THE PATHOLOGY OF FLEXIBACTER-MARITIMUS IN AQUACULTURE SPECIES IN TASMANIA, AUSTRALIA

Macroscopic and microscopic features of natural and experimental Flexi bacter maritimus infection, and epidemiological aspects of the disease , have been reported in a number of species of fish in Tasmanian aquac ulture including Atlantic salmon, Salmo salar L., rainbow trout, Oncor hynchus mykiss (Walbaum), greenback flounder, Rhombosolea tapirina Gun ther, 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 salmon ids 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 rema rkable lack of inflammatory response. The earliest lesions show consis tent fragmentation and degeneration of the epithelium, with infiltrati on of amorphous protein-like materials and occasionally intra-epitheli al 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 bef ore full epithelial erosion.