Sentinels in Salmon Aquaculture: Heart Rates Across Seasons and During Crowding Events

Abstract

Advances in tag technology now make it possible to monitor the behavior of small groups of individual fish as bioindicators of population wellbeing in commercial aquaculture settings. For example, tags may detect unusual patterns in fish heart rate, which could serve as an early indicator of whether fish health or welfare is becoming compromised. Here, we investigated the use of commercially available heart rate biologgers implanted into 24 Atlantic salmon weighing 3.6 ± 0.8 kg (mean ± SD) to monitor fish over 5 months in a standard 12 m × 12 m square sea cage containing ∼6,000 conspecifics. Post tagging, fish established a diurnal heart rate rhythm within 24 h, which stabilized after 4 days. Whilst the registered tagged fish mortality over the trial period was 0%, only 75% of tagged fish were recaptured at harvest, resulting in an unexplained tag loss rate of 25%. After 5 months, tagged fish were approximately 20% lighter and 8% shorter, but of the similar condition when compared to untagged fish. Distinct diurnal heart rate patterns were observed and changed with seasonal day length of natural illumination. Fish exhibited lower heart rates at night [winter 39 ± 0.2 beats per min (bpm), spring 37 ± 0.2 bpm, summer 43 ± 0.3 bpm, mean ± SE] than during the day (winter 50 ± 0.3 bpm, spring 48 ± 0.2 bpm, summer 49 ± 0.2 bpm) with the difference between night and day heart rates near half during the summer (6 bpm) compared to winter and spring (both 11 bpm). When fish experienced moderate and severe crowding events in early summer, the highest hourly heart rates reached 60 ± 2.5 bpm and 72 ± 2.4 bpm, respectively, on the day of crowding. Here, if the negative sublethal effects on fish that carry tags (e.g., growth rate) can be substantially reduced, the ability to monitor diurnal heart rate patterns across seasons and detect changes during crowding events, and using heart rate biologgers could be a useful warning mechanism for detecting sudden changes in fish behavior in sea cages.

A Review of Factors Affecting Farmed Atlantic Salmon (Salmo salar) Welfare in Australia and Beyond

“…One study showed untagged conspecifics had significantly higher weights, fork lengths and condition factors than tagged fish, suggesting a negative effect on fish welfare (Hvas et al 2020a). This is consistent with reductions in growth rates following transplantation of heart rate biologgers as shown by Warren-Myers et al (2021). Macaulay et al (2021b) quantified mortality of tagged fish was ~10 times higher in sea pens than in tanks and the mortality of tagged fish was higher in longer trials (from 4% in single-day trials to 36% after 100 days).…”

Revising the Impact and Prospects of Activity and Ventilation Rate Bio-Loggers for Tracking Welfare and Fish-Environment Interactions in Salmonids and Mediterranean Farmed Fish

“…Therefore, to turn quantitative behavioral analysis into practical OWI, technological advances on machine vision, biotelemetry and miniaturized bio-loggers need to be applied and adapted to the demand of fish welfare monitoring. Thus, as reviewed by Macaulay et al (2021), electronic transmitter tags (e.g., acoustic accelerometers) were first developed for studying wild fish behavior, but they are now rapidly transitioned into the world of farmed fish for an individual-based behavioral assessment, acting tagged individuals as "sentinel fish" to provide useful welfare-related information for monitoring and managing feeding, growth and disease outbreaks (Kolarevic et al, 2016;Føre et al, 2017Føre et al, , 2018Warren-Myers et al, 2021). In any case, the proposed monitoring solutions should be different depending on the asked question, the species biology, and the culture system (tank-based systems, ponds, lagoons, sea cages, etc.…”

Heart rate as an indicator of stress during the critical swimming speed test of farmed Atlantic salmon (Salmo salar L.)

“…The catecholamines (adrenaline and noradrenaline) released with stress are known to increase f H and affect energy mobilization by gluconeogenesis and glycogenolysis in fish (Madaro et al, 2015). Thus, several studies have shown that elevated f H can be used as an indicator of stress in several fish species, including farmed Atlantic salmon (Brijs et al, 2018, 2019; Føre et al, 2021; Hvas et al, 2020a; Mignucci et al, 2021; Siemann et al, 2018; Warren‐Myers et al, 2021; Yousaf et al, 2022; Zrini et al, 2021; Zrini & Gamperl, 2021). To determine the continuous f H in free‐swimming fish, the abovementioned studies used fully implantable tags.…”