Partner und Internationale Organisationen
(Englisch)
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BE, CY, DK, ES, FI, FR, GR, HU, IE, IL, IS, IT, NL, NO, PL, SE, TR, UK
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Abstract
(Englisch)
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Freedom from disease is one of the five freedoms used as criteria for assessing fish health and welfare. Given the difficulty of applying positive criteria to fish wellbeing, the absence of negative factors assumes particular importance. Fish are normally surrounded with commensural bacteria, to whiich they are resistant as long as the barriers to infection are intact, including the immune system. Stressed fish have increased susceptibility to infection, so that one aim current research is to establish the nature of bacteria able to pass from a commensural to a pathogenic state. Epitheliocystis is an infectious disease that affects a wide range of fish species, especially under conditions of stress. Susceptible hostes includes not only food fish species of major economic importance such as salmon, rainbow trout, sea bass and sea bream, but also aquarium fish. Mortalities can be as high as 100%, the causative agents being related to a group of obligate intracellular bacteria already known as pathogens for other vertebrates, including humans, and known as chlamydia. Prior to this study, there were indications that various chlamydial species could serve as the causative agents of epitheliocystis and this may, in part, explain variabilities reported on the prevalence, host species, geographic distribution, and disease severity. The major aim for this short term project was to characterize the prevalence and biodiversity of Chlamydia-related 'epitheliocystis agents' from fish species from wild and farmed fish populations in Switzerland and the rest of Europe. The networking role played by COST 867: Fish Welfare was to be central to this goal, both in obtaining specimens for analysis and for disseminating the results. The outcome of this 18 month study has been highly successful and gone well beyond our initial goals. We can indeed claim to have made substantial progress, with more than 20 new strains/species identified based on sequence data, and coming from hosts as diverse as leopard shark, discus, brown trout, sea bream and sea bass. In most cases we could also demonstrate the infections, even in individual fish, were plural in nature, and not due to a single chlamydiales species or strain. This implies that a range of chlamydiales were present in the fish environment, and that some signal or stress-related cause led to infection and pathogenesis. Of particular interest for Switzerland, was the demonstration that two species of chlamydiales, previously found in Norway and Ireland in salmonides in aquaculture, was also present in up to 20% of wild brown trout sampled at the end of summer when water temperatures are at their highest. Also here, mixed infections were found at several sites. This pilot study also provided us the necessary reagents and tools (in situ hybridization, specific antibodies, immunohisto-chemistry protocols, specific real-time PCR) to now further investigate the pathogenesis of these chlamydial epitheliocystis agents. The performance and integration of this project within the setting of COST Action 867: Welfare of Fish in European Aquaculture can be judged by a new transWG Fish Health being established within the action and co-chaired by Helmut Segner and Lloyd Vaughan. This will provide excellent opportunities for international collaboration and dissemination of in-formation about this important aquaculture disease. A number of scientific publications arising from this study are either submitted or in preparation. This also includes a scientifc review of fish health and welfare being prepared by members of the new transWG fish health under the leadership of Helmut Segner.
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