Evaluation of macroalgal detritus as food source for juvenile Manila clam,Ruditapes philippinarum: Effects on growth,amino acid content and fatty acid composition

Sufficient high‐quality microalgae are required for indoor nursery of juvenile Ruditapes philippinarum. However, culturing numerous microalgae to support clam feeding is a heavy burden on many hatcheries. The effects of detritus from the macroalgae Ulva pertusa, Chondrus ocellatus and Undaria pinnatifida on the growth, amino acid content and fatty acid profile of R. philippinarum were assessed as potential substitute diets. The green microalga Tetraselmis cordiformis served as comparative diet. Results revealed that the clams ingesting distinct diets presented no significant differences in growth of soft tissues, but the nutritional component of these clams differed dramatically. The clams fed with Undaria + Tetraselmis had the highest content of essential amino acids and proteins. In addition, the clams fed with single macroalgal diets and mixed macroalgal detritus and Tetraselmis showed significantly higher or statistically equal levels in n‐3/n‐6 ratio and docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio with respect to Tetraselmis diets. The relative percentages of EPA and DHA in clams fed with Undaria were 28% and 63% higher than those fed with Tetraselmis, and the arachidonic acid abundances in clams ingesting Undaria + Tetraselmis and Tetraselmis were significantly higher than those in clams ingesting other diets. Together, the diets containing single Undaria or mixed Undaria + Tetraselmis produced Manila clams with nutritional advantages in terms of essential amino acids and polyunsaturated fatty acids. Thus, the detritus of macroalgae, especially Undaria, is an appropriate substitute diet, at least partially, for culture of nutrition‐improved R. philippinarum.     

Abundance and culture trials of Ruditapes philippinarum (Adam and Reeve, 1850), and abundance of Tellina (Quidnipagus) palatum (Iredale, 1929) at two sites in Kāne'ohe Bay,O'ahu,Hawai'i

Abundance, length‐frequencies and distribution of Ruditapes philippinarum (Manila Clams) and Tellina (Quidnipagus) palatum were measured at two beaches in Kāne'ohe Bay, O'ahu, Hawai'i in June, 2010. Abundances had decreased from 866.2 m^?2 to 3.4 m^?2 for Ruditapes and from 75.5 m^?2 to 1.5 m^?2 for T. palatum since 1977. Distribution of both species was patchy, but both were most commonly found >40 m from shore. Size frequencies of live clams compared with empty shells suggest that few Ruditapes survive to sexual maturity. A similar trend was not detected for T. palatum. Aquaculture trials of R. philippinarum were conducted at the He'eia and Moli'i traditional Hawaiian fishponds in the same bay. The clams failed to thrive, although triploid and diploid Crassostrea gigas performed well in concurrent trials in the same fishponds. Current lower abundances for wild R. philippinarum could be due to factors related to predation or nutrient limitations. Previously, two large sewage outfalls existed at the surveyed clam bed areas which may have temporarily increased nutrient availability for both wild and cultured clams. Current nutrient levels may inhibit Manila clam growth and recruitment in Kāne'ohe Bay.     

Small-scale variation in feeding environments for the Manila clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> in a tidal flat in Tokyo Bay

The relative contribution of particulate organic matters (POMs) in water column and sediment as a food source for the Manila clam, Ruditapes philippinarum, was studied using carbon and nitrogen stable isotopic method (δ¹³C and δ¹⁵N) in a tidal flat at Seaside Park, Yokohama, Japan. Comparisons of δ¹³C and δ¹⁵N among R. philippinarum and POMs in surface water, bottom water, and sediment surface indicated that R. philippinarum larger than 5 mm shell length (SL) mainly assimilated benthic POM, and individuals smaller than 5 mm SL assimilated benthic and pelagic POM. Continuous measurements of chlorophyll concentrations in the bottom water revealed tide-driven resuspension of the benthic phytopigments. R. philippinarum showed differences in δ¹³C and δ¹⁵N along an inshore–offshore transect, indicating small-scale spatial differences in POM provision in the tidal flat. These findings suggest that POM in the bottom water, supposedly inhaled by R. philippinarum, is a mixture of a larger proportion of resuspended benthic POM and a smaller proportion of pelagic POM, and that the mixing ratio of the POMs may be affected by the hydrodynamics of flooding water associated with tidal flat topography.     

