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Fluctuating water temperatures can affect fitness in fish when the opportunity to select habitats with appropriate temperature is limited. Despite the importance of the relationships between water temperature and host–pathogen interactions, reports on the susceptibility of fish to infectious viruses under conditions of changing water temperature are limited. Here, we compared the survival rates of common carp (Cyprinus carpio) infected with Cyprinid herpesvirus 3 (CyHV-3) in water in which the temperature varied from 22 °C ± 3 °C and in water with a constant temperature of 22 °C or 25 °C. We also examined changes in concentrations of CyHV-3 DNA and cortisol released from infected fish into ambient water as indicators of CyHV-3 transmission and stress response, respectively. The survival rates of fish infected with CyHV-3 were lower, and concentrations of CyHV-3 DNA and cortisol were higher, in the fluctuating-temperature treatments than in the constant-temperature treatments. Our findings provide direct evidence that carp are highly susceptible to CyHV-3 infection when water temperatures change diurnally. Moreover, such temperature fluctuations can promote transmission of CyHV-3 in the wild. Preserving a variety of aquatic environments including water temperature may help to prevent disease outbreaks and to conserve fish populations. |
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