Culture possibilities of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

This study investigated razor clam Ensis arcuatus culture from larval rearing to commercial size to assess it's aquaculture potential. Broodstock was spawned several times in hatchery facilities to demonstrate that larval availability is not a constraint for hatchery production. Larval culture lasted 20 days, showing an average survival of 14.35%. The razor clam seed reached a size of 28.5 mm at 4 months. Seed culture is feasible; however, it is constrained by the fact that razor clams need to be buried. Higher survival was observed when culturing razor clam seed with a substrate (82–83%), irrespective of the substrate grain size, while containers held without a substrate showed a significantly lower survival (56.5%). We showed that it is possible to rear E. arcuatus juveniles in bottles, with survival as high as 94–95% being achieved. The length increase of the hatchery‐produced E. arcuatus over 600 days was described by the equation Ln L=4.5+(?141.17/t), where L is length in mm and t is time in days. On‐growing showed adequate survival rates and it took 2–3 years to reach commercial size.     

Genetic variation of the razor clam Ensis siliqua (Jeffreys, 1875) along the European coast based on random amplified polymorphic DNA markers

Ensis siliqua is regarded as an increasingly valuable fishery resource with potential for commercial aquaculture in many European countries. The genetic variation of this razor clam was analysed by randomly amplified polymorphic DNA (RAPD) in six populations from Spain, Portugal and Ireland. Out of the 40 primers tested, five were chosen to assess genetic variation. A total of 61 RAPD loci were developed ranging in size from 400 to 2000 bp. The percentages of polymorphic loci, the allele effective number and the genetic diversity were comparable among populations, and demonstrated a high level of genetic variability. The values of Nei's genetic distance were small among the Spanish and Portuguese populations (0.051–0.065), and high between these and the Irish populations. Cluster and principal coordinate analyses supported these findings. A mantel test performed between geographic and genetic distance matrices showed a significant correlation (r=0.84, P<0.05), suggesting an isolation by distance process.     

Identification of razor clams <Emphasis Type="Italic">Ensis arcuatus</Emphasis> and <Emphasis Type="Italic">Ensis siliqua</Emphasis> by PCR-RFLP analysis of ITS1 region

ABSTRACT:   Ensis arcuatus and Ensis siliqua are the most economically important species of razor clams in the European Union. Due to similarities between their shell morphology, and the differing retail value, these species are often misidentified. Therefore, it is necessary to develop an appropriate protocol to allow accurate differentiation between these species of razor clam in order to protect consumer rights, avoid commercial fraud (whether intentional or unintentional), and to enforce labeling and safety regulations. With the aim of developing a rapid and reliable method of differentiation, individuals of E. arcuatus and of E. siliqua were examined by polymerase chain reaction restriction fragment polymorphism (PCR–RFLP) using the internal transcribed spacer region 1 (ITS1). A species-specific restriction endonuclease pattern was found with the enzyme Ksp I for both species, allowing their exact identification. Thus, this work provides a simple, reliable and rapid protocol for accurate discrimination between E. arcuatus and E. siliqua , which proves useful for traceability and enabling the enforcement of labeling regulations.     

Biochemical and fatty acid dynamics during larval development in the razor clam Ensis arcuatus (Bivalvia: Pharidae)

This article reports on the changes in gross biochemical and fatty acid composition of the razor clam Ensis arcuatus larvae throughout development. Protein was the largest component of dried larval tissues. The energy required for embryogenesis in E. arcuatus oocytes was obtained from stored proteins and carbohydrates, while total lipids increased significantly. Lipids and carbohydrates have an important role as energy contributors from day 1 to day 8. During larval development the strategy was to indistinctly store energy reserves (protein, lipid and carbohydrate) to surpass metamorphosis. During embryonic development there was a gain in fatty acids of neutral and polar lipids. A depletion of fatty acids in neutral lipids was observed from day 1 to day 8 in E. arcuatus larvae, mainly due to the decrease in 16:0 and EPA. NMID fatty acids were present in amounts similar to those of some PUFAs in polar lipids, especially 22:2NMID.     

