INFECTIOUS PANCREATIC NECROSIS IN ATLANTIC SALMON SALMO-SALAR IN RELATION TO SPECIFIC ANTIBODIES, SMOLTIFICATION, AND INFECTION WITH ERYTHROCYTIC INCLUSION-BODY SYNDROME (EIBS)

This paper examines the association between (1) specific antibodies ag ainst infectious pancreatic necrosis virus (IPNV), (2) plasma chloride levels, (3) infection with erythrocytic inclusion body syndrome (EIBS ); and the risk of clinical infectious pancreatic necrosis (IPN) and c umulative mortality in sea-cultured Atlantic salmon post-smelt. The fi eld study initially included 29 smelt groups raised in 10 freshwater h atcheries. The groups were transferred to seawater in spring 1993 and monitored from just prior to seawater transfer until 1 October the sam e year. Before seawater transfer, specific antibodies against IPNV wer e found in 62.1% of the groups. Anti-IPNV antibodies were most frequen tly detected in fish which had suffered from clinical IPN during the f ry period. However, only antibody-positive groups in which no earlier outbreaks of IPN had been recorded during the freshwater stage appeare d to be protected against IPN outbreaks after transfer to the sea. The cumulative mortalities in seawater for groups which were positive or negative for IPNV-antibodies prior to seawater transfer were 3.9 and 6 .6%, respectively. No relationship was found between the hypo-osmoregu latory capacity or infection with EIBS and the risk of clinical IPN af ter seawater transfer. The group-level prevalence of EIBS was 48.3% be fore seawater transfer, decreasing to 42.1 and 28.9% for the first and second samplings after seawater transfer, respectively. The protectiv e effect of acquired specific humoral immunity shown in the present st udy may be important for the control of IPN in farmed salmonids.