Scallop Species Research Articles

Seasonal and inter-species variations in nutrient components and taste characteristics of farmed scallops from Northern China

Scallops are considered a healthy seafood due to their abundant nutrition and pleasant taste. However, the biochemical composition of scallops harvested in different seasons varies, which affect their quality. To identify the superior breeding species and optimal harvesting time, the seasonal- and species-specific variations in nutrient and flavor components were investigated for two species of scallops (Chlamys farreri and Patinopecten yessoensis) using accredited methods. Regarding seasonality, the levels of proteins, fat, fatty acids, and water-soluble vitamins were significantly higher in summer. Both species of scallop had superior taste in summer and spring. Conversely, winter scallops had a healthier proportion of unsaturated fatty acids for humans, as well as richer fat-soluble vitamins. As for species differences, C. farreri exhibited higher protein proportion and vitamin B5 content, while P. yessoensis exhibited more fat and essential amino acids. Flavor indexes suggested that P. yessoensis was more delicious than C. farreri in the same season. Overall, a comprehensive assessment of the nutritional quality of scallops, using the integrated biomarker response (IBR) index, revealed that marketable scallops in early summer and late spring exhibited better quality, and P. yessoensis scored higher than C.farreri in terms of nutrition and taste.

Shellfish CO2 excretion is modulated by seawater carbonate chemistry but largely independent of pCO2.

Four species of shellfish, blue mussel (Mytilus galloprovincialis), Pacific abalone (Haliotis discus hannai), zhikong scallops (Chlamys farreri), and Pacific oyster (Crassostrea gigas), were exposed to decoupled carbonate system variables to investigate the impacts of different seawater carbonate parameters on the CO2 excretion process of mariculture shellfish. Six experimental groups with two levels of seawater pH (pH 8.1 and pH 7.7) and three levels of total alkalinity (TA = 1000, 2300, and 3600μmol/kg, respectively) were established, while pH 8.1 and TA = 2300μmol/kg was taken as control. Results showed that the CO2 excretion rates of these tested shellfish were significantly affected by the change in carbonate chemistry (P < 0.05). At the same TA level, animals incubated in the acidified group (pH 7.7) had a lower CO2 excretion rate than those in the control group (pH 8.1). In comparison, at the same pH level, the CO2 excretion rate increased when seawater TA level was elevated. No significant correlation between the CO2 excretion rate and seawater pCO2 levels (P > 0.05) was found; however, a significant correlation (P < 0.05) between CO2 excretion rate and TA-DIC (the difference between total alkalinity and dissolved inorganic carbon) was observed. Blue mussel has a significantly higher CO2 excretion rate than the other three species in the CO2 excretions per unit mass of soft parts, with no significant difference observed among these three species. However, in terms of CO2 excretion rate per unit mass of gills, abalone has the highest CO2 excretion rate, while significant differences were found between each species. Our studies indicate that the CO2 buffering capacity impacts the CO2 excretion rate of four shellfish species largely independent of pCO2. Since CO2 excretion is related to acid-base balancing, the results imply that the effects of other carbonate parameters, particularly the CO2 buffering capacity, should be studied to fully understand the mechanism of how acidification affects shellfish. Besides, the species difference in gill to soft parts proportion may contribute to the species difference in responding to ocean acidification.

Amino Acid Composition in Different Tissues of Iceland Scallop from the Barents Sea.

The Iceland scallop from the Barents Sea is a commercially important species with promising aquaculture potential, but information on the biochemical properties of its tissues is limited. Our analysis of the adductor muscle, gonad, and mantle of this bivalve mollusk from coastal waters provided insight into its amino acid composition. Biochemical analysis revealed predominant levels of glycine (11.8, 11.5, and 9.6 mg g-1, respectively) and arginine (11.2, 8.3, and 5.8 mg g-1, respectively). While multivariate comparisons did not reveal significant differences in amino acid composition between the tissues, single comparisons showed significantly higher levels of arginine and leucine in the adductor muscle compared to those of the mantle. The abundant presence of glycine and arginine underscores their importance in maintaining basic physiological processes, consistent with other scallop species. Redundancy analysis identified water depth and scallop gonad index as influential factors shaping the amino acid profile in the adductor muscle. In the case of the mantle, water temperature emerged as the main driver of amino acid content. Our results confirm the richness of essential amino acids in scallop by-products and highlight their potential for human consumption, production of feed ingredients for farmed animals, and nutraceuticals.

