The pre-ingestive selection of microphytobenthic algae by the cockle Cerastoderma edule was studied in comparison with diets containing the pelagic diatom Phaeodactylum tricomutum. Treatments with the different diets covered a range of seston concentrations and organic content similar to field conditions. Rejection rates of C. edule exposed to the different treatments were significantly correlated with the concentration of total particulate matter. No significant differences in total rejection rates were found between pelagic and benthic diets. Organic rejection rate was significantly correlated with particulate organic matter of the treatments and no significant differences were found between both diets. Selection efficiency was significantly correlated with particulate organic matter concentration in both diets and no significant differences were found between the diets. Analysis of the pseudofeces composition by flow cytometry from cockles exposed to a mixed diet of microphytobenthic algae and P. tricornutum, showed a preferential ingestion of the pelagic diatom. Benthic species, such as small pennates and Navicula sp., were preferentially ingested in comparison to larger microphytobenthic species. The largest microphytobenthic species, Cylindrotheca sp., was significantly rejected. In general, C. edule is an opportunistic filter feeder that takes advantage of both pelagic and benthic algal cells.
Journal of shellfish research, vol. 9, nr. 1, 103-108 Similar to the observation period August 1987-April 1988 a continuous period of accumulation of okadaic acid (OA) in the mussels in the north (N 58°37' and further north) started in the beginning of October 1988, and the OA concentrations remained elevated until February 1989. OA levels up to 218 µg per 100 g mussel meat were recorded. During this period mussels further south in the Orust-Tjörn-Lyrön area (N 58°04-06') consistently showed lower levels, usually below 20 µg OA per 100 g mussel meat. In May, June and July 1988 the levels were below 10 µg OA per 100 g mussel meat at all sampling sites. Large differences were observed between closely located sites. In late November 1988, when one site located far out in the archipelago showed 218 µg OA per 100 g mussel meat, a satellite farm situated ca one nautical mile further towards the mainland showed 63 µg. In January 1989, when the OA-levels were fairly stable, mussels were collected all along the coast and analyzed. Low OA levels (<10 µg OA per 100 g mussel meat) were found in mussels grown close to the mainland, particularly where fresh water was discharged into the sea. Moderately high levels (ca. 50 µg OA per 100 g) were found quite south (N 57°35') in mussels from the outer archipelago. The highest levels (134 µg OA per 100 g) were observed in mussels from the open archipelago at N 58°18'. The observations indicate that toxic Dinophysis sp. carry the OA to the mussels from the open sea. Coastal water with lower salinity may antagonize the OA contamination of the mussels by producing unfavourable conditions for OA synthesis and by supporting the growth of non-toxic algae.
Genetic variation in eastern oysters (Crassostrea virginica) collected from 13 sites in the Gulf of Mexico was examined using a combination of mitochondrial DNA (mtDNA) sequencing, mtDNA restriction fragment length polymorphism analysis, and nuclear single nucleotide polymorphism analysis. Both mitochondrial and nuclear markers showed significant differentiation among samples. Combined with previous allozyme and microsatellite data, these results indicate considerable population subdivision throughout the Gulf of Mexico, despite the potentially homogenizing effect of larval dispersal.
The aim of this study was to evaluate the performance of Patagonian octopus fed with moist diets formulated with several local feed ingredients. All formulated diets were based on crab paste (70%) and the experimental feed ingredient (30%). Experiment I assayed salmon meal, prime sardine meal, and wheat gluten, using fresh fish as a control; experiment 2 assayed prime fish meal and macroalgal meal against crab paste alone as a control. The ingestion rate was lower than expected for all diets except those of fresh fish, crab paste alone, and crab paste plus prime sardine meal. No significant differences were found in the observed digestibility of the diets, indicating, in general, low digestibility, even for fresh fish. The highest protease values were observed for crab paste plus prime sardine meal in both experiments. The better growth of Enteroctopus. megalocyathus was obtained when these were fed fresh fish, which was associated with the greater consumption observed in this diet, as neither the digestibility nor the enzymatic activities of the hepatopancreas were related to this greater growth.
Pheromones are chemicals used to communicate between animals of the same species, and are thought to be used by most marine animals. With limited vision, abalone primarily sense their world chemically, and pheromones may play an important role in settlement, attraction, recognition, alarm, and reproduction. Despite this, there has been no detailed investigation into pheromone substances, both in their precise biochemical nature or pheromonal function. In this study, we investigated the presence of pheromonelike substances from the hypobranchial gland of the abalone Haliotis asinina using bioassays, immunohistochemistry, Western blotting, and reverse-phase high-performance liquid chromatography (RP-HPLC). The hypobranchial gland of many prosobranchial marine molluscs has been classified as a sex auxiliary gland releasing unknown substances during spawning. In our study, cephalic tentacle assays demonstrated that the cell extracts of the hypobranchial gland contain chemical cues that are sensed by conspecifics. An antibody against the sea slug "attractin" pheromone was used as a probe to localize a similar protein in the mucin-secreting cells of the epithelial lining the hypobranchial gland of both male and female abalone. The approximate molecular weight of this abalone attractin-like protein is 30 kDa in both males and females. Fractionation of hypobranchial gland extracts by C5 RP-HPLC could not selectively purify this protein, and no sex-specific differences were observed. We predict that the attractin-like protein could be one of a number of important proteins involved in maturation, aggregation, and/or spawning behavior of abalone. In future research, additional hypobranchial gland components will be tested further for these types of behavior.
A total of 241 samples of small abalone (Nation's diversicolor) from 8 full-sib families of market size were used in this experiment. Shell length (X-1), shell width (X-2), shell height (X-3), apex height (X-4), body weight (Y-1), muscle weight (Y-2), and shell weight (Y-3) were measured, and the correlation coefficient matrix was calculated. The shell shape traits were used as independent variables, then body weight and muscle weight were used as dependent variable for path analysis. Path coefficients, determination coefficients, and correlation index were calculated. The results showed that correlation coefficients between each shell shape trait and body weight, muscle weight, and shell weight were all significant (P < 0.01). For the 4 shell morphological traits, body weight (Y-1) had the highest correlation coefficient with shell length (X-1), and muscle weight (Y-2) had the highest correlation coefficient with shell width (X-2). The results of high correlation index would be useful for selecting important growth-related traits in genetic breeding program of small abalone.
