Carpet Shell Research Articles

Estimating a new suitable catch size for two clam species: Implications for shellfishery management

The present study analyzes the weight gain patterns per unit of size and estimates the minimum suitable catch size of two clam species: the carpet shell clam Ruditapes decussatus and the Manila clam Ruditapes philippinarum. For this purpose, data from the two largest estuaries along the northern coast of Spain (Cantabrian Sea) were used. The length–weight relationship of both studied species was estimated using two models: a classic allometric model and a nonparametric regression model based on local linear kernel smoothers. Additionally, first derivatives were used to estimate a minimum capture size for this species, corresponding to the size at which the first derivative reached the maximum. Within this context, the models application showed (a) the nonparametric model resulted in a better fit of data for both species (b) different minimum catch sizes for each species based on maximum length (49.5 mm for R. decussatus and 44.7 mm for R. philippinarum), both considerably larger than the currently established in EU and (c) an effect of estuaries and zones on individuals weight gain patterns. This confirmed the nonparametric model as an alternative approach to analyze the length–weight relationship for the studied species and to estimate a minimum suitable catch size of capture. The application of the specific catch sizes obtained in this study could lead to an increase in available commercial stocks of both species and positive effects on the conservation of the native species. In addition, the estimated zone-specific weight-gain patterns and minimum catch sizes could support a zone-based management. Therefore, this study provides a preliminary study and a starting point to consider the revision of the minimum legal size of the studied species in order to improve the current shellfishery management model.

Molecular detection of prokaryote and protozoan parasites in the commercial bivalve Ruditapes decussatus from southern Portugal

A parasite screening combining histological and molecular techniques was performed on healthy grooved carpet shell clams collected from a commercial shellfish bed in Southern Portugal. The study included the first attempt to develop molecular techniques to detect and identify Rickettsia/Chlamydia-like bacteria and gill ciliates infecting this high-value bivalve. Although the animals failed to reveal significant pathologies relatable to infectious agents, both techniques detected low-moderate levels of infection by bacteria and protozoans, the latter including the apicomplexan Perkinsus olseni, the ciliate Boveria subcylindrica and a yet unclassified haplosporidian. Infections by P. olseni and bacteria were the most frequent and most disseminated within the two surveyed organs, gills and digestive glands. Gill and digestive gland bacteria belonged to distinct groups, the former more related to Rickettsiales and the latter to Chlamydiales. However, while gill bacteria could be clearly allocated within the Spongiobacter/Endocoizomonas group, thus likely belonging to Oceanospirillales, no evident taxonomic position could be attributed to digestive gland bacteria, most possibly consisting of a new species of parasite. In face of the current findings, symbiotic or commensal relationships between these bacteria and the bivalve should not be excluded. The results showed that healthy clams act as a repository of multiple agents of infection, which is of particular importance to a species that is known to be particularly sensitive to parasitism. The PCR techniques developed for the detection of Boveria sp. and bacteria were proven efficient and were appended to the methods for Perkinsus sp. and haplosporidians described elsewhere.

Phage particles infecting branchial Rickettsiales-like organisms in banded carpet shell Polititapes virgineus (Bivalvia) from Galicia (NW Spain)

Basophilic intracellular prokaryotic-like colonies were observed in the gills of banded carpet shell Polititapes virgineus (= Tapes rhomboides) (Linnaeus, 1767) from a natural bed in Galicia (NW Spain). Light microscope observations suggested the presence of 2 types of colonies, but transmission electron microscopy revealed that these were the same Rickettsiales-like colonies, one infected and the other uninfected by phage particles. This is the first report of the presence of phage particles in Rickettsiales-like organisms in the gills of P. virgineus.