双台子河口两种滩涂埋栖性贝类的营养价值及安全性分析评价

为全面评价文蛤和四角蛤蜊的营养价值和食用安全性,采用常规方法对这两种滩涂埋栖性贝类的一般营养成分和Cd、As、Cr及Hg等重金属含量进行了分析。结果显示,文蛤和四角蛤蜊的粗蛋白质含量均较高,分别为58.24和57.38 g/100 g;灰分含量分别为18.35和25.39 g/1 00 g;粗脂肪含量均较低。文蛤和四角蛤蜊氨基酸总量分别为44.87和37.20 g/100 g,其中必需氨基酸含量分别为18.39和15.16 g/100 g,呈味氨基酸含量分别为18.89和15.58 g/100 g。文蛤和四角蛤蜊中Cd的含量最高,Hg的含量最低。研究表明,文蛤及四角蛤蜊均为营养价值、经济价值较高的滩涂埋栖性贝类,且文蛤在蛋白质、氨基酸组成与含量方面更优。文蛤和四角蛤蜊中Cr、Hg符合我国《无公害食品水产品中有毒有害物质限量》等卫生要求,而Cd、As含量超标。文蛤和四角蛤蜊中的重金属含量可能对人体存在一定的摄食健康风险。     

Mortality of the short-neck clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> induced by the toxic dinoflagellate <Emphasis Type="Italic">Heterocapsa circularisquama</Emphasis>

Mortality of the short-neck clam Ruditapes philippinarum exposed to the toxic dinoflagellate Heterocapsa circularisquama was studied under controlled conditions to clarify the mechanisms of recurrent mass deaths of clams occurring in western Japanese coastal areas. One-week mortality tests, involving three water temperatures, six H. circularisquama concentrations, and two clam body sizes, showed a significant increase in mortality with increasing temperature, H. circularisquama concentration, exposure duration, and body size (ANOVA, P < 0.01). Clam death was observed at concentrations as low as 50 cells/ml and temperatures as low as 15°C. Prior to death, clams showed an extreme retraction of their mantle edge and siphon, along with recurrent vomiting behavior before initiating a closure reaction followed by paralysis then death. Gills of paralyzed clams showed an important uptake of dye, implying gill damage. This study is the first laboratory evidence of bivalve mortality induced by H. circularisquama at low concentrations and low temperature, and the first report of differential effects according to the body size of bivalves.     

Effect of dried algae diets on conditioning and fecundity of Manila clam, Tapes philippinarum (Adams and Reeve)

Abstract The effectiveness of live-algae replacement diets for the conditioning and spawning success of adult Manila clam, Tapes philippinarum (Adams and Reeve), was assessed. Two dried diets were tested: a diet of dried Tetrasetmis suecica (Kylin) Butch, and a mixed diet of dried T. suecica (70%) and dried Cyclotella cryptica Reimann et al. (30%). These diets were compared with three live diets: Skeletonema costatum (Grev.) Cleve, Dunaliella tertiolecta (Butcher) and T. suecica. An unfed group was used as a control. The same ration (dry weight) of food was supplied for all groups at 6% of the dry meat weight per day. The broodstock were conditioned for 7 weeks. After 4 weeks none of the animals was ready to spawn. After 6 weeks all the diets promoted spawning and after 7 weeks the unfed group also spawned. It seems that dried algal diets are effective for conditioning and spawning of Manila clams, as the dry meat weight, condition index and fecundity of broodstock fed these diets were significantly greater than for unfed animals. However, the fecundity and proportion of parental lipid released in the eggs of clams conditioned with dried diets was lower than for the clams conditioned with live algae.     

