Infectious pancreatic necrosis is an economically important, contagious acute viral disease of young salmonids that can be associated with high levels of mortality. Infectious pancreatic necrosis is caused by an aquabirnavirus. Predominant features include necrosis of pancreatic acinar tissue, intestinal enterocytes, renal hematopoietic tissue, and, on occasion, the liver. The ability of various direct- or indirect-acting chemical carcinogens to induce primary liver, biliary and pancreatic tumors in fish is well-documented. Systemically infected fish can have hepatic and/or pancreatic involvement, although organs such as the kidney and spleen tend to be more common internal targets. Hepatic lipidosis is characterized by excessive fat accumulation within the cytoplasm of hepatocytes. Cleanup of chemical contamination in waterways has proven effective at decreasing the occurrence of hepatic, biliary, and/or pancreatic tumors in some fish species, and the incidence of such tumors in repeated survey studies has been used to monitor the success of remediation efforts in some localities.