title: Longitudinal study of winter mortality disease in Sydney rock oysters Saccostrea glomerata.
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.
authors: NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, New South Wales 2568, Australia.
authors: Zoe B
authors: ZB
authors: Spiers
authors: Melinda
authors: M
authors: Gabor
authors: Shayne A
authors: SA
authors: Fell
authors: Ryan B
authors: RB
authors: Carnegie
authors: Michael
authors: M
authors: Dove
authors: Wayne
authors: W
authors: O'Connor
authors: Jane
authors: J
authors: Frances
authors: Jeffrey
authors: J
authors: Go
authors: Ian B
authors: IB
authors: Marsh
authors: Cheryl
authors: C
authors: Jenkins
mesh_terms: D000818:Animals; D041602:Haplosporida / Q000502:physiology*; D006790:Host-Parasite Interactions; D008137:Longitudinal Studies; D009517:New South Wales; D010125:Ostreidae / Q000469:parasitology*; D012621:Seasons