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.     

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.     

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。     

Effects of temperature on early development of the New Zealand geoduck Panopea zelandica (Quoy & Gaimard, 1835)

Ambient seawater temperature is an important factor during the early life stages of marine invertebrates. Temperature is often manipulated in hatcheries to shorten the incubation period before the larval rearing phase. In this study, the effect of temperature on the early development of the geoduck Panopea zelandica was investigated over a 48‐hr period to identify the optimum temperature for fertilization and development in a controlled environment. Eggs and sperm collected from broodstock were exposed to ten temperatures ranging between 11.8 and 23.7°C, and fertilization and subsequent development were monitored over 48 hr. Highest percentages of fertilization were achieved at 23.7°C, which was the highest temperature tested in this study. However, the development of P. zelandica embryos was greatly hindered at temperatures >18.5°C due to a range of abnormalities arising from uneven cell division and cellular blebbing. All larvae died at the highest temperature of 23.7°C within 48 hr of exposure. The combined fertilization success and embryo development data indicate that 18.5°C is the optimal temperature for incubating P. zelandica embryos under hatchery conditions.     

Mortality event involving larvae of the carpet shell clam Ruditapes decussatus in a hatchery: isolation of the pathogen Vibrio tubiashii subsp. europaeus

Diseases caused by bacteria belonging to the genus Vibrio are a common, as yet unresolved, cause of mortality in shellfish hatcheries. In this study, we report the results of routine microbiological monitoring of larval cultures of the carpet shell clam Ruditapes decussatus in a hatchery in Galicia (NW Spain). Previous episodes of mortality with signs similar to those of vibriosis affecting other species in the installation indicated the possibility of bacterial infection and led to division of the culture at the early D‐veliger larval stage. One batch was cultured under routine conditions, and the other was experimentally treated with antibiotic (chloramphenicol). Differences in larval survival were assessed, and culturable bacterial population in clams and sea water was evaluated, with particular attention given to vibrios. Severe mortalities were recorded from the first stages of culture onwards. The pathogen Vibrio tubiashii subsp. europaeus was detected in both batches, mainly associated with larvae. Moreover, initial detection of the pathogen in the eggs suggested the vertical transmission from broodstock as a possible source. Experimental use of antibiotic reduced the presence and diversity of vibrios in sea water, but proved inefficient in controlling vibrios associated with larvae from early stages and it did not stop mortalities.     

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.     

Survival,growth and physiology of the juvenile razor clam (Sinonovacula constricta) under Na+/K+ ratio stress

In this study, we investigated the response of the Chinese razor clam (Sinonovacula constricta) under the Na⁺/K⁺ ratio in inland saline water. Acute and long‐term (30 days) stresses were studied to better delineate the process of the effect. At the end of the test, only the groups of Na⁺/K⁺ ratio from 21.28 to 159.95 contained surviving Juvenile S. constricta, and the Na⁺/K⁺ ratio 31.91 and 47.27 groups showed significantly higher survival rates (p < .001). In test groups of Na⁺/K⁺ ratio, the growth rate (shell length growth rate and weight gain rate) was significantly lower under than that the control group (p < .05 and p < .001 for length and weight). The Na⁺/K⁺‐ATPase activities in the test Na⁺/K⁺ ratio groups (R3, R5, R6, R7 and R8) were significantly higher than that in the control group during 30 days (p < .05). The superoxide dismutase activity in the higher Na⁺/K⁺ ratio groups (R7 and R8) was significantly higher than that in the control group during 30 days. However, in the test groups, the aspartate aminotransferase (R3, R6, R7 and R8), acetylcholinesterase (R3, R7 and R8) and lysozyme (R7 and R8) activities were lower than that control group during 30 days. Under ultrahigh and ultralow Na⁺/K⁺ ratio acute stress, the oxygen consumption rate, phagocytosis rate and metabolic activity fluctuated significantly. Unbalances of Na⁺/K⁺ ratio may affect ion regulation, metabolism, immunity and neuromodulation. Juvenile S. constricta adapted to a range of Na⁺/K⁺ ratios and keep to growth. This suggested the possibility of breeding S. constricta to resist inland saline water.     

