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Tenacibaculum maritimum is a cosmopolitan bacterial pathogen with the potential to cause significant losses in a broad range of farmed and wild marine fish species. This study investigated the antigenic diversity of T. maritimum isolated in culture from farmed Chinook (king) salmon (Oncorhynchus tshawytscha) from the Marlborough Sounds in New Zealand. A total of 36 isolates were examined using antibody serotyping and rapid molecular serotyping via multiplex PCR (mPCR) targeting genes encoding O-antigen biosynthesis enzymes. Serological analysis using three different polyclonal antisera developed against T. maritimum isolated from farmed Atlantic salmon (Salmo salar) in Tasmania, Australia revealed that there are three putative serotypes of T. maritimum that occur in New Zealand. The predominant serotype was defined by a positive reaction to all three Tasmanian antisera (antisera A, B and C), designated as serotype ABC. This serotype was found at all nine farm locations tested and represented 81% of all isolates examined. The same library of isolates was evaluated by mPCR serotyping and found three O-AGC types among tested isolates. O-AGC Type 3 was not only the predominant type (72%) present, but it also had a wide distribution, having been isolated at eight of the nine farms. Two other O-AGC types (O-AGC Type 2–1 and O-AGC Type 3–2) were identified, providing evidence of genetic variation. However, there was only partial concordance between the two serotyping techniques, which is likely linked to differences in the way serotypes are defined in the two approaches that were used. Nevertheless, in broad terms there is good evidence of intraspecific antigenic variation within our library of isolates, and collectively these data will be of crucial importance for assessing the pathogenicity of the isolates and the subsequent development of a vaccine for this emerging disease in New Zealand marine salmon farms. • Three putative serogroups of Tenacibaculum maritimum occur in New Zealand fish farms. • The predominant serotype occurred at all farm sites tested and represented 81% of all isolates examined. • There was partial concordance between two serotyping techniques. • Subsequent pathogenicity testing of the isolates will guide vaccine development. [ABSTRACT FROM AUTHOR]

Pilchard orthomyxovirus (POMV) is a virus of concern to the Atlantic salmon aquaculture industry in Tasmania. First isolated from wild pilchards in southern Australia in 1998, the virus is now a recognised pathogen of farmed Atlantic salmon (Salmo salar) in Tasmania. While the current real-time PCR for POMV targets segment 5 of the viral genome, recent viral gene expression data suggests that other segments of the POMV genome presented higher transcription levels and thus may be better candidates for the early detection of the virus. This study aimed to design and begin validating a more sensitive reverse transcriptase real-time PCR (RT-qPCR) assay to detect POMV. Primers and probes were developed targeting two independent viral genes derived from segments 7 and 8, which presented higher transcription levels than segment 5 in both cell culture and infected fish. These were compared with the current POMV RT-qPCR. The POMV segment 8 assay had a higher analytical sensitivity than segment 7, detecting at least 1 plasmid copy μl−1, and was 10-fold more sensitive than both POMV segment 7 and 5 assays when analysing nucleic acid from a positive field sample. Both new assays also had high analytical specificity, detecting the 11 POMV isolates tested (inclusivity testing) and not amplifying nucleic acids from other viruses, including ISAV, a related orthomyxovirus. In the latent class model analysis, the diagnostic sensitivity of the segment 8 and 7 assays were higher than segment 5 in 93% and 92% of simulations, respectively. Seven samples (18.4%), all from subclinical fish infected with POMV, returned a positive result only with the segment 8 assay. Both new assays showed reproducible results when applied to aliquots of the same samples tested in three different laboratories. The new POMV segment 8 assay shows promising results as a surveillance tool for detecting POMV in fish without any symptoms. • POMV is an emerging virus of farmed salmon affecting the largest aquaculture industry in Australia. • A new diagnostic tool for the early detection of POMV is presented and validated. • The newly developed assays are more sensitive than the currently available PCR method. [ABSTRACT FROM AUTHOR]