Growth and survival of hatchery-bred giant clams (<Emphasis Type="Italic">Tridacna gigas</Emphasis>) in an ocean nursery in Sagay Marine Reserve,Philippines

To restore the diminishing population of the giant clam Tridacna gigas in Sagay Marine Reserve (SMR), Negros Occidental, central Philippines, two size classes [8- and 10-cm shell length (SL)] of hatchery-bred T. gigas were reared in an adjacent ocean nursery for restocking to Carbin Reef later upon reaching grow-out size of ≥20 cm SL. Growth rates did not significantly differ for both sizes and were on average 0.67 cm month⁻¹. However, survival after 382 days of rearing T. gigas was significantly higher in the 10-cm SL clams than the 8-cm SL clams (96 and 83%, respectively). For future restocking projects, the use of 8-cm SL clams is recommended because the lower survival of this size class is compensated by its cheaper price. While rearing the clams to attain grow-out size, the population of wild clams (Family Tridacnidae) in Carbin Reef was assessed using ten 50 × 2-m belt transects. Four species of tridacnid clams have been recorded: Hippopus hippopus, Tridacna crocea, T. maxima, and T. squamosa. T. crocea comprised 12.5–93.9% of all the clams observed in all ten transects. There was a significant difference in clam density between species (ANOVA, F = 6.94, P < 0.001), with T. crocea having the highest density. Living T. gigas were absent, but presence of dead shells was indicative of its presence in the reef in the past. It can be expected that the release of hatchery-bred T. gigas juveniles in Carbin Reef could provide future breeders that will repopulate this reef and the adjacent reef communities.     

Protein expression profiling in haemocytes and plasma of the Manila clam Ruditapes philippinarum in response to infection with Perkinsus olseni

The protein expression profiling in clam haemocytes and plasma in response to Perkinsus olseni was addressed. Adult Manila clams from a P. olseni‐free bed were experimentally challenged with parasite zoospores to analyse immune response. In another experiment, the effects of longer term infection were assessed in adult clams collected from a P. olseni‐affected bed, by comparing moderate to very heavily infected clams with non‐infected ones. Haemocyte and plasma proteins were separated by two‐dimensional electrophoresis; spot patterns were qualitatively compared between treatments within each experiment and the spots indicating differential protein expression associated with P. olseni challenge or with field infection were processed for protein identification. Fifteen clam proteins (four in haemocytes and eleven in plasma) of which expression was markedly affected by P. olseni were identified. Some of the identified proteins have a well‐known role in clam immune response against the parasite, such as lysozyme and lectins. Rho GTPase‐activating protein 6 could be a marker of resistance against P. olseni, which should be further studied.     

Growth Improvement of Shell Length in the Orange Strain of Manila Clam,Ruditapes philippinarum

Mass selection for shell length was conducted in the orange strain of the Manila clam, Ruditapes philippinarum, in this study. Based on the size‐frequency distribution, the clams constituting the largest 10% of the distribution were selected as parents for the selected line. An equal number of clams of the orange strain were randomly chosen as parents for the control line prior to the size selection. The responses to selection and realized heritability were 2.37 and 0.61, respectively. In addition, 97.3% of the progenies inherited the orange shell color. Our results suggest that mass selection for fast growth of shell length in this orange strain of the Manila clam is effective.     