Abnormal mortalities of the carpet shell clam Ruditapes decussatus (Linnaeus 1756) in natural bed populations: a practical approach

In situ controlled systems based on PVC cages surrounded by a net mesh and buried in sand were designed to determine the causes of important mortalities in producing locations of carpet shell clam, Ruditapes decussatus, in two important production areas of Galicia (NW Spain). The pathogenic status of the clam populations (focusing mainly on Perkinsus sp. and clam haplosporidian) as well as changes in water temperature and salinity were recorded. Sampling was conducted during a short period of time when high mortalities were present in the two locations and in a 1‐year study when no important mortalities were registered. We found that the environmental conditions and not the presence of pathogens seemed to be related to mortalities in the study. Our results suggest that mortality rates, especially in natural beds, can emerge from a complex synergy of different factors. Moreover, we propose in situ controlled systems based on PVC cages as a useful method to control infaunal bivalve mortalities in natural beds.     

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.     

The effect of several microalgae isolated from East China Sea on growth and survival rate of postset juveniles of razor clam,Sinonovacula constricta (Lamarck, 1818)

Four species of microalgae (Thalassiosira weissflogii, Thalassiosira pseudonana, Nannochloropsis sp. and an unidentified species) were isolated from natural seawater of East China Sea. By studying the effect on growth and survival rates of two sizes of postset juveniles of razor clam, Sinonovacula constricta (Lamarck, 1818) (shell length 0.37 ± 0.05 mm and 1.07 ± 0.08 mm, respectively), the food value of these microalgae and four other commonly used microalgal species in China (Chaetoceros calcitrans, Isochrysis galbana, Platymonas subcordiformis and Nannochloropsis oculata) in single and two algal species diets were evaluated and compared. For smaller juvenile, when used as a monospecies diet, C. calcitrans and I. galbana supported the greatest shell growth and the highest survival rate, and P. subcordiformis, N. oculata and T. weissflogii produced the smallest shell growth and the lowest survival rate. Meanwhile, for the larger juvenile, single‐species algal diet had the greatest and weakest food value on T. weissflogii and N. oculata, respectively. Full‐mixed algal diets exhibited the strongest food value and most of the two species diets supported more food value than corresponding individual single microalgae diet. Moreover, shell growths and the survival rates of larger juvenile fed most of the two species diets were lower than fed single species of T. weissflogii.     

Probiotic activity of bacteria associated with egg capsules of Concholepas concholepas (common name ‘Loco’)

Egg capsules of Concholepas concholepas were analysed microbiologically, showing the presence of bacteria inside the capsules. The bacteria were isolated and identified, and their probiotic potential on early larvae of C. concholepas was evaluated. From 32 capsules that were examined, 45 bacterial strains were isolated, of which 67% belonged to the genus Bacillus. Survival bioassays were carried out with all the isolated bacterial strains on C. concholepas larvae. It was found that 71% of the bacteria had positive effects on larval survival. This research determined that bacteria of the genera Bacillus and Vibrio present in the capsules have probiotic potential. The bacteria that led to the greatest larval survival were Bacillus pumilus, which may be used in the cultivation of C. concholepas, because one of the limiting factors for the cultivation of this species is larval survival; thus, we propose that the probiotic strains identified in this study will be used during the cultivation of C. concholepas to enhance the chances of larval survival.     

Effect of ration on gonad development of the Pacific geoduck clam,Panopea generosa (Gould, 1850)

The effect of ration on Panopea generosa gonad development was tested over 52 days. Clams were fed Isochrysis sp. and Chaetoceros muelleri (50 : 50 cell count) at rations of 0.8 × 10⁹, 2.4 × 10⁹, 4.0 × 10⁹, 5.6 × 10⁹, 7.2 × 10⁹ and 10.0 × 10⁹ cells clam^?1 day^?1 (R₁, R₂, R₃, R₄, R₅ and R₆, respectively). The highest ration (R₆) caused a 25% die‐off within 3 days and was discontinued. Ration did not significantly affect condition index, gonadosomatic index, connective tissue occupation index or oocyte diameter. Clams fed the R₅ ration (85% of which spawned from day 26 to 52) were more spent than clams in any other treatment with significantly fewer oocytes mm^?2 than those fed the R₁, R₂ and R₃ rations and significantly lower levels of sperm occupation than clams fed any other ration. Spawn percentages were low from day 26 to 52 in R₁, R₂ and R₄ (15, 0 and 0%, respectively). Clams in the R₃ treatment had a similar spawn percentage (100% from day 26 to 52) to those in the R₅ treatment yet maintained gonads in a more ripened condition with higher levels of gamete occupation, making R₃ the most likely ration to maximize gamete output over time.     

