sedate the fish for easier handling.
"But it needs to be done carefully. Too sudden a temperature drop causes the fish major problems." Dr Roth emphasises that the handling of fish during crowding and pumping prior to anaesthesia also greatly affects the well-being of the fish. "There is a clear correlation between how the live fish is handled pre-slaughter and its quality post-slaughter."

Written by:
Anne Ditlefsen Seniorrådgiver 22 03 71 54 adi@forskningsradet.no
Published:
01.09.2009
Last updated:
01.09.2009