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1.
Bonamiosis affects the viability of oyster culture in Galicia (NW Spain). This study shows the effects of the disease on three oyster populations from hatcheries in different culture areas (Cambados and Bueu) and different origin: stock A [F1], stock B [F2], and stock C [F2]. These stocks were cultured between November 1998 and November 2000 in Cambados and Bueu. In the Cambados area, bonamiosis is considered to be endemic, while the disease does not generally affect Bueu area. Sampling was conducted at 3-month intervals to study prevalence of Bonamia, mortality and growth rates. In the Cambados area, bonamiosis was detected 12 months after beginning culture but in the Bueu area, it was not detected until 24 months after initiating cultures. Our results suggest that there is a relationship between presence of Bonamia ostreae and oyster mortalities, which were observed in the three stocks from Cambados. These mortalities were associated with the culture area (Cambados) and not with stock of oysters. Growth was satisfactory in both areas as oysters reached commercial size (60 mm) 15 months after beginning the cultures. In an area where Bonamia is present, such as Cambados, the oysters should be marketed promptly (after approximately 15–18 months of culture) but in areas where Bonamia is not present, such as Bueu, the oyster farmer can culture oysters over a long period of time, prior to harvest, if necessary.  相似文献   

2.
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   

3.
Growth, intensity of Perkinsus marinus (Levine) infection, and survival of synchronously spawned North Carolina (NC) and Chesapeake Bay‐heritage (CB) oysters, Crassostrea virginica (Gmelin) were evaluated under standard tray culture conditions at several sites in both regions (Wye River, Maryland; Mobjack Bay, Virginia; Pamlico River, NC and Bogue Banks, NC). Infection prevalence reached 100% in oysters held at all high‐ and moderate‐salinity sites, at which time the CB strain ceased to grow. Shortly after growth ceased, CB oysters exhibited mortality that rapidly progressed to 100%. Unlike the CB strain, growth continued in the NC strain despite high P. marinus prevalence. When mortality did occur in the NC strain, at a reduced rate of 37–40%, it was associated with higher intensity of P. marinus than the infection intensity correlated with death of CB oysters. At the low‐salinity site in NC, P. marinus infection persisted at low weighted prevalence throughout the latter portion of the culture period but was not associated with mortality of either strain. These trends in growth and disease resistance for the two strains demonstrate that aquaculture performance is related to the level of disease resistance in oyster strains, salinity of water in growing areas and virulence of P. marinus.  相似文献   

4.
Filtration rates of hatchery-reared king scallop (Pecten maximus L.) juveniles, fed a single species alga diet (Pavlova lutheri (Droop) Green), were measured at a range of temperatures (6–21 °C). Weight specific filtration rate (ml min−1 g−1 (live weight)) of juveniles of a selected size range of 17–19 mm shell height (0.26–0.36 g live weight) increased with temperature above 16 °C and decreased below 11 °C, but was not significantly different between these two temperatures. Measurements at 16 °C using juveniles with a wider size range of 10–25 mm shell height (0.05–0.8 g live weight) gave the allometric equation: filtration rate (ml min−1)=12.19×weight (g)0.887. Filtration rate decreased significantly when the cell concentration was greater than 200 cells μl−1 (4.25 mg (organic weight) l−1). With six other algae food species, filtration rates similar to those with P. lutheri were only achieved with Chaetoceros calcitrans (Paulsen) Takano. All other algae species tested were cleared from suspension at significantly lower rates. Experiments with diet mixtures of P. lutheri and these other algae suggested that this was usually a reflection of lowered filtration activity, rather than pre-ingestive rejection of cells. In experimental outdoor nursery rearing systems, the filtration rate was inversely proportional to the concentration of cells in the inflow, in the range 5–210 cells μl−1. It was not affected by flow rate (2–130 l h−1, equivalent to 0.12–28.38 l h−1 g−1 (live weight)) with scallop juveniles stocked from 2 to 62 g l−1. The results are discussed in relation to on-growing scallops at field sites.  相似文献   

