Accumulation Of Paralytic Shellfish Toxins Research Articles

Modelling paralytic shellfish toxins (PST) accumulation in Crassostrea gigas by using Dynamic Energy Budgets (DEB)

As other filter-feeders, Crassostrea gigas can concentrate paralytic shellfish toxins (PST) by consuming dinoflagellate phytoplankton species like Alexandrium minutum. Intake of PST in oyster tissues mainly results from feeding processes, i.e. clearance rate, pre-ingestive sorting and ingestion that are directly influenced by environmental conditions (trophic sources, temperature). This study aimed to develop a mechanistic model coupling the kinetics of PST accumulation and bioenergetics in C. gigas based on Dynamic Energy Budget (DEB) theory. For the first time, the Synthesizing Units (SU) concept was applied to formalize the feeding preference of oysters between non-toxic and toxic microalgae. Toxin intake and accumulation were both dependent on the physiological status of oysters. The accumulation was modelled through the dynamics of two toxin compartments: (1) a compartment of ingested but non-assimilated toxins, with labile toxins within the digestive gland eliminated via faeces production; (2) a compartment of assimilated toxins with a rapid detoxification rate (within a few days). Firstly, the DEB-PST model was calibrated using data from two laboratory experiments where oysters have been exposed to A. minutum. Secondly, it was validated using data from another laboratory experiment and from three field surveys carried out in the Bay of Brest (France) from 2012 to 2014. To account for the variability in PST content of A. minutum cells, the saxitoxin (STX) amount per energy units in a toxic algae (ρPST) was adjusted for each dataset. Additionally, the effects of PST on the oyster bioenergetics were calibrated during the first laboratory experiment. However, these effects were shown to depend on the strain of A. minutum. Results of this study could be of great importance for monitoring agencies and decision makers to identify risky conditions (e.g. production areas, seawater temperature), to properly assess detoxification step (e.g. duration, modalities) before any commercialization or to improve predictions regarding closing of shellfish areas.

Sources of paralytic shellfish toxin accumulation variability in the Pacific oyster Crassostrea gigas

This study was designed to assess the contribution of feeding behavior to inter-individual variability of paralytic shellfish toxin (PST) accumulation in the Pacific oyster Crassostrea gigas. For this purpose 42 oysters were exposed for 2 days to non-toxic algae and then for 2 other days to the PST producer Alexandrium minutum. Individual clearance rate (CR) of oysters was continuously monitored over the 4 days using an ecophysiological measurement system. Comparison of CR values when exposed to toxic and non toxic algae allowed to estimate a clearance rate inhibition index (CRII). Toxin concentration of oysters was quantified at the end of the experiment. These data allowed to estimate the toxin accumulation efficiency (TAE) as the ratio of toxin accumulated on toxin consumed. Changes of clearance rate during the experiment indicated that all individuals stopped feeding immediately after being exposed to A. minutum for at least 7 h. This fast response likely corresponded to a behavioral mechanism of avoidance rather to a toxin-induced response. Individuals also showed high inter-variability in their recovery of filtration after this period. Most of the inter-individual variability (78%) in PST accumulation in C. gigas could be explained by the consumption of A. minutum cells, thus emphasizing the importance of the feeding behavior in accumulation. Based on the toxin concentration in their tissues, oysters were clustered in 3 groups showing contrasted patterns of PST accumulation: the high accumulation group was characterized by high feeding rates both on non-toxic and toxic diet and subsequently a low CRII and high TAE. Inversely, the low accumulation group was characterized by low filtration rates, high CRII and low TAE. Both filtration capacity and sensitivity of oysters to toxins may account for the differences in their accumulation. The contribution of TAE in PST accumulation is discussed and might result from differences in assimilation and detoxification abilities among individuals.