Human exposure to lead, cadmium and mercury through fish and seafood product consumption in Italy: a pilot evaluation

The presence of selected toxic heavy metals, such as cadmium (Cd), lead (Pb) and mercury (Hg), was investigated in fish and seafood products, namely, blue mussel, carpet shell clam, European squid, veined squid, deep-water rose shrimp, red mullet, European seabass, gilthead seabream, Atlantic cod, European hake, Atlantic bluefin tuna and swordfish so as to assess their human exposure through diet. Metals were detected by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) and hydride generation atomic absorption spectrometry (Hg-AAS). Measurements of Cd, Pb and Hg were performed by means of analytical methods validated in compliance with UNI CEI EN ISO/IEC 17025 [2005. General requirements for the competence of testing and calibration laboratories. Milano (Italy): UNI Ente Nazionale Italiano di Unificazione]. The exposure assessment was undertaken matching the levels of Cd, Pb and total Hg with consumption data related to fish and seafood products selected for this purpose. In order to establish human health implications, the estimated weekly intakes (EWIs) for Cd, Pb and Hg were compared with the standard tolerable weekly intakes (TWI) for Cd and provisional tolerable weekly intakes (PTWIs) for Pb and Hg stipulated by the European Food Safety Authority (EFSA) and the Food and Agriculture Organization/World Health Organization (FAO/WHO) Joint Expert Committee on Food Additives (JECFA). The found metal concentrations were largely below the maximum levels (MLs) established at the European Union level with the exception of Cd. This metal exceeded the MLs in squid, red mullet, European hake and Atlantic cod. Squid and blue mussel showed the highest Pb concentrations which accounted for 60% and 10% of the MLs, respectively. Highest Hg levels were found in predatory fish. The concentrations of Hg in swordfish, Atlantic bluefin tuna and red mullet accounted for 50%, 30% and 30% of the MLs, respectively. The EWIs for Cd, Pb and Hg related to the consumption of fish and seafood products by the median of the Italian total population accounted for 20%, 1.5% and 10% of the standard TWI for Cd as well as PTWIs for Pb and Hg, respectively. Furthermore, the EWIs estimated using consumption data concerning Italian consumers did not exceed the standard TWI and PTWIs, except for Cd at 95th percentile.

Domoic Acid, Okadaic Acid and Spirolides: Inter-Species Variability in Contamination and Cooking Effects

The inter-species variability of contamination by domoic acid (DA), okadaic acid and analogues (OAs) and spirolides (SPX) in mussels, oysters, cockles, carpet shell clams and razor clams was assessed. DA concentrations were measured using both high performance liquid chromatography (HPLC) with Ultra Violet (UV) detection and HPLC cou- pled with tandem mass spectrometry (HPLC-MS/MS); OAs and SPX were measured using HPLC-MS/MS. Observations showed that for each phycotoxin, the contamination rates are species-dependent and the most contaminated species differ according to the kind of phycotoxin. For DA and SPX, cockles appear to be the most contaminated species whereas mus- sels seem to be the predominant vector for OAs. The effect of cooking process on DA concentrations was investigated in five different bivalve species by comparing toxin concentrations in whole raw flesh with concentrations in whole cooked flesh. The DA concentration decreased in cooked cockles and razor clams whereas it increased in cooked mussels, carpet shell clams and donax. Thus the impact of cooking is bivalve species-dependent. For OAs and SPX, the cooking process was studied on mussels and resulted in an increase in the toxin concentration because of their lipophilic nature. These re- sults should be taken into consideration in exposure assessments and in the design of regulatory monitoring programs, as the current banning levels based on raw bivalves may over- or under-protect consumers when shellfish are eaten cooked.

Differential distribution pattern of native Ruditapes decussatus and introduced Ruditapes phillippinarum clam populations in the Bay of Santander (Gulf of Biscay): Considerations for fisheries management

The aim of the present study is to provide a first characterization of the grooved carpet shell clam Ruditapes decussatus (native) and the Manila clam Ruditapes phillippinarum (nonindigenous) populations in the Bay of Santander in order to improve the management of these commercially exploited resources. For this purpose a field survey was carried out in different fishing areas where samples were taken on transects, following artisanal shellfisher exploitation techniques. Biometric relationships, size frequency distributions, densities and stocks were evaluated for different fishing zones. In addition, a hydrodynamic model was applied in order to understand larval transport and recruitment patterns associated to the tidal currents and water flow. Within this context, the first evaluation of the clam populations in the Bay of Santander showed: (a) that fishing activity is performed on individuals under the minimum legal size (40 mm) and in closed areas, (b) a significant differences on density by zone (c) a distribution pattern with areas where both species coexist and areas where one of them dominates, (d) R. decussatus occurs at relatively low density in stations near the culture parks and (e) a limited recruitment in the inner parts of Cubas tidal fresh for R. phillippinarum and in the southern zones for R. decussatus. Based on this study, some managing guidelines are presented mainly focused on avoiding the overfishing of the native clam R. decussatus.

