Egg-associated transmission of IPN virus of trouts

Infectious pancreatic necrosis virus (IPN) of salmonid fishes has been isolated and identified in suspect but normal-appearing stocks of adult brook trout (Salvelinus fontinalis), and thus a pattern for the epizootiology of the virus has been demonstrated. Virus titers as high as 10^6.5 ID₅₀ were found in egg fluids from 7 of 12 fish tested. In contrast, egg homogenates contained much less virus; their maximum titer was 10^1.8 ID⁵⁰. The presence of virus within the eggs, however, was not established. Viral neutralizing ability of serum from the same fish showed an inverse relationship to the presence of virus in “ovarian fluid.” The highest serum titers occurred in those fish from which little or no virus had been isolated.