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Non-invasive recording of brain function in rainbow trout: Evaluations of the effects of MS-222 anaesthesia induction

Journal article
Authors Jennifer Bowman
P. Hjelmstedt
A. Grans
Published in Aquaculture Research
Volume 50
Issue 11
Pages 3420-3428
ISSN 1355-557X
Publication year 2019
Published at Department of Biological and Environmental Sciences
Pages 3420-3428
Language en
Keywords electroencephalography, rainbow trout, stunning, unconsciousness, welfare, anguilla-anguilla l., catfish clarias-gariepinus, salmon salmo-salar, electrical-activity, slaughter, responses, eeg, electroencephalogram, unconsciousness, castration, Fisheries
Subject categories Biological Sciences


Effective methods of producing instantaneous and irreversible unconsciousness at the time of slaughter are crucial for ensuring animal welfare in commercial aquaculture. However, the traditional method of visually evaluating unconsciousness has been shown to be insufficient and may lead to misjudgements of stunning efficiency. In this study, we developed a non-invasive technique that measures brain activity in fish as an alternative to traditional invasive, brain implants and used it to determine when a change in consciousness occurs in trout during anaesthesia induction. Nine rainbow trout (Oncorhynchus mykiss) were equipped with a custom designed silicone cup fitted with electrodes and submerged in 10 degrees C water with dissolved MS-222. During anaesthesia, the state of consciousness was assessed by recordings of electroencephalogram (EEG). The EEG recordings were analysed both by visually evoked responses from light stimulation (VERs) and from changes in signal amplitude, median frequency and relative signal power. According to the loss of VERs and decrease in signal amplitude, trout transitioned to surgical depth of anaesthesia within 5 min. Our results show that consciousness, or loss of, can be determined using a non-invasive system to record EEG in fish.

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