Development of histopathological indices in a commercial marine bivalve (Ruditapes decussatus) to determine environmental quality

Bivalve histopathology is an acknowledged tool in environmental toxicology studies, however geographically restricted, limited to a few species and still lacking the degree of detail needed to develop effective (semi)quantitative approaches. A first-time detailed histopathological screening was performed on grooved carpet shell clams collected from commercial shellfish beds in distinct coastal ecosystems of the Southern Portuguese coast: two parted sites within an impacted estuary (S1 and S2), an inlet channel of a fish farm at a considered pristine estuary (site M) and a site allocated in a clean coastal lagoon (A). A total of thirty histopathological lesions and alterations were analysed in the gills and digestive glands following a weighted condition indices approach, including inflammation-related responses, necrosis, neoplastic diseases and parasites. Digestive glands were consistently more damaged than gills, except for animals collected from site M, where the most severe lesions were found in both organs, immediately followed by S2. Clams from sites S1 and A were overall the least damaged. Neoplastic diseases were infrequent in all cases. Inflammation-related traits were some of the most common alterations progressing in animals enduring severe lesions such as digestive tubule (diverticula) and intertubular tissue necrosis. Some alterations, such as lipofuscin aggregates within digestive tubule cells, did not relate to histological lesions. Granulocytomas only occurred in heavily infected tissues. Animals from M and A presented the highest infections in the digestive gland, especially by protozoa. Gill infections were more similar between sites. Still, the level of infection does not account for all histopathological lesions in either organ. Overall, the results are in accordance with environmental parameters, such as distance to pollution sources, sediment type and hydrodynamics, and show that the combination of multiple histopathological features in these clams provides good sensitivity for inter-site distinction even when low or moderate anthropogenic impacts are at stake.

Volatile profile of Atlantic shellfish species by HS-SPME GC/MS

A procedure based on headspace solid-phase microextraction (HS-SPME) and GC–MS analysis was developed to investigate the volatile organic compounds (VOCs) of Atlantic shellfish species. The experimental conditions (fiber coating, sample volume, time and temperature of incubation) were optimized for the extraction of VOCs from shellfish. The incubation of a Carboxen/Polydimethylsiloxane (CAR-PDMS) fiber with 6mL of saline aqueous extract heated at 80°C for 30min gave the most effective and accurate extraction of the analytes. Under these experimental conditions, thermal degradations of volatiles that could be occurred during the extraction process were not observed. The method was validated in terms of linearity, repeatability, inter-day precision, recovery and sensitivity. Then, the optimized method was applied to study the volatile profile of mussels (Mytilus galloprovincialis), pullet carpet shells (Venerupis pullastra), oysters (Ostrea edulis), pod razor shells (Ensis ensis), common cockle (Cerastoderma edule) and goose barnacle (Pollicipes cornucopia). The results showed significant differences in the volatile profile, resulting some of the compound characteristic for the shellfish species. The fatty acid profile has been also investigated and the occurrence of non methylen interrupted fatty acids (NMI) in these species was related with specific volatiles. The present investigation provides the first VOC description of Atlantic E. ensis, V. pullastra, C. edule and P. cornucopia and highlights the important contribution of SPME methodology to identify volatile markers of the natural flavor of seafood, which are useful for the evaluation of origin and represent a starting point to find useful volatiles as freshness markers before commercialization or changes due to processing.