Accumulation and depuration of paralytic shellfish toxins by Australian abalone Haliotis rubra: Conclusive association with Gymnodinium catenatum dinoflagellate blooms

Paralytic shellfish toxins (PST) were detected in abalone (Haliotis rubra) in April 2011 in south-east Tasmania, Australia, during a dinoflagellate bloom of Gymnodinium catenatum. This led to restrictions on abalone harvesting and triggered continued PST monitoring by Ultra Performance Liquid Chromatography (UPLC-FLD) of abalone and mussels (Mytilus galloprovincialis), and concurrent phytoplankton monitoring, between 2011 and 2013. PST up to 2437 μg STX eq kg−1 (three times the bivalve regulatory limit) were confirmed in abalone viscera, with toxicity up to 586 μg STX eq kg−1 in the muscular foot (mainly doSTX and minor proportions of STX and dcSTX). Mussels accumulated PST at a faster rate than abalone which suggests they can serve as sentinels of PST accumulation to inform abalone risk management protocols.Three lines of evidence for G. catenatum as the source of PST in abalone were established: (1) PST in abalone tissues increased and declined in association with dinoflagellate blooms; (2) G. catenatum DNA was detected by real-time PCR in abalone digestive tracts; and (3) the PST analogues (toxin profile) observed in both abalone viscera and mussels were similar suggesting a common PST source. This is the first time a conclusive linkage between the occurrence of PST in abalone and a dinoflagellate source has been demonstrated.

Exposure to the toxic dinoflagellate Alexandrium catenella modulates juvenile oyster Crassostrea gigas hemocyte variables subjected to different biotic conditions.

The Pacific oyster Crassostrea gigas is an important commercial species cultured throughout the world. Oyster production practices often include transfers of animals into new environments that can be stressful, especially at young ages. This study was undertaken to determine if a toxic Alexandrium bloom, occurring repeatedly in French oyster beds, could modulate juvenile oyster cellular immune responses (i.e. hemocyte variables). We simulated planting on commercial beds by conducting a cohabitation exposure of juvenile, "specific pathogen-free" (SPF) oysters (naïve from the environment) with previously field-exposed oysters to induce interactions with new microorganisms. Indeed, toxic Alexandrium spp. exposures have been reported to modulate bivalve interaction with specific pathogens, as well as physiological and immunological variables in bivalves. In summary, SPF oysters were subjected to an artificial bloom of Alexandrium catenella, simultaneously with a cohabitation challenge. Exposure to A.catenella, and thus to the paralytic shellfish toxins (PSTs) and extracellular bioactive compounds produced by this alga, induced higher concentration, size, complexity and reactive oxygen species (ROS) production of circulating hemocytes. Challenge by cohabitation with field-exposed oysters also activated these hemocyte responses, suggesting a defense response to new microorganism exposure. These hemocyte responses to cohabitation challenge, however, were partially inhibited by A.catenella exposure, which enhanced hemocyte mortality, suggesting either detrimental effects of the interaction of both stressors on immune capacity, or the implementation of an alternative immune strategy through apoptosis. Indeed, no infection with specific pathogens (herpesvirus OsHV-1 or Vibrio aesturianus) was detected. Additionally, lower PST accumulation in challenged oysters suggests a physiological impairment through alteration of feeding-related processes. Overall, results of this study show that a short-term exposure to A.catenella combined with an exposure to a modified microbial community inhibited some hemocyte responses, and likely compromised physiological condition of the juvenile oysters.

Influence of gametogenesis pattern and sex on paralytic shellfish toxin levels in triploid Pacific oyster Crassostrea gigas exposed to a natural bloom of Alexandrium minutum

