Challenge model for effluent mediated transmission of diseases between fish species

Waterborne transmission of fish pathogens between different fish species in aquaculture is an important issue. Particularly because there is increased interest in expanding the number of fish species in fish farming. In this study, challenge models for effluent transmission of classical vibriosis and atypical furunculosis between Atlantic salmon, cod and halibut have been evaluated by the use of a tank system designed for transmission via effluent. The system was tested with effluent transmission of classical vibriosis caused by Vibrio anguillarum serotype O2a from infected salmon to cod. Subsequently infected cod developed chronic infections with clinical signs such as petechial haemorrhages and ulcerations on the ventral abdominal wall, in addition to fin erosion. However, transmission of V. anguillarum serotype O2b could not be demonstrated from infected cod to salmon, as V. anguillarum could not be reisolated from moribund or dead salmon.Transmission via effluent of atypical furunculosis from infected halibut to healthy cod and halibut was confirmed. The mortality of cod and halibut in the receiving tanks was low, but physical stress seemed to provoke an outbreak in cod, but not in halibut.