INFLUENCE OF MARINE WATER CONDITIONS ON SALMONELLA ENTERICA SEROVAR TYPHIMURIUM SURVIVAL

ABSTRACTSalmonella enterica serovar Typhimurium strains were isolated during a monitoring survey of the carpet shell clam (Ruditapes decussatus) collected from 23 stations along the Tunisian coast. The effect of starvation on Salmonella Typhimurium survival was investigated in vitro using microcosms composed of filtered (0.2 µm) marine water under dark and ambient temperature conditions (25C for 30 days). Eventual changes in physiological, biochemical properties, serotyping, biotyping and antimicrobial sensitivity for the environmentally adapted Salmonella Typhimurium were monitored. In response to stress conditions, the Salmonella Typhimurium strains progressively lost culturability in the absence of notable changes in the total cell count (during all the period of 30 days). Strains appeared to enter into a viable but noncultureable state as determined by epifluorescence method. We have also observed that the T90 value (time required for the reduction of 90% of cells) for the five different Salmonella strains ranged between 25 and 30 h; this indicated the survivability of Salmonella under stress conditions. This state was also characterized by biochemical and antimicrobial changes.PRACTICAL APPLICATIONThis research highlighted the acquisition of the viable but nonculturable state of bacteria. This form of adaptation of certain pathogens does not really reflect their presence or absence in the marine environment and thus in foods of marine origin. Hence the use of conventional methods of bacterial identification must be completed more advanced research tools before declaring a healthy product or environment.

Study of perkinsosis in the grooved carpet shell clam Ruditapes decussatus in Galicia (NW Spain). III. The effects of Perkinsus olseni infection on clam reproduction

This study evaluated the effects of the protistan parasite Perkinsus olseni on the reproduction of the grooved carpet shell clam Ruditapes decussatus from Ria de Arousa, Galicia (NW Spain). Clams collected during a one-year period were processed by histology, and their histological sections were examined for gonadal stage, volume fraction of the gonadal components, and infection by P. olseni. R. decussatus had an annual cycle with four gonadal periods: rest (November–January), gametogenesis (February–March), ripeness (April–August) and reabsorption (September–October). The effects of the disease on the gonadal cycle occurred mainly during the gametogenesis and ripeness periods. P. olseni inhibited the gonadal development during the gametogenesis months, delaying the process until the ripeness period, and reduced the percentage of ripe individuals during the ripeness months. The inflammatory reaction caused by P. olseni infection affected the volume fraction (VF) of the gonadal components by increasing the VF occupied by hemocytes, and so reducing the VF of gametes, intrafollicular empty space, follicular walls, and connective tissue. However, no significant effect of infection on gonadal index, fecundity or spawning efficiency was obtained. Therefore, infected R. decussatus may recover from the delay of late gametogenesis, produce gametes and spawn without affecting spawning efficiency or fecundity.

Evidence of non-random chromosome loss in bivalves: Differential chromosomal susceptibility in aneuploid metaphases of Crassostrea angulata (Ostreidae) and Ruditapes decussatus (Veneridae)

Aneuploidy is a cytogenetic phenomenon known as an abnormal diploid chromosome number. A negative relationship between growth rate, one of the biggest problems faced by bivalve producers, and this phenomenon was already verified for two oyster species, the Japanese oyster Crassostrea gigas, the Portuguese oyster Crassostrea angulata and their interspecific hybrids and, more recently, in the carpet shell clam Ruditapes decussatus. The main objective of this study was to assess whether chromosome losses in aneuploid situations could be explained by differential chromosomal susceptibility, as previously reported in the oyster C. gigas. Thereby, we applied the restriction enzyme (RE) digestion chromosome banding technique to aneuploid karyotypes of R. decussatus and C. angulata, in order to identify the missing chromosomes. The results of this study showed that 4 out of the 19 chromosome pairs (viz. 1, 6, 12, and 19) of R. decussatus and 3 out of the 10 chromosome pairs (viz. 1, 9, and 10) of C. angulata were preferentially affected by the loss of one homologous chromosome. The chromosomal loss in C. angulata was very similar to the one previously observed in C. gigas. These results open a new field for further research in order to have a better understanding of the aneuploidy phenomenon in bivalves and particularly its negative relationship with growth rate.