Vibrios in hatchery cultures of the razor clam,Solen marginatus (Pulteney)

Hatchery culture of the razor clam, Solen marginatus (Pulteney), has recently been developed in Galicia (NW Spain). However, recurrent episodes of mortalities of larval and post‐larval cultures have been recorded during the course of various studies. The disease signs were similar to those described for other bivalve species in outbreaks caused by bacteria of the genus Vibrio. In this article, we present the results of microbiological monitoring of two batches of razor clams with different survival rates. All fermentative isolates were identified as members of the Splendidus clade within the genus Vibrio. Some of these isolates, identified as Vibrio splendidus‐like, were clearly associated with the batch suffering mortalities, indicating their possible role as pathogens. Similar strains were found in the broodstock, suggesting vertical transmission of these bacteria. This is the first study of the microbiota associated with hatchery culture of S. marginatus, and the results will provide useful information for the optimization of a protocol for hatchery culture of this bivalve species.     

Environmental impact of razor clam harvesting using salt in Ria Formosa lagoon (Southern Portugal) and subsequent recovery of associated benthic communities

• 1. Razor clams are found in different habitats ranging from sheltered systems (e.g. lagoons and estuaries) to open coasts. They are distributed worldwide and comprise a small number of species of high economic value. Depending on the specific habitat and species exploited, different mechanical and hand‐harvesting techniques are employed. While the environmental effects resulting from mechanized methods have been described by several authors, the impacts caused by traditional hand‐harvesting methods remain unknown. Therefore, a study was undertaken in Ria Formosa lagoon (South of Portugal) addressing the environmental effects resulting from harvesting Solen marginatus with salt.
• 2. No significant impact on the sediment was found; the main effect was an increase in salinity after covering the area with salt, which decreased rapidly with the flood tide and after a few hours had returned to pre‐harvesting levels.
• 3. No effects on benthic communities were observed, with similar fluctuation patterns recorded in control and experimental areas, the observed differences being attributed to the natural variability of benthic populations.
• 4. Based on the results obtained in the present study, a razor clam fishery using salt in intertidal areas can be considered environmentally ‘friendly’.

Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of stocking density on intermediate culture of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

Commercial production of most bivalve species involves a phase of intermediate cultivation during which juveniles are grown under protected conditions until they can be transferred to the final grow‐out location. Consequently, the aim of this study was investigating the effect of density on growth and survival in the intermediate culture of the razor clam Ensis arcuatus in raft. Two series of experiments were performed, using in the first experiment two holding systems: 5‐L plastic bottles and PVC cylinders, both perforated, covered with a 1 mm mesh net to prevent razor clam escape and a 10‐cm layer of coarse grained sand (300–1200 μm grain diameter). In this trial, two stocking densities were tested: 0.15 and 0.30 kg m^?2. In the second one‐two densities were essayed (0.62 and 1.24 kg m^?2) in the PCV cylinders. In the first experiment after 27 of trial higher growth in cylinders at low density was observed. At the end of this trial all juveniles died in the 5‐L plastic bottles and higher growth and survival were recorded in the cylinders at low density. In the second experiment, significant differences in growth and survival were found on day 70, with the best results at low density. Five‐L plastic bottles must be rejected as holding system for the intermediate culture of E. arcuatus and the PVC cylinders at low densities could be a good alternative. At the end of the experiment razor clams reached the adequate size for their transfer into the grow‐out system.     

Quantifying current and future risks of invasiveness of non-native aquatic species in highly urbanised estuarine ecosystems—A case study of the River Neretva Estuary (Eastern Adriatic Sea: Croatia and Bosnia–Herzegovina)

Biological invasions are a major driver of global environmental change as invasive non-native species can exert severe environmental impacts on invaded ecosystems. Estuaries are especially vulnerable to biological invasions, which in highly urbanised areas are further facilitated by introduction pathways linked to commercial activities. This study provides a risk screening of non-native invasive species for the highly urbanised River Neretva Estuary (Eastern Adriatic Sea: Croatia and Bosnia–Herzegovina). In total, 12 species of non-native aquatic organisms were identified and screened for their invasiveness with the Aquatic Species Invasiveness Screening Kit. Of these species, eight were classified as carrying a high risk of invasiveness under current climate conditions and nine under future climate conditions. Amongst the high-risk species, blue crab Callinectes sapidus has already caused impacts in the risk assessment area, where it also represents an important economic resource. The “horizon” species Pacific oyster Crassostrea gigas and Manila clam Ruditapes philippinarum also carried a high risk of invasiveness, which for the latter species applied under predicted global warming. The present findings will contribute towards preventative management and control measures for the conservation of the natural ecosystem of the River Neretva Estuary whilst accounting for aquatic farming demands.     