5.
Hizikia fusiforme (Harv.) Okamura (brown seaweed) was cultured using aeration with two CO2 conditions: outdoor air (actual atmospheric CO2 concentration, averaging 360 μl l− 1) and CO2-enriched air (averaging 700 μl l− 1), to investigate the possible adjustments of elevated atmospheric CO2 to the growth, photosynthesis and nitrogen metabolism in this mariculture species. Aeration with CO2-enriched air reduced the pH in the culture medium in comparison with aeration with air. The mean relative growth rate was enhanced when H. fusiforme was grown at high CO2 with respect to normal CO2. There was little change in the rate of light-saturated photosynthesis, dark respiratory rate and apparent photosynthetic efficiency, measured in natural seawater, between thalli grown in high and normal CO2 contents. However, both the mean nitrate uptake rate and the activity of nitrate reductase at light period were increased following culture at high CO2, indicating an enhanced nitrogen assimilation of H. fusiforme thalli with the CO2 enrichment in culture. It was proposed that the intensive cultivation of H. fusiforme would remove nutrients more efficiently with the future elevation of CO2 levels in seawater, which could be a possible solution to the problem of ongoing coastal eutrophication.  相似文献   

6.
San Quintin Bay (Baja, California, Mexico) is extensively utilized by artisanal farmers to cultivate Pacific oysters ( Crassostrea gigas ) using a rope/rack system. A large juvenile oyster mortality event was significantly correlated with the presence of native predatory whelks, Macron trochlea . Surveys, field and lab experiments were performed to identify the predatory behaviour of the whelk, determine factors affecting oyster mortality, and quantify the impact on oyster farmers. Macron trochlea was found to be a voracious, active predator, which can consume ∼4 juvenile oysters day−1. Juvenile oysters suffer significantly higher mortality in the presence of whelks. Macron trochlea has the largest impact on small oysters. Once oysters grow to >30 mm they reach a size refuge above which there is much lower mortality. At average growth rates, an oyster can escape predation after ∼3 months. But, in areas of highest whelk densities, at average predation rates, whelks could consume the standing crop of juvenile oysters in approximately 43 days. For the artisanal oyster farmers of San Quintin this represents a substantial economic loss, which was unaccounted for previously. Farmers can reduce loss to whelk predation by seeding juvenile oysters in low whelk density areas until oysters reach the size refuge.  相似文献   

7.
Many oyster handling and processing devices require oysters to enter in a specific orientation. Unfortunately wild caught oysters exhibit great variability in shape and configuration. Thus, orienting them automatically is challenging. Orientation and transfer devices were developed and the efficiency of both orienting single wild caught oysters from the Chesapeake Bay region and transferring them from the orientation device to an exit conveyor were determined.The computer program, OYSORS, developed to control the orienting device was found to be able to orient only 51% of the oysters within ±0.35 radians when using only the basic program and 68% when using the basic program plus the Adjust modification. The total orientation and transfer system efficiency using the Adjust algorithm was determined for oysters from three oyster bars in the Chesapeake Bay Region: Tangier Sound, Wicomico River, and Potomac River. The total system was found to be able to orient and transfer oysters while holding their orientation within ±0.35 radians for between 50 and 66% of the oysters depending on the origin of the oysters. The transfer system alone was shown to be able to transfer oysters from the orienter to the exit conveyor within an allowable deflection of ±0.17 radians in 75–95% of the oysters depending on the origin of the oysters. It was shown that the transfer system was actually able to correct the orientation of some of the oysters incorrectly oriented by the computer program OYSORS.  相似文献   

8.
Farming triploid oysters   总被引：1，自引：0，他引：1  
Although the commercial benefits of triploidy have been evaluated in the Pacific oyster Crassostrea gigas (Thunberg, 1793), eastern oyster C. virginica (Gmelin, 1791), Sydney rock oyster Saccostrea glomerata (Gould, 1850) and European flat oyster Ostrea edulis (Linnaeus, 1750), so far this technique has only been commercialised for Pacific oysters.

Commercial production of triploids on the West Coast of North America began in 1985. Since then production of triploids has greatly increased and the use of tetraploid males to fertilise eggs from diploids to produce batches of 100% triploids has been developed. In 1999/2000, triploid Pacific oysters made up 30% of all Pacific oysters farmed on the West Coast of North America. Some hatcheries now use tetraploid males instead of chemical or physical stress to produce triploids. The rapid uptake of triploid and tetraploidy techniques has been facilitated by the almost total dependence that these oyster industries have on hatcheries for the supply of seed. This industry in the Pacific Northwest of the US and in British Columbia, Canada, would not have developed to its current size without hatchery seed supplies. Triploids are preferred over diploids in summer because diploids are less marketable when in spawning condition.

There was only limited interest in triploidy production in France until 1999, when IFREMER began to make sperm from tetraploids available to commercial hatcheries. In 1999/2000, only 10% to 20% of all the hatchery-supplied Pacific oyster spat were triploids, but with the use of sperm from tetraploid oysters, this could increase sharply.

