The mucosal surfaces and associated microbiota of fish are an important primary barrier and provide the first line of defense against potential pathogens. An understanding of the skin and gill microbial assemblages and the factors which drive their composition may provide useful insights into the broad dynamics of fish host–microbial relationships, and may reveal underlying changes in health status. This is particularly pertinent to cultivated systems whereby various stressors may led to conditions (like enteritis) which impinge on productivity. As an economically important species, we assessed whether the outer-surface bacterial communities reflect a change in gut health status of cultivated Yellowtail Kingfish (Seriola lalandi). Active bacterial assemblages were surveyed from RNA extracts from swabs of the skin and gills by constructing Illumina 16S rRNA gene amplicon libraries. Proteobacteria and Bacteroidetes were predominant in both the skin and gills, with enrichment of key β-proteobacteria in the gills (Nitrosomonadales and Ferrovales). Fish exhibiting early stage chronic lymphocytic enteritis comprised markedly different global bacterial assemblages compared to those deemed healthy and exhibiting late stages of the disease. This corresponded to an overall loss of diversity and enrichment of Proteobacteria and Actinobacteria, particularly in the gills. In contrast, bacterial assemblages of fish with late stage enteritis were generally similar to those of healthy individuals, though with some distinct taxa. In conclusion, gut health status is an important factor which defines the skin and gill bacterial assemblages of fish and likely reflects changes in immune states and barrier systems during the early onset of conditions like enteritis. This study represents the first to investigate the microbiota of the outer mucosal surfaces of fish in response to underlying chronic gut enteritis, revealing potential biomarkers for assessing fish health in commercial aquaculture systems.

Disease agents and pests associated with freshwater crayfish fall into six main categories-viruses, bacteria, rickettsia-like organisms (RLOs), fungi, protists, and metazoans. Data and information on specific disease agents and pests from each of these categories are presented in this synopsis. Each agent or group of agents is considered under the following headings-condition, causative agent(s), life cycle/life history, epizootiology, pathology, pathogen viability. Information for the synopsis was obtained from the published literature and from personal contact with internationally recognized experts in freshwater crayfish aquaculture, biology, and disease. Data of relevance for import risk analysis are summarized.Import risk analysis is the process by which the risks associated with importation of animals and plants, and products derived from animals and plants, are assessed and managed. Hazard identification is essential and is the first component of an import risk analysis. In 1996, the Australian Quarantine and Inspection Service (AQIS) commenced a review of policy relating to the importation of nonviable freshwater crayfish products, along with a suite of other aquatic animal products. AQIS2 commissioned a synopsis of freshwater crayfish pests and pathogens for use as a resource document for hazard identification in the formal IRA process.

One of 14 goldfish (Carassius auratus) died 4 weeks after purchase and was investigated by necropsy and histological examination. Routine formalin fixation of the goldfish was followed by histopathology. Formalin fixed spleen and kidney from the fish was further processed by embedding in epoxy resin and examined by transmission electron microscopy (EM). Severe, diffuse necrosis of haematopoietic tissue in the spleen, thymus and kidney and severe, diffuse hyperplasia in the gill epithelial cells were seen. In the spleen there was severe, diffuse necrosis of lymphocytes and many nuclei with marginated chromatin and intranuclear inclusions were scattered throughout the necrotic tissue. EM of affected tissues demonstrated intranuclear particles morphologically similar to herpesvirus. The presence of an agent similar to a herpesvirus in a goldfish with severe haematopoietic necrosis suggests that the herpesvirus responsible for haematopoietic necrosis in cyprinid species throughout the world has entered the goldfish population in Australia.

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