Twelve half-sib groups and 36 full-sib groups of small abalone Haliotis diversicolor were obtained by the unbalanced nest design using artificial fertilization of 3 females by each male. Heritabilities of growth-related traits were estimated from postlarva to market size at days 10, 40, 120, 220, 320, and 420. The estimated heritabilities based on sire components for shell length and shell width were 0.15-0.37 and 0.18-0.42, respectively. Heritability estimate for shell length and shell width based on dam component were larger than those based on sire component. The results in the current study indicate that genetic improvement through selective breeding conducted on small abalone might be available and would be an efficient method to obtain a positive response to selection.
The performance of Haliotis asinina Linnaeus fed four commercially available diets formulated for temperate Australian species was assessed relative to a natural diet of Gracilaria edulis. parameters measured included growth in terms of total wet body weight (TWBW) and shell length (SL), survival, food conversion ratio (FCR), condition index (CI), and sexual maturation, The results of these measurements indicated that two of the formulated diets could be used for commercial culture of H. asinina. Nutritional and physical parameters of these diets were used in a multivariate regression analysis to identify variables that explained the most variation in growth between diets. Parameters that were selected by this analysis were the ratio of crude protein (CP) to gross energy (GE) and the rate that protein leached from the formulated diets. The resulting regression equation was highly significant in its explanation of the variation in growth (P = 2.2 x 10(-6)). To determine the quality of the dietary CP in each diet, the essential amino acid profile of each diet was compared to that of whole soft body tissue in H. asinina. Methionine seemed to be deficient in all of the diets. Animals fed G. edulis did not seem to suffer from a lack of n-3 PUFAs.
Interspecific hybrid families of female Haliotis diversicolor X male H. discus discus were produced and analyzed using amplified fragment length polymorphism (AFLP) technology to reveal the genetic makeup of F1 progenies. The survival rates of the hybrid F1 were very low, ranging from 0-0.13%. Twenty hybrid F1 from 3 families along with 3 different female parents and their common male parent were analyzed with 3 AFLP primer combinations. In total, 266 markers were detected. Genetic relationships among the progenies and the parents were evaluated by generating a similarity and genetic distance matrix. The genetic divergence between Haliotis diversicolor and Haliotis discus was at a high level, with genetic distance ranging from 1.471-1.492. The AFLP band patterns of hybrid F1 progeny were similar to those of the female parents, but were quite different from that of the male parent. The mean genetic distance between hybrid F1 and their female parents were 0.024-0.039, slightly less than that among the female parents, which indicates that the hybrid F1 shared high genetic similarity with their female parents, Haliotis diversicolor. However, 0-0.8% of total AFLP bands of each individual were found to be parental bands, and 0-3.3% were found to be nonparental bands. The possible reason for the presence of paternal-specific and nonparental bands is discussed.
On the southern Great Barrier Reef, Haliotis asinina (Vetigastropoda: Pleurotomarioidea) synchronously spawn every 2 wk in a predictable fashion. allowing detailed analysis of reproduction, gametogenesis, and gonad development. Histological examination of the ovaries of members of the Heron Reef population during this semilunar cycle reveals that oogenesis is also synchronous and predictable, and requires more than two spawning cycles (i.e. >28 days) to complete. Shortly after a spawning event the ovary comprises two cohorts of primary oocytes, one of which will be released at the next spawning event, and clusters of oogonia. At this time there is a rapid proliferation and expansion of trabeculae, germinal epithelial, and oogonia, and a dramatic increase in the size of the vitellogenic oocytes to be: spawned at the next spawning event. Within 4 days these oocytes have filled the ovary. On the day of the next spawning a lumen forms in the ovary as a result of localized degradation of trabeculae. The large primary oocytes dissociate from the receding trabeculae. initiate maturation, and accumulate in the lumen; these oocytes become embedded in a jelly coat layer. The next cohort of oocytes remain attached to the trabeculae. The jelly coat appears to be completely dissolved within 30 min of spawning. Comparison of the oogenesis and ovary development in II. asinina with other abalone species indicates that these processes are very similar in tropical and temperate abalone. This suggests that insights into the regulation of reproduction and spawning in H. asinina are likely to be applicable to other haliotids.
Although information on bivalve nutrition is still very scarce, several studies have demonstrated the importance of lipids, in particular triglycerides, as a source of energy and essential fatty acids in the early life stages. Experimental diets used so far to study bivalve nutrition either heavily pollute the water or are too complex to prepare in a hatchery. The potential use of lipid emulsions as off-the-shelf supplements was evaluated through the analytical verification of the ingestion and incorporation of n-3 highly unsaturated fatty acids (HUFA) by the juvenile sea scallop Placopecten magellanicus fed lipid emulsions of different fatty acid composition as a supplement to Isochrysis sp. (clone T-Iso). The average lipid content on the scallops fed the lipid supplements was 20% higher compared to that in the control fed algae only (3.29 ± 0.16 versus 2.75% of dry weight, respectively). Changes in the fatty acid composition, in particular of n-3 HUFA, were demonstrated in total lipids, polar lipids, and triglycerides of juvenile sea scallops supplemented with lipid emulsions on the basis of ethyl ester concentrates of n-3 HUFA and were dependent on the level and proportion of 20:5n-3 and 22:6n-3 present in the emulsion. The effective incorporation of essential fatty acids from lipid emulsions indicated that the supplementation of lipid emulsions to live algae may improve and standardize the dietary supply of lipids and fatty acids in hatchery production of bivalves.