Photo-induced Toxicity of Four Polycyclic Aromatic Hydrocarbons (PAHs) to Embryos and Larvae of the Carpet Shell Clam Ruditapes decussatus

In this work, we assessed the photo-toxicity of four polycyclic aromatic hydrocarbons (PAHs) to embryos and larvae of the European clam Ruditapes decussatus. The exposure of R. decussatus embryos (24 h) and larvae (96 h) to anthracene, fluoranthene, pyrene and benzo[a]pyrene resulted in reduction of normal D-veliger percentages and high larval mortality, both in darkness and under sunlight conditions. Based on the calculated EC(50) and LC(50) values, the toxicity of the forementioned PAHs was respectively enhanced 72, 35, 60 and 23 times in the embryotoxicity test and 32, 31, 12 and 61 times in the larval mortality test when exposures were performed under sunlight conditions. Simultaneous exposure to sunlight and these PAHs enhanced their toxicity in comparison to dark conditions. The clam embryos and larvae appear to be environmentally relevant life-stages in assessing the toxic and photo-toxic risk of PAHs that enter the marine environment.

Age, Growth and Condition Index of Venerupis decussata (Linnaeus, 1758) in the Eastern Adriatic Sea

Age, growth and condition index of commercially important chequered carpet shell Venerupis decussata (Linnaeus, 1758) were studied in the Pag Bay - eastern Adriatic Sea. Monthly samples were collected from commercial catch from January to November 2007. Age and growth were determined from internal growth bands of 69 shells ranging in length from 17.7 to 43.5 mm. Marginal increment analysis performed on 68 shells (26.4±3.4 mm) confirmed that growth bands are annually formed in February. Condition index was determined monthly on 30 specimens, and maximal value was recorded in April. Formation of growth bands corresponded to a period of slow growth which was recorded prior to the increase of condition index. Distance from the umbo to the each visible growth ring was measured and growth parameters L∞ and k were estimated using the Gulland-Holt method (38.73 mm and 0.52 year-1, respectively) and by fitting length at age data to a von Bertalanffy growth curve (37.91 mm and 0.57 year-1). Majority of analysed specimens were two years old and the oldest specimens analysed had six years. In conclusion, these data suggest that V. decussata is a short - living species with the most intensive growth occurring during the first two years.

Occurrence of Brown Ring Disease in Carpet Shell ClamsRuditapes decussatusfrom the Gulf of Gabes (Tunisia, Central Mediterranean Sea)

The occurrence and spread of brown ring disease (BRD) to several northern Mediterranean coasts is described. We report the results of a 6-y surveillance of BRD in natural populations of carpet shell clams (Ruditapes decussatus) in 14 zones along the Gulf of Gabes in Tunisia (southern Mediterranean Sea). BRD symptoms in adult animals resulting from conchiolin deposits in inner parts of carpet shell were observed in all zones surveyed. Infestation rates within each site ranged from 65–100%, and BRD prevalence varied from 1–58% of clams in winter and from 1–33% in summer. Positive correlations were demonstrated between BRD prevalence and Vibrio spp. concentrations in clams. Vibrio tapetis was not identified among the bacterial organisms, suggesting that other marine Vibrio species are capable of causing BRD-like illness in carpet shell clams.

Morphological characterization and functional immune response of the carpet shell clam ( Ruditapes decussatus) haemocytes after bacterial stimulation

The morphology and functionality of Ruditapes decussatus haemocytes have been characterized by light microscopy and flow cytometry, leading to the identification of three different cellular subpopulations. Granulocytes were the largest cells, the hyalinocytes were smaller and contained fewer granules and the intermediate cells showed a size similar to hyalinocytes and a higher number of granules. The phagocytosis of different particles and the associated production of oxygen radicals were measured by flow cytometric methods. Granulocytes were the most active cells, followed by the intermediate cells and hyalinocytes. The effect of stimulation of haemocytes with lipopolysaccharide (LPS), with a heat inactivated bacterial mixture or with the infection of Vibrio splendidus on the cell viability and the expression of selected immune-related genes were studied. While significant low levels of damaged cells were registered in LPS-stimulated cells, the treatment with dead bacteria or V. splendidus reduced cell viability 1 h, 3 h and 6 h after treatment. The stimulation of haemocytes with LPS and dead bacteria induced changes in the expression of defender against cell death (DAD-1), thrombin, prosaposin, inhibitor of apoptosis (IAP), factor B and C3 complement component.