Elsewhere around the world, the commercial uptake of triploid oysters has been slow to develop. However, in countries where the production of Pacific oysters is based on hatchery supply of seed, it is likely that with the use of tetraploid oysters, the farming of triploid oysters will increase in the near future.  相似文献   


9.
A population dynamics model was used to simulate variations in the standing stock of the Pacific oyster, Crassostrea gigas, to assess the marketable production in Thau Lagoon (France) and to evaluate the sensitivity of this production to environmental conditions. The model is based on a continuous equation of the oyster abundance as a function of individual growth rate, inter-individual growth variability and mortality rate. The growth model depends on water temperature, particulate organic matter concentration and total individual mass. Inter-individual growth variability was introduced into the general population dynamics equation by a diffusion coefficient K that was set to 0.05. The population dynamics model took into account the two culture methods (i.e. “collées” and “pignes” oysters) and rearing strategies of oyster farmers by using timetables of seeding and harvesting obtained through interviews of oyster farmers. Distributions of standing stocks were obtained through assessments conducted in the lagoon in March 2000, October 2000 and March 2001 and were used to calibrate the model. The model estimated the total marketable production at ca. 17,900 t between March 2000 and March 2001. The major part of the production (ca. 70%) was in spring. Seventy percent of the annual production came from “collées” oysters. Sensitivity analyses showed that the key parameters are those related to harvesting. The model was used to evaluate the effects of different environmental conditions (e.g. a decrease in the oyster growth rate, a harvesting closure due a toxic algae bloom, a massive summer mortality due to an anoxic crisis) on short- and long-term variations in the standing stock and the production for both culture methods. A decrease in the growth rate of ca. 20% resulted in losses of 18% in the first year of production for both culture methods. Long-term simulations showed that the production of “pignes” oysters was more affected than that of the “collées” oysters (reductions of 26% and 4%, respectively). Simulated scenarios included a 2-month long harvesting closure (i.e. November and December) or a massive summer mortality (i.e. 45% and 20% for “collées” and “pignes” oysters, respectively). No long-term effect was predicted for either event, although losses of ca. 10% were estimated in the first year of production for both culture techniques. The model can be a useful tool for predicting marketable production of oysters as a function of rearing strategy and environmental conditions.  相似文献   

10.
Triploidy of the pearl oyster, Pinctada martensii Dunker, was induced with hydrostatic pressure shock. The efficiency of inductions changed with the time of initiation of treatment, the duration of treatment and the intensity of pressure. The most effective procedure for inducing triploidy was the treatment of eggs at 200–250 kg/cm2 5–7 min (for the first polar body retention) and 17–19 min (for the second polar body retention) after insemination for 10 min duration, which resulted in 76% triploid embryos. Under this optimal treatment, high hatchability was also obtained.  相似文献   

11.
A new method of oyster cultivation, the Stanway oyster cylinder, has been investigated in the Bay of Arcachon since 1989. A comparative study was carried out between the growth of spat and 18-month-old Crassostrea gigas oysters, in cylinders and in traditional bags. The growth in height and in whole weight was lower in cylinders. In contrast, the tests showed a better quality of the meat, with higher condition index and higher carbohydrate content, and a better quality of the shell, with higher density and better shape. Therefore, because of the improvement in oyster quality, the use of the cylinder seems to be advantageous for the Arcachon oyster industry.  相似文献   

12.
Gene transfer has offered a new tool for the development of improved fish strains for aquaculture. Monosex fish populations could minimize the impact of genetically modified organisms in the environment. In Oreochromis aureus, the use of pseudofemale spawners (sex-reversed male with a female phenotype) is an alternative technique for producing genetically male tilapia offspring. O. aureus fry were treated with 17β-estradiol at 100 mg/kg of food for 45 days. We obtained 77.1% females and 45.9% in the control group. Females randomly taken from the treated group were crossed with normal males. Fry from pseudofemales producing more than 90% male progenies were submitted to 17 β-estradiol treatment to obtain F2 pseudofemales. The results of the sex-reversal were low and variable ranging between 66.0 and 84.3% females. F2 pseudofemales were crossed with transgenic males from the F70 line (O. aureus × O. urolepis hornorum) and non-transgenic (O. aureus) males. The sex ratio of progeny of F2 pseudofemale deviated significantly (P < 0.01) in favor of males in the crosses with transgenic (90.2%) and non-transgenic (89.3%) males compared to the results observed with normal females (51.0 and 52.3%, respectively). The mean fry production with pseudofemales (per m2/day) was similar to the normal females in the crosses with transgenic and non-transgenic males. To our knowledge this is the first report on the production of a near monosex population in genetically modified fish.  相似文献   

