Excavating sponges that are destructive to farmed pearl oysters in Western and Northern Australia

Species of the family Clionaidae (Porifera: Demospongiae) that excavate shell of the silver‐lip pearl oyster, Pinctada maxima, in north Western and Northern Australia are described. Two species belong to the genus Cliona and one species to the closely related genus Pione. Cliona orientalis has only recently been reported from Australia in living and dead coral on the Great Barrier Reef, and this is the first report of this species from north Western and Northern Australia. Cliona dissimilis is reported from Australia for the first time. Pione velans was first described from Shark Bay, Western Australia and this study extends its distribution from Albany, south Western Australia to Port Bremer in the Northern Territory. The most common species found was C. dissimilis. Pione velans and C. orientalis were also present, although the latter species was rare. Cliona dissimilis and P. velans were found to be sexually reproductive in some shells with specimens of C. dissimilis with oocytes in May and P. velans in September 1999. Egg development was synchronous, indicating that the sponges were oviparous and would broadcast gametes in a spawning event.     

Tetraploid induction in tropical oysters,Crassostrea belcheri (Sowerby) and Crassostrea iredalei (Faustino)

Tetraploid induction has been conducted on temperate oysters but not on tropical oysters. In this study, different heat shocks (32, 35 and 38°C) and cold shocks (1, 4 and 7°C) were used to induce tetraploidy in two tropical oyster species, Crassostrea belcheri and Crassostrea iredalei, through meiosis I inhibition. Temperature shocks were applied on the newly fertilized eggs at 8–10 min post fertilization and terminated when second polar bodies began to form in the control eggs. The ploidy of the larvae and spat was determined via direct chromosome count. The percentage of larval survival until Day 20 was low (between 0.4% and 42.9%) for both temperature shocks and oyster species. No surviving larva was recorded for induction at 1, 4 and 38°C. Tetraploid spat was only recorded in C. iredalei but the percentage is low through heat shock induction of 32 and 35°C. This study shows that the tetraploid induction success rate was slightly higher in C. iredalei compared to C. belcheri. No surviving tetraploid spat were recorded for both oyster species through the cold shock method. This study shows that heat shock can be used to inhibit meiosis for the production of tetraploids but more experiments need to be conducted to determine the optimum temperature when dealing with tropical oysters.     

Siltation increases the susceptibility of surface‐cultured eastern oysters (Crassostrea virginica) to parasitism by the mudworm Polydora websteri

Mudworm (Polydora websteri) parasitism is known to result in unsightly mud blisters in eastern oysters (Crassostrea virginica), resulting in reduced product quality and increased vulnerability to illness and environmental stress. While typically a concern only for bottom‐grown oysters, an abnormal severe outbreak of P. websteri in surface‐cultured oysters in New Brunswick, Canada, was reported in 2013, along with an anecdotally reported concurrent increase in siltation. Although heavier loads of silt are reported to increase P. websteri infestations in oysters, studies report mixed effects of siltation to this regard. Here, we report the results of a field experiment testing the effect of siltation on P. websteri recruitment in surface‐grown oysters at an aquaculture site in Richibucto, New Brunswick. Live oysters of similar size were deployed at the aquaculture site and were left to collect P. websteri recruits under one of two siltation treatments (high vs. low) for 50 days. Results suggested that P. websteri recruitment correlated with metrics of oyster size (shell weight, length, width, depth and surface area). When P. websteri counts were standardized for oyster shell morphometry, P. websteri recruitment was significantly higher in oysters exposed to the high siltation treatment, accumulating approximately 1.5× as many P. websteri as oysters exposed to the low siltation treatment. Our results suggest that higher amounts of siltation on surface‐cultured oysters can result in increased rates of P. websteri parasitism. Enhanced cleaning regimes may help to alleviate the impacts of P. websteri in surface‐grown oysters, although other mitigation strategies exist.     

Quantitative quality evaluation of Eastern oyster (Crassostrea virginica) cultured by two different methods

In order to evaluate the quality of oysters and whether a production method affects quality or not, a set of objective quantitative quality measures was developed. Eastern oysters (Crassostrea virginica) were cultured using two different treatments (never desiccated or desiccated daily with tidal exposure) and the meats were tested by textural, physico‐chemical and chemical analyses over a 25‐day cold storage period. Texture analyses parameters (cutting force and chewiness on oyster adductor muscles) were strongly correlated with storage time before the death of oysters and could be used as a quality indicator for oyster. Total volatile basic nitrogen (TVBN) could be used as freshness indicator for raw Eastern oysters, with the acceptability of 11 mg/100 g. Models for evaluating the quality of oysters were established that reflect the impact of a biofouling treatment on oyster's shelf life and texture attributes. The methods and quality indicators developed in this study were effective in evaluating the quality and freshness of Eastern oysters objectively, and could serve as routine quality check of oyster meat for the industry.     

声光动力联合杀菌技术对牡蛎的保鲜效果

针对单独光动力杀菌、声动力杀菌技术的缺陷,探究声光动力联合杀菌技术（Sono-photodynamic sterilization treatment,SPDT）对牡蛎的保鲜效果。该研究以牡蛎为研究对象,在以姜黄素浓度、声光动力处理时间及超声波功率为单因素试验的基础上进行正交试验,优化声光动力联合杀菌技术对牡蛎保鲜的工艺条件,同时对比不同处理前后的牡蛎进行理化指标及感官评分。结果表明：在姜黄素浓度50μmol/L、超声波功率600 W及声光动力处理时间60 min的条件下,对牡蛎的保鲜效果明显,菌落总数为4.52 lg (CFU/g)。此外,声光动力联合杀菌技术与空白对照组、姜黄素组、光照组、超声波组比较,较好维持牡蛎的pH值、硫代巴比妥酸和挥发性盐基氮在较低数值,保持了牡蛎的外观、硬度及色泽等感官品质,使牡蛎在4℃下贮藏货架期由6d延长至12d。因此,声光动力联合杀菌技术具有良好的杀菌特性,可用于生鲜牡蛎的保鲜,为声光动力联合杀菌技术应用于食品领域提供理论指导与技术参考。     

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。     

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。     

Parasites, pathological conditions and mortality in QX-resistant and wild-caught Sydney rock oysters, Saccostrea glomerata

Differences in the survival of QX-resistant fifth generation (QXR₅) and wild-caught (Wild-Caught) Sydney rock oysters were assessed over the QX-disease risk period in the Pimpama River, SE Queensland. Cumulative mortality of Wild-Caught oysters (31.7%) was significantly greater than QXR₅ oysters (0.0%) over the 118 days of the experiment. PCR and histological results showed that Wild-Caught oyster did not die from QX disease. Histology revealed oysters were infected with disseminating hemocytic neoplasia, a Steinhausia-like infection, a Rickettsia-like organism infecting epithelial cells of the gill, digenean flukes encysted in the gonadal tissue and a gill response to an unknown toxin. The cause of mortality is attributed to disseminating hemocytic neoplasia.     

养殖牡蛎的敌害

论述了养殖牡蛎面临的敌害问题,所涉及的敌害包括绿蛎病、瘤、敌害生物、赤潮、环境压力和综合性因素的恶化等,相信中国的相关研究将走向深广。