Underwater hyperspectral imaging technology has potential to differentiate and monitor scallop populations

Accurate and low-impact monitoring of scallop abundance is critical for stock assessment, especially in sensitive habitats. The possibility of using low-impact hyperspectral imaging (HSI) for differentiating scallop species in the marine environment was investigated. Live saucer (Ylistrum balloti) and mud (Ylistrum pleuronectes) scallops (N = 31) were scanned inside a sea simulator using a visible to near infrared (400–1000 nm) line-scanner HSI camera. Partial least square discriminant analysis (PLS-DA) was trained to distinguish between the species using their spectral signatures. Important wavelengths were identified and new models were developed using these wavelengths to reduce the model complexity and potentially increase the imaging speed when applied under at-sea conditions. The PLS-DA model distinguished between saucer and mud scallops using any area of the left valve that was exposed above the sediments, with 90.73% accuracy when all 462 available wavelengths were used. Using the subset of important wavelengths (N = 13) reduced the classification accuracy to 84%. Overall, our results showed that HSI has potential for detecting, distinguishing and counting commercially important saucer scallops for low-impact monitoring and resource management, and to complement RGB imaging that relies solely on morphological properties.Graphical abstract

Chromosome-level genome assembly of sea scallop Placopecten magellanicus provides insights into the genetic characteristics and adaptive evolution of large scallops

Placopecten magellanicus (Gmelin, 1791), a deep-sea Atlantic scallop, holds significant commercial value as a benthic marine bivalve along the northwest Atlantic coast. Recognizing its economic importance, the need to reconstruct its genome assembly becomes apparent, fostering insights into natural resources and generic breeding potential. This study reports a high-quality chromosome-level genome of P. magellanicus, achieved through the integration of Illumina short read sequencing, PacBio HiFi sequencing, and Hi-C sequencing techniques. The resulting assembly spans 1778 Mb with a scaffold N50 of 86.71 Mb. An intriguing observation arises – the genome size of P. magellanicus surpasses that of its Pectinidae family peers by 1.80 to 2.46 times. Within this genome, 28,111 protein-coding genes were identified. Comparative genomic analysis involving five scallop species unveils the critical determinant of this expanded genome: the proliferation of repetitive sequences recently inserted, contributing to its enlarged size. The landscape of whole genome collinearity sheds light on the relationships among scallop species, enhancing our broader understanding of their genomic framework. This genome provides genomic resources for future molecular biology research on scallops and serves as a guide for the exploration of longevity-related genes in scallops.

Offshore Wind Farms in South Korea: A Potential Site for Scallop Culture

Owing to the constant wind generated by the vast ocean, energy production from offshore wind farms (OWFs) plays an important role in the expansion of renewable energy. However, areas close to large wind farms are often left unutilized, and aquaculture farmers find it difficult to efficiently utilize these unoccupied spaces due to limited information showing the feasibility of utilization of OWFs as potential scallop culture sites. To analyze whether the two scallop species Zhikong scallop (Chlamys farreri) and bay scallop (Argopecten irradians) can be grown at OWFs of Gochang and Buan, Jeollabuk-do, Republic of Korea, the growth characteristics of the two scallop species were analyzed and compared with those grown at the Tongyeong Megacosm Test Station. The results clearly showed that the growth of scallops at the OWF was significantly lower with respect to the shell lengths, height, width, and weight, compared to those grown at the megacosm station. However, scallops grown at the OWF still showed consistent growth in parallel with those grown at the megacosm test station. Yet, there was a species-specific mortality rate between the two sites. In addition, our results suggest that temperature may be a key determinant of the growth of C. farreri and A. irradians. Overall, this study contributes to establishing a foundation for the stable and continuous farming of marine bivalves (e.g., clams, oysters, mussels, and scallops) in OWF areas.

