Validating Star-Oddi heart rate and acceleration data storage tags for use in Atlantic salmon (Salmo salar)

Abstract

Background Data storage tags (DSTs) record and store information about animals and their environment, and can provide important data relevant to fish culture, ecology and conservation. A DST has recently been developed that records heart rate (fH), electrocardiograms (ECGs), tri-axial acceleration and temperature. However, at the time of this study, no research using these tags had been performed on fish or determined the quality of the data collected. Thus, our research asked: do these DSTs provide reliable and meaningful data? To examine this question, Atlantic salmon (1.4 ± 0.7 kg) were implanted with DSTs, then swam at increasing speeds in a swim tunnel after 1 week of recovery. Further, in two separate experiments, salmon (2.4 ± 0.1 kg) were implanted with DSTs and held in a large tank with conspecifics for 1 week at 11 °C or 6 weeks at 8–12 °C. Results External acceleration (EA) and variation in EA (VAR) increased exponentially with swimming speed and tail beat frequency. The quality index (QI) assigned to ECG recordings (where QI0 means very good quality, and QI1, QI2 and QI3 are of reduced quality) did not change significantly with increasing swimming speed (QI0 ~ 60–80%). However, we found that the accuracy of the tag algorithm in estimating fH from ECGs was reduced when QI>0. Diurnal patterns of fH and EA were evident from the time the salmon were placed in the tank. Heart rate appeared to stabilize by ~ 4 days post-surgery in the first experiment, but extended holding showed that fH declined for 2–3 weeks. During extended holding, the tag had difficulty recording low fH values < 30 bpm, and for this reason, in addition to the fact that the algorithm can miscalculate fH, it is highly recommended that ECGs be saved when possible for quality control and so that fH values with QI>0 can be manually calculated. Conclusions With these DSTs, parameters of acceleration can be used to monitor the activity of free-swimming salmon. Further, changes in fH and heart rate variability (HRV) due to diurnal rhythms, and in response to temperature, activity and stressors, can be recorded.

Does hydrostatic pressure influence lumpfish (Cyclopterus lumpus) heart rate and its response to environmental challenges?

“…These data may indicate that the lumpfish had not fully recovered from surgery and that this explains their high resting f H . This would agree with recent research on Atlantic salmon showing that while f H decreases most during the first week post-implantation it continues to fall for 2–3 weeks post-surgery ( Hvas et al , 2020 ; Zrini and Gamperl, 2021 ). However, it is also possible given the low aerobic scope and U crit of this species ( Hvas et al ., 2018 ) that a large scope for f H is not required.…”

“…2 ). However, we do not believe that this was the main factor affecting ECG quality because the percentage of QI 0 recordings in Atlantic salmon during a U crit swim test never fell below 50% ( Zrini and Gamperl, 2021 ). Instead, we believe that it was the low amplitude of the signal received by the logger that was the primary issue.…”

“…However, day-time values were only significantly different than night-time values on the first day post-surgery, and diel variations in f H were relatively small (2 to 4 bpm). Conversely, Atlantic salmon had average diel variations of 7 bpm (and up to 14 bpm) at similar temperatures and time points post-surgery that were synchronous with changes in swimming activity ( Zrini and Gamperl, 2021 ). It is possible that the dampened diel variations in f H were related to low day-time activity of the lumpfish; however, this parameter was not monitored in this study.…”

“…All reported measurements of f H were calculated manually using a previously described method ( Zrini and Gamperl, 2021 ). Briefly, the average time between R wave peaks was measured (in seconds), and then 60 was divided by this number to obtain the fish’s f H in beats per minute (bpm).…”

“…Given that lumpfish can be found at a variety of depths and that data on their cardiovascular physiology and environmental tolerances are lacking, we set out to determine how hydrostatic pressure influences their capacity to deal with other abiotic factors. Star-Oddi micro-HRT loggers have been shown to provide reliable measurements of f H in other fish species ( Brijs et al , 2019 ; Zrini and Gamperl, 2021 ) and would allow us to collect measurements of f H in a sealed pressure chamber (IPOCAMP, formally named ‘Incubateur Pressurisé pour l’Observation et la Culture d’Animaux Marins Profonds’). Considering the lack of information on the effects of pressure on the cardiovascular system of fish, we used these two unique pieces of equipment to examine: (i) the f H response of lumpfish to increasing hydrostatic pressure up to 80 bar (800 m in depth); (ii) the effect of prior exposure to 80 bar on the post-chase f H of lumpfish; and (iii) the f H response to decreasing temperature (12 to 5°C), increasing temperature (12 to 20°C) or decreasing oxygen levels (101–55% air saturation at 12°C) in the absence and presence of 80 bar of pressure.…”