Randolph H. Richards

The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod which feeds on the mucus, skin and blood of salmonid fish species. The parasite can persist on the surface of the fish without any effective control being exerted by the host immune system. Other ectoparasitic invertebrates produce compounds in their saliva, excretions and/or secretions which modulate the host immune responses allowing them to remain on or in the host during development. Similarly, compounds are produced in secretions of L. salmonis which are thought to be responsible for immunomodulation of the host responses as well as other aspects of crucial host-parasite interactions. In this study we have identified and characterised the proteins in the excretory/secretory (E/S) products of L. salmonis using LC-ESI-MS/MS. In total 187 individual proteins were identified in the E/S collected from adult lice and pre-adult sea lice. Fifty-three proteins, including 13 serine-type endopeptidases, 1 peroxidase and 5 vitellogenin-like proteins were common to both adult and pre-adult E/S products. One hundred and seven proteins were identified in the adult E/S but not in the pre-adult E/S and these included serine and cysteine-type endopeptidases, vitellogenins, sphingomyelinase and calreticulin. A total of 27 proteins were identified in pre-adult E/S products but not in adult E/S. The assigned functions of these E/S products and the potential roles they play in host-parasite interaction is discussed.

Salmonid alphavirus (SAV) is an enveloped, single-stranded, positive sense RNA virus belonging to the family Togaviridae. It causes economically devastating disease in cultured salmonids. The characteristic features of SAV infection include severe histopathological changes in the heart, pancreas and skeletal muscles of diseased fish. Although the presence of virus has been reported in a wider range of tissues, the mechanisms responsible for viral tissue tropism and for lesion development during the disease are not clearly described or understood. Previously, we have described membrane-dependent morphogenesis of SAV and associated apoptosis-mediated cell death in vitro. The aims of the present study were to explore ultrastructural changes associated with SAV infection in vivo. Cytolytic changes were observed in heart, but not in gill and head-kidney of virus-infected fish, although they still exhibited signs of SAV morphogenesis. Ultrastructural changes associated with virus replication were also noted in leukocytes in the head kidney of virus-infected fish. These results further describe the presence of degenerative lesions in the heart as expected, but not in the gills and in the kidney.

Marine cultured meagre, Argyrosomus regius Asso, in central and western Greece were affected by an outbreak of systemic granulomatous disease subsequently demonstrated to be nocardiosis. The fish were originally imported as juveniles from hatcheries in France and Italy and on‐grown in Greece, the latter also providing broodstock for a small number of local Greek hatcheries for the production of second‐generation juveniles. The disease in cage reared fish had been present throughout the year, particularly in the 1+ and 2+ year old fish with a low to variable morbidity and 1–4% total mortality. Multiple lesions were visible externally on the skin of affected fish, with severe ulcerations and necrosis. Internally, multifocal yellowish‐white nodules, 0.1–0.5 cm in diameter, were visible on the surface of several internal organs. Histopathology revealed systemic granulomatous inflammation. Fite‐Faraco staining clearly demonstrated the presence of Nocardia‐like organisms which were Gram‐positive, long, rod to beaded filamentous bacteria. Nocardia genus‐specific 16s RNA primers NG1 and NG2 were used to generate a 600 bp fragment recovered from affected tissue, confirming the diagnosis of Nocardia spp. To our knowledge, this is the first report of nocardiosis in meagre.