Selection of lactic acid bacteria as candidate probiotics for Vibrio parahaemolyticus depuration in pacific oysters (Crassostrea gigas)

The application of probiotics in food is now widespread and is widely accepted by consumers. Lactic Acid Bacteria (LAB) were isolated from traditional salted fish and then characterized by its ability to inhibit Vibrio parahaemolyticus growth using minimal inhibitory concentration tests. Five out of these strains were identified as Lactobacillus delbrueckii, Lactobacillus casei and three Lactobacillus gasseri by PCR using 16S and 23S rRNA genes. Antibiofilm activity of Lactobacillus spp. extracts were also tested in 96 polystyrene plates. A potential antibiofilm effect was demonstrated as most LAB. Although most LAB extract were able to eradicate pre‐formed biofilm, results demonstrated that five Lactobacillus spp. exhibited a stronger inhibitory effect against V. parahaemolyticus in infected oysters. Vibrio parahaemolyticus viable cells number declined from 10⁶ UFC to 10⁴ UFC after 3 days of incubation with Lactobacillus spp. Probiotic applications, in biological control of seafood associated pathogens can be an alternative solution, providing consumer with a product of good quality owing to the use of non‐toxic compounds. Based on our results, LAB could be used as a bioprotective culture in oyster's depuration to prevent V. parahaemolyticus growth.     

牡蛎中GⅡ型诺如病毒巢式RT-PCR检测方法的优化与评价

为了解决目前巢式PCR法检测牡蛎样品中GII型诺如病毒时存在的非特异性扩增、假阴性等问题,本研究对NCBI数据库中在线获得的所有GII型诺如病毒序列进行系统分析,重新设计出针对GII型诺如病毒检测的通用型巢式PCR引物(NG2OF/NG2OR),并从基因型覆盖度、特异性、灵敏度和实际样品检测的稳定性几个方面对新设计的引物进行评估。结果显示：(1)新引物的特异性好,只对GII型诺如病毒进行有效扩增,且不受牡蛎样品本底的影响。(2)新引物灵敏度高,最低可检测至26.4个拷贝。(3)在对92个牡蛎样品进行检测时,新引物的阳性检出率为28.3%,比经典引物高出7.5%。因此,新建立的GII型诺如病毒巢式PCR检测方法在检测牡蛎样品时特异性更强,灵敏度更高,为牡蛎中诺如病毒的检测提供了一种新的、可靠的技术手段。     

Application of packed bed reactor theory and Bayesian inference to upweller culture of juvenile oysters

The use of upweller culture units in bivalve nurseries is widely practiced as a technique that enhances the ability to rear large quantities in a semi-controlled environment. However, guidance has varied for optimal flow rates, and thus there is a need to develop a more mechanistic assessment. The application of packed bed reactor theory, including axial diffusion models, would improve optimization of these culture methods. The following paper presents a series of controlled experiments to determine the hydrodynamic properties of a packed bed of oysters. The data gained from these experiments was used to develop mechanistic models calibrated through Bayesian inference. Specifically, the Ergun equation and the axial diffusion model were used to predict the experimental data. The Ergun equation was able to predict the hydrodynamic equivalent diameter distribution of oyster shells (μ = 3.18 mm, σ = 0.74 mm). This oyster shell diameter and void ratio distribution gained through the Ergun equation were used in the relationship of axial diffusion and superficial velocity. The mean axial diffusion coefficient in the oyster bed was estimated 1.65 × 10⁴ m²/s at 0.01 m/s and 7.26 × 10⁴ m²/s at 0.08 m/s. The use of Bayesian inference allows for greater understanding of the credibility of individual parameter distributions (i.e., rates and physical attributes) within these mechanistic formulations. This work establishes a baseline methodology to systematically evaluate and optimize bivalve upweller culture systems.     

Individual growth variation and its relationship with survival in juvenile Pacific oysters, Crassostrea gigas (Thunberg)

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.     

Volatile Organic Compounds Profile Obtained from Processing Steps of Pacific Oysters (Crassostrea gigas) as Perspective for Food Industry

ABSTRACT

In the heat treatment of oysters, many aroma compounds are lost in the cooking steam and water. In this study, aroma compound profiles from oyster processing were identified by gas chromatography- mass spectrometry (GC-MS). The compounds were extracted by headspace-solid phase microextraction (HS-SPME), while the best process conditions such as temperature, extraction time, and desorption time were studied. The aroma compounds were obtained from raw oysters, from oysters after thermal treatment, from water released from raw oysters, from cooking steam, and from oyster boiling juice. All compounds were identified and semi-quantified by GC-MS. The major oyster aroma compounds were 1-octen-3-ol, hexanal, and benzaldehyde. Most of the components from oysters were lost both to the cooking steam and to the oyster boiling juice. The concentration range of volatile organic compounds transferred for oyster boiling juice between 14 and 90 mg L^?1 shows that the residues from oyster processing have great technological potential, and they can be recovered for application as aromas by the food industry.     

The impacts of aquacultured oysters, Crassostrea virginica (Gmelin, 1791) on water column nitrogen and sedimentation: results of a mesocosm study

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=50.65w^0.699 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.     