Preliminary study of laser-induced breakdown spectroscopy for Mg/Ca investigation in cultured scallop shells

The element ratio of Mg/Ca is a primary proxy in studying the composition of seashells, and laser-induced breakdown spectroscopy (LIBS) is a practical technique for elemental analysis. In this work, we tried to apply LIBS to investigate the Mg/Ca ratio in cultured seashells of two scallop species (Chlamys farreri and Patinopecten yessoensis). It was found that LIBS was capable of tracking Mg/Ca variation on the cross section of the scallop shell (Chlamys farreri), and the variation trend was well verified by the measurement of SEM-EDS. Based on this, LIBS detection was carried out for Mg/Ca investigation on another species of the scallop shell (Patinopecten yessoensis), and the intensity ratio of Mg/Ca presented a similar variation to δ18O measurement under mass spectroscopy. The result also indicated that the LIBS technique is appropriate in the Mg/Ca investigation for scallop shells, and in cultured scallops, the Mg/Ca ratio would be equally useful for tracking temperature variations. In the future, LIBS is expected to be developed as a diagnostic tool in seashell cultivation, and more elemental compositions would be involved in this kind of investigation.

Heterogeneous Genomic Divergence Landscape in Two Commercially Important European Scallop Species.

Two commercially important scallop species of the genus Pecten are found in Europe: the north Atlantic Pecten maximus and the Mediterranean Pecten jacobaeus whose distributions abut at the Almeria-Orán front. Whilst previous studies have quantified genetic divergence between these species, the pattern of differentiation along the Pecten genome is unknown. Here, we mapped RADseq data from 235 P. maximus and 27 P. jacobaeus to a chromosome-level reference genome, finding a heterogeneous landscape of genomic differentiation. Highly divergent genomic regions were identified across 14 chromosomes, while the remaining five showed little differentiation. Demographic and comparative genomics analyses suggest that this pattern resulted from an initial extended period of isolation, which promoted divergence, followed by differential gene flow across the genome during secondary contact. Single nucleotide polymorphisms present within highly divergent genomic regions were located in areas of low recombination and contrasting patterns of LD decay were found between the two species, hinting at the presence of chromosomal inversions in P. jacobaeus. Functional annotations revealed that highly differentiated regions were enriched for immune-related processes and mRNA modification. While future work is necessary to characterize structural differences, this study provides new insights into the speciation genomics of P. maximus and P. jacobaeus.

Different life strategies of the three commercially exploited scallop species living under the same environmental conditions

To understand the response of marine species to a changing environment, it is crucial to have deep insight into their main biological traits. This study used a multi-species approach to comparatively analyse the reproductive and growth strategies of three commercially important scallop species. Target taxa were larger sized Mediterranean scallop Pecten jacobeaus, and two smaller sized species Aequipecten opercularis and Flexopecten glaber. Specimens were collected at approximate monthly intervals from February 2017 to October 2018 from a commercial beam trawl in the northern Adriatic area (west coast of the Istria peninsula, 25-35 m depth). Three different complementary methods were applied to obtain comprehensive knowledge about the reproductive cycle including assessment of the gonadosomatic index (GSI), histological analysis of gonad tissue, and measuring oocyte size. Growth strategies of three target species were analyzed using high-resolution stable oxygen isotope data that were temporally aligned on sea water temperature data obtained by AdriSC ROMS model. Results indicate diverse strategies employed by these taxonomically related species exposed to the same environmental conditions. Pecten jacobaeus spawned in the late summer and early fall, while shell growth slowed down during warmer season. Aequipecten opercularis spawned in the winter and slowed down shell deposition process during the cold season. Spawning of F. glaber occurred during early to mid-summer and growth slowed down during warmer season. This study provides an important scientific baseline for sustainable management and future aquaculture attempts of scallops.

Antalya Körfezi’nden Toplanan Akdeniz Deniz Tarağı (Pecten jacobaeus)’nın Mevsimsel Ham Besin Bileşimi, Amino Asit ve İz Metal İçerikleri

This study evaluated the seasonal nutrient content and trace element composition of the great Mediterranean scallop (Pecten jacobaeus), which is among the economic scallop species. The samples were obtained as by-catch from the trawler nets of commercial fishing boats operating in the Gulf of Antalya seasonally between 2017 and 2018. After determining the scallops' growth indices of the scallops; proximate composition, amino acid and element analyses were carried out. According to the results; condition index and gonadosomatic index were found highest in the summer, while meat yield was found highest in the autumn. The muscle tissue's crude protein and ash ratio decreased to mimimum values in summer. Crude fat was determined at the highest level in the spring and decreased after the summer when the reproduction period was over (P

Transcriptome analysis provides insight into adaptive mechanisms of scallops under environmental stress