13.
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   


14.
The distribution, abundance and biological interactions of the cutlassfish Trichiurus lepturus in the southern Brazil subtropical convergence ecosystem were studied from demersal trawl surveys conducted along the continental shelf and upper slope from Cape Santa Marta Grande (28 °36′S) to Chui (34 °45′S) between 1981 and 1987. Trichiurus lepturus was more abundant at bottom water temperatures of over 16 °C and in the 40–120 m depth range. From late spring to fall, juveniles of 5–30 cm total length (TL) were found in coastal waters, subadults (TL 30–70 cm) mainly in inner shelf waters and adults (TL > 70 cm) in coastal, inner and outer shelf waters. Higher catches of subadults and adults were found associated with thermal fronts in the western boundary of the Subtropical Convergence or with a shelf break upwelling observed in summer. The standing stock in a 58 000 km2 shelf area estimated by the swept area method, ranged from 3066 t (±46% CI) in September 1981 to 37814 t (±22% CI) in January 1982. Correlation between occurrences of different size groups of cutlassfishes and other fishes caught in 250 bottom trawl hauls was analyzed. A positive correlation between cutlassfish and juvenile weakfish, Cynoscion guatucupa, was associated with similar spatial distribution but also indicated trophic competition.  相似文献   

15.
The progeny of four breeding lines of Sydney rock oysters, Saccostrea commercialis, selected for faster growth over two generations, were compared with controls in an 18-month farming experiment. Mean whole weights of oysters from all four selection lines did not differ significantly from each other but, were significantly greater (P<0.05) than mean whole weight of controls (spat produced from two groups of non-selected oyster populations). The mean increase in weight for the selection lines over the controls of 18% (range 14–23%) after two generations of selection (third generation) compares extremely favourably with the 4% reported previously after one generation of selection.  相似文献   

16.
The giant fresh water prawn Macrobrachium rosenbergii is known to be highly tolerant to white spot syndrome virus (WSSV) infections when compared to the widely cultured marine tiger shrimp Penaeus monodon. At present, the exact mechanism of tolerance by M. rosenbergii to WSSV is not known. In this study, we attempt to study the effect of WSSV injections on the hemagglutination activity of the hemolymph serum of both P. monodon and M. rosenbergii and look for changes if any, on their hemolymph serum protein electrophoretic patterns. Our results show that M. rosenbergii had significantly (p < 0.05) higher hemagglutinating activity against mouse erythrocytes when compared to P. monodon. As the infection progressed to 48 h there was a further increase (p < 0.05) in the hemagglutination activity in M. rosenbergii, while it decreased in P. monodon. 12% SDS-PAGE analysis of the hemolymph serum of M. rosenbergii infected with WSSV did not show any new protein bands, whereas few bands with decreased intensity was observed in moribund P. monodon where the hemagglutinating activity was also observed to be decreased. The results indicate that hemolymph hemagglutinin levels are modulated in crustaceans as a response to viral infections.  相似文献   

17.
Levels of glucose, lactate, pO2, pCO2, HCO3−, TCO2, Na+, K+, Cl−, protein, and oxyhemocyanin in the hemolymph and its osmolality and pH were measured when tiger shrimp, Penaeus monodon (13.5 ± 1.5 g body weight), were individually injected with saline or dopamine at 10− 8, 10− 7, or 10− 6 mol shrimp− 1. Results showed that hemolymph glucose, lactate, pCO2, HCO3−, and TCO2 values increased from 2 to 4 h; hemolymph osmolality, Na+, and total protein had increased at 2 h; and hemolymph K+ decreased from 2 to 8 h after the dopamine injection. All physiological parameters returned to the control values 4–16 h after receiving dopamine. The dopamine injection also significantly decreased the oxyhemocyanin/protein ratio of P. monodon which occurred at 2 h, resulting from an elevation of hemolymph protein and a slight decrease of oxyhemocyanin. These results suggest that stress-inducing dopamine caused a transient period of modulation of energy metabolism, osmoregulation, respiration, and the acid–base balance in P. monodon in adapting to this environmental stress.  相似文献   