文蛤浮游期发病幼虫细菌群落分析和致病菌的分离鉴定

为研究文蛤育苗过程中幼虫病害及其主要致病菌,实验通过构建细菌16S rDNA克隆文库、病原菌分离纯化、人工感染和药敏实验等方法对育苗场发病的浮游期文蛤壳顶幼虫样品进行了系统分析。结果显示,发病的文蛤壳顶幼虫细菌群落多样性低,地中海弧菌占比高达75%以上,推断其可能为引发此次幼虫发病的主要致病菌。从发病幼虫的匀浆组织中分离获得该优势菌株,测序及系统发育鉴定为地中海弧菌。人工感染实验确定了其致病性,菌株US2-01在1.0×10⁶ CFU/mL的菌液浓度下浸泡感染文蛤浮游幼虫,96 h累计死亡率为84%。药敏实验表明,地中海弧菌菌株US2-01在12种抗生素的测试中对常用的青霉素、氨苄西林、红霉素等抗生素具有一定的耐药性,对四环素和多西环素中度敏感,对头孢他啶、庆大霉素、卡那霉素等其余7种抗生素呈现高度敏感。本研究首次报道了地中海弧菌为文蛤浮游期幼虫致病的一种潜在病原,研究结果可为文蛤幼虫疾病研究及贝类苗种培育过程中的病害防控提供科学依据。     

The effect of temperature on the energy budget of the Manila clam, <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>

In this study, the energy budget of the Manila clam, Ruditapes philippinarum, was evaluated after one-week acclimation periods at 5, 10, 15, 20, and 25°C. Small clams (151 ± 12 mg DW) and large clams (353 ± 16 mg DW) were fed with the microalgae, Isochrysis galbana. Filtration rate, ingestion rate, assimilation efficiency, oxygen-consumption rate, and ammonia excretion rate were measured. Both filtration rate and ingestion rate of small and large clams were found to be related to temperature. The highest Q ₁₀ values were measured in the range 15–20°C for both small and large clams. Assimilation efficiency of both small and large clams was not significantly influenced by temperature, although the maximum mean values were detected at 20°C. Oxygen consumption rate and ammonia excretion rate of small and large clams were found to be related directly to temperature over the entire range, with a maximum being detected at 25°C. The highest Q ₁₀ value was estimated in the range 10–15°C with regard to oxygen consumption rate, and in the range of 15–20°C with regard to ammonia excretion rate. Scope for growth (SFG) was positive at all temperatures, achieving a maximum value at 20°C in both small and large clams, primarily as a consequence of the enhanced ingestion rate which offset the concomitant elevation in the metabolic rate. In this study we have estimated the thermal optimum for this species at 20°C.     

Status of giant clam resources around Okinawa‐jima Island,Ryukyu Archipelago,Japan

相似文献   

Clam farming quality as a management tool: A proposal based on recent studies in Northern Adriatic lagoons

The rapid and extensive spread of the clam Tapes philippinarum in Northern Adriatic lagoons, mostly in the lagoon of Venice (550 kmq), has led to severe exploitation by mainly free fishing, thus breaching the law. To contrast this unsustainable overexploitation, to which the present decreasing clam harvests are at least partly due, the local fishing authority has recently prepared a Master Fishing Plan for clam production, which is at present under way: the free fishing system must be replaced by a licencing system aimed at regulating market supply and mainly at converting more than 1000 fishermen into clam farmers. Moreover, a number of regulations for both vessels and harvesting techniques and management rules, such as daily clam harvests and fishing times, have been established. Although these newly introduced regulations may be regarded as valuable tools for preserving both the lagoon environment and the resource itself, they do not adequately consider protection for consumers. Although the licensed water areas have been evaluated as safe according to Italian law, at present no guarantees certify the quality of the clams harvested from them, due to the fact that the lagoon of Venice has polluted areas from which clams may be collected illegally and recycled to the legal market simply by putting them into the approved licensed areas before harvesting and marketing them. This paper therefore proposes a number of measures to be undertaken within the framework of good farming practices. The aim is to improve product quality by certification procedures in all production phases, and to guarantee the definite origin of farmed clams.     

