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Doctoral thesis2022Open access

Safeguarding the Welfare of Fish in Aquaculture : Physiological Assessments of Stress and Welfare During Handling, Transport and Slaughter

Hjelmstedt, Per


The increased demand of fish for human consumption has led to a rapid expansion of aquaculture. However, there are major knowledge gaps regarding species-specific needs, which entails an increased risk that fish are exposed to various aquaculture practices that have negative effects on their welfare. The purpose of this thesis has been to gain knowledge that can be used to assess the welfare of fish in aquaculture. To do so I have investigated various physiological indicators of fish welfare during handling, transport, and slaughter. First, the long-term effect of implantation of a heart rate bio-logger in the rainbow trout (Oncorhynchus mykiss) was investigated. I found no indications of impaired health three weeks after surgery, and concluded that these individuals can be assumed to represent a healthy population. The same type of bio-logger was then used, in combination with other biochemical stress indicators, to investigate the effect of repeated stress from handling, transport and slaughter in European whitefish (Coregonus lavaretus). The results clearly showed that the animals were stressed during crowding and brailing prior to transportation and during subsequent stunning before killing. To evaluate the reliability of a range of practical visual indicators of unconsciousness, measurements of Electroencephalogram was used, where changes in brain activity of rainbow trout before and after stunning with carbon dioxide, bolt-gun and electricity were investigated. Unfortunately, the result showed that the practical visual indicators used to assess unconsciousness was in poor agreement with the assessment based on brain activity. In summary, several important findings are presented here that can be used to improve fish welfare in aquaculture, and which can form the basis for future regulations and general advice on how fish should be handled, kept, cared for, and stunned and killed. 


EEG; stress; rainbow trout; European whitefish; stunning; cortisol; heart rate

Published in

Acta Universitatis Agriculturae Sueciae
2022, number: 2022:14ISBN: 978-91-7760-903-2, eISBN: 978-91-7760-904-9
Publisher: Swedish University of Agricultural Sciences