High temperature and hypoxia greatly threaten marine life and aquaculture. Scallops, a diverse and ecologically important group of high economic value, mostly thrive in fluctuating environments, and are vulnerable to environmental stress. In the present study, the molecular response mechanism of scallops to a combination of environmental stressors was investigated via transcriptome analysis of the gill tissues in three scallop species, the Yesso scallop (Patinopecten yessoensis), Zhikong scallop (Chlamys farreri) and bay scallop (Argopecten irradians) that were exposed to transient heat, hypoxia and a combination thereof. The Yesso scallop had the most differentially expressed genes (DEGs) compared with the other two scallop species, indicating the highest sensitivity of the Yesso scallop to environmental stress. With increased temperature and decreased dissolved oxygen, the number of DEGs was greatly increased in the three scallop species, indicative of the enhancement in gene expression regulation in scallops in response to severe environmental changes. Heat and hypoxia had a synergistic effect on scallops. GO and KEGG enrichment analysis of DEGs under different stressors revealed overlapping molecular mechanisms of response in scallops following exposure to heat and hypoxia. Several immune and apoptosis-related pathways were highly enriched in the upregulated DEGs of the three scallops, suggesting that immune system activation and apoptosis promotion occurred in scallops in response to environmental stress. Heat shock proteins (HSPs) were significantly upregulated under heat and hypoxia, which likely assisted in correct protein folding to facilitate the adaption of the scallops to the altered environment. Additionally, the HIF-1 signaling pathway—the key pathway associated with hypoxia response—was triggered by extremely acute environmental changes. Comparative transcriptome analysis revealed 239 positively selected genes among the different scallops, including those involved in immune system and environmental adaptation, suggesting a long-term mechanism of environmental adaptation. The present study provides new insights into the molecular response mechanism in scallops to multiple environmental stressors and improves our understanding of the adaptive mechanisms of marine organisms under changing global climate conditions.

Expression Plasticity of Peroxisomal Acyl-Coenzyme A Oxidase Genes Implies Their Involvement in Redox Regulation in Scallops Exposed to PST-Producing Alexandrium.

Filter-feeding bivalves can accumulate paralytic shellfish toxins (PST) produced by toxic microalgae, which may induce oxidative stress and lipid peroxidation. Peroxisomal acyl-coenzyme A oxidases (ACOXs) are key enzymes functioning in maintaining redox and lipid homeostasis, but their roles in PST response in bivalves are less understood. Herein, a total of six and six ACOXs were identified in the Chlamys farreri and Patinopecten yessoensis genome, respectively, and the expansion of ACOX1s was observed. Gene expression analysis revealed an organ/tissue-specific expression pattern in both scallops, with all ACOXs being predominantly expressed in the two most toxic organs, digestive glands and kidneys. The regulation patterns of scallop ACOXs after exposure to different PST-producing algaes Alexandrium catenella (ACDH) and A. minutum (AM-1) were revealed. After ACDH exposure, more differentially expressed genes (DEGs) were identified in C. farreri digestive glands (three) and kidneys (five) than that in P. yessoensis (two), but the up-regulated DEGs showed similar expression patterns in both species. In C. farreri, three DEGs were found in both digestive glands and kidneys after AM-1 exposure, with two same CfACOX1s being acutely and chronically induced, respectively. Notably, these two CfACOX1s also showed different expression patterns in kidneys between ACDH (acute response) and AM-1 (chronic response) exposure. Moreover, inductive expression of CfACOXs after AM-1 exposure was observed in gills and mantles, and all DEGs in both tissues were up-regulated and their common DEGs exhibited both acute and chronic induction. These results indicate the involvement of scallop ACOXs in PST response, and their plasticity expression patterns between scallop species, among tissues, and between the exposure of different PST analogs.

Variation in eye abundance among scallops reveals ontogenetic and evolutionary convergence associated with life habits.

Eyes are remarkable systems to investigate the complex interaction between ecological drivers and phenotypic outcomes. Some animals, such as scallops, have many eyes for visual perception, but to date, the evolution of multiple-eye systems remains obscure. For instance, it is unclear whether eye number changes over a lifetime or varies among species. Scallops are a suitable model group to investigate these questions considering the interspecific variation of adult size and ecological diversity. We tested whether eye abundance scales with body size among individuals and species and whether it varies with life habits. We performed comparative analyses, including a phylogenetic ANCOVA and evolutionary model comparisons, based on eye count and shell height (as a proxy of body size) across 31 scallop species. Our analyses reveal that patterns of increasing relationship with body size are not concordant among taxa and suggest ontogenetic convergence caused by similar ecologies. Accordingly, selective optima in eye numbers are associated with shifts in life habits. For instance, species with increased mobility have significantly more eyes than less mobile species. The convergent evolution of greater eye abundance in more mobile scallops likely indicates a visual improvement based on increased levels of oversampling of the surrounding environment.

