Epizootic mortality in the pilchard Sardinops sagax neopilchardus in Australia and New Zealand in 1995. I. Pathology and epizootiology

A large-scale epizootic occurred in the Australasian pilchard Sardinops sagax neopilchardus between March and September 1995 over more than 5000 km of the Australian coastline and 500 km of the New Zealand coastline. Affected fish died within a few minutes of clinical signs of respiratory distress and death was associated with hypoxaemia and hypercapnea. Significant lesions were confined to the gills and comprised acute to subacute inflammation followed by bizarre epithelial hypertrophy and hyperplasia. The lesions were initially focal but progressed to become generalised over about 4 d. Pathological changes in affected fish from western Australia, eastern Australia and New Zealand were similar, suggesting a common aetiology The lesions were unlike those associated with ichthyotoxic algae, siliceous algae, physicochemical factors, fungi, bacteria, dinoflagellates, amoebae, other protozoa and metazoa. A herpesvirus was consistently present in gills of affected fish and absent from unaffected pilchards and is proposed as the aetiological agent The rate of spread of the mortality front (approximately 30 km d -1) in relation to the migration rate of pilchards and prevailing currents suggests that a vector was involved. The disease may have been newly introduced into Australian waters

Epizootic mortality in the pilchard Sardinops sagax neopilchardus in Australia and New Zealand in 1995. II. Identification of a herpesvirus within the gill epithelium

Mass mortalities, among pilchards Sardinops sagax neopilchardus occurred around Australia and New Zealand from March to September 1995 The mortalities spread rapidly both with and against currents and usually affected fish longer than 11 cm. Examination showed mortalities to be associated with the presence of replicating herpesvirus in the gill epithelium; herpesviruses were not observed within equivalent cells of unaffected fish collected ahead of the mortality front By negative contrast ele ctron microscopy the virus was demonstrated to possess a 96 nm icosahedral capsid containing 162 capsomers. Many virions were enveloped and possessed surface projections. The nuclei of infected epithelial cells contained nuclcoids, capsids and nucleocapsids which were released from the nucleus into the surrounding cytoplasm following degeneration of the nuclear membrane. Within the cytoplasm, the capsids and nucleocapsids acquired a tegument and subsequently were enveloped by passing into smooth-surfaced vesicles or by budding from the plasma membrane. Release of viruses from the cells was in the main, associated with lysis of infected gill epithelial cells. The morphology of the virus and ultrastructure of infected cells suggest that this virus belongs to the family Herpesviridae. The presence of a replicating herpesvirus within the gill epithelium is discussed in context with the epizootic

Australasian pilchard mortalities

A large-scale epizootic occurred in the Australasian pilchard Sardinops sagax between March and September 1995. The deaths occurred along 5000km of the Australian coastline and 500km of the New Zealand coastline. Affected fish died within a few minutes of clinical signs of respiratory distress and death was associated with hypoxaemia and hypercapnia. Significant lesions were confined to the gills and comprised acute to subacute inflammation followed by epithelial hypertrophy and hyperplasia. The lesions were initially focal but progressed to become generalized over about 4days. Only a herpesvirus was consistently present in gills of affected fish and absent from unaffected pilchards. There was no correlation with oceanographic conditions or the presence of plankton. The rate of spread of the mortality front (approximately 30km/day) in relation to the migration rate of pilchards and prevailing currents suggested that a vector might be involved. The disease may be the result of a virus introduced into Australian waters, or of a newly emerged virus

Mapping Bathymetry and Depositional Facies on Great Bahama Bank

Satellite imagery and an extensive set of water-depth measurements have been used to map and critically evaluate the magnitude and patterns of bathymetry across Great Bahama Bank. Descriptions of previously collected sediment samples were combined with satellite imagery to map and refine the interpreted distribution of surficial carbonate sediments (depositional facies). Data reveal that 60% of Great Bahama Bank lies in 5 m or less of water. The deep portion occurs mainly in a generally east–west trending area in the southern portion of the platform. The re-evaluation of the facies reveals that Great Bahama Bank is essentially a very grainy platform with muddier accumulations primarily in the lee of Andros Island. This area of Great Bahama Bank also experiences currents related to an excursion of the Florida Current onto the platform top; possibly enhancing sediment mud production through the generation of whitings. Sediment equivalents to mudstones, wackestones and mud-rich packstones cover 8%, 5% and 14%, respectively, of the platform top, whereas sediment equivalents to mud-poor packstones, grainstones and rudstones account for 20%, 45% and 3% of the surface area. Boundstones (reefs) were not specifically mapped in this study due to the resolution of the mapping. There is a poor relationship between the occurrence of the depositional texture and water depth, in that the grainier sediment types are abundant across the full range of water depths. The most abrupt lateral facies changes portrayed on the facies maps are observed leeward of islands, areas which also hold the highest diversity in facies type. The majority of the islands on the platform align with the north-west/south-east strike of the platform margin and these islands, in turn, exert control on the shape and orientation of facies belts that develop in proximity to them. For this reason, regions of the platform that contain principal islands host facies belts that align with the principal axis of the platform, whereas for regions lacking islands, the facies belts adopt an east–west trend consistent with prevailing winds and currents. There is a clear trend that the wide southern portion of the platform hosts the most continuous expanses of grain-rich sediments