Juvenile Tapes philippinarum (Adams and Reeve) were reared for three weeks on different rations of Chaetoceros neogracile which were either centrifuged and stored or fed together with the culture medium. Algal rations were adjusted daily in order to feed constant weight-specific daily rations. Growth of T. philippinarum fed the concentrate of C. neogracile was maximal at a daily ration of 1% (algal dry weight per clam live weight). T. philippinarum fed single or mixed diets of C. neogracile and Isochrysis sp. (clone T-Iso) directly from the algal cultures, maximized growth at a ration of 1,3% day <sup>-1</sup>. Higher growth rates and gross growth rates efficiencies were obtained with C. neogracile fed together with the culture medium. A set of grazing experiments showed that the incipient limiting concentration was about 26 C. neogracile cells µ1<sup>-1</sup>. Measurements of cell concentration during the growth tests demonstrated a discontinuous feeding activity in the treatments receiving the optimal ration for maximum growth.
This article describes the population ecology of Thais kiosquiformis Duclos, the dominant predatory gastropod of the root system of Costa Rican mangroves. T. kiosquiformis was shown to cope with the extreme living conditions of its habitat (risk of desiccation and overheating through several hours of daily air and sun exposure, strong salinity, and current changes during the tidal cycle) by using the following strategies: (1) extremely slow growth (~1 mm/y), cessation of growth at the onset of maturity (at ~24 mm in shell length), (2) maintaining high interindividual plasticity in growth and shell thickness as a response to abiotical conditions, food availability, and population density, and (3) migrating ontogenetically for the benefit of lowering desiccation and predation mortality. Because of its high density and biomass (192.2 ± 102.4 g wet weight/m2), and the predation pressure it exerts mostly on the barnacles of the mangrove roots, T. kiosquiformis seems to occupy a central role in maintaining the functioning and productivity of mangroves through 'cleaning' their root system from the encrusting fauna.
Giant scallops, Placopecten magellanicus, respond to the presence of starfish predators with an escape response consisting of a series of rapid valve adductions that allow the scallop to jump or swim away from the predator. To evaluate the coordination of the activity of the tonic and phasic muscles during such escape responses, we recorded their force production by attaching a force gauge to the shell of intact scallops and then stimulating the scallops with starfish. These recordings showed series of phasic contractions (claps) separated by prolonged tonic contractions. Numerous characteristics could be quantified from these recordings including the maximal force, mean force during the first minute, force, frequency and number of claps per series, as well as the force and duration of tonic contractions. The number of claps per series declined and the duration of the tonic contractions increased as the escape response continued. For most scallops, phasic and tonic contractions produced similar levels of force that changed little during the escape responses. The alternation between phasic and tonic contractions suggests that periods of tonic contraction allow the phasic muscle to recuperate and facilitate subsequent phasic contractions. Principal component analysis (PCA) confirmed the coordination between the phasic and tonic adductor muscles, because characteristics of each type of contraction, were closely associated. This method combines the advantages of stimulation of scallops by their predators with the simplicity of force gauge measurements. Force production during escape responses by individual scallops was highly reproducible, suggesting these measurements have considerable potential for tracking changes in the physiologic status of giant scallops.
Lipid spray beads (SB) were prepared containing 13% w/w particulate riboflavin. Beads suspended in seawater lost 73% riboflavin after 24 h. Release of riboflavin from SE ingested by Pacific oyster (Crassostrea gigas) larvae was observed under epifluorescent light. Riboflavin concentrations in tissues of adult oysters fed on riboflavin-SB were significantly (SNK, P < 0.05) greater than those of oysters fed on seawater-filled SE. Concentrations of riboflavin in oysters exposed to dissolved riboflavin were not significantly greater than those of oysters fed on seawater-filled SE: indicating that elevated riboflavin concentrations in oysters fed on riboflavin-SB were attributable to breakdown of ingested beads rather than uptake of dissolved riboflavin leaked from SE into the culture medium. SE seem to be a promising means of delivering water-soluble nutrients to bivalve suspension feeders.
Pacific oysters were introduced into the Eastern Scheldt in 1964 for breeding purposes. The first spatfall of wild Pacific oysters was recorded in 1976, and a second larval outburst in 1982 definitely settled wild Pacific oysters in the Eastern Scheldt waters. Oyster beds on intertidal and subtidal areas have been growing since. The objective of this study is to research the potential of aerial photography for estimating surface areas of intertidal Pacific oyster beds. Black & white and false-color aerial photographs were used to locate Pacific oyster beds. For verification purposes, oyster bed contours were measured in the field. The accuracy of the method used was comparable with accuracies found in other studies, with a chance of underestimating the surface areas in the field. With aerial photographs of 1980 and 1990 the surface areas of Pacific oysters in both years were reconstructed, showing an increase in surface area of Pacific oyster beds. The study shows aerial photography has the potential to be an aid in surveying intertidal Pacific oyster beds
In this study, effects of sperm concentration and gamete age on fertilization success of Haliotis discus hannai (D) X H. gigantea (G) were investigated. Results showed that the fertilization rates of heterologous crosses H. discus hannai female x H. gigantea male (DG) and H. gigantec female X H. discus hannai male (GD) were consistently lower than those of homospecific groups H. discus hannai female x H. discus hannai male (DD) and H. gigame female X H. gigantea male (GG). In sperm concentration experiments, the sperm concentrations that yielded maximum fertilization rates with the least abnormality in subsequent development were 4.66 X 10(7) sperm/mL for the DG cross and 2.6 x 10(7) sperm/mL for the reciprocal cross GD. In gamete age experiments, the optimal fertilization rates were achieved in heterologous crosses when freshly spawned ova were fertilized with sperm that were released within 0.5 h. Furthermore, in heterospecific crosses, when ova were fertilized 10 min after being spawned, fertilization rates declined significantly with increasing ova age. It is suggested to use fresh gametes and higher sperm concentrations for hybridization between H. discus hannai and H. gigantea.
