Infectious Pancreatic Necrosis Virus Can Be Transmitted Through Cohabitation From Atlantic Cod ( <i>Gadus morhua</i> ) to Atlantic Cod, Atlantic Salmon ( <i>Salmo salar</i> ), Atlantic Halibut ( <i>Hippoglossus hippiglossus</i> ) and Lumpfish ( <i>Cy

Infectious pancreatic necrosis virus (IPNV) can cause devastating disease in Atlantic salmon (Salmon salar). IPNV has a broad host range and may threaten other aquaculture species. Understanding interspecies transmission of IPNV is crucial for protecting the aquaculture industry. With the expansion of fish farming (in Norway), it is important to assess whether a pathogen can transmit from one fish species to another and cause disease. We investigated whether IPNV-infected Atlantic cod can shed IPNV, leading to infection in other fish important to Norwegian aquaculture: halibut, salmon and lumpfish, using the cohabitation experimental trial method. Virus shedding, transmission, fish mortality and pathology were assessed. We documented virus shedding in water and mortality in IPNV-injected Atlantic cod. No mortality was observed in the cohabitated fish species during the experimental period. We confirmed lesions consistent with IPN by histopathology and immunohistochemistry in IPNV-injected Atlantic cod and in IPNV-PCR positive cohabitant Atlantic halibut. Cohabitant Atlantic cod, Atlantic salmon, Atlantic halibut and lumpfish were also found positive for IPNV by PCR, suggesting that IPNV-infected Atlantic cod can transfer infection to other farmed fish species. These findings highlight the potential risk of pathogen spread among farmed fish species and demonstrate the importance of understanding infectious fish disease epidemiology.