A large-scale eplzootic occurred In the Austialas~an pllchard S a r d~n o p s sagax neop~l c h a r d u s between March and September 1995 ovei more than 5000 km of the Australian coastline and 500 km of the New Zealand coastline Affected fish died wlthln a tew mlnutes of cl~nical slgns of respiratory distress and death was associated wlth hypoxaemla a n d hypercapnea Significant leslons were confined to the gllls and comprised acute to subacute inflammation followed by blzal re epithelia1 hypertrophy and hyperplasia The lesions were initially focal but progressed to become generalised over about 4 d Pathological changes in atfeded fish from xvestern Australia eastern Australia a n d New Zealand were simila~, suggesting a common aetiology The lesions were unllke those associated w~t h ichthyotoxic algae, s~l~c e o u s algae, phys~cochemical factors fungi, bacterla dinoflagellates, amoebde, other protozoa and inetazoa A herpesvlrus was consistently present In gills of affected flsh and absent from unaffected pilchards and IS proposed as the aetiological agent T h e late of spread of the mortal~ty front (approulmately 30 km d ' ) In relation to the migration late of pilchaids a n d plevaillng currents suggests that a vector was involved The dlsease may have been newly introduced lnto Australian wateis KEY WORDS Clupeoldel . Pllchard . Sardinops sagax neopilchardus . Gill dlseases . Pathology .

Eosinophilic intranuclear inclusions are reported from agranular haemocytes and eosinophilic granulocytes of Ostrea angasi (Sowerby, 1871). Ultrastructurally, ovoid to hexagonal capsids 98 ? 4 nm (range 90 to 105 nm; n = 60) in diameter formed around a n ovoid, fine granular inclusion at the periphery of the nucleus Strands and rod-like configurations of dark material near the centre of the nucleus developed into a coarse granular matrix along the edge of which capsids acquired a fibrillar, vermiform or rod-like core. Many capsids appeared to degenerate along the nuclear periphery Those passing into the cytoplasm acquired an envelope in the perinuclear space, and cytoplasmic nucleocapsids acquired an envelope when passing into endoplasm~c reticulum or cytoplasmic vesicles. The few virions observed had tails and were 135 to 140 nm across. Nuclear stages of replication are more similar to cytomegaloviruses (Betaherpesvirinae) than to herpes simplex viruses (Alphaherpesvirinae). Incomplete replication and the low level of virion production are attributed to sampling in late summer and winter when temperatures are sub-optimal.

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The genus Bonamia (Haplosporidia) includes economically significant oyster parasites. Described species were thought to have fairly circumscribed host and geographic ranges: B. ostreae infecting Ostrea edulis in Europe and North America, B. exitiosa infecting O. chilensis in New Zealand, and B. roughleyi infecting Saccostrea glomerata in Australia. The discovery of B. exitiosa-like parasites in new locations and the observation of a novel species, B. perspora, in noncommercial O. stentina altered this perception and prompted our wider evaluation of the global diversity of Bonamia parasites. Samples of 13 oyster species from 21 locations were screened for Bonamia spp. by PCR, and small subunit and internal transcribed spacer regions of Bonamia sp. ribosomal DNA were sequenced from PCR-positive individuals. Infections were confirmed histologically. Phylogenetic analyses using parsimony and Bayesian methods revealed one species, B. exitiosa, to be widely distributed, infecting 7 oyster species from Australia, New Zealand, Argentina, eastern and western USA, and Tunisia. More limited host and geographic distributions of B. ostreae and B. perspora were confirmed, but nothing genetically identifiable as B. roughleyi was found in Australia or elsewhere. Newly discovered diversity included a Bonamia sp.

Apparent replication of small DNA-negative vlrus-like particles (VLPs) is described from digestive and secretory (= basiphil) cells of scallops Pecten novaezelandiae, Reeve, 1853 and tohcroa Paphies ventricosunl (Gray, 1843) sampled during mass rnortalities, and compared w~t h apparently healthy individuals. In scallop digestive cells with putative VLPs, endocytotic and smooth membrane vesicles increased, endoplasmic reticulum (ER) proliferated, and VLPs 22 to 30 nrn across were seen in an orderly array on the surfaces of the outer nuclear membrane and along ER. Proliferating ER membranes, lined with VLPs and enclosing a dense matnx, were arranged in a reticulated configuratlon. The ER cisternae dilated to form vacuolar inclusions (VI) containing elongated bodles, spherical in section, in a flocculent matrix which were ornated with VLPs arrays on the external membrane. Enclosed bodies also formed by budding of cytoplasm into the VI. In scallop secretory cells VLPs replaced ribosomes on ER, and ER cisternae dilated, but V1 seldom formed Toheroa diverticular epithelium showed similar changes, but secretory cells differed in that the outel-membrane of the nucleus and Golgi cisternae, rather than ER, proliferated. In addit~on, complete V1 were apparently not formed. The cytological changes observed in both bivalves are similar to those associated with enteroviruses (Picornaviridae) and caliciviruses. The possible role of VLPs In bivalve pathology is discussed.