Amplified fragment length polymorphism (AFLP) analysis of the population genetic structure and genetic diversity of Haliotis discus hannai (D), Haliotis gigantea (G), and their reciprocal hybrids D female x G male (DG) and G female x D male (GD) was carried out in this study. A total of 479 unambiguous and highly repeatable AFLP markers, 311 of which (64.93%) were polymorphic, were obtained using 7 primer combinations. The reciprocal hybrids inherited bands from both parents, indicating that the hybrids were truly heterogeneous. The Shannon diversity index for D, G, and their reciprocal hybrid populations DG and GD was 0.169 +/- 0.188, 0.211 +/- 0.227, 0.236 +/- 0.267, and 0.231 +/- 0.242, respectively. Analysis of molecular variance revealed that 29.58% of the variance was among populations, whereas 71.42% of variance was within populations. Genetic distance was maximum (0.681) between D and G, and was minimum (0.482) between GD and G. The 4 populations were clustered into 2 major clades using the unweighted pair group method with arithmetic mean. All genetic parameters indicated that there was plentiful genetic diversity in the reciprocal hybrids of D X G. Results of this study suggest that these AFLP markers can be used in the future to enhance current breeding practices in abalone culture because of the large numbers of polymorphic markers.
The subcellular fractionation of the digestive gland cells of the common cuttlefish Sepia officinalis was performed to investigate the distribution of metals between organelles and cytosol and the different cytosolic fractions separated by gel-filtration chromatography. Total metal concentrations vary over 3 orders of magnitude, ranging from dwt for Pb to dwt for Zn. With the exception of Cd, Co, and Cu, metals were mostly bound to the organelles. Whereas no specific organelle compartment was found for Mn, Ph, and Zn, Fe was mainly associated with nucleus, brown body, and "boule" fraction (i.e., 52%) and 44% of the total Ag was contained in the lysosomal and mitochondria enriched fraction. The link of metals with hydrosoluble proteins in the cytosolic fraction was investigated at 254 and 280 not. Direct relationship between cytosolic metal and metallothioneins could only be established for Ag and Cu, whereas Cd and Zn seem to mainly bind high (> 70 kDa) and low (< 4 kDa) molecular weight proteins.
The mass-production of micro-algae has been recognized by several authors as the main bottle-neck for the culture of bivalve seed. This has prompted a search for alternatives to on-site algal production, such as dried heterotrophically-grown algae, preserved algal pastes, micro-encapsulated diets, and yeasts. However the extent to which these products have been tried, and rejected or retained by hatchery operators is poorly documented. Also, the actual algal requirement and production cost of the bivalve seed industry is difficult to estimate. The present inquiry allowed the collection of data concerning the requirement of live algae and its associated costs encountered in 50 commercial and experimental hatcheries from all over the world. Furthermore, the hatchery operators were questioned about their experience with alternatives for live algae, the quality and quantity of hatchery produced algae and bivalve seed, and the employment of this sector in aquaculture. The capacity of the algal production facilities ranged between 1 m³ for a few research laboratories to nearly 500 m³ for one commercial hatchery. The total algal production capacity reported by 37 hatcheries amounted to about 500 m³ algal culture day<sup>-1</sup>, which is equivalent to about 50 kg of dry biomass. The total cost of algal production in 1990 reported by 20 hatcheries approximated US $700,000 and averaged about 30% of the total seed production cost. The estimates for the algal production cost ranged from US $50 to 400 per kg dry weight. About a third of the questioned operators considered algal production as a limiting factor in the rearing of bivalve seed, whereas over 50% planned an expansion of the algal cultures and more than 90% was interested in the use of suitable artificial diet. The large interest for alternatives for on-site algal production was further demonstrated by the fact that more than 50% of the operators claimed to have experimented with artificial diets. Despite the extensive research efforts, artificial diets are rarely applied in the routine process of bivalve seed production and are mostly considered as a useful backup diet.
In the frame work of a PhD thesis dealing with the use of artificial diets as an algal substitute for mollusks, the Laboratory of Aquaculture & Artemia Reference Center (State University of Ghent, Belgium) is organizing an inquiry which aims at drawing up an inventory of algal substitutes, their cost and applications, and their relative importance and cost-efficiency compared to live algae. The questionnaire has been sent to more than 200 people who are involved in the practice of culturing bivalves. The results will be treated as part of the PhD work and a free copy of the resulting report will be sent to all those who are returning the form. The questionnaire will be presented at Aquaculture Europe 1991 in Dublin under the form of a poster. The possibility will be offered to take copies of the form and to add your name to the mailing list for receiving the report. The success of this questionnaire strongly depends on the cooperation and support from the people who are involved in the farming of bivalves. The authors hope that a common interest will result in a compilation of data that will be useful for many of you.
Juveniles of the white shrimp Litopenaeus vannamei were kept Without food for between 0 to 15 clays to evaluate the impact of starvation oil physiologic state (oxygen consumption, poststarvation refeeding, index, nitrogen excretion, and O:N ratio) and digestive enzymes activity. Physiologic changes were found after 6 days of fasting, and refeeding ability declined as a result. Nevertheless. the shrimp were able to Survive 16 days Without food. Starvation Caused metabolism to drop progressively toward a basal level (21 J (.) h(-1 .) g(-1)) and a decrease in the rate of ammonia excretion, because of the catabolism of amino acids front soluble protein in the hepatopancreas. This decrease led to an increase in digestive enzymes specific activity (U/mg protein). But, expressed as total U. all digestive enzyme activities decreased in the absence of substrate from 0.016 to 0.007 U/hepatopancreas (HP) for alpha-amylase and 2.58 to 0.63 U/HP for total trypsin. L. vannamei juveniles showed a true physiologic adaptation mechanism to food depiivation: no changes in body weight but loss in hepatosomatic index, no exuviations, including the utilization of HP soluble proteins (a drop from 269 to 53 mg/mL). After 10 days. a neoglycogenic pathway and the corresponding tissue enzymes activities seemed enhanced, and the animals derived all energetic Substrates mainly from protein (O:N ratio of 17) to cover their metabolic costs. Estimates of basal metabolism (Hem) from the routine respiration rate per clay (from 361 to 725 J (.) g ww(-1) (.) day(-1) through the 15-day starvation period). and loss of nonfecal energy (HxE) from the nitrogen excretion rate (varying from 39 to 57 J (.) g ww(-1) (.) day(-1) during the same period) were used in a bioenergetic partition model of a fasting juvenile. Which indicated that the energetic requirement to Survive Without feeding was in the range of 418 and 771 J (.) g ww(-1) (.) day(-1) during the 15-day period of starvation.
