Multiple whole bacterial antigens in polyvalent vaccine may result in inhibition of specific responses in rainbow trout (Oncorhynchus mykiss).

The goal of fish vaccination today is to protect fish against multiple bacterial fish pathogens simultaneously using polyvalent vaccines. However, many immunological processes such as antigenic cross-reaction, antigenic competition, affinity maturation and antigen-induced suppression may affect the specificity, avidity and level of antibodies. Consequently, the biological function of antibodies may be markedly different from that predicted by conventional serologic tests.

Characterisation of atypical Aeromonas salmonicida infection in Arctic charr Salvelinus alpinus and European grayling Thymallus thymallus.

Cultured stocks of Arctic charr Salvelinus alpinus and European grayling Thymallus thymallus are vulnerable to infection by achromogenic atypical Aeromonas salmonicida (AAS). In Finland, natural stocks of both fish species have to be supported by restocking, and AAS infection poses a threat to successful restocking because no preventive means are available. In this study, we analysed AAS isolates from Arctic charr and European grayling and from other sources genetically, and characterised the signs and pathology of AAS infection in Arctic charr and European grayling both under farming conditions and after experimental challenge.

Survival and virulence of Flavobacterium psychrophilum in water microcosms.

Flavobacterium psychrophilum, the causative agent of rainbow trout fry syndrome and cold water disease in salmonids, causes serious disease outbreaks in fish farms worldwide. The aim of the present study was to examine the survival capacity of F. psychrophilum in laboratory microcosms containing sterilised water under different environmental conditions and to examine the virulence of starving F.

Occurrence of Flavobacterium psychrophilum in fish-farming environments.

Occurrence of Flavobacterium psychrophilum in fish farms and fish-farming environments was studied using agar plate cultivation, the immunoflourescence antibody technique (IFAT) and nested PCR. Characteristics of 64 F. psychrophilum isolates from rainbow trout Oncorhynchus mykiss, fish farm rearing water, ovarian fluid and wild fish were serotyped, ribotyped and compared biochemically.

Detection of the fish pathogen Flavobacterium psychrophilum in water from fish farms.

Rainbow trout fry syndrome and cold-water disease are serious diseases in farmed salmonid fish. In the present study, three methods were compared, for the detection of the causative pathogen, Flavobacterium psychrophilum in water. The methods included traditional agar plate cultivation on tryptone yeast extract salts (TYES) agar, immunofluorescence antibody technique (IFAT) and nested PCR.