海南岛沿岸牡蛎体内六六六的时空变化特征分析及风险评价

于2006—2011年间每年的3月份,在海南岛沿岸选取的4个重要港湾(马袅港、东寨港、八所港、榆林港)采集近江牡蛎(Crassostrea rivularis Gould)成体30只,用气相色谱法测定其六六六(HCHs,包括α-、β-、γ-、δ-HCH)含量。结果显示,2006—2011年近江牡蛎体中HCHs含量范围是未检出～1.16 ng.g-1,平均含量是0.15 ng·g-1,与1985年海南岛贝类体内的HCHs残留量相比,20多年间浓度降低至原来的1/45。在这6年中HCHs含量于2006—2008年先略微下降,之后小范围上下波动,但总体上呈平稳的趋势;样品中HCHs区域平均含量由高到低依次为马袅港>东寨港>八所港>榆林港。通过对HCHs的组分特征分析,认为海南岛采样海域周围近年没有新的HCHs污染源输入。与世界其他海域贝类体内HCHs含量比较,海南岛沿岸牡蛎体内HCHs残留量较低,符合中国《海洋生物质量》一类质量标准。通过计算安全消费量,认为海南岛沿岸海域牡蛎体内HCHs致癌风险和暴露风险均在可接受的范围之内。     

冷冻牡蛎加工工艺研究及模糊数学感官评价

[目的]优化冷冻牡蛎加工工艺。[方法]以牡蛎为主要原料制成冷冻牡蛎,研究了臭氧水浓度、三聚磷酸钠浓度、食盐和茉莉花茶复配物浓度和壳聚糖浓度对冷冻牡蛎感官质量、干耗和汁液损失率的影响,采用正交试验和模糊数学感官评价法对冷冻牡蛎的加工工艺进行优化。[结果]试验表明,选用臭氧水消毒、三聚磷酸钠漂洗、食盐和茉莉花茶复配物去腥和壳聚糖溶液进行镀冰衣处理,冷冻牡蛎的模糊综合评价总分均高于未处理的冷冻牡蛎,而干耗和汁液流失率均低于后者;应用模糊数学感官评价法优化的冷冻牡蛎最佳加工工艺条件为食盐和茉莉花茶复配物浓度3.0%、三聚磷酸钠浓度3.0 g/kg、壳聚糖浓度3.0%、臭氧水浓度2.0 mg/L。[结论]研究可为冷冻牡蛎工业化生产及质量安全控制提供理论基础。     

牡蛎养殖过程中副溶血弧菌与水质因子间的关系

为了研究牡蛎养殖过程中副溶血弧菌与水质因子之间的关系,2009年3月到11月从广东阳西某牡蛎养殖场采集牡蛎样品检测其副溶血弧菌的感染情况,并检测水体温度、盐度、pH和溶解氧。实验结果表明：副溶血弧菌总量的检出率为94.38%。水温和副溶血弧菌总量呈正相关,盐度和副溶血弧菌总量呈负相关,pH和溶解氧与副溶血弧菌总量的相关性不明显。对水温和盐度与副溶血弧菌总量的对数进行回归分析,水温和副溶血弧菌浓度的拟合回归方程为：lgVP= 0.093×T-0.685(R₂=0.336);盐度和副溶血弧菌浓度的拟合回归方程为：lgVP=1.199+0.116×S-0.004×S₂(R₂=0.217);水温和盐度对副溶血弧菌浓度的拟合回归方程为：lgVP=-1.941 0.116×T 0.058×S-0.001×S₂(R₂=0.414)。研究结果可为牡蛎养殖过程中副溶血弧菌的风险分析提供参考依据。     

Short term effects of a commercial eastern oyster nursery upon nutrient and plankton dynamics of a coastal embayment: observations from mesocosm experiments

Two mesocosm experiments were conducted to study the interaction of a commercial oyster‐nursery system with the surrounding embayment, specifically, nutrient and plankton dynamics. The nursery was stocked with 80–200 L of oysters, sized 3–5 mm. Ambient water and the water passed through the oyster nursery were incubated in mesocosms, and nutrients and plankton were monitored over the course of 27‐h incubations. The first experiment conducted in July 2009 captured a phytoplankton community dominated by Peridinium quinquecorne, a rare dinoflagellate not previously reported in the northeastern USA. Dissolved nitrogen compounds in all mesocosms were depleted within the first 6 h. The second experiment was conducted in September 2009, when a more typical and diverse phytoplankton community was present. Unlike the first experiment, Nitrate plus nitrite in the mesocosms was not depleted. Both experiments indicated little difference between the water passed through the oyster nursery and the ambient water in terms of subsequent nutrient and plankton dynamics, indicating little ‘legacy effect’ of the oyster nursery upon nutrients and plankton in this embayment. This conclusion was reached under the specific operating conditions typical for this nursery system, as chosen by the commercial partner in the study; changes in oyster stocking or flow rate are likely to change the results.     