Circulatory and Metabolic Physiology Disorder in Different Organs of the Subtropical Scallop Species Chlamys nobilis Under Thermal and Hypoxia Stress, Revealed by Doppler Ultrasonography Technique

Extremely high temperature and hypoxia are mounting problems affecting the world’s coastal waters under the global warming environment, with severe consequences for marine life. Scallop is one of the most fragile species to hypoxia stress for their high respiration rate and lack of self-protection ability such as long-time shell closing. Circulatory physiology rhythm is sensitive to environmental stress and is an important means for shellfish to quickly respond to environmental stress. Therefore, monitoring the circulatory physiology indexes of Chlamys nobilis under hypoxia and high temperature stress is helpful to quickly diagnose its stress state and reveal the response process of circulatory system to the stress. In this study, using real-time Doppler ultrasonography technique, we continuously monitored the circulatory physiological indexes [heart rate (HR), blood flow volume (FV), blood velocity (PS and ED), resistance index (RI) and S/D ratio) of the scallop organs (gill, mantle and adductor muscle) under hypoxia (mild 4 mg/L DO, moderate 3 mg/L DO and severe 2 mg/L DO)] and fluctuating high temperature stress (29-31°C). Important metabolic function indexes [adenosine triphosphate (ATP), pyruvate kinase (PK) and cytochrome C oxidase (COX)] of various tissues were measured simultaneously. The results show that scallops are very sensitive to the changes of temperature and dissolved oxygen. Both high temperature and hypoxia will increase the HR, and severe hypoxia will bring greater load to the heart of the scallop. Hypoxia stress mainly caused the changes of PS, and the RI and S/D of the gill gradually increased. At 2mg/L DO level, the total blood flow of the mantle and adductor muscle decreased, but the blood flow supply in the gill was stable. The scallop is very sensitive to the change of high temperature and can make adjustments immediately. High temperature increased blood flow in various organs and preferentially supplied to the gill. The RI and S/D of branchial vessels under high temperature were lower than those under hypoxia. The ATP content of the mantle was continuous accumulated under high temperature and was significantly higher than that of the gill and adductor muscle, indicating the specificity of tissue metabolism. The overall circulatory physiological indexes of the gill showed a more positive response to the stress environment than the mantle and adductor muscle. All the results proved that the gill has the best resistance to the hypoxia and high temperature stress. Our study revealed the circulatory physiology regulation mechanism of the noble scallop C. nobilis under environmental stress, and provide effective data and technique supports for the timely diagnose of stress condition of the species, so as to formulate necessary handling strategies for the scallop farm.

Analysis and gonadal localization of Speedy A mRNA transcript, a novel gene associated with early germline cells in the scallop, Argopecten purpuratus

The Speedy A (spdya) gene is a member of the Speedy/RINGO family, encoding a spdya protein associated with cellular cycle and meiosis in vertebrates. Results from genetic analyses indicated spdya conditional knockout mice are sterile, suggesting that this protein has essential functions in mammalian reproduction. There, however, are no published reports on the localization of spdya mRNA in the germline or in somatic cell lineages within the gonads from mollusks or other invertebrate species. Using a previously obtained transcriptome assembly from the scallop Argopecten purpuratus, an economically important hermaphroditic scallop species from Chile and Peru, there was identification of a complete coding sequence of the spdya mRNA. Phylogenetically spdya protein has sequence conservation homology with other scallops and mollusks. The relative mRNA transcript abundances at different gametogenic stages was assessed using quantitative PCR procedures. Results indicated there was an increase of spdya mRNA transcript abundance in testicular region samples at the late active stage, followed by a decrease in testis of reproductively mature individuals. To gain insight into the cellular localization of ap-spdya transcript within the gonads, specific RNA probes were synthesized for in situ hybridization analyses of gonad histological sections. Results indicated spdya mRNA is located exclusively in early germline (previtellogenic oocytes and spermatogonia) and somatic proliferative tissues of A. purpuratus ovarian and testicular regions. Overall, these results indicate there are putative functions of spdya in the early oogenesis and spermatogenesis of A. purpuratus and will contribute to furthering the understanding of gametogenesis in this species.

