Prevalence and infection
intensity of the ovarian parasite Marteilioides chungmuensis during
an annual reproductive cycle of the oyster Crassostrea gigas
T.T.T. Ngo, F.C.J. Berthe, K.-S. Choi-2003
Diseases of Aquatic Organisms, 56(3): 259-267
Abstract:
The occurrence of Marteilioides chungmuensis, a
protozoan paramyxean parasite in the reproductive system of the Pacific
oyster Crassostrea gigas, was observed at Gosung Bay, Korea. Seasonal
variation in gonad development was investigated in a suspended cultured
oyster population. Gametogenesis began in February and first-spawning was
observed between mid and late June when surface water temperature reached 22
to 25°C. Spawning activity extended from mid June to late September, with 2
marked spawning peaks in June and August. Histological examination indicated
that gonad development paralleled seasonal fluctuations in water
temperature. Spawning in late June was partly associated with a sudden drop
in salinity due to large freshwater inputs to the Bay with the summer
monsoon. M. chungmuensis occurred in developing and fully mature eggs
of spawning oysters in late June to January, but were not observed from
February to May. Monthly mean infection intensity was high in late June when
most oysters had their first spawning period. The infection level was also
relatively high in late August and November, when oysters were spawning or
had completed spawning. Several oysters collected in November (11.4%) and
December (16.3%) carried a large quantity of ripe but M. chungmuensis-infected
eggs, suggesting that infection also causes spawning failure by delaying
spawning and destroying ripe oocytes.
(School of Applied Marine Science, College of Ocean
Science, Cheju National University, 1 Ara 1- Dong, Jeju, Jeju-do 690-756,
Korea, e-mail of K.-S. Choi: skchoi@cheju.ac.kr)