Larvae of hatchery-reared Pacific oysters Crassostrea gigas Thunberg ceased feedlng 3 to 4 d after spawning, and 60 to l00 O/ O mortalities occurred after 7 to l l d. Up to 25 '!?o of moribund larvae had putative phagocyte precursors and fibroblasts with enlarged nuclei of abnormal shape and chromatin pattern, which contained ovoid to hexagonal, non-enveloped, 97 + 4 nm diameter capsids and nucleocapsids of a herpes-like virus. Nucleocapsids became enveloped and de-enveloped as they passed through the nuclear membranes. Some became enveloped in intranuclear sacs containing tubular elements Naked cytoplasmic nucleocapsids became enveloped by budding into vesicles or Golgi cisternae, and probably acquired a tegument from large dense granular masses near Golgi complexes. Extracellular enveloped virions usually had a tegument, and were 131 + 9 nm In diameter Extracellular naked nucleocapsids were thought to denve from lysed cells. Non-enveloped ovoid to hexagonal 86 t 12 nm virions, thought to be degraded herpesvirions, were abundant in inter-digitating processes of putative phagocytes in > 5 0 % of moribund larvae. Comparison w~t h groups within the Herpesviridae was made, and similarities to cytomegaloviruses noted. Elevated temperature and crowding may increase susceptibility of oyster larvae to herpes-like virus infection.

Three species of epiphytic dinoflagellates-Ostreopsis siamensis, O. lenticularis, and O. ovata have recently been found on both the east and west coasts of the upper North Island, New Zealand. The morphological differences of all three Received 29 August 1998; accepted 27 September 1999 Ostreopsis spp. have been studied with both light and scanning electron microscopes. Detailed studies of the inner face of the thecal wall of Ostreopsis siamensis revealed two types of trichocyst pores: small, simple pores and large multipore structures. The multipore structures apparently have not been previously reported. Surveys conducted during the period from November 1995 to April 1997 showed that all three Ostreopsis spp. were fairly widespread in northern New Zealand, and all three species were found to occur south of 35°S latitude. Cell concentrations of Ostreopsis spp. in summer were substantially higher than in early spring. There was also a clear regional difference in distribution; cell concentrations of the dominant species, O. siamensis, were greatest in Rarawa and Tokerau on the north-east coast. Other less abundant epiphytic species recorded during the same period included Prorocentrum lima, P. compressum, and Coolia monotis. These species were generally more sporadic in distribution than Ostreopsis spp. M98061

Aims:  To investigate the comparative elimination of three different human enterically transmitted viruses [i.e. hepatitis A virus (HAV), norovirus (NoV) and poliovirus (PV)] and inactivation of HAV and PV by Pacific oysters. Methods and Results:  New Zealand grown Pacific oysters (Crassostrea gigas) were allowed to bioaccumulate HAV, NoV and PV. Samples of oyster gut, faeces and pseudofaeces were then analysed by using real‐time RT‐PCR to determine the amount of viral RNA and cell culture methods to identify changes in the number of plaque forming units. The results suggest that the majority of the PV present in the oyster gut and oyster faeces is noninfectious, while in contrast, most of the HAV detected in the oyster gut are infectious. Depuration experiments identified a large drop in the count of PV in the gut over a 23‐h cleansing period, whereas the levels of HAV and NoV did not significantly decrease. Conclusions:  Human enterically transmitted viruses are eliminated and inactivated at different rates by Pacific oysters. Significance and Impact of Study:  The research presented in this article has implications for risk management techniques that are used to improve the removal of infectious human enteric viruses from bivalve molluscs.

Aims:  To examine the uptake and tissue distribution of norovirus (NoV) and poliovirus (PV) experimentally bioaccumulated in feeding Pacific oysters (Crassostrea gigas). Methods and Results:  Pacific oysters were allowed to bioaccumulated either PV or NoV under tidally synchronized feeding conditions in laboratory tanks. Oysters were then either fixed and paraffin wax embedded prior to localizing virus within tissues by immunohistochemistry (IHC), or they were dissected into digestive tract (stomach, intestine and digestive diverticula), gill and labial palp tissues, and the viral load determined by quantitative RT‐PCR. Both PV and NoV immunoreactivities were predominantly found in the lumen and within cells of the digestive tract tissues; however, PV was also found within cells of nondigestive tract tissues, and in the gills and labial palp. Quantitative RT‐PCR of tissue extracts corroborate the immunohistochemical data in that the major site for virus localization is the gut, but significant amounts of viral RNA were identified in the gills and labial palp. Conclusions:  The human enteric viruses, PV and NoV, are readily bioaccumulated by feeding Pacific oysters and that some of the virus is internalized within cells of both digestive and nondigestive tissues. Significance and Impact of the Study:  Oysters that have been virally contaminated even after depuration (cleaning) in uncontaminated seawater could pose a human health risk if consumed.

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