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Research article - Peer-reviewed, 2021

Continuous physiological welfare evaluation of European whitefish (Coregonus lavaretus) during common aquaculture practices leading up to slaughter

Hjelmstedt, P.; Brijs, J.; Berg, C.; Axelsson, M.; Sandblom, E.; Roques, J. A. C.; Sundh, H.; Sundell, K.; Kiessling, A.; Grans, A.;

Abstract

European whitefish (Coregonus lavaretus) is an aquaculture species with the potential for expanded cultivation in the fresh and brackish waters of Northern Europe. Yet, relatively little species-specific information is available regarding the stress responses and associated welfare implications for this species in captivity. We addressed this knowledge gap by using a combination of implantable heart rate bio-loggers and a range of traditional stress indicators (e.g. haematological parameters and plasma concentrations of cortisol, glucose and ions) to comprehensively evaluate the physiological responses of freely swimming whitefish in captivity, as well as when subjected to aquaculture practices and stressors that commonly occur prior to and during slaughter. Whitefish appeared to recover rapidly from surgery, as resting heart rate decreased within 36 h to stabilize at similar to 25 beats min(-1) for the next 18 days when fish were left relatively undisturbed (i.e. personnel were only present when feeding fish). In contrast with previous studies on farmed rainbow trout and Atlantic salmon, whitefish did not exhibit a clear circadian heart rate rhythm, which may be related to species-specific differences in diurnal locomotor activity. Whitefish also appear to have a well-developed capacity for thermal acclimation of heart rate, as daily resting heart rate did not change during the undisturbed period despite an increase in body temperature from similar to 6.8 to 11.2 degrees C. Following acute stressors such as crowding and transportation, the physiological response of whitefish typically involved transient elevations in heart rate, plasma cortisol and glucose, and red blood cell swelling, while plasma [K+] decreased. In contrast, the heart rate of whitefish plummeted following the combination of brailing (i.e. to haul in fish with a brail/net) and CO2 exposure prior to slaughter, while plasma cortisol, glucose and [Ca2+] significantly increased. An unforeseen finding concerns the substantial and long-lasting physiological stress response observed in whitefish when held in close proximity (i.e. within similar to 10 m) to a rainbow trout net pen, as the mean heart rate of whitefish increased from similar to 32 to 43 beats min(-1) (i.e. an increase of similar to 34%). This may represent an innate physiological response to the threat of predation, which consequently increases the allostatic load and energetic expenditure of whitefish when farmed alongside salmonids. To conclude, this study highlights the importance of performing long-term, species-specific evaluations of freely swimming fish in real aquaculture settings, and provides a platform for further research aiming to determine the welfare implications of simultaneously farming predatory and prey species in close proximity.

Keywords

Heart rate; Cortisol; Stress; Crowding; Brailing; Transport; CO2 exposure

Published in

Aquaculture

2021, volume: 534, article number: 736258
Publisher: ELSEVIER

Authors' information

Swedish University of Agricultural Sciences, Department of Animal Environment and Health
Brijs, Jeroen
Swedish University of Agricultural Sciences, Department of Animal Environment and Health
Berg, Charlotte (Berg, Lotta)
Swedish University of Agricultural Sciences, Department of Animal Environment and Health
Axelsson, M.
University of Gothenburg
Sandblom, E.
University of Gothenburg
Roques, J. A. C.
University of Gothenburg
Sundh, H.
University of Gothenburg
Sundell, K.
University of Gothenburg
Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management
Swedish University of Agricultural Sciences, Department of Animal Environment and Health

UKÄ Subject classification

Fish and Aquacultural Science

Publication Identifiers

DOI: https://doi.org/10.1016/j.aquaculture.2020.736258

URI (permanent link to this page)

https://res.slu.se/id/publ/110933