Haplosporidium sp. of Pearl Oysters


Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Haplosporidium sp.

Scientific name or taxonomic affiliation

Haplosporidium sp.

Geographic distribution

Hatcheries in north Western Australia.

Host species

Pinctada maxima.

Impact on the host

This parasite was first detected in 6 of 105 P. maxima spat (5 to 10 mm in shell height) that were being examined histologically for disease clearance prior to being sold. Despite the crowded infection observed in the connective tissue of the digestive gland, the gut and digestive diverticulae appeared to retain their structure. This parasite has been detected on two other occasions and each time the oysters on the infected farm site were destroyed (Jones and Creeper 2006). On one occasion in late December 1995, 4.6% of 150 pearl oysters were found infected. By the time the oysters were destroyed 15 days later, the prevalence had increased to 10% (n = 238) (Jones and Creeper 2006). To date, the affect of infection on the health and survival of P. maxima in not known but its presence is considered to be of concern (Hine & Thorn 1998).

Diagnostic techniques

Histology: Presporulation and sporulation stages (sporoblasts were ovoid, 3.8-5.3 µm by 3.3-4.6 µm) occur mainly in the connective tissue of the digestive gland and mantle and with fewer numbers in the heart, gills, foot and adductor muscle. Spores were pleomorphic but usually ovoid (6.7-7.7 µm by 3.8-4.3 µm).

Electron Microscopy: Sporoblasts were binucleate and had round to pyriform haplosporosomes in the cytoplasm. Spores had an operculum, a wall (160 nm thick) composed of three layers and were ornamented with filaments. The sporoplasm of spores contained a nucleus, dense ovoid vesicles that appeared to be developing into ovoid haplosporosomes with an internal axehead-shaped membrane, and spherical haplosporosomes (230 nm in diameter). Apparent senescent spores, with a dense content, were also observed.

Methods of control

No known methods of prevention or control.


Hine, P.M. and T. Thorne. 1998. Haplosporidium sp. (Haplosporidia) in hatchery-reared pearl oysters, Pinctada maxima (Jameson, 1901), in north Western Australia. Journal of Invertebrate Pathology 71: 48-52.

Hine, P.M. and T. Thorne. 2000. A survey of some parasites and diseases of several species of bivalve mollusc in northern Western Australia. Diseases of Aquatic Organisms 40: 67-78.

Humphrey, J., M. Connell, J. Norton, B. Jones, M. Barton, C. Shelley and J. Creeper. 1999. Pathogens, parasites and diseases of pearl oysters Pinctada maxima in northern Australian waters. In: C.L. Browdy and R. Fletcher (co-program chairs). Book of Abstracts. The Annual International Conference and Exposition of the World Aquaculture Society, 26 April-2 May, 1999, Sydney, Australia. p. 345. (Abstract).

Jones, J.B. and J. Creeper. 2006. Diseases of pearl oysters and other molluscs: a Western Australian perspective. Journal of Shellfish Research 25: 233-238.

Citation Information

Bower, S.M. (2007): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Haplosporidium sp. of Pearl Oysters.

Date last revised: June 2007
Comments to Susan Bower

Date modified: