Electricity = humane + good food quality

Consumers, animal welfare organisations and supermarket chains are all demanding that fish should not be subjected to unnecessary pain and stress during slaughtering.

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Bjørn Roth

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Whether the new slaughtering processes are really an improvement compared with the earlier use of carbon dioxide gas is currently under debate. “Our results show clearly that both electricity and percussive stunning are humane – and industrially efficient,” says Bjørn Roth, a researcher at Nofima Mat.

Correct electricity levels and percussion strengths

During the project, the methods electricity, percussive stunning, AQUI-S and carbon monoxide gas were tested. The aim has been to clarify which method is most humane, while remaining industrially efficient, as well as looking at how slaughter methods may affect food quality.

One of the objections to using electricity has been that it affects food quality. Now the researchers have found out what level of electricity ensures almost instant sedation without affecting quality. Electricity works for all fish sizes and species, but the optimum voltage varies from species to species. Cod and halibut, for example, are much more sensitive than salmon.

During the course of the research it was found that percussive stunning does not necessarily kill the fish instantly, as had previously been thought. Percussive stunning can cause the fish to appear to be dead, but brain activity shows a different picture until the fish dies of cerebral haemorrhage. This is very much dependent on the percussion strength, which can be ensured by increasing pressure to the machines.

“Stunning is essentially the best for food quality, but if electricity is used correctly, with regard to voltage and length of charge and similar, then it has no negative effect on quality. In this research project, we have also discovered what levels of electricity are best for the different species,” says Roth.

New slaughter line developed

An automated and more streamlined slaughter line has now been developed, consisting of the elements electricity, percussive stunning and gill cutting – in that order. Such a slaughter line, including an electric sedator, has been developed by Seaside at Stranda and is now on the market. It can be used both at fish farms and on fishing boats. There are other interesting methods and concepts involving percussive stunning and gas that are either at the trial stage or on the market.

Cold fish

Another important aspect for fish welfare and food quality is how much cold the fish can tolerate before it affects stress level. Salmon tolerates a cold shock from 16 degrees to 4 and from 12 degrees to zero relatively well, without triggering the primary stress responses. This is important for the concept of live chilling and the relationship between temperature, water quality and the positive effects on shelf life that result from an early chilling process. “Now we are starting to test what concentration of carbon dioxide gives the best effect,” concludes Roth.

This research is being carried out in collaboration with the University of Bergen, the Institute of Marine Research, Akvaplan-niva, Marine Harvest, Grieg Seafood, Lerøy, Seaside, Bremnes and Scanvacc.

The project is financed by Norges forskningsråd and FHF, and by private companies.

Seafood industry  

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