18.
为探究香港巨牡蛎(Crassostrea hongkongensis)的繁殖特性以及春季死亡原因,采用肉眼观察、活体镜检和组织切片方法研究了茅尾海沙井的香港巨牡蛎苗种吊养于大风江黄场的1龄牡蛎的性腺发育周年变化,并建立了快速判断香港巨牡蛎性腺发育程度的方法.对比分析了吊养在茅尾海沙井、大风江入海口内的黄场和入海口外的鑫丰场的2龄牡蛎性腺发育的启动和发展过程.结果显示,广西茅尾海的香港巨牡蛎每年只有1个繁殖周期,性腺发育过程可划分为未分化期(1-3月)、分化期(4月)、成熟排放期(5-10月)及休止期(11-12月)4个阶段;1龄和2龄牡蛎的性腺发育基本同步;大风江入海口外的牡蛎的性腺发育较入海口内的牡蛎提前约15d,而比茅尾海内海的牡蛎提前约30 d,入海口外的牡蛎的性腺4月即发育到成熟排放期,冬季饵料的丰富程度和温度、盐度等因素可能是造成这种差异的原因.研究还发现,高温少雨天气下,海水盐度高,抑制了牡蛎性细胞的排放,导致入海口外侧吊养牡蛎的大规模死亡,濒临死亡的牡蛎性腺处于退化和崩解状态.鉴于此,认为4月初即需密切监测吊养于入海口外的牡蛎性腺的发育状况和天气状况,及时收获性腺饱满的牡蛎,或将吊养牡蛎的蚝排放置在河流入海口内区域过冬.  相似文献   

19.
The safety and efficacy of emamectin benzoate, administered in-feed to Atlantic salmon smolts, Salmo salar L., held in freshwater, was evaluated as a preventative treatment against sea lice, Lepeophtheirus salmonis, following transfer of fish to seawater.

In the safety study, salmon smolts held in freshwater were fed with diets containing emamectin benzoate at nominal doses of 0 (control), 50 (recommended dose) and 250 (5× recommended dose) μg kg−1 fish day−1 for 7 days (days 0–6). Actual dose rates, based on measured concentrations of emamectin benzoate in feed, differences in fish weight, and feed consumed, were 0, 54, and 272 μg kg−1 day−1, respectively. On day 9, fish were transferred to seawater and observed for 14 days. No differences in feeding response, coordination, behaviour, gross and histological appearance were observed between control fish and those that received 54 μg kg−1 day−1. Among smolts that received 272 μg kg−1 day−1, approximately 50% exhibited darker coloration, and one fish (1%) exhibited uncoordinated swimming behaviour. No pathognomonic signs of emamectin benzoate toxicity were identified.

In the efficacy study, smolts held in freshwater were fed an unmedicated ration (control group) or emamectin benzoate at 50 μg kg−1 day−1 (treated group) for 7 days (days 0–6). On day 9, fish were re-distributed to eight seawater tanks, each holding 30 control and 30 treated fish. On days 28, 56, 77 and 109, respectively, control and treated fish in two tanks were challenged with L. salmonis copepodites. When lice in each group reached chalimus stage IV, fish were sampled and the numbers of lice were recorded. Fish challenged at day 109 were sampled for the second time when lice were at the adult stage. Efficacy was calculated as the reduction in the mean number of lice on treated fish relative to the mean on control fish. Treatment with emamectin benzoate resulted in an efficacy of 85.0–99.8% in fish challenged at days 28–77, from the start of treatment, and lice counts were significantly lower (P<0.001) on treated fish than on controls. When fish challenged at day 109 were sampled at day 128, efficacy was 44.3%, but survival of chalimus to adult lice on treated fish was lower, and at day 159, efficacy had increased to 73%. These results demonstrate that treatment of salmon smolts with emamectin benzoate in freshwater was well tolerated and highly effective in preventing sea lice infestation following transfer of fish to seawater.  相似文献   


20.
Eggs of the European flat oyster, Ostrea edulis, were treated with cytochalasin B (1 mg/l, 20°C, 20 min), at different time intervals after in vitro fertilization. Ploidy levels were assessed by chromosome counting on 1- and 54-day-old specimens. Evidence for bimodal distribution was found to separate meiotic I and meiotic II triploids. Peaks were located at 30–35 min and 90–100 min post-fertilization, triploid rates reaching 70% and 68% respectively. Tetraploid embryos were induced in two major groups. The effective shocks were those applied at 5–25 min and 260–280 min after fertilization (respectively 40% and 53% tetraploid metaphases). Karyological examinations of embryos and spat, carried out 20 h and 54 days after fertilization, showed a differential mortality among triploids and diploids in all treated groups and no tetraploids among the spat.  相似文献   

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