Patterns of heart rate and cardiac pausing in unrestrained resting decapod crustaceans

Abstract

Measurement of heart rate (HR) has been used as an important physiological indicator in a broad range of taxa. In the present study HR patterns were measured in five species of unrestrained, resting decapod crustaceans. In addition to variation in HR among individuals, it was also very variable within an individual animal. While some of this variation was related to activity, there was also a non‐locomotory component. Unstressed, resting crabs exhibited intermittent heart activity, whereas HR in stressed crabs was more stable, suggesting differential control of HR in resting crabs. Once the animals settled in the experimental apparatus they exhibited regular and extended cardiac pauses (acardia) of 15–300‐s duration. As with HR, there was a significant variation in the frequency and length of acardic events, which were only observed in inactive crabs. Regaining of HR, following a period of acardia, was characterized by small adjustments in position and movement of the mouthparts. This rhythmic pattern, and the fact that entry into and out of acardia was not instantaneous, suggested that these events were related to release of neurohormones and their subsequent degradation in the system, rather than direct neural control of the heart. Because HR was variable and interrupted by regular periods of acardia, caution is recommended when calculating baseline levels of HR, or using HR alone as an indicator of physiological stress. Incorporating a coefficient of variation for HR and/or measuring the periods of acardia may be a more reliable indicator of physiological stress in decapod crustaceans.

Anaesthesia of decapod crustaceans

“… Species Beats per minute Acardia time Condition Refs. Crab Cancer irroratus Say, 1817 91.0 ± 0.9 59.6 ± 7.2 s Unrestrained McGaw & Nancollas, 2021 Cancer maenas Linnaeus, 1758 79.3 ± 1.2 27.6 ± 0.9 s Cancer magister Dana, 1852 91.8 ± 1.3 28.5 ± 2.1 s Cancer gracilis Dana, 1852 65.6 ± 1.4 46.4 ± 2.8 s Cancer productus Randall, 1840 99.0 ± 1.2 83.8 ± 5.1 s Poppiana dentata Randall, 1840 83.0 ± 28.0 26° – 32 °C † 74.0 ± 14.0 26° – 30 °C † 70.0 ± 16.0 26 °C † N/C Unrestrained Singh et al., 2019 Lobster Homarus ammericanus Edwards, 1837 54.0 ± 13.0 Resting 90.0 ± 5.0 Exercising N/C Unrestrained Guirguis & Wilkens, 1995 Panulirus japonicus von Siebold, 1824 82.2 ± 12.6 5 – 15 min 13.8 ± 4.84 BPM Resting Unrestrained Yazawa & Katsuyama, 2001 103.2 ± 19.8 N/C Restrained Crayfish Cherax destructor Clark, 1936 85.27 ± 7.41 20 °C † 141.61 ± 7.98 30 °C † N/C Unrestrained Goudkamp et al., 2004 Procambarus clarkia Girard, 1852 90.0 ± 31.2 ‡ N/C Unrestrained Bini & Chelazzi, 2006 …”

“…Noteworthy, the heart rate of decapod crustaceans varies to some degree between species as well as among individuals of the same species and even on the same individual animal ( Table 1 ). They also present temporary periods of acardia (i.e., temporary cardiac pausing) and apnoea ( DeFur, 1988 ; McGaw & Nancollas, 2021 ). For this reason, McGaw & Nancollas (2021) advise using the heart rate with caution if examined as a single clinical parameter and, ideally, use this physiological indicator associated with a coefficient of variation, taking into consideration the acardia periods.…”

“…They also present temporary periods of acardia (i.e., temporary cardiac pausing) and apnoea ( DeFur, 1988 ; McGaw & Nancollas, 2021 ). For this reason, McGaw & Nancollas (2021) advise using the heart rate with caution if examined as a single clinical parameter and, ideally, use this physiological indicator associated with a coefficient of variation, taking into consideration the acardia periods. The authors also present crucial recommendations when assessing the heart rate of decapod crustaceans, such as long-term animal acclimation, restriction of animal movement but without immobilization, and continuous heartbeat monitoring.…”

“…To monitor the heart rate of decapods, practitioner benefits from electrocardiogram (ECG) pads or Doppler probes placed on the carapace above the heart ( Noga et al., 2020 ; Quesada et al., 2011 ). Noteworthy, decapods have a neurogenic heart, i.e., decapod heart rate is driven by the cardiac ganglion via nerve impulse, though also influenced by the central nervous system and neurohormones ( McGaw & Nancollas, 2021 ). The decapod heart thus can be used as a bio index to assess the effect of anaesthetic agents ( Wycoff et al., 2018 ) and the heartbeats indicate neuronal function.…”

“…The red rock crab ( Cancer productus Randall 1840) often regurgitates during aerial exposure ( McGaw, 2007 ). McGaw & Nancollas (2021) , however, exposed green crabs ( Cancer sp. Linnaeus, 1758) to air for 15 min may not present detectable impairments.…”