Parasitic Infections In Carpet Shell Clams ( Ruditapes decussatus L.) From İzmir Bay Türkiye And Their Seasonal Distribution

Hemocytes of the carpet shell clam ( Ruditapes decussatus) and the Manila clam ( Ruditapes philippinarum): Current knowledge and future prospects

Nitric oxide production by carpet shell clam ( Ruditapes decussatus) hemocytes

In this study, we investigate the impacts of two water treatment regimes, the closed aquaculture system (CAS) and flow-through system (FTS), on the carpet shell clam (Ruditapes decussatus) larval microbiota, growth and survival. A bacteriological barrier (B) was created among breeder stage treated by florfenicol (FF, 8 mg L−1day−1 per 5 days). After spawning, larvae were maintained in five different rearing techniques: CAS; FTS; B + CAS; B + FTS and B + CAS + FF (8 mg L−1 day−1 per 3 days). Significant decrease was observed in both total bacterial count and presumptive Vibrio count (PVC) in FF-treated breeders. Besides, larvae reared in B + FTS showed significantly lower PVC than larvae maintained in other rearing techniques. It was also determined that growth and survival of larvae reared in B + CAS + FF and B + FTS were significantly better than those reared in other systems. One hundred and twelve Vibrio strains, isolated from breeders, eggs and larvae, were subjected to some bacteriological tests (API 20E strips, vibriostatic agent O/129, growth at different temperatures and salinity). Vibrio alginolyticus was the predominant isolated species (36.61 %), followed by V. fluvialis (25 %), V. vunificus (17.86 %), V. cholera (13.39 %) and V. paraheamolyticus (7.14 %). These results may contribute to the understanding of the effect of rearing techniques on the bacterial load, survival and growth of early life stages of R. decussatus larvae.

The South Lagoon of Tunis (Tunisia) is a Mediterranean lagoon adversely affected by industrial contaminants, harbour activity and untreated urban sewage. In this lagoon, the clam Ruditapes decussatus has been widely used as a biomonitor of seawater pollution through measurements of parameters related to oxidative stress and neurotoxicity. However, few studies have considered parameters of the immune system of this species in the South Lagoon of Tunis. Therefore, the aim of the present work was to evaluate several immune-related parameters in the cell-free haemolymph of carpet shell clams sampled during August and February from three polluted sites in the South Lagoon of Tunis (S1, S2 and S3) and one less polluted site as a reference site (RS) in order to identify suitable biomarkers for environmental quality assessments of this ecosystem. Concerning the immune-related parameters, seasonal factors modulated phenoloxidase, lysozyme, protease and esterase activity, with lower values measured for samples collected in August than for samples collected in February. In fact, bactericidal activity against two of the pathogenic bacteria tested and the activity of most immune-related enzymes were reduced in the cell-free haemolymph of clams collected from the most sampling sites in August compared to February one. In addition, values of abiotic parameters (temperature, salinity and pH) and metal (cadmium, copper, iron, lead and zinc) concentrations in the clams’ soft tissues, previously obtained and published by the authors, as well as the values of immune-related parameters were integrated using principal component analyses. Results indicated that the values of all measured immune-related parameters were negatively correlated with the temperature values and the variations most of these parameters highlighted that the chemical industrial area (S3) was the most impacted location within the South Lagoon of Tunis. The present study illustrates that the immune-related parameters measured in carpet shell clam cell-free haemolymph represent suitable biomarkers for environmental quality assessments because they provide effective seasonal and spatial discrimination.

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.

Hypnospores detected by RFTM in clam ( Ruditapes decussatus) tissues belong to two different protozoan organisms, Perkinsus atlanticus and a Perkinsus-like organism

Chemical sensing of the surrounding environment is crucial for many aspects of bivalve biology, such as food detection and predator avoidance. Aquatic organisms strongly depend on chemosensory systems; however, little is known about chemosensory systems in bivalves. To understand how the carpet shell clam (Ruditapes decussatus) senses its surrounding chemical environment, we used an electrophysiological technique – the electro-osphradiogram – to assess the sensitivity of the osphradium to different putative odorants (amino acids, bile acids) and odours (predator-released cues and signals from con- and heterospecific bivalves). The clam osphradium was sensitive to most proteinogenic L-amino acids, evoking negative, tonic, and concentration-dependent responses. However, acidic amino acids (L-glutamic and L-aspartic acid), L-arginine and bile acids (cholic, taurocholic and taurolithocholic acid) failed to evoke any response. Surprisingly, while cues from injured bivalves (con- and heterospecific) evoked strong responses, predator-released cues (green crab, Carcinus maenas) failed to elicit any response, whether fed or unfed. That predator-released cues failed to evoke an electrophysiological response in the clam osphradium may indicate that they use cues released by injured prey – alarm cues – to avoid predation and/or that predators are detected by different sensory modalities. Indeed, the behavioural assays, performed to understand how clams make use of such sensory inputs, revealed that the activity index decreased after exposure to water conditioned with injured conspecifics, suggesting the origin of such alarm cues. Further research is needed to identify the chemical nature of these cues. We suggest that the electro-osphradiogram will be a useful tool in this endeavour.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00359-025-01757-2.

