COMPARISON OF INFECTIVITY AND PATHOGENICITY OF MERONT (TROPHOZOITE) AND PREZOOSPORANGIAE STAGES OF THE OYSTER PATHOGEN PERKINSUS-MARINUS INEASTERN OYSTERS, CRASSOSTREA-VIRGINICA (GMELIN, 1791)
Ak. Volety et Fle. Chu, COMPARISON OF INFECTIVITY AND PATHOGENICITY OF MERONT (TROPHOZOITE) AND PREZOOSPORANGIAE STAGES OF THE OYSTER PATHOGEN PERKINSUS-MARINUS INEASTERN OYSTERS, CRASSOSTREA-VIRGINICA (GMELIN, 1791), Journal of shellfish research, 13(2), 1994, pp. 521-527
Two experiments were conducted to compare the infectivity and pathogen
icity of two life stages of the parasite Perkinsus marinus, meronts (t
rophozoites) and prezoosporangia (hypnospores), in eastern oysters, Cr
assostrea virginica. Oysters were inoculated with 5 X 10(4) meronts or
prezoosporangia per oyster by injection into the shell cavity. Preval
ence and intensity of P. marinus infections, condition index, serum pr
otein concentrations, and lysozyme activities were measured in oysters
after 15, 25, 40, and 65 days in experiment 1 and after 20, 40, 50, 6
5, and 75 days postchallenge by P. marinus cells in experiment 2. Cont
rols were injected with filtered York River water. In the first experi
ment, P. marinus infections were initially detected in oysters exposed
to prezoosporangia after 15 days postchallenge. In the second experim
ent, 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 c
hallenged by meronts compared with prezoosporangia-challenged oysters
at the end of both experiments. In experiment 1, a significant decreas
e (p < 0.05) was observed in serum protein in infected oysters challen
ged by prezoosporangia compared with uninfected oysters. Condition ind
ex was higher in uninfected oysters compared with infected oysters cha
llenged by prezoosporangia. The differences in condition index and pro
tein were insignificant between oysters infected by meronts or prezoos
porangia. Lysozyme activities were significantly lower (p < 0.05) in i
nfected oysters than in uninfected oysters challenged with meronts. No
significant differences were observed in condition index, protein con
centrations, and lysozyme activities between oysters challenged by mer
onts and prezoosporangia in experiment 2. Lower condition index and pr
otein concentrations in the groups of oysters infected with prezoospor
angia compared with the groups infected by meronts and nonchallenged a
t the end of experiment 1 suggest a higher energetic demand on these o
ysters.