Document Type



Virginia Institute of Marine Science

Publication Date



Journal Of Shellfish Research





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Two experiments were conducted to compare the infectivity and pathogenicity of two life stages of the parasite Perkinsus marinus, meronts (trophozoites) and prezoosporangia (hypnospores), in eastern oysters, Crassostrea virginica. Oysters were inoculated with 5 X 10(4) meronts or prezoosporangia per oyster by injection into the shell cavity. Prevalence and intensity of P. marinus infections, condition index, serum protein concentrations, and lysozyme activities were measured in oysters after 15, 25, 40, and 65 days in experiment 1 and after 20, 40, 50, 65, and 75 days postchallenge by P. marinus cells in experiment 2. Controls were injected with filtered York River water. In the first experiment, P. marinus infections were initially detected in oysters exposed to prezoosporangia after 15 days postchallenge. In the second experiment, infection was not detected in oysters until 40 days postchallenge with either meronts or prezoosporangia. Intensity and prevalence of P. marinus infection were significantly higher (p < 0.002) in oysters challenged by meronts compared with prezoosporangia-challenged oysters at the end of both experiments. In experiment 1, a significant decrease (p < 0.05) was observed in serum protein in infected oysters challenged by prezoosporangia compared with uninfected oysters. Condition index was higher in uninfected oysters compared with infected oysters challenged by prezoosporangia. The differences in condition index and protein were insignificant between oysters infected by meronts or prezoosporangia. Lysozyme activities were significantly lower (p < 0.05) in infected oysters than in uninfected oysters challenged with meronts. No significant differences were observed in condition index, protein concentrations, and lysozyme activities between oysters challenged by meronts and prezoosporangia in experiment 2. Lower condition index and protein concentrations in the groups of oysters infected with prezoosporangia compared with the groups infected by meronts and nonchallenged at the end of experiment 1 suggest a higher energetic demand on these oysters.


Perkinsus Marinus; Crassostrea Virginica; Oyster Disease; Lysozyme; Condition Index; Protein

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This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.