DAO 84:201-208 (2009)  -  DOI: https://doi.org/10.3354/dao02041

ABSTRACT: The effects of various water temperature treatments on the development of red sea bream iridovirus disease (RSIVD) in rock bream Oplegnathus fasciatus challenged with iridovirus Sachun (IVS-1) were determined by measuring the mortality and the viral concentration in the spleen of infected fish. Experimental infections of rock bream with IVS-1 at water temperatures of 18, 21, and 25°C resulted in a cumulative mortality of 100%, but infections at 13°C resulted in 0% mortality, even after 45 d. The disease progressed more rapidly at higher water temperatures; at 25, 21, and 18°C, the mean numbers of days until death were 17, 20, and 30 d, respectively. When the water temperature for fish infected with iridovirus by intramuscular injection was shifted from 13 to 25°C, the cumulative mortality reached 100%, with rapid onset of the disease, independent of the time at which the temperature was shifted, i.e. 7, 14, or 30 d after injection at 13°C. Real-time PCR data revealed that the viral genome copy number in the spleen of rock bream maintained at 13°C increased with time, suggesting the occurrence of viral replication even at 13°C. In the reverse experiment, when the water temperature for fish that were infected at a higher temperature was shifted to 13°C, 3 or 7 d after injection at 25°C, the fish showed 100% cumulative mortality, although the mean number of days until death was higher than that observed for fish maintained at a constant temperature of 25°C. The viral DNA concentration in the spleen of rock bream that had been shifted down to 13°C, 3 or 7 d after injection at 25°C, was not suppressed, but increased and eventually reached levels sufficient to induce mortality at 13°C. However, the level of viral genome copy numbers in the spleen of dead fish at 25°C, regardless of whether those fish were held at a constant temperature of 25°C or shifted up from 13°C, appeared to be greater than the level found in the dead fish shifted down to 13°C after inoculation at 25°C.

KEY WORDS: Temperature shift · Iridovirus · Oplegnathus fasciatus · Quantification