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

Abstract

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°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.

Evaluation of the reliability of indicators of consciousness during CO2stunning of rainbow trout and the effects of temperature

“…Previous studies have shown that loss of VERs indicates a degree of brain failure indicative of insensibility in fish (Bowman et al., 2019; Bullock, Hofmann, New, & Nahm, 1991; Kestin et al., 1991, 1995; Readman, 2015; Retter et al., 2018; Robb & Roth, 2003; Robb et al., 2000; van de Vis et al., 2003), chickens and ducks (Gregory & Wotton, 1986) and livestock (Verhoeven, Gerritzen, Hellebrekers, & Kemp, 2014). While visual indicators of a loss of consciousness in fish are susceptible to misinterpretation from subjective visual observation, the use of EEG to assess VERs allows for a more definitive method of determining when sensibility is lost.…”

“…EEG is a method for recording and measuring the electrical activity of the brain through the use of electrodes that are either surgically implanted in the brain (Kestin et al., 2002; Kestin, Wotton, & Gregory, 1991; Quick & Laming, 1990), or attached externally to the head (Bowman, Hjelmstedt, & Gräns, 2019; Cho et al., 2017). EEG allows the investigator to detect changes in brain activity indicative of a loss of consciousness and/or sensibility.…”

Electroencephalographic Response in Juvenile Tambaqui, Colossoma macropomum, Exposed to Short-Term Anaesthetic Baths with Geraniol and Citronellol

“…Due to the complexity in capturing neuronal signals and the different monoterpene mechanisms of action, these compounds can elicit different EEG responses. Despite the recent advances in research relating the effects of various compounds on the fish brain activity [1,2,[25][26][27], no studies are available to date, for instance, on the frequency bands and their correlation with general anaesthesia in fish. These are future research arenas that should be explored to best clarify how the fish brain responds to general anaesthesia.…”

Research Before Policy: Identifying Gaps in Salmonid Welfare Research That Require Further Study to Inform Evidence-Based Aquaculture Guidelines in Canada

“…It is therefore imperative that we continue to research teleost brain region function in commercially relevant lineages. Second, electroencephalography (EEG) has been used to assess brain electrical activity in fish in a number of laboratory experiments and has been shown to be one of the most reliable methods of assessing consciousness [e.g., (162,165,(170)(171)(172)(173)]. However, in a commercial fish farm setting, registration of EEGs is impossible to perform, instead forcing farmers to rely exclusively on behavioral indicators to evaluate the degree of consciousness in fish [e.g., coordinated swimming and escape behaviors, ability to maintain equilibrium, "eye roll" reflex, and ventilatory reflexes; (170)].…”