Development of a DNA Metabarcoding Method for the Identification of Bivalve Species in Seafood Products.

The production of bivalve species has been increasing in the last decades. In spite of strict requirements for species declaration, incorrect labelling of bivalve products has repeatedly been detected. We present a DNA metabarcoding method allowing the identification of bivalve species belonging to the bivalve families Mytilidae (mussels), Pectinidae (scallops), and Ostreidae (oysters) in foodstuffs. The method, developed on Illumina instruments, targets a 150 bp fragment of mitochondrial 16S rDNA. We designed seven primers (three primers for mussel species, two primers for scallop species and a primer pair for oyster species) and combined them in a triplex PCR assay. In each of eleven reference samples, the bivalve species was identified correctly. In ten DNA extract mixtures, not only the main component (97.0–98.0%) but also the minor components (0.5–1.5%) were detected correctly, with only a few exceptions. The DNA metabarcoding method was found to be applicable to complex and processed foodstuffs, allowing the identification of bivalves in, e.g., marinated form, in sauces, in seafood mixes and even in instant noodle seafood. The method is highly suitable for food authentication in routine analysis, in particular in combination with a DNA metabarcoding method for mammalian and poultry species published recently.

A case report and statewide surveillance of “weak meat” condition of Alaska weathervane scallops, Patinopecten caurinus, linked to a recently identified pathogenic parasite, Merocystis kathae (Apicomplexa: Aggregatidae)

Weathervane scallop, Patinopecten caurinus, the largest scallop species in the world, is distributed from northern California, U.S.A., to the Bering Sea, and is only commercially harvested in Alaska. The fishery is considered well managed by the State of Alaska (U.S.A) Department of Fish and Game (ADF&G) and federal government, with many precautionary measures in place to avoid overharvest. There have been episodic declines in some management areas due to unknown causes. Fishermen also encounter scallops with abnormal adductor muscles, a condition colloquially termed “weak meat”, characterized by the retention of muscle when shucked, an obvious darkened discoloration, and/or an abnormal texture making the product unacceptable for marketing. A similar syndrome in Atlantic sea scallops, Placopecten magellanicus, described as “gray meat”, occurs in the eastern U.S. and Canada, and proposed causes include senescence, loss of bioenergetics due to chronic infestations, or a synergism of these factors. Recently a severe apicomplexan infection was found to cause a gray meat condition in Iceland scallops, Chlamys islandica, and the collapse of that stock. This parasite was subsequently detected in Atlantic sea scallops with the gray meat condition off the U.S. East Coast. Studies that followed identified the parasite as Merocystis kathae, previously described from the common whelk, Buccinum undatum, more than 100 years ago. In 2015 Bering Sea fishermen reported weak meat in their catch, so samples were submitted to ADF&G for diagnosis. Adductor muscles from all affected scallops had many large foci of an apicomplexan associated with necrosis, fibrosis, and muscular atrophy. Given the reduced quality, marketability, and possibly fitness of affected scallops, we performed a survey to estimate prevalence, intensity, and geographic distribution of this apicomplexan in Alaskan weathervane scallops. We sampled 180 scallops, from individual beds within each of the three major geographically broad scallop areas in Alaska. Overall prevalence was about 82%, ranging from 69 to 100% by district. Overall mean infection intensity, based on the number of parasite foci/section, was about 9 (range of 5–29, by location), with scallops from the Bering Sea and Southwest Kodiak being most severely infected. Molecular analyses confirmed that the Alaskan parasite is M. kathae, i.e., the same apicomplexan that caused the collapse of Icelandic scallops and a suspected cause for gray meat and mass mortality of Atlantic sea scallops in northeast North America.