It has been previously reported that the saucer scallop, Amusium balloti, either lacked the ability to produce byssal threads or could do so only briefly. This present study reports our main conclusion that in the early spat stages, A. balloti does indeed secrete byssus, albeit at a time different from most scallops. We found that A. balloti first attaches by a byssus only after metamorphosis (indicated by the presence of dissoconch shell), and we found no evidence of the byssal attachment before or during early metamorphosis. By the time spat reach a shell height of 1-2 mm they secrete two or three fine byssal filaments. Byssal attachment is maintained until the spat reaches 4 5 mm, around the stage where they develop the ability to swim. This pattern is unlike that found in most other scallops that initiate byssal production and attachment before metamorphosis. We also describe post-settlement behavior of A. balloti. The newly settled postlarvae (similar to200 mum shell height) crawl along the substratum by using their foot. During attachment, spat change their positions daily, moving an average of 17 mm per day. In culture, a gentle water jet and hypersaline bath (40parts per thousand) effectively detached spat, with the majority rapidly reattaching.
The Pacific oyster, Crassostrea gigas (Thunberg), and the Portuguese oyster, C. angulata (Lamarck), are two closely related taxa. Although these two taxa were both introduced from Asia into Europe. one (C. gigas) was voluntarily introduced in the early 1970s, whereas the other (C. angulata) was presumed to be present in Europe for at least four centuries, but nearly disappeared because of disease. Few C. angulata populations remained in southern Portugal, Spain and Morocco and their putative origin was traced in Taiwan. The present paper reports evidence for its presence in Northern China. We reanalyzed recently published mitochondrial cytochrome oxidase C subunit I (COI) sequence data from presumed Dalianwan oysters (C. talienwhanensis) and compared them with those of C. gigas and C. angulata. Additionally, two new C. angulata haplotypes from Portugal were identified. The results clearly showed that some of the C. talienwhanensis sequences cluster with C. angulata sequences. The relative divergence between C. gigas, C. angulata, and C. talienwhanensis haplotypes indicated that C. angulata-like oysters are present in northern China. This opens new perspectives in terms of genetic resources and population genetics of C. gigas and C. angulata, two oyster species of aquacultural importance.
In the Netherlands, wild stocks of mussel seed are fished and mussels are cultured on bottom plots. In addition, wild stocks of the edible cockle are dredged for harvest. Two of the areas where these activities are carried out are nature reserves. In 1993, the government implemented a policy in these reserves to ensure the conservation, protection and development of natural values and processes in which human activities should fit in. Fishing for shellfish is considered a traditional activity in these waters. Therefore, it is allowed, but under the restriction that no negative effects are caused. As a result of this policy, fishing for mussel seed and cockles is not allowed in areas with a high potential for the development of mussel beds and seagrass fields. A number of bird species are dependent on shellfish for their food requirements. Therefore, the policy makes use of a reservation system. This means that, in years when mussel and cockle stocks are low, an amount is reserved for the birds and cannot be fished. The government and shellfish industry agreed on co-management, (i.e., the fishermen are responsible for implementing the measures). This task is carried out by Producers' Organizations. An overview of the viewpoints of the interest groups and the role of policy makers and scientists is given.
Summer seed mortality (SSM) has occurred yearly in Tomales Bay, California since 1993. SSM has resulted in up to 90% cumulative losses, and has been associated with extreme temperature, phytoplankton blooms, and an oyster herpesvirus. In this study, three stocks of Pacific oysters were planted at three sites in California (Inner Tomales Bay, Outer Tomales Bay, and Bodega Harbor) in October of 2000 (Fall) and April of 2001 (Spring) and monitored for mortality, growth, and health status. In April of 2001, a similar study was conducted in Totten Inlet, WA state using cohorts of oysters planted in California; animals were monitored for mortality and growth. Temperature data were collected at all sites; phytoplankton abundance data were collected at the California sites. Mortality occurred only at the Inner Tomales Bay site where losses were correlated with maximum temperatures (r = 0.949) and preferentially affected faster growing oysters (r = 0.916). Significant differences in cumulative mortality were identified among oysters stocks and two of the three oysters stocks planted in the fall outperformed their cohorts planted in the spring (P < 0.0001). Microscopic changes in connective tissue and digestive tubules are consistent with previous observations of herpesvirus infections in oysters including: diffuse to multifocal pertibular hemocyte infiltration, diapedesis, dilation of the digestive tubules, nuclear hypertrophy, and chromatin margination. Nuclear hypertrophy and chromatin margination, in particular, are suggestive of herpesvirus infections; these histological changes were rare indicating the need to use multiple diagnostic methods when oyster herpesviruses are suspected to cause SSM. Temperature maxima (~25°C) experienced at the Inner Tomales Bay site are not considered extreme for Pacific oyster survival; the association between oyster herpesviruses and temperature in Tomales Bay, California is discussed.
