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.

Haplosporidium sp. is described from rock oysters Saccostrea cuccullata Born, 1778 experiencing epizootics on the northwestern coast of Western Australia. All stages were observed as focal infections in the connective tissue of the gills, or as disseminated infections in the mantle and around digestive diverticulae. Haplosporidium sp. occurred between epithelial cells of the gut, in focal lesions in the gills, but not in the epithelium of the digestive diverticulae, and sporulation was confined to the connective tissue. Plasmodia developed into sporonts and sporocysts in a loose syncytium that gave rise to binucleate and uninucleate sporoblasts from which spores developed. Spores were flask-shaped, 5.6-6.7 x 3.3-4.0 microm, with a characteristic operculum, a few filamentous wrappings and rod-like structures in the posterior sporoplasm. Mature spores had a wall comprising inner (90 nm wide), middle (30 nm wide) and outer (130 nm wide) layers, and a surface coat of microtubules giving them a furry appearance. Oysters with empty gonad follicles were most heavily infected, and oyster condition and mortality appeared to be related to degree of infection.

No abstract

Pteriid oysters (Pinctada maxima, Pinctada margaritifera, Pinctada albina, Pteria penguin), rock oysters (Saccostrea glomerata, Saccostrea cuccullata, Saccostrea echinata) and representatives of other taxa (Malleidae, Isognomonidae, Pinnidae, Mytilidae, Spondylidae, Arcidae) from the wild, and 4670 hatchery-reared P. maxima, from northern and Western Australia, were examined for parasites and diseases. Rickettsiales-like inclusions and metacestodes of Tylocephalum occurred in most species. Intranuclear virus-like inclusions occurred in U415 wild P. maxima, W1254 S. cuccullata, 3/58 lsognomon isogr~omum, 1/80 Pinna bicolor and 1/45 Plnna deltodes. Perkinsus was histologically observed in W4670 P. maxima spat, 2/469 P. albina, 1/933 S. glomerata, 16/20 Malleus nieridianus, 12/58 I. isognomm, 1/45 P. deltodes, 5/12 Spondylussp., 1/16 Septifer bilocularisand 3/6 Barbatia helblingii. One of 1254 S. cuccullata was heavily systemically infected with Perkinsus merozoites, meronts and schizonts, and was patently diseased. Other potentially serious pathogens included Haplospondium sp. in 6/4670 P. maxima spat, Marteilia sydneyl from 1/933 S. glomerata, and Marteilia sp. (probably M. lengehi) (1/1254) and Haplospondium sp. (125/1254) from S. cuccullata. The latter were associated with epizootics on offshore islands, with heaviest prevalence (45%) in oysters with empty gonad follicles. Marteiboides sp. infected the oocytes of 9/10 female S. echinata from Darwin Harbour. Details of geographical distribution and pathology are given, and the health of the bivalves examined is discussed.

The myxosporean parasite Kudoa thyrsites (Gilehrist) is well reeognised as a eause of flesh liquefaction post-mortem in several fishes from both hemispheres. The observation of this condition in cultured mahi mahi, Corvphaena hippurus L., in Western Australia ied us to seareh for possible reservoirs of infection amongst the abundant clupeoid fishes of the area. Prevalent and severe infeetions were found in Sardinops sagax neopdchardus (Steindaehner), which we eonsider to be a major reservoir host for K. thyrsites in south-west Australian eoastal waters. The parasite oeeurred less frequently in Spratelloides robustus Ogilby. Sardinella lemitrit Bieeker and Engraidis australis (Shaw) from the same waters. Infection was not deteeted in Hyperlophus vittatus (Castelnau), Etrumeus teres (De Kay) or Neinatulosa vlaminghi (Munro). whieh may refleet differenees in range or dietary eomposition. Engraulis japonieus (Temminek & Sehlegel) imported from Japan were also infected, but a single sample of E. niordax Girard from California contained only an equipolar Kudoa speeies. These reeords expand the known host range of A', thyrsites to 20 speeies in 10 families, and several of these host speeies appear to be major reservoirs of infeetion in eertain loeations. Flesh spoilage due to the liquefaetive effects of the parasite eould oecur in any of these hosts, and was seen here in S. sagax neopilchardus. S. robustus and E. japonicus in assoeiation with mature spores. Detection of infeetion with ultra-violet light was found to be ineffeetivc because a eellular host response was not mounted by the elupeoids.