Effects of single‐species microalgae diet on accumulation of lipid and carotenoid and expression of lipid‐related genes in Nan'ao Golden ScallopChlamys nobilis

Nan'ao Golden Scallop, Chlamys nobilis, is an important scallop species in aquaculture and is rich in lipids and carotenoid. Previous studies have shown that microalgae diet has a significant effect on the accumulation of total lipid content (TLC) and total carotenoid content (TCC) in bivalves. However, the effects of single-species microalgae diet on accumulation of TLC and TCC at molecular level are unclear. In this study, we used C. nobilis as a bivalve animal model to assess the effects of single-species microalgae diet (Tetraselmis subcordiformis, Dicrateria zhanjiangensis and Chaetoceros mulleri) on the accumulation of lipids and carotenoids, and the expression of stearoyl-CoA desaturase (SCD) and scavenger receptor class B-like-3 (SRB-like-3) genes in C. nobilis. The results of this study indicated that high lipid microalgae diet promoted the accumulation of TCC in C. nobilis tissues. The expression of SCD and SRB-like-3 genes was highly affected by the lipid composition of diet, in which high expression of SCD and SRB-like-3 genes was correlated with low C16:1n-9 and/or C18:1n-9t and/or C16:1/C16:0 and/or C18:1/C18:0. In intestine and adductor muscle, the expression of SCD gene was positively correlated with accumulation of TCC, TLC and fatty acid content, suggesting that SCD gene may indirectly promote the accumulation of TCC (lipid soluble) by promoting lipid accumulation. For SRB-like-3 gene, the high expression of SRB-like-3 was only correlated to the high TCC in intestine, suggesting that SRB-like-3 may be a candidate gene for carotenoid absorption in C. nobilis and has nothing to do with the transport or accumulation of carotenoid. The findings of this study are of great significance for further understanding how microalgae diet affects the accumulation of TCC and TLC, and the expression of lipid-related genes in bivalves.

Evaluation of the shucking of certain species of scallops contaminated with domoic acid with a view to the production of edible parts meeting the safety requirements foreseen in the Union legislation.

EFSA was asked by the European Commission to provide information on the levels of domoic acid (DA) in whole scallops that would ensure that levels in edible parts are below the regulatory limit after shucking. This should include five species of scallops. In addition, EFSA was asked to recommend the number of scallops to be used in an analytical sample. To address these questions, EFSA received suitable data on DA for only one scallop species, Pecten maximus, i.e. data on pooled samples of edible and non‐edible parts. A large part of the concentration levels was above the limit of quantification (LOQ) and only these data were used for the assessment. Shucking in most cases resulted in a strong decrease in the toxin levels. Statistical analysis of the data showed that levels in whole scallops should not exceed 24 mg DA/kg, 59 mg DA/kg and 127 mg DA/kg to ensure that levels in, respectively, gonads, muscle and muscle plus gonads are below the regulatory limit of 20 mg DA/kg with 99% certainty. Such an analysis was not possible for the other scallop species. In the absence of data from member states, published data of variations between scallops were used to calculate the sample size to ensure a 95% correct prediction on whether the level in scallops in an area or lot is correctly predicted to be compliant/non‐compliant. It was shown that 10 scallops per sample would be sufficient to predict with 95% certainty if DA levels in the area/lot were twofold below or above the regulatory limit for the highest reported coefficient of variance (CV) of 1.06. To predict with 95% certainty for levels between 15 and 27 mg DA/kg, a pooled sample of more than 30 scallops would have to be tested.

Cloning and characterization ofRARs andRXRs from noble scallopChlamys nobilis, a bivalve rich in carotenoids

The noble scallop Chlamys nobilis that rich in carotenoids is one of the most popular scallop species for aquaculture. Very little is known whether bivalve SRB-like-3 gene expression is regulated by retinoic acid receptor (RAR) and/or retinoic X receptor (RXR). In this study, the full-length cDNA of RAR and RXR genes of C. nobilis was cloned and characterized for the first time, and then, the tissue differential expression of RAR and RXR mRNA in polymorphic C. nobilis was assessed. The roles of RAR and RXR in carotenoid accumulation in C. nobilis were assessed by manipulating the carotenoid content in tissues of C. nobilis via inhibiting the expression of SRB-like-3 gene. The results revealed that two isoforms of RAR (cnRARa (1958 bp/434 aa) and cnRARb (1901 bp/415 aa)) and four RXR isoforms (cnRXRa (1353-bp/450 aa), cnRXRb (1341-bp/446 aa), cnRXRc (1298-bp/436 aa) and cnRXRd (1286-bp/432 aa)) were cloned and characterized from C. nobilis. The reduction of carotenoid content caused by inhibition of SRB-like-3 gene induced the up-regulation of RAR and RXR genes, suggesting that RAR and RXR genes may play a role in the regulation of carotenoid accumulation in haemolymph of C. nobilis. The findings of this study provide important clues for the regulation mechanism of total carotenoid accumulation in C. nobilis.