Chromosome preparations of the Olympia oyster Ostrea conchaphila Carpenter were studied using conventional Giemsa, silver staining, and C-banding techniques. The karyotype consists of six metacentric (1, 2, 4, 6, 8, and 10) and four submetacentric (3, 5, 7, 9) chromosome pairs. The silver-stained nucleolus organizer regions (Ag-NORs) were terminally located on the short arms of the submetacentric pair 5 (56% of cases) and on the long arms of submetacentric pair 7 (6% of cases). Constitutive heterochromatin was observed as telomeric C-bands on the short arm of the NOR-bearing chromosome pair 5 and as centromeric blocks of several chromosome pairs. Comparative analysis of patterns of karyotype, Ag-NORs, and C-bands of this species and of five other flat oysters, Ostrea angasi, O. chilensis, O. denselamellosa, O. edulis, and O. puelchana, for which data have been previously published, were performed, allowing the inference of cytotaxonomic relationships within Ostreinae.
Mussels of the genus Mytilus are ecologically and commercially important worldwide, and they form hybrid complexes where their distributions overlap. Allozyme and nuclear markers have bee It Used to investigate their genetics over many years, but successful development of reliable highly valuable microsatellite markers has lagged be hind other shellfish species. We have developed and characterized tell novel microsatellite loci that amplify reliably for the blue mussel Mytilus edulis. The number of alleles among 30 individuals from a wild population (Menai Strait, North Wales UK) ranged between 9 and 29 and the observed heterozygosity between 0.300 and 0.954. Significant heterozygote deficiencies against the Hardy-Weinberg model were observed at 6 out of 10 loci. Analyses using MICRO-CHECKER suggested the presence of null alleles at 8 out of 10 microsatellites with estimated null allele frequencies ranging front 0.105-0.305. The 10 newly developed microsatellites will have value to discriminate between Mytilus species, to support studies of introgression and hybridization and to strengthen and improve the available genetic linkage map.
The European oyster (Ostrea edulis) was introduced to the Nova Scotia aquaculture industry 30 years ago using stocks imported from naturalized populations in Maine whose ancestors originated in the Netherlands. This study used 5 microsatellites to assess the level of genetic diversity in several hatchery stocks and naturalized populations from Nova Scotia, New Brunswick, British Columbia and Maine. Some genetic erosion was shown to have occurred in the Maritimes populations, with the largest loss of alleles being experienced by the hatchery stocks. In spite of this loss, genetic diversity and heterozygosity in the Maritimes populations are still relatively high. Relationships within and between the populations and the existence of kin groups within the collections were overall consistent with our knowledge of the historical transfers of oysters between different locations. Furthermore, the established database allowed to assign with good confidence unknown oyster samples to their geographic origin. This would be a useful forensics tool in the case of an illegal transfer from a diseased area.
Brown ring disease (BRD) in the Manila clam is characterized by the formation of a brown deposit of conchiolin on the inner surface of the shell that gives the disease its name. The development of the signs of BRD may be favored by the entry of bacteria in the extrapallial compartments via mechanical disruptions of the periostracal lamina and/or chipping of the shell margin. In order to test this hypothesis, we conducted an experiment simulating clam handling under aquaculture conditions and we checked for prevalence of BRD signs. Our results assess that rough handling of R. philippinarum in presence of the bacterium V. tapetis significantly increase the prevalence of BRD signs. As a consequence our results show that minimizing manipulations and transfers of clams during culture is beneficial to avoid the development of BRD signs.
Production of clams is the third most important bivalve production in France and was estimated at 3400 metric tons in 2001 among which 60% came from aquaculture and 40% from fisheries. Surveillance of clam diseases mainly relies on histology and thioglycolate culture, two techniques allowing detection of parasites of the genus Perkinsus but not specific enough to determine the parasite species. Based on a previous study aiming at estimating distribution and prevalence of perkinsosis in France, we selected 34 infected clams from 4 different producing areas in order to characterize the parasite species. Molecular characterization was done by PCR-RFLP targeting the ITS region as described by Abollo et al. (2006). 16 PCR products were cloned and 10 to 20 clones per individual were selected for PCR-RFLP to test potential intra individual polymorphism. 23 clones, including the ones which yielded non expected restriction profiles, were finally selected for sequencing. All the obtained sequences displayed 99 to 100% of homology with Perkinsus olseni confirming the presence of this protozoan in at least four different French marine areas (Golfe du Morbihan, Thau, Leucate, Arcachon). Polymorphism between clones obtained from a same clam or from different clams did not appear geographic dependent.
This study reports mortality under laboratory conditions in unselected controls and two lines of juvenile Pacific oysters Crassostrea gigas, previously selected for their high or low survival in the field during the summer period. Oysters were also deployed in field conditions and mortality between both conditions was then compared. In the laboratory, mortality was observed in all experiments and it always lasted for a week indicating that mortality under laboratory conditions was a short-term event. It was also shown that mortality could be repeated for a batch in several experiments using oysters which never experienced any abnormal mortality. This approach could facilitate further studies to investigate the causes of mortality by allowing repeated trials during a summer. Differences in mortality between the resistant and the susceptible selected lines confirmed the positive response to selection under laboratory conditions. Batches that performed well in the laboratory also showed high survival in the field, and the results of those exhibiting low survival in the laboratory trials were also mirrored in the field. Finally, challenging oysters with heat stress is proposed as a useful method for estimating the survival capacity of hatchery-produced and wild-caught spat used by the oyster industry.
The history of French oyster culture consists of a succession of developmental phases using different species, followed by collapses caused by diseases. The indigenous species Ostrea edulis was replaced first with Crassostrea angulata, then C. gigas. France is now the top producer and consumer of oysters in Europe, producing around 120,000 t of the cupped oyster C. gigas annually, and an additional 1500 t of the flat oyster O. edulis. Cupped oysters are produced all along the French coast from natural and hatchery spat. Various structures are used to collect spat from the wild. After a growing-on period, oysters are Cultivated by three main methods: (1) on-bottom culture in the intertidal zone or in deep water, (2) off-bottom culture in plastic mesh bags in the intertidal zone, or (3) suspended Culture on ropes in the open sea. The main recent development is the increasing use of hatchery oyster spat, especially triploids. Almost all oyster production is sold fresh and eaten raw straight from the shell. There is marked seasonality in sales, with the majority being made during Christmas and New Year. Abundant production and the lack of market organization induce strong competition among the production areas, causing prices to fall. Oyster farmers have developed strategies of sales promotion and regional quality labeling to overcome this difficulty. There are numerous production hazards, including environmental crises (microbiological pollution), unexplained mortality, and overstocking, and recent problems with toxic algae have disrupted oyster sales. However, oyster Culture has many assets, including a coastal environment offering favorable sites for Mollusc growth and reproduction. Oysters have been consumed in France since ancient times, and their culture is now well established with a concession system that favors small family firms. There is a young, well-educated farmer population, with technical expertise and savoir faire. Careful seawater quality monitoring ensures good consumer protection, and research is making innovative contributions (,selection and polyploids). These points and opportunities for market expansion should bolster this industry's future, although the problem of toxic algae, probably linked to global warming and anthropogenic factors, and the threat of new diseases, pose vital questions for future research.
