Influence of temperature shifts on the onset and development of red sea bream iridoviral disease in rock bream Oplegnathus fasciatus

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 · QuantificationResale or republication not permitted without written consent of the publisher

Iridovirus infections in finfish – critical review with emphasis on ranaviruses

“…The same trend was observed recently in a study of the megalocytivirus red sea bream iridovirus in rock bream, Oplegnathus fasciatus Temminck & Schlegel: the minimum temperature permissive for infection was 13 °C, and incubation period progressively decreased up to 30 °C (Jun, Jeong, Kim, Nam, Shin, Kim, Kang & Jeong 2009).…”

Development of red sea bream iridovirus concentration method in seawater by iron flocculation

“…Although we cannot exclude a possibility that the viral shedding level is less than the detection limit of our developed method, direct evidence of viral shedding from surviving fish could not be demonstrated in this experiment. In the RSIV-infected rock bream Oplegnathus fasciatus that no mortality was observed at 13°C for more than 30 days, the sifting of water temperature from 13°C to 25°C induced rapid onset of the disease (Jun et al, 2009). The seasonal shifting of water temperature might induce the viral shedding of surviving fish.…”

Effects of temperature on Renibacterium salmoninarum infection and transmission potential in Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

“…; Jun et al . ). Some studies indicate that higher water temperatures increase BKD mortality (Austin & Austin ; Jones, Moffit & Peters ), while other studies have reported the opposite (Sanders, Pilcher & Fryer ).…”