Impact of a native predatory whelk on cultivated oysters (Crassostrea gigas) crops in San Quintin Bay, Mexico

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.     

The consequences of differential family survival rates and equalizing maternal contributions on the effective population size (Ne) of cultured silver‐lipped pearl oysters,Pinctada maxima

The effective population size (N_e) is a critical gauge of how efficiently an aquaculture operation is capturing or maintaining genetic diversity and can govern the long‐term success of genetic selection programmes. In communally reared pearl oysters (Pinctada maxima), high variance in family sizes is a significant contributor towards low N_e and its severity may be compounded by differential survival rates of individual families. To determine the effect of variable survival on N_e in cultured P. maxima, families from two commercial populations were analysed using DNA parentage analyses to monitor survival and changes in relative contributions. Significant shifts in relative contributions were observed between 72 days and 18 months of age in both commercial cohorts (P<0.001). Survival rates were found to be highly variable among families (ranging from 2.5% to 49.5%) when reared in a common environment. Additionally, we investigated whether equalizing maternal family sizes before communal rearing will reduce family size variance, and increase N_e, compared with stocking at naturally produced proportions. Family equalization (E) significantly improved N_e (P=0.013) compared with rearing at natural (N) proportions (E: N_e=7.18±0.34; N: N_e=5.60±0.15); however, this practice may unintentionally magnify negative influences of poor performing families if survival is correlated with other commercially important traits. It is concluded that highly variable family survival will affect N_e in communally reared P. maxima, and the practice of equalizing family sizes in order to maximize N_e may only become consistently beneficial once further progress is made towards understanding, and then reducing variation in family survival rates.     

Isolation and use of beneficial microbiota from the digestive tract of lions‐paw scallop Nodipecten subnodosus and winged pearl oyster Pteria sterna in oyster aquaculture

We isolated microbiota from the digestive tract of Nodipecten subnodosus and Pteria sterna and determined in vitro their haemolytic activity, antagonism against Vibrio spp., bacterial hydrophobicity, production of extracellular enzymes and molecular identification. Five bacterial strains were selected: RL5 and C3 (Lactobacillus spp.) and PB1‐1, PB1‐5 and PB1‐6 (Bacillus spp.). The RL5 and C3 isolates showed antimicrobial activity against Vibrio spp. and the PB1‐1, PB1‐5 and PB1‐6 isolates showed enzymatic activity for amylase, protease, lipase and cellulose; the C3 and PB1‐5 isolates were highly hydrophobic. The selected strains of bacteria were tested in vivo as probiotics, together with a treatment of ampicillin and a control without bacteria on juvenile Kumamoto oysters Crassostrea sikamea. The strains were provided individually and as mixes of isolates. Survival, growth and biochemical composition of the juveniles were determined as in vivo indicators. Juveniles grew significantly larger and faster when treated with a specific mix of isolates (MIX‐B), compared with the control. The protein, lipid and carbohydrate concentrations were also significantly higher in oysters exposed to probiotic treatments, compared with the control and the antibiotic treatment. The selected microbiota showed probiotic proprieties for cultivating C. sikamea juveniles.     

Effects of Ozonated Water Treatment on the Microbial Population,Quality, and Shelf Life of Shucked Oysters (Crassostrea plicatula)

An ozonated water treatment system was designed for the sanitation of shucked oysters (Crassostrea plicatula). The effects of ozone (O₃) on shelf life were examined under refrigerated conditions (4 ± 1°C). Microbiological, chemical, and color quality were also evaluated by determining total aerobic plate counts (APC), total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), and L, a, and b values. Single and orthogonal experiment results showed that oysters treated with 9 mg/L of O₃ in aqueous solution (oyster: ozonated water = 1:6, w/v) for 10 min at 5°C significantly reduced the total APC by about 2-log—from 4.97 ± 0.11 to 2.93 ± 0.17 log CFU/g (p < 0.05). O₃ treatment did not cause significant changes in TVB-N, TBA, a, and b values, although L values were significantly affected. During refrigerated storage, O₃-treated samples expressed lower TVB-N, TBA, a, and b values and higher L values than control samples. The shelf life of O₃-treated samples was 20 to 25 days, while that for the controls was 5 to 10 days. The current study confirms that treatment with ozonated water can effectively prolong the shelf life and maintain the quality of oysters.