Induction of infectious pancreatic necrosis (IPN) in Atlantic salmon Salmo salar and brook trout Salvelinus fontinalis by bath challenge of fry with infectious pancreatic necrosis virus (IPNV) serotype Sp

Thirteen week old Atlantic salmon Salmo salar fry and 15 wk old brook trout Salvelinus fontinalis with average weights of 0.19 and 0.17 g, respectively, were bath challenged with infectious pancreatic necrosis virus (IPNV), serotype Sp, N1 strain. The virus had been isolated from a clinical outbreak of infectious pancreatic necrosis (IPN) in Atlantic salmon parr. Cell culture supernatant after a first passage of virus was used as the infective material. Approximately 400 fry of each species were divided into 2 parallel tanks with challenged fish and 2 parallel tanks with non-challenged fish. At 69 d after challenge, cumulative mortalities of Atlantic salmon were 76 and 82% for the challenged groups and 6 and 15% for the non-challenged groups. The corresponding values for brook trout were 42 and 43% for the challenged groups and 8 and 10% for the non-challenged groups. The onset of mortality in challenged Atlantic salmon was delayed compared with the onset in brook trout. IPNV was reisolated from the fry of all challenged groups. Histological examination of sampled moribund fish showed hepatic degeneration or necrosis and exocrine pancreatic necrosis in fry from all challenged groups. The presence of IPNV in the lesions was demonstrated immunohistochemically. Virological, histological and immunohistochemical examinations of fry sampled prior to challenge and of non-challenged fry gave negative results. This study represents, to our knowledge, the first report of an experimental induction of clinical IPN in Atlantic salmon fry.