缢蛏育苗过程中几个问题的探讨

缢蛏(Sinonovacula constricta Lamarck)俗称蛏子(福建)、蜻子(浙江)、跣子(山东、河北和辽宁),隶属软体动物门(Mollusca)、瓣鳃纲(Lamelli-branchia)、真瓣鳃目(Eulamellibranchia)、竹蛏科(Solenidae),是我国养殖产量和面积最大的贝类之一,以前养殖缢蛏的苗种来自野生苗,但随着养殖面积的扩大,野生苗已远远不能满足生产的需要。     

Ingestion of food pellets containing Escherichia coli overexpressing the heat‐shock protein DnaK protects Penaeus vannamei (Boone) against Vibrio harveyi (Baumann) infection

Feeding aquatic animals with bacterial encapsulated heat‐shock proteins (Hsps) is potentially a new method to combat vibriosis, an important disease affecting aquatic animals used in aquaculture. Food pellets comprised of shrimp and containing Escherichia coli overexpressing either DnaK‐DnaJ‐GrpE, the prokaryotic equivalents of Hsp70‐Hsp40‐Hsp20, or only DnaK were fed to juveniles of the white leg shrimp Penaeus vannamei, and protection against pathogenic Vibrio harveyi was determined. Maintaining pellets at different temperatures for varying lengths of time reduced the number of live adhering E. coli, as did contact with sea water, demonstrating that storage and immersion adversely affected bacterial survival and attachment to pellets. Feeding P. vannamei with E. coli did not compromise their survival, indicating that the bacteria were not pathogenic to shrimp. Feeding P. vannamei with pellets containing bacteria overproducing DnaK (approximately 60 cells g^?1 pellets) boosted P. vannamei survival twofold against V. harveyi, suggesting that DnaK plays a role in Vibrio tolerance. Pellets containing DnaK were effective in providing protection to P. vannamei for up to 2 weeks before loss of viability and that DnaK encapsulated by these bacteria enhanced shrimp resistance against Vibrio infection.     

青蛤生境及生长

青蛤生境及生长ＨＡＢＩＴＡＴＡＮＤＧＲＯＷＴＨＯＦＣＬＡＭ（ＣＹＣＬＩＮＡＳＩＮＥＮＳＩＳＧＭＥＬＩＮ）￥ＹｕＹｅｓｈａｏａｎｄＷａｎｇＨｕｉ（ＥａｓｔＣｈｉｎａＳｅａＦｉｓｈｅｒｉｅｓＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅ，ＡＳＦ，Ｓｈａｎｇｈａｉ２０...     

Use of essential oils extracted from three Origanum species for disinfection of cultured rotifers (Brachionus plicatilis)

Essential oils extracted from three plant species of the genus Origanum, Origanum vulgare subsp. hirtum, Origanum onites L. and Origanum marjorana L., were assayed as potential antibacterial agents for disinfection of rotifers Brachionus plicatilis. Survival of rotifers in seawater with added oregano essential oils was significantly higher than in the control treatment (P < 0.05). When rotifers were incubated in seawater with added oregano essential oils at a final concentration of 10 mg L^?1 for 4 h, the numbers of total culturable bacteria were not significantly lower than in the control treatment (P > 0.05), while the numbers of presumptive Vibrio in rotifers were significantly reduced compared with the control treatment (P < 0.05).     

Seasonality of QPX disease in the Raritan Bay (NY) wild hard clam (Mercenaria mercenaria) population

Quahog Parasite Unknown (QPX) is a potentially lethal pathogen of the hard clam Mercenaria mercenaria along the northeastern coast of the United States. In the Raritan Bay wild clam population, QPX prevalence and infection intensity at three sites were examined by both histology and quantitative PCR in 2006. At two of three sites, QPX infection showed a seasonal pattern, with prevalence and weighted prevalence increasing through the spring, peaking in the summer and declining in the fall, while at the other site, the highest QPX prevalence and infection intensity were observed in the spring although overall prevalence at this site was generally low. Our data suggested that temperature may be an important environmental factor regulating the seasonal pattern of QPX disease in wild clams but also demonstrated that seasonal patterns vary from site to site, possibly linked to the clam density or other environmental factors. Over‐winter sampling and further investigations focusing on environmental factors, clam density and clam mortality as related to QPX infection are needed to better characterize and understand the seasonality of QPX disease.