Heart rates of Atlantic salmon Salmo salar during a critical swim speed test and subsequent recovery

Abstract

In this study, heart rate (HR) bio‐loggers were implanted in the abdominal cavity of 12 post‐smolt Atlantic salmon Salmo salar weighing 1024 ± 31 g and acclimated to 12°C sea water. One week after the surgical procedure, a critical swim speed (Ucrit) test was performed on tagged and untagged conspecifics, whereafter tagged fish were maintained in their holding tanks for another week. The Ucrit was statistically similar between tagged and untagged fish (2.67 ± 0.04 and 2.74 ± 0.05 body lengths s−1, respectively) showing that the bio‐logger did not compromise the swimming performance. In the pre‐swim week, a diurnal cycle was apparent with HR peaking at 65 beats min−1 during the day and approaching 40 beats min−1 at night. In the Ucrit test, HR increased approximately exponentially with swimming speed until a plateau was reached at the final speed before fatigue with a maximum of 85.2 ± 0.7 beats min−1. During subsequent recovery tagged fish could be divided into a surviving group (N = 8) and a moribund group (N = 4). In surviving fish HR had fully recovered to pre‐swim levels after 24 h, including reestablishment of a diurnal HR cycle. In moribund fish HR never recovered and remained elevated at c. 80 beats min−1 for 4 days, whereafter they started dying. We did not identify a proximal cause of death in moribund fish, but possible explanations are discussed. Tail beat frequency (TBF) was also measured and showed a more consistent response to increased swimming speeds. As such, when exploring correlations between HR, TBF and metabolic rates at different swimming speeds, TBF provides better predictions. On the contrary, HR measurements in free swimming fish over extended periods of time are useful for other purposes such as assessing the accumulative burden of various stressors and recovery trajectories from exhaustive exercise.

Atlantic Salmon (Salmo salar) Cage-Site Distribution, Behavior, and Physiology During a Newfoundland Heat Wave

“…For example, the pattern of changes in mean f H and temperature was very similar ( Figures 4B,C ); f H during both the day-time and night-time was significantly related to temperature ( p < 0.001) and had Q 10 values from 9 to 19°C of ~2.0 and 2.6, respectively ( Figure 5A ); and f H was ~ 12 bpm higher in the day-time as compared to the night-time ( Figure 5A ). The f Hs reported for our salmon at various temperatures are extremely similar to those recorded by several authors for free-swimming rainbow trout ( O. mykiss ) and salmon fitted with data loggers once temperature is taken into account (temperatures 4–14°C; Brijs et al, 2018 , 2019 ; Hjelmstedt et al, 2020 ; Hvas et al, 2020 , 2021 ; Føre et al, 2021 ; Svendsen et al, 2021 ). However, they are much lower than those measured in salmon of similar stocks fitted with blood flow probes in respirometers after 1–2 days of recovery (e.g., see Penney et al, 2014 ).…”

“…That there was a diurnal difference in f H in the present study is also consistent with the literature (see Aissaoui et al, 2000 and references herein). Data from previous studies appear to suggest that the difference in f H in free-swimming salmon between the day-time and night-time increases with water temperature; i.e., it was reported to be ∼5 bpm at 4-5 • C (Føre et al, 2021;Svendsen et al, 2021), 10 bpm at 10 • C (Hjelmstedt et al, 2020;Hvas et al, 2021), and 25 bpm at 14-15 • C (Brijs et al, 2018). However, our data, where the difference in f H was consistently ∼ 12 bpm in the salmon from ∼ 8-19.5 • C, does not support this conclusion.…”

Tag use to monitor fish behaviour in aquaculture: a review of benefits, problems and solutions

“…This is demonstrated in a recent DST heart rate study fish with moribund fish displaying deviating results (Hvas et al . 2021).…”

Heart rate and swimming activity as indicators of post-surgical recovery time of Atlantic salmon (Salmo salar)

“…Conversely, the circadian rhythm in heart rate was more like expected (higher during daytime), meaning that the sh displayed generally higher heart rates when measured activity was low than when activity was high. This may seem counter-intuitive as one would expect more active sh to display higher heart rates since salmon tend to display increased heart rates with increased swimming activity (Hvas et al, 2020b). However, it is possible that the higher heart rates during daytime were caused by effects such as feeding activity (Eliason et al, 2008;Gräns et al, 2009) or perceived increased predation risk due to higher light levels (Johnsson et al, 2001).…”