Fluctuations in the heart rate of abalone in response to low salinity stress

The tremendous expansion of Chinese abalone production has not been without challenges such as low salinity stress, which may occur during severe summer rainstorms and typhoon events. Interspecific hybrids have, however, been of great use to the aquaculture industry in withstanding environmental stresses. This study adopted the non-invasive method of measuring heart rate to monitor the cardiac performance of the Pacific abalone and two of its interspecific hybrids during the incidence of continuous salinity decrease. The results showed that low salinity significantly influences the heart rate of abalone. Fluctuation in the abalone’s heartbeat suggests a pattern with three phases and two breakpoints of salinity (BOS1 and BOS2). BOS1 represents an isosmotic point, and BOS2 represents lethal salinity. We argue that relatively lower BOS suggests better tolerance to low salinity, and long-term exposure to salinities around BOS2 could be detrimental to all three species. The hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) recorded the lowest BOS1 and BOS2, which was also significantly different (P = 0.01) from DD at BOS1, suggesting a better tolerance potential for low salinities than the other species. Altogether, our data establish species-specific BOS and reveal the cardiac mechanism by which abalone responds to low salinity. The results confirm that the non-invasive heart rate detection method could likewise be adopted to define critical salinities for abalone, and hybridization could be a potential method to breed the more stress-resilient aquatic animals.