Molecular species diagnosis confirmed the occurrence of Kumamoto oyster <Emphasis Type="Italic">Crassostrea sikamea</Emphasis> in Korean waters

In order to develop an appropriate natural resource management policy, it is important to elucidate the cryptic habitats of species. Oyster species are likely to have such unrecognized habitats owing to the difficulty involved in morphological species identification. In this study, we discovered a novel cryptic habitat of the Kumamoto oyster Crassostrea sikamea, a sibling species of the Pacific oyster C. gigas, in Korean waters. We collected 50 oyster samples from Suncheon Bay, located in the southern Korean Peninsula, among which 20 individuals of C. sikamea, 29 of C. gigas, and one C. sikamea/C. gigas hybrid were identified based on mitochondrial and nuclear DNA markers. There were no significant differences in shell morphology between the two species, which is consistent with how difficult it is to delineate them based on their shell features. Our identification of this novel C. sikamea habitat should help to improve the resource management of East Asian oysters.     

Two epizootic Perkinsus spp. events in commercial oyster farms at Santa Catarina,Brazil

Perkinsus spp. have been detected in various bivalve species from north‐east Brazil. Santa Catarina is a South Brasil state with the highest national oyster production. Considering the pathogenicity of some Perkinsus spp., a study was carried out to survey perkinsosis in two oyster species cultured in this State, the mangrove oyster Crassostrea gasar and the Pacific oyster Crassostrea gigas. Sampling involved eight sites along the state coast, and oyster sampling was collected during the period between January 2013 and December 2014. For the detection of Perkinsus, Ray's fluid thioglycollate medium (RFTM) and histology were used, and for the identification of the species, PCR and DNA sequencing were used. Perkinsus spp. was found by RFTM in C. gigas and C. gasar from São Francisco do Sul. This pathology was also detected in C. gasar from Balneário Barra do Sul both, by RFTM and histology. Perkinsus marinus was identified in C. gigas and C. gasar from São Francisco do Sul and Perkinsus beihaiensis in C. gasar from Balneário Barra do Sul. This is the first report of P. marinus in C. gigas from South America. Results of this preliminary study suggest that both oyster species tolerate the species of Perkinsus identified, without suffering heavy lesions.     

Mitochondrial DNA barcoding for Okinawan oysters: a cryptic population of the Portuguese oyster Crassostrea angulata in Japanese waters

We used mitochondrial (mt) DNA barcoding to evaluate the species diversity of oysters sampled from the coast of Okinawa Island, Japan. Our analysis revealed the presence of a hitherto-unrecognized population of the Portuguese oyster Crassostrea angulata, a putative species closely related to the Pacific oyster C. gigas. Forty-eight Okinawan oyster specimens were collected and subjected to species diagnosis trials based on mtDNA barcodes. Of the 30 Crassostrea specimens, 17 were identified as C. angulata, seven as C. gigas and six as C. bilineata (syn. C. iredalei). The remaining 18 Saccostrea specimens formed several divergent clades in phylogenetic trees, although they could not be identified to species level because of the confounding taxonomy of the Saccostrea species complex. Our results stress the necessity for reviewing the species diversity of Okinawan oysters.     

CMC在缢蛏涂覆保鲜上的应用研究

采用羧甲基纤维素钠（CMC）作为缢蛏（Sinonovacula constricta）保鲜涂覆胶,在5℃下保藏7 d,以缢蛏的活泼度、成活率、水分蒸发量及挂胶量等为指标对其保鲜效果进行评价。试验结果表明,采用CMC保鲜胶涂覆的缢蛏,5℃下7 d的成活率为100%,而对照组的成活率为60%,涂膜处理能降低水分蒸发速度,保鲜效果显著。     

响应面法对缢蛏粗多糖提取工艺的优化

以秦皇岛海域的缢蛏为原料,通过不同提取方法的比较,确定超声辅助酶解提取法为较优的多糖提取方法,并通过响应面法对缢蛏多糖提取工艺进行优化。试验结果表明,原料超声预处理30min后再进行酶解提取,在添加3.99%的木瓜蛋白酶、50.9℃、酶提8.94h条件下缢蛏多糖提取量达9.41mg/g(鲜)。该方法对研究海水贝类多糖功能性产品原料的选取及产品的开发与应用有重要意义。     

