Haplosporidium sp. (Haplosporidia) in hatchery-reared pearl oysters, Pinctada maxima (Jameson, 1901), in north Western Australia

A species of Haplosporidium is described from 6 of 105 pearl oyster (Pinctada maxima) spat from a hatchery at Carnarvon in north Western Australia. Presporulation and sporulation stages occurred in the connective tissue surrounding the digestive gland and were common in mantle connective tissue, but only light to moderate infections were observed in the heart, gills, foot, and adductor muscle. No stages were observed in epithelia, and the gut and diverticulae remained intact. Ultrastructurally, sporoblasts were binucleate with the two nuclei either closely apposed to form a diplokaryon or separated, with the cytoplasm containing round to pyriform haplosporosomes. In spores the sporoplasm contained a basal, or sometimes equatorial, nucleus, dense ovoid vesicles that appeared to develop to ovoid haplosporosomes with an internal axehead-shaped membrane, and spherical haplosporosomes. Apparently senescent spores with a dense content were also present and they, and normal spores, were ornamented with filaments placing the parasite in the genus Haplosporidium. (C) 1998 Academic Press.