This study investigated the effect of gametogenesis pattern and sex on levels of paralytic shellfish toxins (PST) accumulated by triploid oysters Crassostrea gigas exposed to a natural bloom of the toxic dinoflagellate Alexandrium minutum in the Bay of Brest (Western Brittany, France), over the summer 2014. Toxin accumulation in oysters was proposed to be influenced by the proportion of energy allocated to reproduction versus other metabolisms, as proposed by Haberkorn et al. (2010). Thus, we hypothesized that triploid oysters with different gametogenesis patterns (α or β, producing respectively numerous gametes or rare gametes) could result in differences in toxin accumulation. Toxin level could also be different according to the gender of the oysters. To test these hypotheses, PST levels were measured in the digestive gland of oysters using an ELISA method. Sex, gametogenesis stage and pattern (α or β) of the triploid oysters were determined by histology. Males (24%), females (38%) and hermaphrodites (38%), including synchronous or successive hermaphrodites were represented among the sampled oysters. All of them were at mature stage (III) of gametogenesis. Both α (46%) and β (54%) patterns were represented in the sample set. In these oysters, PST levels appeared independent from sex and gametogenesis pattern. These results suggest that, in triploid oysters, PST accumulation is not influenced by energy allocated to reproduction. Statement of relevanceThis study appears to be the first to investigate toxin levels depending on gametogenesis pattern in triploid oysters.This study highlighted that triploid oysters were divided into two classes, α (triploid oysters that maturate with unlocked germ cells and have a consequent number of gametes) and β (triploid oysters that display strongly reduced number of gametes and locked gonial mitosis), with the latter class subdivided into two categories: β1, which presents no germinal cell lineage, and β2, which presents germinal cell lineage.This study showed that toxin levels in the digestive glands of triploids were not significantly different, neither between gametogenesis patterns nor between sexes. Additionally, despite the different patterns of gametogenesis in the triploid oysters of the present study, no difference in toxin levels accumulated in the digestive glands was detected between α and β oysters, suggesting that reproductive investment in triploid oysters does not influence toxin accumulation.

A comparison of the physiological responses, behaviour and biotransformation of paralytic shellfish poisoning toxins in a surf-clam (Paphies donacina) and the green-lipped mussel (Perna canaliculus)

The accumulation of paralytic shellfish toxins (PSTs) in bivalves is species specific. We compared the physiological responses and the toxin profiles in tissues of the burrowing surf clam, Paphies donacina, and the green-lipped mussel, Perna canaliculus, exposed to the toxic dinoflagellate Alexandrium tamarense. Bivalves were supplied with the toxic algae for 10 days, then allowed a detoxification period of 8 days. Clearance rates of mussels and clams were similar when fed either with toxic A. tamarense or non-toxic A. margalefi. Byssus production in the mussel was inhibited and exhalent siphon activity in clams was erratic following exposure to A. tamarense. There were considerable differences in the toxic profile between the dinoflagellate A. tamarense, and tissues of the mussel and the surf clam, indicating that bioconversion of the PSTs had taken place. Toxin profiles of the tissues were both species and tissue specific. Following an 8-day detoxification period, total PSTs in mussels had fallen to safe concentrations below 50µg per 100g, whereas concentrations in clams remained high, with an average value greater than 600µg STX di-HCL equivalents per 100g. The results confirmed that mussels and clams are important monitoring organisms for toxic algal blooms and can be used to minimise the health risk of PSTs to humans.

Interaction between toxic dinoflagellate Alexandrium catenella exposure and disease associated with herpesvirus OsHV-1 μVar in Pacific oyster spat Crassostrea gigas

