Macroscopic and microscopic features of natural and experimental Flexibacter maritimus infection, and epidemiological aspects of the disease, have been reported in a number of species of fish in Tasmanian aquaculture including Atlantic salmon, Salmo salar L., rainbow trout, Oncorhynchus mykiss (Walbaum), greenback flounder, Rhombosolea tapirina Günther, and striped trumpeter, Latris lineata (Bloch & Schneider). There is a great deal of consistency in the pathology in salmonids and non‐salmonid species, with erosive lesions of external surfaces being the most prominent clinical sign. Experimentally induced disease of salmonids and flounder is similar to natural infection. Mature lesions show dermal and gill erosion, with dermal bacterial invasion into the dense connective tissue and occasionally underlying musculature, but a remarkable lack of inflammatory response. The earliest lesions show consistent fragmentation and degeneration of the epithelium, with infiltration of amorphous protein‐like materials and occasionally intra‐epithelial cellular inflammatory cells, plus congestion and haemorrhage of the superficial dermis, but without visible bacteria in standard sections. Variable scale loss, oedema and a low level of inflammation in scale pockets, plus variable small adherent bacterial mats, are evident before full epithelial erosion.

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A recent outbreak of mortality in Australian abalone was associated with neurotropic lesions, which have not previously been described in this country. The on farm and between farm pattern of spread of the outbreak, a history of abalone movements linking farms, clinical observation of moribund and dead abalone were all highly suggestive of a virulent infectious agent.

The recent emergence of a herpes-like virus in both farmed and wild populations of abalone in Victoria, Australia, has been associated with high mortality rates in animals of all ages. Based on viral genome sequence information, a virus-specific real-time TaqMan assay was developed for detection and identification of the abalone herpes-like virus (AbHV). The assay was shown to be specific as it did not detect other viruses from either the Herpesvirales or the Iridovirales orders which have genome sequence similarities. However, the TaqMan assay was able to detect DNA from the Taiwanese abalone herpes-like virus, suggesting a relationship between the Taiwanese and Australian viruses. In addition, the assay detected < 300 copies of recombinant plasmid DNA per reaction. Performance characteristics for the AbHV TaqMan assay were established using 1673 samples from different abalone populations in Victoria and Tasmania. The highest diagnostic sensitivity and specificity were 96.7 (95% CI: 82.7 to 99.4) and 99.7 (95% CI: 99.3 to 99.9), respectively, at a threshold cycle (C T ) value of 35.8. The results from 2 separate laboratories indicated good repeatability and reproducibility. This molecular assay has already proven useful in confirming presumptive diagnosis (based on the presence of ganglioneuritis) of diseased abalone in Victorian waters as well as being a tool for surveillance of wild abalone stocks in other parts of Australia.

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