Infectious pancreatic necrosis in a recirculating rainbow trout (Oncorhynchus mykiss) culture system

During October 2009, a suspected outbreak of infectious pancreatic necrosis, with typical signs and high mortality, was observed in cultured rainbow trout (Oncorhynchus mykiss) fry (mean weight of 9 g) in a recirculating system in Fars Province, Iran. Tissue samples, including pyloric caeca as well as pancreatic tissues, liver, kidney, and spleen, were aseptically collected from 20 aff ected moribund fish for histopathological and molecular assays. Histopathologically, the exocrine pancreatic acinar cells exhibited the most notable pathology, including focal to extensive degeneration and coagulative necrosis with mononuclear infl ammatory infiltrates. To confirm the diagnosis of clinical infectious pancreatic necrosis (IPN), a reverse transcription-polymerase chain reaction (RT-PCR) and sequence analysis were used. A 224-bp fragment of the IPN virus NS/VP3 (segment A) gene was amplified using cDNA prepared from infected pooled tissues of pancreas, liver, kidney, and spleen. Th e nucleotide sequence was most closely identified with the Sp serotype.