Abstract
Investigating the mechanisms that fish employ to maintain homeostasis in their everyday life requires measurements of physiological and behavioural responses in the field. With multivariate bio-loggers, we continuously measured gastrointestinal blood flow (GBF), heart rate, activity and body temperature in rainbow trout (Oncorhynchus mykiss) swimming freely amongst ~5000 conspecifics in a sea cage. Our findings clearly demonstrate that while both acute aquaculture-related stress and spontaneous activity resulted in transient reductions in GBF (i.e. reductions of up to 65%), recovery from stressful handling practices subsequently involved a substantial and prolonged gastrointestinal hyperemia far beyond the level observed prior to the stressor. The gastrointestinal hyperemia may be necessary to repair the damage to the gastrointestinal tract caused by acute stress. Furthermore, heart rate responses to acute stress or voluntary activity differed depending on the individual’s physiological state. Stressed fish (i.e. mean heart rates >70 beats min−1) exhibited a bradycardic response to acute stress or activity, whereas fish with mean heart rates <60 beats min−1 instead demonstrated strong tachycardic responses. Remote monitoring of physiological and behavioural variables using bio-loggers can provide unique insights into ‘real-life’ responses of animals, which can largely differ from the responses observed in confined laboratory settings.
Highlights
To discover the mechanisms that free-living organisms employ to maintain homeostasis in their everyday life, physiological responses need to be measured in the field rather than in controlled laboratory environments[1,2]
The high-resolution measurements obtained by the bio-loggers clearly demonstrate the simultaneous reductions that occur in gastrointestinal blood flow (GBF) during bursts of activity (Fig. 1C,D)
Visual inspection of GBF and activity traces revealed that the magnitude of the reductions in GBF were generally associated with the intensity and duration of the bursts of activity (Fig. 1C,D)
Summary
To discover the mechanisms that free-living organisms employ to maintain homeostasis in their everyday life, physiological responses need to be measured in the field rather than in controlled laboratory environments[1,2]. A relatively recent innovation is the development of a fully implantable, multivariate bio-logger system (i.e. a bio-telemetric implant combined with a logger) that has the capacity to simultaneously measure blood flow (i.e. GBF), electrocardiogram (ECG), activity (via acceleration), and body temperature in freely swimming fish (Transonic EndoGear[3] Implant and custom-built Logger, Transonic Systems Inc, Ithaca, New York, USA) With this novel system, it is possible to continuously monitor multiple physiological processes in fish over extended periods of time in semi-natural and aquaculture settings. This information is invaluable for answering questions concerning fundamental stress biology in fish, as well as for the development of specific recommendations for future legislation aiming to improve fish welfare in aquaculture
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