Effect of acclimatization on hemocyte functional characteristics of the Pacific oyster ( Crassostrea gigas) and carpet shell clam ( Ruditapes decussatus)

Most experimental procedures on molluscs are done after acclimatization of wild animals to lab conditions. Similarly, short-term acclimation is often unavoidable in a field survey when biological analysis cannot be done within the day of sample collection. However, acclimatization can affect the general physiological condition and particularly the immune cell responses of molluscs. Our aim was to study the changes in the hemocyte characteristics of the Pacific oyster Crassostrea gigas and the carpet shell clam Ruditapes decussatus acclimated 1 or 2 days under emersed conditions at 14 ± 1 °C and for 1, 2, 7, or 10 days to flowing seawater conditions (submerged) at 9 ± 1 °C, when compared to hemolymph withdrawn from organisms sampled in the field and immediately analyzed in the laboratory (unacclimated). The hemocyte characteristics assessed by flow cytometry were the total (THC) and differential hemocyte count, percentage of dead cells, phagocytosis, and reactive oxygen species (ROS) production. Dead hemocytes were lower in oysters acclimated both in emersed and submerged conditions (1%–5%) compared to those sampled in the field (7%). Compared to oysters, the percentage of dead hemocytes was lower in clams (0.4% vs. 1.1%) and showed a tendency to decrease during acclimatization in both emersed and submerged conditions. In comparison to organisms not acclimated, the phagocytosis of hemocytes decreased in both oysters and clams acclimated under submerged conditions, but was similar in those acclimated in emersed conditions. The ROS production remained stable in both oysters and clams acclimated in emersed conditions, whereas in submerged conditions ROS production did not change in both the hyalinocytes and granulocytes of oysters, but increased in clams. In oysters, the THC decreased when they were acclimated 1 and 2 days in submerged conditions and was mainly caused by a decrease in granulocytes, but the decrease in THC in oysters acclimated 2 days in emersed conditions was caused by a decrease in hyalinocytes and small agranular cells. In clams, the THC was significantly lower in comparison to those not acclimated, regardless of the conditions of the acclimatization. These findings demonstrate that hemocyte characteristics were differentially affected in both species by the tested conditions of acclimatization. The phagocytosis and ROS production in clams and phagocytosis in oysters were not different in those acclimated for 1 day under both conditions, i.e. emersed and submerged, and those sampled in the field (unacclimated). The THC was significantly affected by acclimatization conditions, so the differences between clams and oysters should be considered in studies where important concentrations of hemocytes are required. The difference in the immune response between both species could be related to their habitat (epifaunal vs. infaunal) and their ability of resilience to manipulation and adaptation to captivity. Our results suggest that functional characteristics of hemocytes should be analyzed in both oysters and clams during the first 1 or 2 days, preferably acclimated under emersed rather than submerged conditions.

Gene expression analysis of clams Ruditapes philippinarum and Ruditapes decussatus following bacterial infection yields molecular insights into pathogen resistance and immunity

The carpet shell clam ( Ruditapes decussatus) and Manila clam ( Ruditapes philippinarum), which are cultured bivalve species with important commercial value, are affected by diseases that result in large economic losses. Because the molecular mechanism of the immune response of bivalves, especially clams, is scarce and fragmentary, we have examined all Expressed Sequence Tags (EST) resources available in public databases for these two species in order to increase our knowledge on genes related with the immune function in these animals. After automatic annotation and classification of the 3784 not-annotated ESTs of R. decussatus and 4607 of R. philippinarum found in GenBank, 424 ESTs of R. decussatus and 464 of R. philippinarum were found to be putatively involved in immune response. These were carefully reviewed and reannotated. As a result, 13 immune-related ESTs were selected and studied to compare the immune response of R. decussatus and R. philippinarum following a Vibrio alginolyticus challenge. Quantitative PCR was performed, and the expression of each EST was determined. The results showed that, in R. philippinarum, the immune response seems to be faster than that in R. decussatus. Additionally, expression of NF-κB activating genes in R. decussatus did not seem to be sufficient to promote an immune response after Vibrio infection. R. philippinarum, however, was able to trigger and efficiently regulate the transcriptional activity of NF-κB, even when low expression values were reported.