Hns对紫贻贝和牡蛎的急性毒性试验

采用环境毒理学急性毒性试验分析方法,分别于24、48、72和96 h研究Hns对海洋污损生物紫贻贝和牡蛎的半数致死浓度、95%置信区间和安全浓度(CS)。结果表明,Hns对紫贻贝的毒性比对牡蛎的毒性高,安全质量浓度为0.854 mg/L,几乎是Hns对牡蛎毒性的8倍。     

Bacteria flora and heavy metals in cultivated oysters <Emphasis Type="Italic">Crassostrea iredalei</Emphasis> of Setiu Wetland,East Coast Peninsular Malaysia

Slipper oyster Crassostrea iredalei is a species of good demand for its sweet flavor and white coloured flesh. The filter feeding nature predisposes oysters to accumulation of pathogenic and heavy metals in waters impacted by sewage pollutions and may thus render the oysters unfit for human consumption. A study was undertaken to investigate the presence of bacteria flora and heavy metal concentrations in cultivated oysters Crassostrea iredalei at Setiu Wetland, Terengganu, the only source of cultivated oysters in East Coast of Malaysia. A total of 200 slipper oyster samples were analyzed. The bacteria were isolated using non selective agar such as TSA agar and selective agars before they were then identified using conventional methods in combination with BBL Crystal identification kit. Heavy metals such as zinc (Zn), copper (Cu), cadmium (Cd), and lead (Pb) concentrations were determined using atomic absorption spectrophotometry. Results showed that the oysters harbor predominantly Shewanella putrifaciens followed by Vibrio parahaemolyticus, Vibrio vulnificus, Vibrio cholerae, Enterobacter cloacae, Escherichia coli and Chromobacterium violaceum. They also contain high concentration of Zn (785.68 ± 285.88 μg/g) with the lowest heavy metal was Pb (0.17 ± 0.15 μg/g), whilst the concentrations of other heavy metals were Cu (38.9 ± 13.2 μg/g) and Cd (1.60 ± 0.28 μg/g). The study is very useful to evaluate the type of bacteria and heavy metal present in oyster meat for human consumption.     

Economic analysis of stake and rack-hanging methods of farming oysters (Crassostrea iredalei) in the Philippines

The cost efficiency of stake and rack-hanging methods of farming oysters are compared. Annual costs and returns data for both methods were obtained from a socioeconomic survey conducted in 1991 at the Aquaculture Department of the Southeast Asian Fisheries Development Center (SEAFDEC/AQD). On average, 14 kg m⁻² (shell-on) and 22 kg m⁻² (shell-on) were produced using the stake and rack-hanging methods, respectively. The translog cost function for 58 oyster farms was estimated using iterative seemingly unrelated regression (SUR). Statistical analysis indicates that the higher production from the rack-hanging method is significantly different (=0.10) from the production using the stake method. The cost-efficient method varied based on production levels. At output levels less that 9044 kg (shell-on), the rack-hanging method had lower average cost per unit, and for higher production levels the stake method had the lower average costs. Similar conclusions were drawn from the marginal cost analysis. Results imply when production is less than 9044 kg, then the most efficient technology is the rack-hanging method and if production is greater than 9044 kg, the most efficient method is the stake method.     

Risk factors associated with increased mortality of farmed Pacific oysters in Ireland during 2011

The Pacific oyster, Crassostrea gigas, plays a significant role in the aquaculture industry in Ireland. Episodes of increased mortality in C. gigas have been described in many countries, and in Ireland since 2008. The cause of mortality events in C. gigas spat and larvae is suspected to be multifactorial, with ostreid herpesvirus 1 (OsHV-1, in particular OsHV-1 μvar) considered a necessary, but not sufficient, cause. The objectives of the current study were to describe mortality events that occurred in C. gigas in Ireland during the summer of 2011 and to identify any associated environmental, husbandry and oyster endogenous factors. A prospective cohort study was conducted during 2010–2012, involving 80 study batches, located at 24 sites within 17 bays. All 17 bays had previously tested positive for OsHV-1 μvar. All study farmers were initially surveyed to gather relevant data on each study batch, which was then tracked from placement in the bay to first grading. The outcome of interest was cumulative batch-level mortality (%). Environmental data at high and low mortality sites were compared, and a risk factor analysis, using a multiple linear regression mixed effects model, was conducted. Cumulative batch mortality ranged from 2% to 100% (median = 16%, interquartile range: 10–34%). The final multivariable risk factor model indicated that batches imported from French hatcheries had significantly lower mortalities than non-French hatcheries; sites which tested negative for OsHV-1 μvar during the study had significantly lower mortalities than sites which tested positive and mortalities increased with temperature until a peak was reached. There were several differences between the seed stocks from French and non-French hatcheries, including prior OsHV-1 μvar exposure and ploidy. A range of risk factors relating to farm management were also considered, but were not found significant. The relative importance of prior OsHV-1 μvar infection and ploidy will become clearer with ongoing selection towards OsHV-1 μvar resistant oysters. Work is currently underway in Ireland to investigate these factors further, by tracking seed from various hatchery sources which were put to sea in 2012 under similar husbandry and environmental conditions.