We examined the distribution of iridoviruses in 10 freshwater ornamental fish species hatched in Korea and imported from other Asian countries using both 1-step and 2-step polymerase chain reation (PCR). None of the 10 fish species analyzed were free of iridovirus as shown by 2-step PCR positive results, and 3 species yielded 1-step PCR positive results with associated mortality. Cloned PCR amplicons of the adenosine triphosphatase (ATPase) and major capsid protein (MCP) genes in genomic DNA of iridovirus showed the same nucleotide sequences as that of infectious spleen and kidney necrosis virus (ISKNV) isolated from the mandarinfish Siniperca chuatsi. These results indicate the presence of ISKNV disease in various ornamental fish as new host species and that the disease is widespread throughout different Asian countries including Korea, Singapore and China. Such infections were either clinical with associated mortality (and 1-step PCR positive) or asymptomatic in fish that were externally healthy (and only positive in 2-step PCR). Molecular analyses of the K2 region performed on iridovirus samples isolated from freshwater ornamental fishes revealed deletion/insertion of repetitive sequences of various lengths (42 to 339 bp), depending on the ISKNV isolates, without substitutions. Experimental infection of pearl gourami Trichogaster leeri and silver gourami T. microlepis with a tissue homogenate of pearl gourami infected by ISKNV induced 70 and 20% cumulative mortalities in the pearl and silver gourami, respectively. KEY WORDS: Iridovirus · ISKNV · Ornamental fish · Asymptomatic infection · Asian countries Resale or republication not permitted without written consent of the publisherDis Aquat Org 78: [209][210][211][212][213][214][215] 2008 (ALIV) and dwarf gourami C. lalia iridovirus (DGIV) in Japan.Infectious spleen and kidney necrosis virus (ISKNV), recently assigned to the new Megalocytivirus genus of the Iridoviridae family, based on morphological and genetic characteristics (Chinchar et al. 2005), has caused significant economic loss in the mandarinfish Siniperca chuatsi aquaculture sector of China (He et al. 2000). In studies to elucidate the transmission and host range of ISKNV, mandarinfish appears to be the only species infected naturally and the most susceptible species, followed by largemouth bass in experimental infections of 21 fish species tested (He et al. 2002). In addition, the presence of ISKNV has only been reported in China. Jeong et al. (2006a), using 2-step polymerase chain reation (PCR), reported megalocytivirus in marine fish species that were externally healthy, a condition that could be called persistent or asymptomatic infection. Moreover, investigation of largemouth bass Micropterus salmoides salmoides, using a 1-step PCR technique after the occurrence of mass mortality, has also revealed the long-term persistence of ranavirus, largemouth bass virus (LMBV), in the population (Hanson & Petrie-Hanson 2001).Although Megalocytivirus and Ranavirus are epidemiologically and g...

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

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Freshwater pearl gourami Trichogaster leeri and seawater rock bream Oplegnathus fasciatus infected by the iridoviruses PGIV-SP and IVS-1 were carrying similar numbers of viral particles (2.52 × 10 8 and 2.46 × 10 8 viral genome copies mg -1 spleen tissue, respectively). The viral genome copy number for both iridoviruses decreased much faster in seawater than in freshwater, reaching a concentration of less than 0.5%, versus 26 to 54% in freshwater, after 4 d of incubation at 25°C. The decrease in copy number altered the infectivity of the viruses, as reflected by the decreased cumulative mortality of rock bream injected intraperitoneally with the incubated iridoviruses. Moreover, uninfected rock bream cohabitated with PGIV-SP-challenged rock bream showed 100% cumulative mortality; a similar experiment using IVS-1 had the same result, implying the potential for iridoviral transmission from freshwater ornamental fish to marine fish even in a marine environment. Of 58 outwardly healthy marine fish groups collected from various markets, 2 rock bream groups and 1 sea perch group Lateolabrax sp. tested positive for PGIV-SP by 2-step polymerase chain reaction (PCR). Thus, PGIV-SP from freshwater ornamental fish may have crossed both environmental and species barriers to infect marine fish such as rock bream.

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