Blooms of toxic dinoflagellates can co-occur with mass mortality events associated with herpesvirus OsHV-1μVar infection that have been decimating Pacific oyster Crassostrea gigas spat and juveniles every summer since 2008 in France. This study investigated the possible effect of a harmful dinoflagellate, Alexandrium catenella, a producer of Paralytic Shellfish Toxins (PSTs), upon the oyster spat–herpesvirus interaction. Oyster spat from a hatchery were challenged by cohabitation with oysters contaminated in the field with OsHV-1μVar and possibly other pathogens. Simultaneously, the oysters were exposed to cultured A. catenella. Infection with OsHV-1μVar and PST accumulation were measured after 4 days of experimental exposure.Exposure to Alexandrium catenella modified the host–pathogen interaction by reducing prevalence of OsHV-1μVar infection. In addition, oysters challenged with OsHV-1μVar and possibly other pathogens from the environment accumulated smaller amounts of PSTs than unchallenged oysters. Three possible mechanisms are suggested by these results: (i) possible direct interactions between A. catenella and herpesvirus (or associated pathogens) could reduce viral transmission and algal availability for oyster consumption; (ii) oyster feeding behavior or digestive functions may have been altered, thus decreasing both uptake of viral particles and consumption or digestion of toxic algae and consequent toxin accumulation; (iii) immuno-activation by A. catenella could enhance defense efficiency against OsHV-1μVar infection. These findings suggest further research on relationships between OsHV-1μVar and toxic dinoflagellates and their combined effects upon disease transmission and proliferation processes, as well as on oyster physiological and immunological involvement in this complex, tripartite interaction.

SxtA and sxtG gene expression and toxin production in the Mediterranean Alexandrium minutum (Dinophyceae).

The dinoflagellate Alexandrium minutum is known for the production of potent neurotoxins affecting the health of human seafood consumers via paralytic shellfish poisoning (PSP). The aim of this study was to investigate the relationship between the toxin content and the expression level of the genes involved in paralytic shellfish toxin (PST) production. The algal cultures were grown both in standard f/2 medium and in phosphorus/nitrogen limitation. In our study, LC-HRMS analyses of PST profile and content in different Mediterranean A. minutum strains confirmed that this species was able to synthesize mainly the saxitoxin analogues Gonyautoxin-1 (GTX1) and Gonyautoxin-4 (GTX4). The average cellular toxin content varied among different strains, and between growth phases, highlighting a decreasing trend from exponential to stationary phase in all culture conditions tested. The absolute quantities of intracellular sxtA1 and sxtG mRNA were not correlated with the amount of intracellular toxins in the analysed A. minutum suggesting that the production of toxins may be regulated by post-transcriptional mechanisms and/or by the concerted actions of alternative genes belonging to the PST biosynthesis gene cluster. Therefore, it is likely that the sxtA1 and sxtG gene expression could not reflect the PST accumulation in the Mediterranean A. minutum populations under the examined standard and nutrient limiting conditions.

Transient isotachophoresis-capillary zone electrophoresis with contactless conductivity and ultraviolet detection for the analysis of paralytic shellfish toxins in mussel samples

The accumulation of paralytic shellfish toxins (PSTs) in contaminated shellfish is a serious health risk making early detection important to improve shellfish safety and biotoxin management. Capillary electrophoresis (CE) has been proven as a high resolution separation technique compatible with miniaturization, making it an attractive choice in the development of portable instrumentation for early, on-site detection of PSTs. In this work, capillary zone electrophoresis (CZE) with capacitively coupled contactless conductivity detector (C4D) and UV detection were examined with counter-flow transient isotachophoresis (tITP) to improve the sensitivity and deal with the high conductivity sample matrix. The high sodium concentration in the sample was used as the leading ion while l-alanine was used as the terminating electrolyte (TE) and background electrolyte (BGE) in which the toxins were separated. Careful optimization of the injected sample volume and duration of the counter-flow resulted in limit of detections (LODs) ranging from 74.2 to 1020ng/mL for tITP-CZE-C4D and 141 to 461ng/mL for tITP-CZE-UV, an 8–97 fold reduction compared to conventional CZE. The LODs were adequate for the analysis of PSTs in shellfish samples close to the regulatory limit. Intra-day and inter-day repeatability values (percentage relative standard deviation, n=3) of tITP-CZE-C4D and tITP-CZE-UV methods for both migration time and peak height were in the range of 0.82–11% and 0.76–10%, respectively. The developed method was applied to the analysis of a contaminated mussel sample and validated against an Association of Official Analytical Chemists (AOAC)-approved method for PSTs analysis by high performance liquid chromatography (HPLC) with fluorescence detection (FLD) after pre-column oxidation of the sample. The method presented has potential for incorporation in to field-deployable devices for the early detection of PSTs on-site.

