a1 Fish Health Unit, Murdoch University, School of Veterinary and Biomedical Sciences, Murdoch Drive, Murdoch, Western Australia 6150
a2 Charles Sturt University, School of Agriculture and Veterinary Science, Boorooma St, Wagga Wagga, NSW Australia
a3 Fish Health Unit, Department of Fisheries, Animal Health Labs, 3 Baron-Hay Court, South Perth, Western Australia 6151
A Minchinia sp. (Haplosporidia: Haplosporidiidae) parasite was identified infecting rock oysters and morphologically described by Hine and Thorne (2002) using light microscopy and transmission electron microscopy (TEM). The parasite was associated with up to 80% mortality in the host species and it is suspected that the parasite would be a major impediment to the development of a tropical rock oyster aquaculture industry in northern Western Australia. However, attempts to identify the parasite following the development of a specific probe for Haplosporidium nelsoni were unsuccessful. The SSU region of the parasite's rRNA gene was later characterized in our laboratory and an in situ hybridization assay for the parasite was developed. This study names the parasite as Minchinia occulta n sp. and morphologically describes the parasite using histology, scanning electron microscopy and transmission electron microscopy. The non-spore stages were unusual in that they consisted primarily of uninucleate stages reminiscent of Bonamia spp. The parasite's spores were ovoid to circular shaped and measured 4·5 μm–5·0 μm×3·5–4·1 μm in size. The nucleus of the sporoplasm measured 1·5–2·3 μm and was centrally located. The spores were covered in a branching network of microtubule-like structures that may degrade as the spore matures.
(Received April 06 2008)
(Revised July 08 2008)
(Accepted July 10 2008)
(Online publication August 28 2008)