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Prevalence of kudoa thyrsited in Pacific Hake (Merluccius productus) and thermal resistance of Kudoa thyrsites and Kudoa paniformis spores Tamkee, Grace


Experiments were conducted to determine the potential of Pacific hake (Merluccius productus) fish meal to act as a vector of Kudoa thyrsites transmission to farmed Atlantic salmon (Salmo salar). This was done by determining the prevalence and intensity of K. thyrsites in Pacific hake destined for fish meal processing, developing a viability test for K. thyrsites, and determining the thermal resistance of K. thyrsites. Thermal resistance experiments were also performed for K. paniformis. Pacific hake samples were collected from the rendering plant in 2001 and 2002. The prevalence of K. thyrsites in the 2001 samples was 78.0%. Of these infections, 36.4% were light and 63.6% were moderate. The 2002 samples had a K. thyrsites prevalence of 80.1% infection, with 24.3% being light and 75.7% being moderate. Dyes used to test viability of other myxosporean parasites were examined for their suitability for K. thyrsites and K. paniformis. Methylene blue, fluorescein diacetate, and propidium iodide were suitable as a potential indicator of K. thyrsites viability. Only methylene blue was tested for K. paniformis, and it was found to be suitable. The decimal reduction times (D-value) of K. paniformis and K. thyrsites were determined using methylene blue as a viability test. The average D-value of K. paniformis in phosphate buffered saline (pH 7.0) was 18 hours at 53°C, while at 62°C and 69°C the average D-value was 4.5 hours and 0.80 hours, respectively. The z-value was 12C°. The average D-value for K. thyrsites at 43°C was 3.0 hours, and at 52°C and 60°C the average D-value was 1.4 hours and 0.030 hours, respectively. The z-value for K. thyrsites was 8.9C0 . Given the available data, the likelihood of K. thyrsites surviving both fish meal and fish feed manufacturing are very low.

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