AUTHOR=Domnik Nicolle J. , Polymeropoulos Elias T. , Elliott Nicholas G. , Frappell Peter B. , Fisher John T. 

TITLE=Automated Non-invasive Video-Microscopy of Oyster Spat Heart Rate during Acute Temperature Change: Impact of Acclimation Temperature

JOURNAL=Frontiers in Physiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2016.00236

DOI=10.3389/fphys.2016.00236

ISSN=1664-042X

ABSTRACT=<p>We developed an automated, non-invasive method to detect real-time cardiac contraction in post-larval (1.1–1.7 mm length), juvenile oysters (i.e., oyster spat) via a fiber-optic trans-illumination system. The system is housed within a temperature-controlled chamber and video microscopy imaging of the heart was coupled with video edge-detection to measure cardiac contraction, inter-beat interval, and heart rate (HR). We used the method to address the hypothesis that cool acclimation (10°C vs. 22°C—T<sub>a10</sub> or T<sub>a22</sub>, respectively; each <italic>n</italic> = 8) would preserve cardiac phenotype (assessed via HR variability, HRV analysis and maintained cardiac activity) during acute temperature changes. The temperature ramp (TR) protocol comprised 2°C steps (10 min/experimental temperature, T<sub>exp</sub>) from 22°C to 10°C to 22°C. HR was related to T<sub>exp</sub> in both acclimation groups. Spat became asystolic at low temperatures, particularly T<sub>a22</sub> spat (T<sub>a22</sub>: 8/8 vs. T<sub>a10</sub>: 3/8 asystolic at T<sub>exp</sub> = 10°C). The rate of HR decrease during cooling was less in T<sub>a10</sub> vs. T<sub>a22</sub> spat when asystole was included in analysis (<italic>P</italic> = 0.026). Time-domain HRV was inversely related to temperature and elevated in T<sub>a10</sub> vs. T<sub>a22</sub> spat (<italic>P</italic> &lt; 0.001), whereas a lack of defined peaks in spectral density precluded frequency-domain analysis. Application of the method during an acute cooling challenge revealed that cool temperature acclimation preserved active cardiac contraction in oyster spat and increased time-domain HRV responses, whereas warm acclimation enhanced asystole. These physiologic changes highlight the need for studies of mechanisms, and have translational potential for oyster aquaculture practices.</p>