HEALTH-STATUS OF 2 SALMONID AQUACULTURE FACILITIES IN NORTH PORTUGAL - CHARACTERIZATION OF THE BACTERIAL AND VIRAL PATHOGENS CAUSING NOTIFIABLE DISEASES

A comparative bacteriological and virological survey was conducted in two fish farms in the North of Portugal. The fish species examined inc luded cultured rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., as well as wild fish captured near both facil ities. The microbial load in the internal organs of apparently healthy fish was monitored over a year, and all the disease problems occurrin g during this period were investigated. Although both farms presented intermediate levels of infection (30-40% infected fish), farm B showed the poorest microbiological quality since constant but low mortalitie s were observed throughout the year. Flavobacterium and Pseudomonas-Xa nthomonas were the predominant bacterial groups, comprising around 40- 50% of the isolates from each farm. In farm B, members of the Enteroba cteriaceae and motile Aeromonas also showed significant prevalence (ab out 20%). The only outbreak of a notifiable disease was an occurrence of furunculosis, caused by Aeromonas salmonicida subsp. salmonicida, i n farm A. However, Yersinia ruckeri was isolated not only from disease d fish, but also from asymptomatic fish, usually in mixed infections w ith motile Aeromonas or infectious pancreatic necrosis virus (IPNV). W hile Y. ruckeri isolates associated with mortalities belonged to the s erotype O1 (subgroup a), those isolated from asymptomatic fish corresp onded to serotype O3. Two strains of IPNV (serotype Ab) were isolated in farm B, which represents the first viral agent detected in Portugue se aquaculture. Qualitative and quantitative differences in microbial load were observed between cultured and wild fish. No notifiable bacte rial or viral pathogens were detected in any of the feral species stud ied.