Timothy J. Bowden

Susceptibility of Atlantic halibut, Hippoglossus hippoglossus (L.) to infection with typical and atypical Aeromonas salmonicida

Abstract Halibut, Hippoglossus hippoglossus (L.) and Atlantic salmon, Salmo salar (L.) were challenged with virulent typical or atypical strains of Aeromonas salmonicida by both injection and bath models. The groups were injected intraperitoneally with 100 μl of logarithmically decreasing dilutions of A. salmonicida (range 108–103 cells/fish) or bathed in 105 CFUs/ml of A. salmonicida for 24 h. Halibut were significantly more resistant to infection, compared to Atlantic salmon, with 106 and 107 typical and atypical A. salmonicida cells/halibut being the minimum lethal dose. No halibut died in the bath challenge although approximately 80% of salmon died by this challenge method. All animals that died during the challenge were positive for A. salmonicida on culture A. salmonicida was cultured from internal organs of approximately 60% of surviving Atlantic salmon while only 2.3% of the surviving halibut were culture positive, but only from the intestinal lumen. All surviving salmon but none of the surviving halibut, showed histological evidence of infection with A. salmonicida. Stress tests of both halibut and Atlantic salmon showed that recovered salmon still had a high carrier rate of A. salmonicida while none of the surviving halibut were carrier test positive. A significant rise in agglutinating antibody titre was observed in surviving Atlantic salmon. However, no rise in antibody titre was observed in the surviving halibut, suggesting that the processing of the bacteria during an acute infection may be fundamentally different between these two species.

Natural environmental impacts on teleost immune function

The environment in which teleosts exist can experience considerable change. Short-term changes can occur in relation to tidal movements or adverse weather events. Long-term changes can be caused by anthropogenic impacts such as climate change, which can result in changes to temperature, acidity, salinity and oxygen capacity of aquatic environments. These changes can have important impacts on the physiology of an animal, including its immune system. This can have consequences on the well-being of the animal and its ability to protect against pathogens. This review will look at recent investigations of these types of environmental change on the immune response in teleosts.

Fat cell necrosis syndrome in Atlantic halibut, Hippoglossus hippoglossus L.

Abstract A progressive degenerative condition of the dorsal sub-dermal fat deposits of farmed Atlantic halibut is reported, nominally termed fat cell necrosis syndrome (FCNS). The disease does not appear to have an infectious or malignant aetiology, but may be related to an imbalance between dietary oxidants and antioxidants combined with an exposure to sunlight. The gross lesions and histopathology are described.

Survey of Potential Reservoir Species for the Oyster Parasite Multinucleate Sphere X (Haplosporidium nelsoni) in and Around Oyster Farms in the Damariscotta River Estuary, Maine

ABSTRACT In the summer of 2010, the Damariscotta River Estuary, ME, experienced the first large multinucleate sphere X disease (Haplosporidium nelsoni) outbreak in commercial stocks of the eastern oyster (Crassostrea virginica). In 2012, biofouling organisms were sampled in and around the commercial oyster operations with the intent of looking for the presence of the parasite to see which, if any, biofouling species may be acting as a reservoir host and harboring the parasite. Organisms collected included tunicates, gastropods, polychaetes, and arthropods, as well as plankton samples from the surrounding water column. A quantitative polymerase chain reaction assay for H. nelsoni using a TaqMan minor groove binder probe, which was originally developed for detection of the parasiteDNAin oysters, was applied to biofouling species. The protozoan parasite H. nelsoniDNA was present in up to 70% of tunicate samples and about 30% of plankton samples. The highest parasite DNA copies (averaging 4 × 104 copies) were detected in tunicates identified as Styela sp., which have been recognized as invasive species in many coastal areas. This study provides evidence for the presence of potential reservoir species that occur close to commercial oyster operations. Reduction or removal of these species may reduce the infectious pressure of this parasite on commercial operations.

The impact of ocean acidification on the byssal threads of the blue mussel (Mytilus edulis)

Blue mussel (Mytilus edulis) produce byssal threads to anchor themselves to the substrate. These threads are always exposed to the surrounding environmental conditions. Understanding how environmental pH affects these threads is crucial in understanding how climate change can affect mussels. This work examines three factors (load at failure, thread extensibility, and total thread counts) that indicate the performance of byssal threads as well as condition index to assess impacts on the physiological condition of mussels held in artificial seawater acidified by the addition of CO2. There was no significant variation between the control (~786 μatm CO2 / ~7.98 pH/ ~2805 μmol kg-1 total alkalinity) and acidified (~2555 μatm CO2 / ~7.47 pH/ ~2650 μmol kg-1 total alkalinity) treatment groups in any of these factors. The results of this study suggest that ocean acidification by CO2 addition has no significant effect on the quality and performance of threads produced by M. edulis.

Morphological characterization via light and electron microscopy of Atlantic jackknife clam (Ensis directus) hemocytes

The Atlantic jackknife clam, Ensis directus, is currently being researched as a potential species for aquaculture operations in Maine. The goal of this study was to describe the hemocytes of this species for the first time and provide a morphological classification scheme. We viewed hemocytes under light microscopy (using Hemacolor, neutral red, and Pappenheims stains) as well as transmission electron microscopy (TEM). The 2 main types of hemocytes found were granulocytes and hyalinocytes (agranular cells). The granulocytes were subdivided into large and small granulocytes while the hyalinocytes were subdivided into large and small hyalinocytes. The large hemocytes had both a larger diameter and smaller nucleus to cell diameter ratio than their smaller counterparts. A rare cell type, the vesicular cell, was also observed and it possessed many vesicles but few or no granules. Using TEM, granulocytes were found to contain both electron-lucent and electron-dense granules of various sizes. These numerous granules were the only structures that took up the neutral red stain. Hyalinocytes had few of these granules relative to granulocytes. Large hyalinocytes had both various organelles and large vesicles in their abundant cytoplasm while small hyalinocytes had little room for organelles in their scant cytoplasm. Total hemocyte counts averaged 1.96×10(6) cells mL(-1) while differential hemocyte counts averaged 11% for small hyalinocytes, 12% for large hyalinocytes, 59% for small granulocytes, and 18% for large granulocytes. The results of this study provide a starting point for future studies on E. directus immune function.