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

Introduction The Great Barrier Reef (GBR), Australia, supports remarkable vertebrate diversity but is one of the most fragile ecosystems globally. Wrasses are among the most species-rich group of vertebrates on the GBR, play key ecological roles supporting fish health, and are an important group in the global ornamental fish trade. Despite their ecological and economic importance, very little is known about diseases affecting wrasses and reef fishes more broadly. Methods We employed traditional veterinary diagnostic techniques and metatranscriptomics to investigate unexplained mortalities in captive wrasses ( Macropharyngodon choati ) from the GBR. Results 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. Discussion This study provides the first evidence of Ranavirus micropterus1 disease in Australian reef fishes and suggests that wild wrasses may serve as natural hosts, emphasising the need for enhanced pathogen monitoring in marine wildlfie increasingly threatened by anthropogenic change.