Two episodes of mortality of cultured carpet shell clams (Ruditapes decussatus) associated with bacterial infections were recorded during 2001 and 2002 in a commercial hatchery located in Spain. Vibrio alginolyticus was isolated as the primary organism from moribund clam larvae that were obtained during the two separate events. Vibrio splendidus biovar II, in addition to V. alginolyticus, was isolated as a result of a mixed Vibrio infection from moribund clam larvae obtained from the second mortality event. The larval mortality rates for these events were 62 and 73%, respectively. Mortality was also detected in spat. To our knowledge, this is the fist time that these bacterial species have been associated with larval and juvenile carpet shell clam mortality. The bacterial strains were identified by morphological and biochemical techniques and also by PCR and sequencing of a conserved region of the 16S rRNA gene. In both cases bacteria isolated in pure culture were inoculated into spat of carpet shell clams by intravalvar injection and by immersion. The mortality was attributed to the inoculated strains, since the bacteria were obtained in pure culture from the soft tissues of experimentally infected clams. V. alginolyticus TA15 and V. splendidus biovar II strain TA2 caused similar histological lesions that affected mainly the mantle, the velum, and the connective tissue of infected organisms. The general enzymatic activity of both live cells and extracellular products (ECPs), as evaluated by the API ZYM system, revealed that whole bacterial cells showed greater enzymatic activity than ECPs and that the activity of most enzymes ceased after heat treatment (100 degrees C for 10 min). Both strain TA15 and strain TA2 produced hydroxamate siderophores, although the activity was greater in strain TA15. ECPs from both bacterial species at high concentrations, as well as viable bacteria, caused significant reductions in hemocyte survival after 4 h of incubation, whereas no significant differences in viability were observed during incubation with heat-killed bacteria.

The grooved carpet shell clam (Ruditapes decussatus) is a bivalve of high commercial value distributed throughout the European coast. Its production has suffered a decline caused by different factors, especially by the parasite Perkinsus olsenii. Improving production of R. decussatus requires genomic resources to ascertain the genetic factors underlying resistance/tolerance to P. olsenii. In this study, the first reference genome of R. decussatus was assembled through long- and short-read sequencing (1677 contigs; 1.386 Mb) and further scaffolded at chromosome level with Hi-C (19 superscaffolds; 95.4% of assembly). Repetitive elements were identified (32%) and masked for annotation of 38,276 coding- and 13,056 non-coding genes. This genome was used as a reference to develop a 2bRAD-Seq 13,438 SNP panel for a genomic screening on six shellfish beds distributed across the Atlantic Ocean and Mediterranean Sea. Beds were selected by perkinsosis prevalence and the infection level was individually evaluated in all the samples. Genetic diversity was significantly higher in the Mediterranean than in the Atlantic region. The main genetic breakage was detected between those regions (FST = 0.224), being the Mediterranean more heterogeneous than the Atlantic. Several loci under divergent selection (394 outliers; 261 genomic windows) were detected across shellfish beds. Samples were also inspected to detect signals of selection for resistance/tolerance to P. olsenii by using infection-level and population-genomics approaches, and 90 common divergent outliers for resistance/tolerance to perkinsosis were identified and used for gene mining. Candidate genes and markers identified provide invaluable information for controlling perkinsosis and for improving production of the grooved carpet shell clam.

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

Probiotics from kefir: Evaluating their immunostimulant and antioxidant potential in the carpet shell clam (Ruditapesdecussatus)

Field validation of immunotoxic responses in the carpet shell clam (Ruditapes decussatus) from contaminated sites in the South Lagoon of Tunis (Tunisia)

The research focused on uptake and accumulation of Toxoplasma gondii and Cryptosporidium parvum oocysts in carpet shell clams (Ruditapes decussatus L.) from İzmir Bay. Molecular identification of T. gondii and C. parvum oocysts was carried out by conventional PCR method. The rate of positiveness of C. parvum was 3.33 % and of T. gondii 4.16 % in 120 pools examined. Statistical analysis revealed slight positive correlation between the monthly rate of positiveness of C. parvum and the clam length. However no statistically significant correlation between clam length and T. gondii monthly rate of positiveness was detected. Shellfish farming in non polluted seawater, depuration before consumption and strict food safety control for emerging enteric protozoan parasites such as T. gondii and C. parvum are recommended.

Immune biomarker and hydrocarbon concentrations in carpet shell clams (Ruditapes decussatus) collected from a Mediterranean coastal lagoon

Okadaic acid (OA), produced by dinoflagellates during harmful algal blooms (HAB), belongs to the Diarrheic Shellfish Poisoning toxins that cause gastrointestinal symptoms in humans after consumption. In the present work, Ruditapes decussatus haemocytes were selected to evaluate the effect of OA on cell viability, enzymatic status and immune capacity through the measure by flow cytometry of apoptosis-cell death, non-specific esterase activity and phagocytosis. In order to compare different exposure conditions, two experiments were developed: in vitro exposure to OA and HAB simulation by feeding clams with the OA producer, Prorocentrum lima. Apoptosis was not OA dose-dependent and cell death increased in both assays. Phagocytosis of latex beads and esterase activity decreased in haemocytes incubated with OA. In contrast, esterases increased during the feeding with P. lima. Our results showed that OA and the simulated HAB caused damages on haemocyte functions and viability.