| Summary: | Ponencia presentada en el Western Fish Disease Workshop celebrado en Oregon del 22 al 24 de junio de 2010 Kudoa thyrsites is a marine myxozoan parasite known to infect a broad range of fish species throughout the Atlantic and Pacific Oceans. Infective and early stages of development are unknown for any species of Kudoa and only the sporogonic and myxospore stages have been well documented. Within British Columbia Atlantic Salmon aquaculture industry K. thyrsites is a parasite of special economic concern. K. thyrsites matures within myocytes and some infected fish develop a delayed softening or liquefaction of muscle tissue following harvest and processing resulting in substantial losses in revenue. How the fish become infected and why only some infected fish will manifest post harvest myoliquefaction remains unknown. Intriguingly severe prevalence of infection and myoliquefaction is more pronounced in specific regions of BC¿s coastal waterways. We are studying changes in prevalence and development of K. thyrsites in several Atlantic Salmon tissues throughout the two year marine phase of a commercial production cycle. Samples are collected monthly from two cohorts raised at sites known to have either a high or low historical incidence of infection. Our results from the first year show that K. thyrsites was detectable by PCR in both populations within one (high incidence) and four (low incidence) months following transfer into seawater. At both sites this was followed by an increase in prevalence, measured by PCR detection, and increased parasite intensity as measured by numbers of plasmodia in histological sections. In addition to muscle tissues, K. thyrsites was detected in blood, skin and gill by PCR. Evidence of host immune response can be seen in the form of inflammatory response and engulfment of myxospores by macrophages; however, after one year, our data does not show a decrease in prevalence. Further results from histology, in situ hybridization and manifestation of myoliquefaction of fillets will be ...
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