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A field survey of hematopoietic neoplasia (Hn) in the soft shell clam Mya arenaria (L.) was undertaken using an immunoperoxidase diagnostic technique.

Shellfish production is often affected by bacterial pathogens that cause high losses in hatcheries and nurseries. We evaluated the relative survival of larvae and juveniles of 3 Crassostrea virginica oyster lines: (1) GHP, a Rhode Island line; (2) NEHY, a line resistant to dermo and multinucleated sphere X diseases; and (3) FLOWERS, a line resistant to Roseovarius oyster disease, experimental challenge with Vibrio spp. isolates RE22 and RE101, causative agents of bacillary necrosis in Pacific oyster larvae, and the type strain of Roseovarius crassostreae, causative agent of Roseovarius oyster disease. All of the isolates were able to induce significant mortalities in oyster larvae and juveniles. Susceptibility to bacterial challenge in larvae was significantly higher at 25°C than at 20°C. Susceptibility decreased with oyster age; mean survival time ranged from 24 h in oyster larvae to more than 6 wk in juveniles. Significant differences in susceptibility to bacterial challenge were observed between oyster lines; NEHY was the most resistant line overall. Extracellular products (ECPs) from Vibrio sp. RE22 and R. crassostreae, as well as viable bacteria, were toxic to hemocytes from the 3 oyster lines, suggesting that ECPs are involved in pathogenesis and that external and mucosal barriers to infection are major contributors to resistance to bacterial challenge. These protocols will be useful in the elucidation of mechanisms of bacterial pathogenesis and resistance to infection in oysters.

Quahog Parasite Unknown (QPX) is the cause of mass mortality events of hard clams Mercenaria mercenaria from Virginia, USA, to New Brunswick, Canada. Aquaculture areas in Massachusetts, USA, have been particularly hard hit. The parasite has been shown to be a directly infective organism, but it is unclear whether it could exist or persist outside of its clam host. We used molecular methods to examine water, sediment, seaweeds, seagrass and various invertebrates for the presence of QPX. Sites in Virginia and Massachusetts were selected based upon the incidence of QPX-induced clam die-offs, and they were monitored seasonally. QPX was detectable in almost all of our different sample types from Massachusetts, indicating that the parasite was widely distributed in the environment. Significantly more samples from Massachusetts were positive than from Virginia, and there was a seasonal pattern to the types of samples positive from Massachusetts. The data suggest that, although it may be difficult to completely eradicate QPX from the environment, it may be possible to keep the incidence of disease under control through good plot husbandry and the removal of infected and dying clams. KEY WORDS: Quahog Parasite Unknown · QPX · Environmental detection · Remediation Resale or republication not permitted without written consent of the publisherDis Aquat Org 81: [219][220][221][222][223][224][225][226][227][228][229] 2008 stages of growth prior to market distribution (Smolowitz et al. 1998). QPX epizootics have decimated clam-growing areas, resulting in cessation of local aquaculture development in some regions. In other locales, following detection of QPX disease in selected clam beds, shellfish growers voluntarily destroyed potentially infected seed clams, worth hundreds of thousands of dollars in marketable clams, in an attempt to minimize the impact of the disease.Recent studies of the parasite have reported on the development of molecular methods to detect its presence (Ragone Calvo et al. 2001, Stokes et al. 2002, Lyons et al. 2005a, Gast et al. 2006, the mechanisms of transmission (Smolowitz et al. 2001, Ford et al. 2002, Dahl & Allam 2007, the general lack of genetic variation between isolates (Qian et al. 2007) and the potential for macroalgae to support growth of the parasite (Lyons et al. 2005b, Bugge & Allam 2007. Currently, there are also studies in progress to elucidate aspects of the parasite physiology, pathogenicity and disease development in clams. The identification of the QPX parasite in environmental reservoirs may provide a better understanding of the associated disease and allow development of more appropriate clam aquaculture management techniques. There has been no reasonable way to identify the parasite in water or sediment samples, and therefore it was not known if QPX persisted in the environment outside of clams or whether it was also found in other organisms. Molecular detection tools are appropriate for searching for QPX in various environments and other species, since these tools a...

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