Consumer Preference and Sensory Properties of the Pacific Cupped Oyster (Crassostrea gigas) and the European Flat Oyster (Ostrea edulis)

ABSTRACT

Experts in the oyster supply chain (farmers, retailers, and gourmet chefs) in The Netherlands have suggested that the European flat oyster (Ostrea edulis) has superior sensory qualities compared to the Pacific cupped oyster (Crassostrea gigas). However, scientific evidence is lacking. The aim of this study was to evaluate consumer preferences for these two oyster species and to determine the sensory properties of both species by consumers. Two-alternative forced choice tests were performed with the oysters involving a panel of 74 naïve consumers. No significant differences in preferences between the oyster species were observed by the consumers. Nine sensory attributes of both oyster species were evaluated. Consumers did not observe significant differences between species in the sensory attributes: overall odor intensity, sea odor, mud odor, sweetness, pungency, and firmness. The Pacific cupped oyster was perceived as significantly saltier and more intense in greenness than the European flat oyster. We concluded that only a few sensory properties of the European flat oyster and the Pacific cupped oyster are perceived as being different by untrained consumers.     

贝类中3种组织血型抗原ELISA检测方法的建立与分型

人类组织血型抗原(histo-blood group antigens,HBGAs)是诺如病毒(NoVs)的结合受体,本研究假设贝类中也存在类似的HBGAs并且特异性地富集NoVs,利用HBGAs单克隆抗体,建立贝类中3种HBGAs的ELISA检测方法,分析牡蛎(Crassostrea gigas)、缢蛏(Sinonovacula constricta)、菲律宾蛤仔(Ruditapes philippinarum)、紫贻贝(Mytilus galloprovincialis)、毛蚶(Scapharca subcrenata)、栉孔扇贝(Chlamys farreri)等6种双壳贝类中HBGAs的类型。结果显示,在上述6种贝类中都检测出A型抗原,其中菲律宾蛤仔的检出率为11.6%(9/77),紫贻贝的检出率为28.1%(16/57),缢蛏样品为72.3%(47/65),栉孔扇贝为84.6%(58/69),其余贝类检出率为100%;只有牡蛎样品检出H抗原,检出率为30.7%(28/91);在缢蛏和毛蚶样品中检测出B型抗原,检出率分别为76.9%(50/65)和77.8(56/72)。结果表明贝类中存在不止1种类型的HBGAs。     

In search of the Kumamoto oyster <Emphasis Type="Italic">Crassostrea sikamea</Emphasis> (Amemiya, 1928) based on molecular markers: is the natural resource at stake?

A cornerstone in conserving wildlife is to resolve taxonomic uncertainties over organisms so that conservationists can define the entity that should be conserved. This is the case for two closely related Crassostrea oysters inhabiting the Ariake Sea (Kyushu, Japan) in sympatry, the kumamoto oyster C. sikamea and Pacific oyster C. gigas, where molecular markers have shed light on their taxonomic separation and species diagnosis. In the past, there was a concern that Kumamoto oysters may be at risk of extinction. However, several field surveys equipped with species-diagnosis molecular markers have provided solid evidence that this perception is incorrect. Nevertheless, previous studies have sometimes given conflicting results, throwing us into confusion about the resource status. Research on natural Kumamoto oysters that the author hopes could help to enhance our understanding of the conservation of this invaluable oyster is reviewed here.

Comparative low temperature tolerance of small juvenile European, Ostrea edulis L., and Pacific oysters, Crassostrea gigas Thunberg

The present investigation was carried out to measure the survival of juvenile oysters (spat) of a native species, European oyster, Ostrea edulis L., and an introduced species, Pacific oyster, Crassostrea gigas Thunberg, at typical winter seawater temperatures in the British Isles. Two size groups of each species were maintained either unfed or with low algae rations at 3, 6 and 9^oC for up to 11 weeks. The majority of O. edulis juveniles survived for 11 weeks at all temperatures. Unfed animals utilized biochemical reserves and lost organic weight during this period. Fed O. edulis showed a small weight loss at 3^oC, but increased in weight at 6^oC and 9^oC. At all temperatures, O. edulis preferentially utilized lipid reserves in treatments in which organic weight was lost. In contrast, C. gigas juveniles preferentially utilized protein as an energy source. All C. gigas juveniles survived at 9 and 6^oC, but high mortalities (> 95%) occurred after 3-7 weeks at 3^oC. Both fed and unfed C. gigas juveniles lost weight, reserves and condition at 3^oC. Juveniles grew when fed at 6 and 9^oC. In both oyster species, the proportion of phospholipid (n-6) fatty acids, principally 20 : 4 (n-6) increased in those juveniles which showed a decrease in organic weight. Food cell consumption rates were lower at lower temperatures and were higher in O. edulis at 9^oC than in C. gigas. The results are discussed with respect to recruitment and winter survival of small juveniles.     