Exposure to the Neurotoxic Dinoflagellate, Alexandrium catenella, Induces Apoptosis of the Hemocytes of the Oyster, Crassostrea gigas

This study assessed the apoptotic process occurring in the hemocytes of the Pacific oyster, Crassostrea gigas, exposed to Alexandrium catenella, a paralytic shellfish toxins (PSTs) producer. Oysters were experimentally exposed during 48 h to the toxic algae. PSTs accumulation, the expression of 12 key apoptotic-related genes, as well as the variation of the number of hemocytes in apoptosis was measured at time intervals during the experiment. Results show a significant increase of the number of hemocytes in apoptosis after 29 h of exposure. Two pro-apoptotic genes (Bax and Bax-like) implicated in the mitochondrial pathway were significantly upregulated at 21 h followed by the overexpression of two caspase executor genes (caspase-3 and caspase-7) at 29 h, suggesting that the intrinsic pathway was activated. No modulation of the expression of genes implicated in the cell signaling Fas-Associated protein with Death Domain (FADD) and initiation-phase (caspase-2) was observed, suggesting that only the extrinsic pathway was not activated. Moreover, the clear time-dependent upregulation of five (Bcl2, BI-1, IAP1, IAP7B and Hsp70) inhibitors of apoptosis-related genes associated with the return to the initial number of hemocytes in apoptosis at 48 h of exposure suggests the involvement of strong regulatory mechanisms of apoptosis occurring in the hemocytes of the Pacific oyster.

Modelling paralytic shellfish toxins (PSTs) transfer and accumulation in populations of two planktonic grazers

A model was developed in this paper in order to study and compare the paralytic shellfish toxin (PST) transfer and accumulation of two different potential PST vectors in the planktonic community, the heterotrophic dinoflagellate in its red form Noctiluca scintillans and the copepod Acartia clausi. Different factors that influence the toxin transfer such as toxin synthesis, grazing on toxic and non-toxic food and population size of PST producers and vectors were considered in the model. Moreover, a laboratory experiment was conducted in order to calculate the detoxification rates of Noctiluca fed on Alexandrium catenella. According to the model results, the two grazers showed a significant difference mainly in the timing of the PST accumulation. Noctiluca exhibited a rapid response to the grazing of Alexandrium with high initial toxin accumulation, followed by a reduction to zero concentration of toxins in a period of almost two days. In contrast, Acartia showed a considerable delay in comparison to Noctiluca to accumulate the same amount of toxin in the population. This delay is linked to the slower reproduction rates that characterize the copepod. The range of the initial values used for the sensitivity analysis of the model is representative of the coastal environment of a Galician ria (embayment located at the NW of Iberian Peninsula), where the two grazers and Alexandrium may co-exist. The model for Acartia showed less sensitivity to these key parameters probably due to the time delay in accumulation of significant amount of toxins. Both grazers showed a rapid (50h) reduction of ingested toxin, suggesting inefficiency to transfer toxins through predation in the food web.

Effects of feeding Alexandrium tamarense, a paralytic shellfish toxin producer, on antioxidant enzymes in scallops (Patinopecten yessoensis) and mussels (Mytilus galloprovincialis)

