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Diseases of Aquatic Organisms

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DAO 110:151-164 (2014)  -  DOI:

Contribution to the DAO Special: 'Microcell parasites of molluscs'

Longitudinal study of winter mortality disease in Sydney rock oysters Saccostrea glomerata

Zoe B. Spiers1, Melinda Gabor1, Shayne A. Fell1, Ryan B. Carnegie2, Michael Dove3, Wayne O’Connor3, Jane Frances3, Jeffrey Go1, Ian B. Marsh1, Cheryl Jenkins1,*

1NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, New South Wales 2568, Australia
2Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23062–1346, USA
3NSW Department of Primary Industries, Port Stephens Fisheries Institute, Port Stephens, New South Wales 2315, Australia
*Corresponding author:

ABSTRACT: Winter mortality (WM) is a poorly studied disease affecting Sydney rock oysters Saccostrea glomerata in estuaries in New South Wales, Australia, where it can cause significant losses. WM is more severe in oysters cultured deeper in the water column and appears linked to higher salinities. Current dogma is that WM is caused by the microcell parasite Bonamia roughleyi, but evidence linking clinical signs and histopathology to molecular data identifying bonamiasis is lacking. We conducted a longitudinal study between February and November 2010 in 2 estuaries where WM has occurred (Georges and Shoalhaven Rivers). Results from molecular testing of experimental oysters for Bonamia spp. were compared to clinical disease signs and histopathology. Available environmental data from the study sites were also collated and compared. Oyster condition declined over the study period, coinciding with decreasing water temperatures, and was inversely correlated with the presence of histological lesions. While mortalities occurred in both estuaries, only oysters from the Georges River study site showed gross clinical signs and histological changes characteristic of WM (lesions were prevalent and intralesional microcell-like structures were sometimes noted). PCR testing for Bonamia spp. revealed the presence of an organism belonging to the B. exitiosa-B. roughleyi clade in some samples; however, the very low prevalence of this organism relative to histological changes and the lack of reactivity of affected oysters in subsequent in situ hybridisation experiments led us to conclude that this Bonamia sp. is not responsible for WM. Another aetiological agent and a confluence of environmental factors are a more likely explanation for the disease.

KEY WORDS: Bonamia roughleyi · Microcell-like structure · Lesion · Haemocyte

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Cite this article as: Spiers ZB, Gabor M, Fell SA, Carnegie RB and others (2014) Longitudinal study of winter mortality disease in Sydney rock oysters Saccostrea glomerata. Dis Aquat Org 110:151-164.

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