To determine the genomic composition of the interspecific hybrid between Haliotis diversicolor supertexta female and H. discus discus male at an early developmental stage, veliger larvae produced from hybrid (SJ-5 and SJ-50) and pure species crosses (SS and JJ) were sampled and analyzed using standard karyological methods and genomic in situ hybridization. In hybrid metaphase spreads, chromosomes from both parents were detected, except one metaphase, which showed the H. diversicolor supertexta haploid karyotype. The genomic composition of the hybrid was also confirmed through preliminary genomic in situ hybridization results. Many more aneuploids and chromosome fragments were found in the hybrids than those in the control pure species crosses, indicating genome instability and chromosome loss in the hybrids. In the hybrid hypodiploid metaphase spreads, two intact sets of H. diversicolor supertexta chromosomes and several H. discus discus chromosomes were detected by pairing. Spontaneous diploidization of the maternal chromosome set was shown to occur in hybrid larvae, as 2.2% heterogeneous triploid and 17.9% hypodiploids with two intact H. diversicolor supertexta chromosome sets for SJ-5. The current findings suggest that uniparental chromosome elimination along with spontaneous diploidization of maternal chromosome sets may be the reason for allogynogenesis production in H. diversicolor supertexta X H. discus discus hybridization.
An international community of biologists presents the Pacific oyster Crassostrea gigas as a candidate for genome sequencing. This oyster has global distribution and for the past several years the highest annual production of any freshwater or marine organism (4.2 million metric tons, worth $3.5 billion US). Economic and cultural importance of oysters motivates a great deal of biologic research, which provides a compelling rationale for sequencing an oyster genome. Strong rationales for sequencing the oyster genome also come from contrasts to other genomes: membership in the Lophotrochozoa, an understudied branch of the Eukaryotes and high fecundity, with concomitantly high DNA sequence polymorphism and a population biology that is more like plants than any of the model animals whose genomes have been sequenced to date. Finally, oysters play an important, sentinel role in the estuarine and coastal marine habitats, where most humans live, environmental degradation is substantial, and oysters suffer intense fishing pressures and natural mortalities from disease and stress. Consumption of contaminated oysters can pose risks to human health from infectious diseases. The genome of the Pacific oyster, at IC = 0.89 pg or similar to 824 Mb, ranks in the bottom 12% of genome sizes for the Phylum Mollusca. The biologic and genomic resources available for the Pacific oyster are unparalleled by resources for any other bivalve mollusc or marine invertebrate. Inbred lines have been developed for experimental crosses and genetics research. Use of DNA from inbred lines is proposed as a strategy for reducing the high nucleotide polymorphism, which can interfere with shotgun sequencing approaches. We have moderately dense linkage maps and various genomic and expressed DNA libraries. The value of these existing resources for a broad range of evolutionary and environmental sciences will be greatly leveraged by having a draft genome sequence.
To establish a noncontagious control for the Ray thioglycollate test for the detection of Perkinsus in mollusks we evaluated nonviable stages of P. olseni for enlargement of hypnospores and blue/black iodine stain. Trophozoites made nonviable with formalin, irradiation or colchicine failed to swell in thioglycollate. They remained small and did not differentially stain in iodine. Trophozoites that had already developed into hypnospores in thioglycollate were rendered inactive by freezing, ethanol or formalin immersion. They retained their iodinophilic properties and thus could provide a partial control for the Ray Test.
The movement of the sea urchin Paracentrotus lividus from a rocky habitat to patches of Posidonia oceanica was investigated with respect to the size of the sea urchins and their location from the edge of the patch. With this aim, a manipulative experiment was conducted (4 times) at a location where several P. oceanica patches were interspersed on rocky platforms. Each time, after an accurate removal of the sea urchins populating them, 15 of these patches were randomly assigned in sets of 3 to 5 different urchin addition treatments, using groups of 10 large or small P. lividus specimens (test diameter >50 and <30 mm, respectively) positioned at close and far distances (25 and 100 cm, respectively) from the edges of the patches as follows: large-close, large-far, small-close, small-far, and control patches where no urchins were added. The abundance of sea urchins inside the patches was counted after 24 h. Results highlighted significant variability because of the distance from the patches, whereas no significant effect was observed for sea urchin size. These results suggested that: P. lividus specimens close to P. oceanica patches might have a greater probability of reaching them, and that the chance to reach the patch does not depend on the size of sea urchins. In fact, a comparable ability to move towards the patches was evident for different-sized specimens, indicating that migration from one habitat to the other is possible even for small-sized individuals.
(Not controled OCR) Because biological systems do not work in isolation, behavioral, biochemical, and physiological tests can give an overview of an individual's vital processes and reaction to stress. Two stress gradients were applied in this study, a short acute desiccation stress and a long-term density stress. These stress gradients were used to assess the usefulness of various techniques for quality assessment: namely, a standard salinity stress test, condition index, recessing speed of the scallop, adenylic energetic charge (AEC). and percentage carbohydrate content of the striated muscle. The results showed that AEC could be used effectively to measure the effect of a short-term stress. In the striated muscle. AEC levels were useful in discriminating between good and poor quality scallops. The total carbohydrate content in the striated adductor muscle and condition index were useful in assessing the effect of long-term stress on scallop quality. The most promising results arose from the recessing trials, because this nondestructive test successfully discriminated the different qualities of scallops arising from both long- and short-term stress.