Contamination of molluscan bivalves with paralytic shellfish toxins (PST) is a frequent occurrence worldwide. Paralytic shellfish poisoning (PSP) events seriously threaten consumers' health and shellfish economy. It is worthwhile to investigate the dynamic response of antioxidant enzymes to PST accumulated by bivalves, since this will help us explore the mechanisms for accumulation and biotransformation of PST in shellfish. In this study, scallops (Patinopecten yessoensis) and mussels (Mytilus galloprovincialis) were fed in the laboratory with Alexandrium tamarense (ATHK), a PST-producing dinoflagellate. Dynamic variations of reactive oxygen species (ROS) and antioxidant enzymes including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and glutathione peroxidase (GSH-Px, EC 1.11.1.9) were monitored in the muscle and digestive gland of experimental shellfish. Results showed that ROS was quickly generated and then disappeared in the tissues of scallop and mussel in the PST-accumulating and depurating periods, and that different response of antioxidant enzymes to ROS occurred in the two different bivalves. SOD activity was obviously inhibited in the tissues of scallop, while the CAT activity was not stimulated by the toxic bait in scallop. However, both SOD and CAT activities were induced in the tissues of mussel to effectively scavenge superoxide anion free radical and H2O2. Similar dynamic fluctuation of GSH-Px activity was also stimulated to remove H2O2 or other superoxide compounds in the tissues of both bivalves, which was hypothetically modulated by the depletion and regeneration of glutathione. Only GSH-Px enzyme was induced to remove ROS in scallop, but all SOD, CAT, and GSH-Px enzymes were stimulated to avoid oxidative stress in mussel. The species specific response of antioxidant enzymes between scallop and mussel fed with toxic A. tamarense has been described here for the first time.

Paralytic shellfish toxins in the Atlantic horse mackerel (<i>Trachurus trachurus</i>) over a bloom of <i>Gymnodinium catenatum</i>: the prevalence of decarbamoylsaxitoxin in the marine food web

This study reports the accumulation of paralytic shellfish toxins (PSTs) in Atlantic horse mackerel ( Trachurus trachurus ) over a bloom of the toxigenic dinoflagellate Gymnodinium catenatum . High levels of toxins, up to 4800 μg STXeq kg –1 , were registered at the peak of the bloom (5.0 10 3 cells l –1 ). The suite of individual PSTs was examined. Decarbamoylsaxitoxin (dcSTX) and B1 constituted nearly 90% of toxins (on a molar basis) determined in mackerel. This profile of toxins markedly differs from the known profile of toxins produced by G. catenatum strains isolated from the Portuguese coast, which is dominated by N-sulfocarbamoyl toxins, in particular the C1+2 toxins. The prevalence of the potent dcSTX in the pelagic environment and its transfer through the marine food web is highlighted in this study. Atlantic horse mackerel is identified as a high potential vector of PSTs along the Portuguese coast. This fish species has a central position in the marine food web, being an important predator of zooplankton and at the same time an important diet item of top predators. This study reveals bioaccumulation values that are important for evaluating potential impacts of blooms of PST-producing dinoflagellates on marine ecosystems or their components, such as fish.

Effects of the toxic dinoflagellate Alexandrium catenella on histopathogical and escape responses of the Northern scallop Argopecten purpuratus

Juvenile Northern scallops Argopecten purpuratus were exposed to cultures of the paralytic shellfish toxin (PST) producing dinoflagellate, Alexandrium catenella, or a non-toxic microalga as a control, T-iso. After 3 and 6 days of exposure to either A. catenella or T-iso, scallops were stimulated to elicit an escape response by exposing them to the predatory sea star Meyenaster gelatinosus. We monitored the escape response of the scallops in terms of reaction time after first contact with the sea star, number of claps (burst of rapid valve closures) until exhaustion, clapping time, clapping rate, the time scallops spent closed when exhausted, and recovery from the initial number of claps, clapping time and clapping rate. Additionally, histopathological and stress responses (through heat-shock protein [hsp70] induction), as well as accumulation of Paralytic Shellfish Poisoning (PSP) toxins, were monitored on scallops after 3 and 6 days of exposure to A. catenella. After 6 days of exposure, scallops exposed to A. catenella accumulated PSTs and reacted more rapidly with a higher clapping rate, however the duration of their escape response was shorter than controls, when exposed to M. gelatinosus. Additionally, scallops exposed to A. catenella showed histopathological features, especially after 6 days of exposure, including increased melanization of the tissues and myopathy, with high levels of degeneration of the muscle fibers. A six-day exposure to A. catenella also caused an increase in prevalence of rickettsiales-like organisms within scallop tissues. This study suggests that PST accumulation can affect the interaction between the Northern scallop and both pathogens and predators, potentially increasing their susceptibility to either of them.