Spatfalls of the non-native Pacific oyster,Crassostrea gigas,in British waters

Light spatfalls of the Pacific oyster, Crassostrea gigas, have occurred in the estuaries of the Rivers Exe, Teign and Dart (Devon) and in the Menai Strait (Gwynedd), near to sites of commercial cultivation of this species. Comparisons of the sizes of the naturally settled oysters with hatchery oysters suggests that the spat from the River Teign and Menai Strait settled in 1989 and 1990. The springs and summers of these years were exceptionally warm with mean monthly air temperatures 0.8°-1.3°C above the 1951–1980 average for the period April to August. Although sitings of Pacific oyster spat were made in Loch Sween and Emsworth Harbour over 20 years ago, there is no evidence that self-sustaining populations have developed. The spatfalls which occurred in some coastal waters of Devon and Gwynedd in 1989 and 1990 are unlikely to sustain natural fisheries and are likely to die out as did the Portuguese oysters which occasionally settled in the River Blackwater, Essex.     

Reproductive performance and offspring quality of Chinese mitten crab Eriocheir sinensis (H. Milne-Edwards) females fed an optimized formulated diet and the razor clam Sinonovacula constricta

After feeding female Eriocheir sinensis on an optimized formulated diet or fresh razor clam Sinonovacula constricta for 7 months, their reproductive performance and offspring quality were compared. To evaluate diet nutrient contents, the proximate, fatty acid and amino acid compositions of the formulated diet and the razor clam were analysed. The nutritional value of the diets was determined by assessing survival, gonadosomatic index (GSI) and hepatosomatic index (HSI) of female crabs from both diet treatments, together with the percentage of females that spawned, total egg production per female and fecundity (number of eggs g^?1 female wet weight). Furthermore, the quality of eggs and newly hatched larvae from the two dietary treatments were determined using the following parameters: egg diameter, wet weight and dry weight, hatchability, proximate and fatty acid profile of eggs, larval carapace length, resistant to starvation and osmotic shock, larval survival and development to the zoea II stage. Higher protein, phospholipids (PL) and amino acids (AA) contents were found in the razor clam while the formulated diet contains higher levels of ash, total lipid (TL) and 18:1n‐9, 18:2n‐6 and 22:6n‐3 fatty acids. Although female crabs fed the two different diets showed similar reproductive performances, newly hatched zoea I larvae produced by the crabs fed the formulated diet had significantly longer mean carapace length and shorter development time to the zoea II stage under identical culture condition (P<0.05). Moreover, dietary fatty acid appeared to have more significant effects on the fatty acid composition of the hepatopancreas than it did on mature ovaries or eggs. This suggests that the fatty acid profile of mature ovaries is indicative of the specific fatty acid required for ovarian development in E. sinensis. In conclusion, our results show that the optimized formulated diet developed in this laboratory can totally replace the razor clam, a broodstock food widely used in E. sinensis hatcheries in China. This encouraging result should facilitate more reliable hatchery production of this important aquaculture species.     

乳山寨滩涂缢蛏半人工采苗的研究

为解决北方沿海缢蛏养殖的苗种问题，在乳山寨滩涂建立缢蛏半人工采苗场，对苗坪适时进行翻耕平整，加强培育管理，１９９３年４ｈ采苗场共采蛏苗８７７０万粒，平均２２１５粒／，平均壳长２．５ｃｍ；１９９４年４０ｈ采苗场共采蛏苗５亿粒，平均１４２８粒／，平均壳长２ｃｍ。结果发现，附苗前翻松平整的苗坪附苗数量远高于未翻松平整的苗坪。山东沿海移养缢蛏性腺于９月中旬至１０月上旬进入成熟期，１０月上、中旬开始放散