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Stunning fish with CO2 or electricity: contradictory results on behavioural and physiological stress responses

Journal article
Authors Albin Gräns
Lars Niklasson
Erik Sandblom
Kristina Sundell
Bo Algers
Lotta Berg
Torbjörn Lundh
Michael Axelsson
Henrik Sundh
Anders Kiessling
Published in Animal
Volume 10
Issue 2
Pages 294-301
ISSN 1751-7311
Publication year 2016
Published at Department of Biological and Environmental Sciences
Pages 294-301
Language en
Keywords aquaculture; narcosis; slaughter; teleost; welfare
Subject categories Animal physiology, Fish and Aquacultural Science


Studies that address fi sh welfare before slaughter have concluded that many of the traditional systems used to stun fi sh including CO 2 narcosis are unacceptable as they cause avoidable stress before death. One system recommended as a better alternative is electrical stunning, however, the welfare aspects of this method are not yet fully understood. To assess welfare in aquaculture both behavioural and physiological measurements have been used, but few studies have examined the relationship between these variables. In an on-site study aversive behaviours and several physiological stress indicators, including plasma levels of cortisol and ions as well as blood physiological variables, were compared in Arctic char ( Salvelinus alpinus ) stunned with CO 2 or electricity. Exposure to water saturated with CO 2 triggered aversive struggling and escape responses for several minutes before immobilization, whereas in fi sh exposed to an electric current immobilization was close to instant. On average, it took 5 min for the fi sh to recover from electrical stunning, whereas fi sh stunned with CO 2 did not recover. Despite this, the electrically stunned fi sh had more than double the plasma levels of cortisol compared with fi sh stunned with CO 2 . This result is surprising considering that the behavioural reactions were much more pronounced following CO 2 exposure. These contradictory results are discussed with regard to animal welfare and stress physiological responses. The present results emphasise the importance of using an integrative and interdisciplinary approach and to include both behavioural and physiological stress indicators in order to make accurate welfare assessments of fish in aquaculture.

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