Growth,mortality and reproduction of the transplanted Manila clam (Ruditapes philippinarum Adams & Reeve 1850) in Jiaozhou Bay

Samples of Manila clam (Ruditapes philippinarum Adams & Reeve 1850) were collected from May 2004 to April 2005 monthly, and plankton net trawling of planktonic larvae and bottom sediment sampling surveys were further conducted from May to October 2006 in Jiaozhou Bay. Based on the data collected, growth, mortality and reproduction of the transplanted Manila clam and the environmental effects were examined. The results showed that the enhanced clams grew well and showed a growth trend similar to the local wild ones. The main growth periods lasted from April to September, with the water temperature being the main factor affecting the growth, which was the same as that of the wild clams. There were also two reproduction cycles for the farmed Manila clams each year in Jiaozhou Bay and the main breeding period was from May to June. The phenomenon of delayed metamorphosis was quite common through larval development. The farmed clams could spawn when they reached sexual maturity, but they could not perform effective recruitment as many planktonic larvae died during metamorphosis and settlement. A preliminary study indicated that sediment perturbation and marine environment pollution were the main factors causing the death of larvae in the development process.     

Application of enzyme-linked immunosorbent assay (ELISA) for the study of reproduction in the Manila clam Ruditapes philippinarum (Mollusca: Bivalvia): II. Impacts of Perkinsus olseni on clam reproduction

We investigated the effects of infection by the protozoan Perkinsus olseni on the reproduction of female Manila clams, Ruditapes philippinarum, from a population in Gomso Bay, Korea. The reproductive effort of the clams was assessed by ELISA using a clam egg-specific antibody and was expressed as a weight-based gonadosomatic index (GSI). The number of Perkinsus infecting each clam was estimated from the gills using Ray's fluid thioglycollate medium (RFTM) along with a NaOH digestion assay. We found that reproductive effort was negatively correlated with the intensity of the Perkinsus infection: more heavily infected clams produced fewer eggs during the spawning period from May to August. Frequency of spawning was also negatively correlated with the level of Perkinsus infection; heavily infected clams (HIC) exhibited a single spawning pulse in late July, whereas lightly infected clams (LIC) showed three spawning peaks in mid-May, late July, and late August. Egg production of HIC was only 30–75% of LIC during spawning. The level of total protein in LIC was also higher year round than in HIC. In conclusion, our investigation demonstrates that a high level of Perkinsus infection affects spawning frequency and reduces egg production, which may have long-term impacts on clam recruitment and population growth.     

Effect of temperature and relative humidity on the tolerance of the Japanese clam, Ruditapes philippinarum (Adams & Reeve), to air exposure

Laboratory studies showed that higher relative humidity (RH) and lower air temperature increase the tolerance of the Japanese clam, Ruditapes philippinarum (Adams & Reeve), to exposure. Aerial respiration of the clam was also measured. At high RH, the exposure time which gave 50% survival (LT₅₀) was 1.97 and 1.75 times longer than in low RH at air temperatures of 15 and 25 °C, respectively. At 15 °C, all clams previously acclimatized at 15 °C survived for 58 h at low RH and 102 h at high RH. These differences can potentially be exploited to improve the shipment of clams. The aerial respiration experiment showed that the increase of the oxygen consumption rate at 25 °C was greater than that at 15 °C, following an increase in exposure time. The aerial respiration rates of the clams were ≈ 41.6% and 50.0% of those in water at 25 and 15 °C, respectively. The survival of the clams in air was dependent on aerobic rather than anaerobic respiration.     

