A new lineage of Ranavirus micropterus1 infects ornamental wrasses from the Great Barrier Reef and causes severe disease in captivity

The Great Barrier Reef (GBR) supports remarkable vertebrate diversity but is among the most fragile ecosystems globally, and diseases affecting reef fishes remain poorly understood. We employed traditional veterinary diagnostic techniques and metatranscriptomics to investigate a disease outbreak with 100% mortality in captive wrasses (Macropharyngodon choati) from the GBR. Histopathology revealed multifocal necrosis of renal tubules, and cytopathic effect was observed in bluegill fry cell lines. A novel ranavirus isolate, Macropharyngodon choati ranavirus (McRV), was identified at exceptionally high transcript abundance across different host tissues, alongside strong expression of host genes linked to cellular stress and immune function. Phylogenetic analysis placed McRV in a distinct clade of wrasse ranaviruses, clustering with a virus previously identified on the GBR, suggesting that wild wrasses serve as natural hosts. These data emphasise the need for enhanced pathogen monitoring in marine wildlife increasingly threatened by anthropogenic change.