Iridovirus isolated from marine giant sea perch causes infection in freshwater ornamental fish

Ornamental fish are frequently infected with iridoviruses and their transport via international trade can easily cause the spread of the viral pathogens. An iridovirus was isolated from farmed giant sea perch (Lates calcarifer) and identified as a grouper iridovirus of Taiwan (TGIV) belonging to the genus Megalocytivirus. High mortality rate in dwarf gouramis was observed when the freshwater ornamental fish dwarf gouramis (Trichogaster lalius) was challenged with spleen tissue extracts of the TGIV-infected giant sea perch. Similar results were obtained when dwarf gouramis were challenged with grouper iridovirus (GIV) isolated from marine fish. The spleen tissue extracts of dwarf gouramis infected with TGIV and GIV were also used to challenge swordtails (Xiphophorus helleri; freshwater ornamental fish); both viruses resulted in high mortality rates in swordtails, indicating that iridovirus, a marine fish pathogen, could also infect freshwater ornamental fish, resulting in high mortality rates. Furthermore, when orange-spotted groupers (Epinephelus coioides) were experimentally challenged with the tissue extracts of TGIV-and GIV-infected dwarf gouramis, both viruses caused infection in orange-spotted groupers. In contrast with the results obtained in freshwater ornamental fish, the mortality rate of the GIV-infected orange-spotted groupers was higher (with earlier deaths) than that of their TGIV-infected counter-parts. The iridovirus isolated from infected freshwater ornamental fish also resulted in high mortality rates in marine fish. Finally, the tissue extracts of the TGIV-and GIV-infected dwarf gouramis were used to infect healthy dwarf gouramis, and TGIV and GIV were subsequently detected in the spleen tissues of healthy dwarf gouramis. The results showed that TGIV was more lethal than GIV in dwarf gouramis. The expression of the viral major capsid protein could be detected. GIV and TGIV infections also resulted in pronounced vacuolation and necrosis of the spleen tissue. Transmission electron microscopy revealed the accumulation of nearly icosahedral viral particles in the spleen tissues of dwarf gouramis infected with TGIV and GIV. This study demonstrated that iridoviruses can survive and be infectious in both fresh and marine water habitats.

Automated summary

Ornamental fish are often infected with iridoviruses, which can easily spread through international trade. The study showed that iridoviruses can be infectious in both freshwater and marine water habitats, resulting in high mortality rates in infected fish. The mortality rate of marine fish infected with iridoviruses was higher than that of freshwater fish.