Haplosporidium hinei of Pearl Oysters
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Category
Category 3 (Host Not in Canada)
Common, generally accepted names of the organism or disease agent
Haplosporidium of pearl oysters
Scientific name or taxonomic affiliation
The Haplosporidium sp. detected in Pinctada maxima by Hine and Thorne (1998, 2000), Humphrey et al. (1999) and Jones and Creeper (2006) was named Haplosporidium hinei by Bearham et al. (2008). Although this parasite was correctly assigned to the phylum Haplosporidia, the taxonomy of haplosporidians needs a thorough revision (Hine et al. 2009).
Geographic distribution
Pearl oyster 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 effect of infection on the health and survival of P. maxima in not known but its presence is considered to be of concern (Hine and Thorn 1998). Also, Humphrey and Norton (2005) and Bearham et al. (2008) considered this parasite to represent a serious potential threat to the pearling industry in Australia.
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 (but not in the epithelia of the digestive tract) 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) (Hine and Thorne 1998, Bearham et al. 2008).
Electron Microscopy
Sporoblasts were binucleate and had round to pyriform haplosporosomes in the cytoplasm. Spores were pleomorphic or elongated and smaller in size (3.5–4 µm by 2.5–3.0 µm) compared to those measured in histological sections (Bearham et al. 2008). 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 (Hine and Thorne 1998). Spores had an operculum, a wall (160 nm thick) composed of three layers and were ornamented with filaments. Spore ornamentation was determined by scanning and transmission electron microscopy and consisted of two filaments that originated from two ‘knob-like' posterior thickenings and wound around the spore. Both filaments passed up one side of the spore together until just below the operculum whereupon each split and passed obliquely under the lip of the opercula lid. Each filament wrapped around the spore about four times. The posterior thickenings seem to appear late in the development of the spore and were composed of spore wall material. A second set of branching tubular filaments composed of a different material was observed on the spore body although not on mature spores possessing a ‘knob-like' posterior thickening. This ornamentation on H. hinei was considered to be unique amongst described haplosporidian species where spore ornamentation is known (Bearham et al. 2008). However, Hine et al. (2009) suggested that spore ornamentation alone is not a reliable taxonomic indicator.
Methods of control
No known methods of prevention or control. Oysters on infected farm sites in Western Australia were destroyed (Jones and Creeper 2006, Jones 2007a). In Western Australia, to reduce problems caused by disease, management of the translocation of pearl oysters is based on the concept of creating a closed population of known disease status that can then be tested with a high degree of confidence (test sample sizes of 300 oysters). The coastline was divided into zones for stock management purposes and the movement of oysters between zones is subject to their being tested for disease. Hatcheries are licensed and are subject to annual inspection and disease testing of production batches. Imports of live shell from out-of-State are generally prohibited (Jones 2007b).
References
Bearham, D., Z. Spiers, S. Raidal, J.B. Jones, E.M. Burreson and P.K. Nicholls. 2008. Spore ornamentation of Haplosporidium hinei n. sp. (Haplosporidia) in pearl oysters Pinctada maxima (Jameson, 1901). Parasitology 135: 521-527.
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.
Hine, P.M., R.B. Carnegie, E.M. Burreson and M.Y. Engelsma. 2009. Inter-relationships of haplosporidians deduced from ultrastructural studies. Diseases of Aquatic Organisms 83: 247-256.
Humphrey, J.D. and J.H. Norton. 2005. The pearl oyster Pinctada maxima (Jameson, 1901). An atlas of functional anatomy, pathology and histopathology. Northern Territory Department of Primary Industry, F.a.M., Queensland Department of, Primary Industries and Fisheries and Fisheries Research and Development Corporation. Northern Territory Government Printing Office, Darwin, Northern Territory, Australia. p. 110 pp.
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. 2007a. Review of pearl oyster mortalities and disease problems, In: Bondad-Reantaso, M.G., S.E. McGladdery, F.C.J. Berthe (eds.) Pearl oyster health management: a manual. FAO, Rome, pp. 61-70.
Jones, J.B. 2007b. The Australian experience: pearl oyster mortalities and disease problems. In: Bondad-Reantaso, M.G., S.E. McGladdery, F.C.J. Berthe (eds.) Pearl oyster health management: a manual. FAO, Rome, pp. 87-93.
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. (2014): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Haplosporidium hinei of Pearl Oysters.
Date last revised: April 2014
Comments to Susan Bower
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