Ž .
Ž .
Goggin and Cannon, 1989; Noury-Sraıri et al., 1990 . Murina and Solonchenko 1991
¨
Ž .
and Teia dos Santos and Coimbra 1995
suggested that the worm may provoke pathological changes in the mussels Mytilus edulis and Mytilus galloproÕinciallis. This
Ž .
was confirmed by Robledo et al. 1994 who demonstrated that U. cyprinae induces severe gill disruption in M. galloproÕincialis.
Ž In Canada, U. cyprinae was reported in the blue mussel M. edulis Fleming et al.,
. Ž
. 1981 . Burt and Drinnan 1968 described the worm from the gills and mantle of the
eastern oyster Crassostrea Õirginica sampled along the Atlantic coast and suggested that it was in all probability a facultative commensal.
Ž .
In their preliminary investigation, Plourde et al. 1991 raised the possibility that there may exist an inverse relationship between the number of worms and the physio-
logical condition of infected oysters. As part of a comprehensive oyster-monitoring Ž
. program, Boghen et al. 1993 reported high levels of infestation of the eastern oyster by
Ž .
U. cyprinae. More recently, Brun et al. 1999a conclusively showed that the worms were strongly attracted to oyster gill mucus, dispelling the likelihood that they were
simply facultative commensals. Aside from any potentially negative effects on oysters, the visible presence of the
worms on the gills, especially when occurring in the hundreds and even thousands, could contribute to a drop in demand by the lucrative half-shell market. Our work
examines the salinity and temperature tolerances of U. cyprinae to gain new insight into the biology of the worm, and help formulate ways of eliminating the parasite from
oysters.
2. Material and methods
Ž .
Adult oysters n s 435 infected with U. cyprinae were collected from Shippagan Bay in northeastern New Brunswick, Canada, during August of 1996 and 1997. Average
ambient temperature and salinity readings were 20 8C and 28‰, respectively. Oysters
were placed on ice, transported to the Universite de Moncton, New Brunswick and
´
maintained at 5 8C for 2–3 days prior to the beginning of the experiments.
2.1. Salinity tolerance of isolated U. cyprinae U. cyprinae were removed by Pasteur pipette from the gills of oysters under a
dissecting microscope and stored overnight in covered 100-ml beakers filled with Ž
. artificial sea water Instant Ocean, Aquarium Systems, OH, USA at 22‰ and 5
8C. The worms were subsequently transferred to petri dishes. Three 25-ml glass petri dishes
Ž .
replicates each containing 10 U. cyprinae were exposed to 21 different salinity–tem- Ž
. perature combinations total of 630 worms in 63 dishes . Tolerance of U. cyprinae to
salinities of 12‰, 13‰, 14‰, 15‰, 22‰, 31‰ and 40‰ were determined at each of the following temperatures: 5
8C, 158C and 208C. The dishes were examined daily for up to 65 days and worm mortalities were recorded. After exposing U. cyprinae to a series
Ž .
of additional salinities 0‰, 2‰, 4‰, 8‰, 10‰, 43‰ and 55‰ , a salinity–tolerance profile that served as a reference base for the second part of our study was established.
2.2. Salinity tolerance of U. cyprinae present in oysters Ten oysters were randomly chosen from the samples collected in Shippagan Bay and
examined for parasites under a dissecting microscope. This was done to confirm the Ž
. presence of U. cyprinae in sufficiently high numbers mean 400 to permit reliable
interpretation of data. A sample of 135 oysters was divided into 15 groups. The animals were in turn
separated and placed into individual, disposable, colour coded, 300 ml plastic bowls. The oysters were maintained at nine different salinity–temperature combinations at the
following salinities, 8‰, 28‰ and 55‰ and temperatures, 10 8C, 158C and 208C,
respectively. The 28‰ salinity represented the control since it coincided with that which was recorded from the sampling site.
Adequate oxygenation was provided to each bowl by individual plastic air-lines attached to small aquarium pumps. Water was changed every second day, thereby
ensuring that ammonia levels never exceeded 0.2 mgrl. Oysters were unfed throughout the study.
The bowls, representing each of the three salinities, were uniformly distributed in an even, yet non-symmetrical pattern for each temperature to avoid positional bias in
experimental design. Three oysters were selected randomly from each of the salinity– temperature combinations every two days, opened and carefully examined for living or
dead U. cyprinae.
3. Results