Growth variation in bivalves: New insights into growth, physiology and somatic aneuploidy in the carpet shell Ruditapes decussatus

The carpet shell, Ruditapes decussatus is a species with a high commercial importance in Portugal and other Southern European countries. However, high growth rate variability is a major problem in the aquacultural production of this species. The objective of this work was then to study the possible differences between fast-, medium- and slow-growing individuals at three times of sampling, of a same cohort of R. decussatus in terms of eventual numerical chromosomal changes, aneuploidy, but also the level of physiological capacity, by assessing the condition index and the biochemical composition: proteins, total lipids, neutral lipids, phospholipids, carbohydrates, free reducing sugars, polysaccharides and total energy. Hypoploid cells of 2n = 37, 36, 35 or 34 were observed in all groups of individuals. The aneuploidy values observed ranging from 19% to 79%, were substantially higher than those observed in previous studies for other bivalve species. The differences in the observed aneuploidy between fast- and slow-growing clams were highly significant and a negative correlation was also observed between the level of aneuploidy and length. In general, the synthesis of the evaluated biochemical components showed no significant differences among groups suggesting that this synthesis could be related to extrinsic factors or that the analyzed biochemical components were not specific to detect the lack of certain aminoacids and enzymes involved in growth. The only exception was for total lipids, which were significantly lower in the medium and slow growing groups relative to the fast growing group. The evaluation of the relationships between all the studied parameters was performed through a principal component analysis (PCA). The results of this study demonstrate the existence of a negative correlation between somatic aneuploidy and growth in the carpet shell, as previously reported for other bivalve species. Moreover, for the first time in this study, this negative correlation is confirmed over time in a same cohort of the clam R. decussatus.

Seasonal Variations in Gross Biochemical Composition, Percent Edibility, and Condition Index of the ClamRuditapes decussatusCultivated in the Ria Formosa (South Portugal)

The grooved carpet shell clam Ruditapes decussatus (L. 1758) is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early 1990s. To understand the seasonality of its nutritional value, thus providing an improved basis for economic valuation of the resource, gross biochemical composition, percent edibility, and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam R. decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and nonprotein nitrogen covaried during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable with that shown by studies elsewhere at similar latitudes, and is underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks.

Genetic and cytological evidence of hybridization between native Ruditapes decussatus and introduced Ruditapes philippinarum (Mollusca, Bivalvia, Veneridae) in NW Spain

The introduction of foreign species in marine ecosystems is an established method to increase productivity and generate income in aquaculture. A good example is the introduction of the Japanese carpet shell, Ruditapes philippinarum, now the major contributor to clam landings in Europe. The similarity of R. philippinarum and the native grooved carpet shell, R. decussatus, the plasticity of their shell morphology and the presence of both species on the same beds make it very difficult sometimes for the morphological identification of specimens that show intermediate shell characteristics. A species identification method using length differences in the internal transcribed spacer (ITS) region of the major ribosomal RNA genes and the whole repeat sequence of the minor ribosomal RNA genes (5S rDNA) was developed for Ruditapes. Following morphological recognition, this method enabled the identification of both species of Ruditapes. However, nine of the 222 individuals morphologically identified as R. decussatus had sequences specific to both R. decussatus and R. philippinarum in both the ITS region and the 5S rDNA and were putative hybrids. Species-specific ITS and 5S rDNAs were used as probes in fluorescent in situ hybridization (FISH) experiments to map these sequences on surface spread synaptonemal complexes (SCs) of R. decussatus and R. philippinarum. Differences on the chromosomal location of those sequences between species were also detected. FISH on the SCs of two of the nine hybrid individuals also showed signal patterns corresponding to those detected in both R. decussatus and R. philippinarum thus confirming their hybrid nature. The hybrids showed 16S mitochondrial rDNA sequences of R. decussatus. In conclusion, genetic and cytological evidence of the occurrence of hybridization between female R. decussatus and male R. philippinarum was obtained.