Past trends and future scenarios for environmental conditions favoring the accumulation of paralytic shellfish toxins in Puget Sound shellfish

The risk of harmful algal blooms (HABs) of the dinoflagellate Alexandrium catenella in Puget Sound, Washington State, can be assessed by identifying and predicting climate and environmental conditions that are favorable for bloom development and the accumulation of paralytic shellfish toxins (PSTs) in shellfish. When these favorable conditions occur in combination, a harmful algal bloom window of opportunity (HAB-WOO) exists for A. catenella. The original HAB-WOO was identified by Moore et al. (2009) for the time period 1993–2007. In general, it showed that warm air and water temperatures, low streamflow, low winds, and small tidal variability precede PST events. Here, we use the HAB-WOO model to examine (i) changes in the annual HAB-WOO duration over the period from 1967 to 2006, and (ii) the potential effect of future climate change on HAB risk through the late 21st century. The annual HAB-WOO duration increased between 1978 and 2006, as did the frequency and geographic extent of PST events. Two step-like changes occurred in 1978 and 1992 with higher annual values attained by the HAB-WOO compared to previous years. The 1978 step change may be related to the 1977 reversal of the Pacific Decadal Oscillation from cool to warm phase. Climate change projections from global climate models and regionally downscaled climate models for the Pacific Northwest are used to evaluate scenarios for the future HAB-WOO. Under a moderate greenhouse gas emissions scenario (i.e., A1B), the annual HAB-WOO for A. catenella in Puget Sound is projected to increase by an average of 13 days by the end of the 21st century. Furthermore, the annual HAB-WOO may begin up to 2 months earlier in the year and persist for up to 1 month later in the year compared to the present day. This research provides managers, health authorities, and shellfish growers in Washington State with critical information for anticipating climate impacts on toxic HABs in the Pacific Northwest now and in a future warmer climate.

The relative influences of El Niño‐Southern Oscillation and Pacific Decadal Oscillation on paralytic shellfish toxin accumulation in northwest Pacific shellfish

Historical records of paralytic shellfish toxins (PSTs) in shellfish from a coastal embayment in the Pacific Northwest of the United States are used to examine the influence of large‐scale climate variations on aspects of Alexandrium catenella bloom dynamics on interannual and interdecadal timescales. An annual index of shellfish toxicity covaries with the number of days annually that sea surface temperature (SST) exceeds 13°C—a known temperature threshold for increased shellfish toxicity in this region—and with an index of the Pacific Decadal Oscillation (PDO). In contrast, no robust relationship exists between our shellfish toxicity index and an index of the El Niño‐Southern Oscillation (ENSO). We hypothesize that this is because anomalously warm water temperatures created during El Niño winters do not generally persist into the seasonal time period that shellfish in this region accumulate PSTs, which is typically in the summer and fall. In contrast, anomalously warm water temperatures created during warm‐phase PDO winters and springs typically persist into the summer and fall, thereby increasing the number of days annually that SST exceeds 13°C, and increasing the window of opportunity for Alexandrium blooms that ultimately lead to shellfish acquiring higher concentrations of PSTs.

Effects of Alexandrium minutum exposure on nutrition-related processes and reproductive output in oysters Crassostrea gigas