Low genetic diversity of cultivated spotted hard clam (Meretrix petechialis) in Taiwan

The aquaculture of spotted hard clams, Meretrix petechialis, is a well‐developed industry in Taiwan. Spats have been produced for decades through artificial propagation using broodstocks selected from neighbouring culture farms on the basis of size and maturity, and the produced spats are resold to these culture farms. Although mass mortality occurs frequently in this practice, the effect of inbreeding depression has never been evaluated. Therefore, genetic diversity of 173 spotted hard clams from museums, two culture farms and three purchased populations was examined in this study. Phylogenetic analyses, based on either COI or cyt b fragments, indicated a division into lineages A and B among the samples. Cultured clams, except for one clustered with M. lusoria, museum specimens, and purchased samples from Hsinchu were all grouped into lineage A. The remaining two purchased populations were placed in both lineages. Compared with cultured clams from the Chinese coast in a previous study, our results exhibited a much lower haplotype (0.354 vs. 0.900) and nucleotide diversity (0.00113 vs. 0.00543). However, whether the loss of genetic variation is a consequence of inbreeding or the founder effect in the initial small broodstocks is unclear. The introduction of broodstocks from northern Vietnam and southern China may facilitate the management of genetic diversity. Environmental factors that potentially cause mass mortality require further investigation.     

SEM observations on larval shell morphology of Manila clam Ruditapes philippinarum and their utility

Manila clam Ruditapes philippinarum is common and abundant on Japanese tidal flats, forming a commercially important clam fishery. However, annual catches of Manila clam have decreased drastically since 1975?C1985. To study larval recruitment processes of Manila clam, we carried out scanning electron microscopy (SEM) observations on larval and juvenile shells of clams reared at 20 and 24?°C. There was no significant difference in final shell length of trochophores between 20 and 24?°C. However, the larval duration was much longer and the shell length of settled size of pediveligers was much larger for clams reared at 20?°C than those reared at 24?°C. These findings suggest that larval duration and growth, as well as settlement size, may vary markedly depending on temperature (and probably on season). The larval shell morphology of Manila clam can provide essential information about larval recruitment processes.     

Effects of mechanical stress in under-sized clams, Tapes philippinarum: a laboratory approach

The present study is a first attempt at evaluating the effects of repeated disturbance, such as that caused by mechanical fishing systems, on the target species, Tapes philippinarum, intensively exploited in the Lagoon of Venice (North-East Italy). In particular, in free-access fishing grounds, detrimental effects of dredging may be suffered by under-sized clams, which are disturbed by fishing tools many times throughout their lives before they are collected. Similar mechanical stress conditions are experienced by T. philippinarum in licensed areas, where they are farmed in aquaculture conditions and undergo the harmful impact of hydraulic dredging. To evaluate the effects of short-term mechanical stress, under-sized clams were subjected to experimental shaking in the laboratory, and detrimental effects on their well-being were investigated by applying the biomarker approach. Changes in physiological, biochemical and behavioural responses were evaluated by determining scope for growth, adenylate energy charge, survival in air time, reburrowing time, and shell damage level. Responses highlighted general worsening in clam condition as mechanical stress increased. Among the various measurements, survival in air and reburrowing time appeared particularly suitable as indices, their responsiveness and applicability suggesting their use in assessing mechanical stress due to dredging in field conditions.     

文蛤动态能量收支模型构建、验证与应用

为评估文蛤生态容量,实验根据动态能量收支理论,基于R语言构建了文蛤动态能量收支模型,采用线性与非线性回归法估算模型参数,通过对比围塘环境下文蛤壳长、湿重、软体部湿重的实测值与模拟值验证模型,并应用于模拟黄海海域滩涂区文蛤的生长过程。结果显示,文蛤模型主要参数形状系数、阿伦纽斯温度系数和单位体积结构物质所需能量分别为0.57、9 278 K和2 056 J/cm³;实测与模拟的文蛤壳长、湿重和软体部湿重相关系数R²平均为0.996,模拟值与实测值的平均误差为3.58%;如东沿海区域6月实测文蛤软体部干重为0.48 g,壳长3.12 cm,模型模拟的软体部干重、湿重和壳长分别为0.476 g,6.6 g和3.2 cm。研究表明,实验构建的文蛤动态能量收支模型的准确度较高,可真实地反映出文蛤在自然水域中的生长过程,为评估文蛤生态容纳量及构建文蛤相关的生态系统模型提供科学参考。