The deep-sea scallop Placopecten magellanicus is an important member of commercial fisheries along the coast of Northeastern United States and Atlantic Canada. A cDNA encoding a glycolytic pathway enzyme fructose-1,6-biphosphate aldolase was isolated from a sea scallop adductor muscle-specific cDNA library and sequenced from both directions. The full-length cDNA is a 1627 base-pair (bp) long sequence that has a 62 bp 5′ untranslated region, a 1092 bp open-reading frame, and a 473 bp 3′ untranslated region including a 24 bp polyA tail. The open-reading frame encodes a 39.3 kDa protein with 363 amino acids. The protein has 183 nonpolar, 94 polar uncharged, and 86 polar-charged amino acids. Several amino acids show bias for codons with G/C at their third position. The cDNA has 28 unique restriction sites, including common restriction enzymes such as SacI, BamHI, TaqI, and BstEII. The aldolase is a highly conserved protein with 66% sequence identity with that of Schistosoma mansoni, 65% with that of Drosophila melanogaster, 62% with that of Homo sapiens, and 57% with that of Oryza sativa. Southern blot analysis indicates that aldolase in sea scallops belongs to a family with 4 to 10 putative genes. Northern blot analysis shows that this gene is expressed only in adductor muscles. Hybridization of an aldolase cDNA probe to genomic DNA from several individuals revealed restriction fragment length polymorphisms at several loci, indicating potential use of this cDNA as a marker in genetic studies of sea scallops.
The use of shell or other coarse material to enhance survival of newly set hard clams (Mercenaria mercenaria) has been suggested as a management strategy to increase clam stocks. Barnegat Bay, New Jersey and surrounding areas supported a large clam fishery throughout the 1950s and 1960s, but this resource has declined in recent years. We established replicate 20 x 70 m plots of high shell density, low shell density, and no shell (control) in a Latin Square design in 1990 and have obtained periodic samples since that time. The shell, obtained from ocean quahog processing plants, had been broken into a variety of sizes. High-density shell received 900 bu per plot, and low-density shell received 300 bu per plot. Plots with high shell density had significantly more clams after 10 years than those with low-density shell or controls. High shell density significantly increased hard clam recruitment, but this exceeded m-2 in only one year, from the years 1990 to 2000. In plots with low shell or in controls, recruitment never exceeded 0.4 m-2, and in half or more of the years no recruitment was found. Some individual plots with shell did not enhance recruitment, indicating that factors not investigated must be important as well. In spite of the low recruitment density, there appears to be an increase in survivorship when the shell content is greater than 8000 gm-2.
This study compared the carbon isotopic composition of individual amino acids from muscle tissue and shell organic matter inclusions in Crassostrea virginica collected along a salinity gradient in the Rookery Bay estuary, Florida. The intent was to assess the extent to which environmental signals relating to spatial and temporal variation in carbon sources were recorded in the amino acids of these materials. There was a trend toward enrichment in delta C-13 in all amino acids moving seaward along the transect in both organic matter pools, consistent with diminishing influence of terrestrial (C-3) production and increased contributions of marine production. The magnitude of this trend was identical for both tissue and shell organic matter, although the values for several constituents of the shell organic matter (aspartic and glutamic acids and glycine) were consistently depleted by approximately 3 parts per thousand relative to their equivalents in tissue samples. Other amino acids were directly comparable despite a 2 parts per thousand offset in bulk isotopic compositions. Sites were distinguishable from one another in both the tissue and shell organic matter data sets. Although samples were collected across an annual cycle to examine seasonal change, no seasonality was found. The results presented here demonstrate that compound-specific amino acid analysis of carbon isotopes is a useful tool in the analysis and interpretation of biomineral organic materials.
The Mussel Watch Program sampled bays on the East, Gulf, and West coasts of the United States over a period of 16 y. Analytical protocols included the recording of parasites and pathologies. Oysters (Crassostrea virginica) harbored significantly more parasitic taxa than mussels (Mytilidae). Cases where body burden was higher in mytilids were exclusively eukaryotic parasites, trematode metacercariae and trematode sporocysts. Oysters had higher body burdens of Nematopsis, alimentary tract ciliates, prokaryotic inclusions, and a number of unique taxa including haplosporidians, Perkinsus marinus, cestodes, and nematodes. Major pathologies were much more common in mytilids. For oysters, many parasitic taxa were more common in the Gulf of Mexico, including Nematopsis, P. marinus, trematode sporocysts, and nematodes. For mytilids, most parasites and pathologies were more common on the East Coast. Most parasite distributions were clinal on the East and West coasts, with clear relationships to well-known provincial boundaries. West Coast mytilids and East Coast oysters showed a similar trend toward increased parasite weighted prevalence in the south. The greater body burdens in Gulf Coast oysters might be a continuation of this trend. East Coast mytilids offer an opposing trend with higher body burdens in the Gulf of Maine. An increasing incidence of pathologies in mytilids at northern latitudes on both coasts runs contrary to the antithetical trends on the two coasts for parasite weighted prevalences. Within the parasite-rich Gulf of Mexico, oysters from the Texas coast were notable for their higher parasite body burdens. Some parasites and pathologies tended to have low variance-to-mean ratios and thus be identified as having even distributional patterns. Others showed a large range of weighted prevalences within a region and thus had contagious distributional patterns. With the exception of P. marinus, most of the contagious parasites were single celled. The multicellular taxa were more uniformly distributed: they tended to have much lower variance-to-mean ratios. Likely, the difference in spatial distribution between single-celled and multicellular taxa is due to the tendency for single-celled organisms to proliferate within the host or, being small, the ability to accumulate in larger numbers within the host.