This study assessed the effects of an artificial bloom of the toxin-producing dinoflagellate, Alexandrium minutum, upon nutrition related processes and reproductive output of the Pacific oyster, Crassostrea gigas. Oysters were exposed to A. minutum, Paralytic Shellfish Toxins (PST) producer and compared to a control batch of oysters fed Isochrysis galbana clone Tahitian (T. Iso). The experiment was performed in June 2008, when oysters were found ripe. Several physiological variables of oysters, such as PSTs accumulation, digestive gland and histological observations as well as spermatozoa quality, were measured at the end of the exposure. Results indicate that the digestive gland was greatly impacted upon A. minutum exposure. Monoacylglycerol and diacylglycerol contents as well as phospholipids (mainly phosphatidylcholine) drastically decreased in the digestive gland of oysters exposed to A. minutum compared to control oysters. At the same time, many oysters exposed to the harmful microalga presented a strong inflammatory response in different tissues of the digestive gland: in intestine as well as in digestive ducts and tubules. Spermatozoa in oysters exposed to A. minutum were morphologically and functionally modified compared to spermatozoa of control oysters. Indeed, spermatozoa were less motile and had lower ATP content in oysters exposed to A. minutum. Meanwhile, spermatozoa produced by control oysters showed higher percentage of mortality and relative DNA content than those produced by A. minutum exposed oysters. Finally, the characteristics of the mitochondria of spermatozoa also appeared to be modified upon A. minutum exposure. The results of this study suggests that an exposure of oysters to A. minutum, reducing energy status and motility of spermatozoa associated to morphological changes at the cellular and sub-cellular levels, can have consequences on spermatozoa fertility and reproduction success.

Accumulation of paralytic shellfish toxins in digestive gland of Octopus vulgaris during bloom events including the dinoflagellate Gymnodinium catenatum

Accumulation of paralytic shellfish toxins in digestive gland of Octopus vulgaris during bloom events including the dinoflagellate Gymnodinium catenatum

Differential accumulation of paralytic shellfish toxins from Alexandrium minutum in the pearl oyster, Pinctada imbricata

To investigate the potential for differential accumulation of paralytic shellfish toxins (PSTs) in various tissues of the akoya pearl oyster, Pinctada imbricata, two feeding trials were carried out using the PST-producing dinoflagellate, Alexandrium minutum. When fed with A. minutum at concentrations between 100 and 1300 cells ml −1, the maximum clearance by P. imbricata was shown to occur at a density of 300 cells ml −1. When fed twice daily at this rate for up 12 days, P. imbricata accumulated analogues of gonyautoxins (GTXs): GTXs 1,4 and 2,3. The levels of GTXs in the viscera increased progressively on days 4, 8 and 12 to peak at 17.9 ± 4.47 μg STX-equivalent 100 g −1 biomass. Following 12 days of depuration, in the absence of A. minutum, GTX levels fell by approximately 65% to 6.0 ± 2.20 μg STX-equivalent 100 g −1 biomass. No GTX was found in the oysters at the start of the trial or in untreated controls. The accumulation of GTX was found to be tissue specific. No GTX was detected in the muscle tissue of P. imbricata during the feeding trial.

Comparison of five tuna plasma analytes measured on two automated blood analyzers

In vitro accumulation of tetrodotoxin (TTX) and paralytic shellfish toxin (PST) in tiger puffer fish Takifugu rubripes was investigated using liver tissue slices. When T. rubripes liver slices were incubated with Leibovitz’s L-15 medium containing 0.13 mM TTX at 20 °C in air with saturated humidity, they accumulated 21.5 ± 7.3 μg TTX g−1 liver after the incubation for 12 h and increased to 55.3 ± 8.2 μg TTX g−1 liver at 48 h. In the incubation of T. rubripes liver slices with 0.13 mM PST-containing medium, PST was detected 6.3 ± 0.9 μg g−1 liver at 12 h and reached a plateau thereafter. These results reveal the difference between TTX and PST in accumulation in T. rubripes liver tissue slices. To examine the variation in PST accumulation among fish species, the liver tissue slices from tiger puffer fish T. rubripes, parrot-bass Oplegnathus fasciatus and green ling Hexagrammos otakii were incubated at a concentration of 0.027 mM PST. The toxin contents of 3.0 μg g−1 liver were observed at 8 h regardless of fish species but were not increased subsequently, showing no variety among these three species as to accumulation patterns of PST. It is noted that the tiger puffer fish T. rubripes liver specifically accumulate TTX in preference to PST.