In order to study individual growth variability and its relationship with survival in juvenile Crassostrea gigas, parental oysters were sampled at four sites located along the French Atlantic coast and bred under controlled hatchery conditions.
Four groups of larvae were obtained by crossing five males and five females from each of the four sites, and a fifth group
by crossing these 20 males and 20 females together in a pool. Larvae were reared under conditions allowing the maintenance
of a maximum variability of size and gave five experimental groups. Oysters were individually monitored for growth and survival
from 3 to 10 months after fertilization. The individual growth performances were relatively stable over time and no noticeable
compensation for growth occurred. Early growth rate was a very good predictor of size later in life: 66% of variation in the
live weight at 10 months could be explained by variation in the initial growth rate calculated between 3 and 4 months. A significant
group effect was observed on survival and on growth rate. Mortality mostly occurred between 3 and 5 months and appeared to
affect the slow-growing animals more. However, two groups can be distinguished among those which died during the experimental
period, one which showed a decrease in weight and the other whose growth was similar to surviving oysters. These results are
discussed in the light of usual oyster farming practices and selective breeding.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
High variability among individuals is often encountered when hemocyte characteristics are measured in bivalves. Such variability is suspected to result partly from genetic factors. In this study, hemocyte characteristics of six families of Crassostrea gigas were compared by flow cytometry at one sampling date in October 2001. These families were obtained from a nested, half-sibling cross design, and reared from July to October 2001 at three sites distributed along the French Atlantic coast from north to south: Baie des Veys (Normandy), Rivière d'Auray (Brittany) and Ronce (Marennes-oléron Basin, Poitou Charentes).
Among the 15 measured hemocyte characteristics, production of reactive oxygen species (ROS) of untreated hemocytes (maintained in filtered sterile seawater) and treated hemocytes (zymosan at 20 particles per hemocyte, and with Vibrio sp. S322 at 50 bacteria per hemocyte) was the most notable differences between families. This supports the existence of a genetic basis, at least partly, for the hemocyte characteristics of oysters, and especially for ROS production.
Among the six families analyzed, three have shown high survival during summer (named as “resistant”, mean mortality 5.2%) and three experienced high mortality during summer (named as “susceptible”, 30.6% mean mortality). Families showing high or low survival to summer mortality had similar hemocyte characteristics, regardless of the environmental conditions or reproductive state. Resistant families were observed to have higher total hemocyte counts and lower production of ROS than susceptible families. Moreover, ROS production of hemocytes from susceptible families was diminished significantly more by pathogenic Vibrio than that of resistant families. However, this study demonstrates also that rearing site strongly affected the hemocyte characteristics of all families of oysters, most notably hemocyte concentration and morphology (size and granularity), production of reactive oxygen species (ROS), and susceptibility to the cytotoxic activity of the pathogenic Vibrio sp. S322 (50 bacteria/hemocyte). Food availability and reproductive state are the most probable explanations for the site differences observed. Finally, it appeared difficult to link oyster survival during summer mortality to hemocyte profiles evaluated at one sampling date; other relevant indicators would probably help explaining oyster survival during summer mortality events. 相似文献
The haemocytes of the Indian edible oyster Crassostrea madrasensis were characterized using light and electron microscopy. The light microscopic study was conducted by staining a monolayer of the haemocytes with Geimsa. Cells without granules and with a large nucleus occupying much of the cytoplasmic area were grouped as hyalinocytes. Those with lesser amounts of basophilic cytoplasmic granules were characterized as semigranulocytes and those with large amounts of a mixture of acidophilic and basophilic granules were termed as granulocytes. Ultrastructural studies also revealed the presence of three types of haemocytes. Scanning electron microscopic studies were used to study the spreading behaviour of the haemocytes. Cytochemical studies revealed the presence of acidphosphatase, peroxidase and prophenol oxidase in the cells. 相似文献
To determine effects of aquacultured oysters Crassostrea virginica (Gmelin, 1791) on the overlying water column, a mesocosm study was performed at the Marine Ecosystem Research Laboratory (MERL) from June to October, 2000. The MERL facility is located adjacent to Narragansett Bay and consists of fourteen 13,000-l mesocosm tanks designed to simulate the Bay environmental conditions. Two hundred oysters (≈35 mm valve height; nominally filtering about 55 l/day/individual) were placed into three mesocosms, and three mesocosms were maintained without oysters as controls. Experiments were run with varying rates of water exchange in the tanks ranging from 0% to 100% per day (13,000 l/day). Parameters that were measured and compared between the two treatments included chlorophyll-a, particulate organic and inorganic matter, sedimentation, nitrate, ammonia, selected phytoplankton species and oyster growth rates. Oysters affected phytoplankton species composition and increased rates of sedimentation. Large diatoms were net sampled, and Nitzchia striata was predominant in mesocosms with oysters, while Skeletonema costatum dominated the control tanks. Ammonia excretion rates were determined for C. virginica using the salicylate–hypochlorite method. Ammonia excretion can be described by the allometric equation E=50.65w0.699 when E is the ammonia excretion rate in μg/h, and w is the soft tissue dry weight in grams. Based on rates of ammonia excretion by oysters and observed steady states of ammonia and other forms of inorganic nitrogen in mesocosm tanks, it can be hypothesized that ammonia generated by oysters is taken up by rapidly regenerating phytoplankton in the water column. 相似文献