Synchronous gonadal maturation and production of high-quality seed are essential for scallop hatchery. This study investigated the effects of two formulations on Chlamys farreri broodstock during the fattening period, and further evaluated their potential to promote ovarian maturation. Group A (control) received distilled water, while Groups B and C were treated with the basic and compound formulations, respectively. Both formulations were applied at 4 mg L⁻¹ by spraying once daily for 20 consecutive days before spawning induction. The results demonstrated that Group C exhibited significantly higher spawning rate (81.35 ± 3.69%) and spermiation rate (79.63 ± 4.90%) relative to Groups A and B (P < 0.01). The hatching rate did not differ significantly among all treatments (P > 0.05). Notably, larval shell length on day 18 in Group C was 3.05% greater than that in Group B and 13.34% greater than that in Group A (P < 0.05). Additionally, superoxide dismutase (SOD), catalase (CAT), lysozyme (LYZ) activity, and total antioxidant capacity (T-AOC), were significantly enhanced in Group C (P < 0.01). Ovarian transcriptomic analysis further revealed that differentially expressed genes (DEGs) in Group C were significantly enriched in pathways associated with steroidogenesis and oocyte maturation. Collectively, these findings indicate that the compound formulation exerts a superior effect in enhancing reproductive output and promoting offspring growth in C. farreri broodstock. This study provides both mechanistic insights and a practical nutritional strategy for optimizing broodstock conditioning and improving seed production efficiency in commercial scallop hatcheries.

With the rapid development of oyster farming and the emergence of new varieties, the identification and evaluation of genetic resources have become fundamental to the effective utilization of oyster germplasm resources. To evaluate the impact of selective breeding on the germplasm of Crassostrea ariakensis, this study conducted genetic structure analysis on five successive generations including four generations selected (F1 to F4) focusing on both fast growth and high glycogen content and one base population (F0) based on partial mitochondrial cox1 and rrnL gene sequences. Results showed that the 649 bp cox1 and 488 bp rrnL sequences exhibited (A+T)-biased composition and showed positive AT skew. A total of 12 haplotypes were found for the cox1 sequences, while only three haplotypes were detected for the rrnL sequences. However, among the F1 to F4 populations, only three cox1 haplotypes and two rrnL haplotypes were observed. Based on cox1 sequences, the values of the haplotype diversity index, average number of nucleotide differences, and nucleotide diversity index all decreased progressively from F1 to F4, indicating a reduction in genetic variation due to selective breeding. All populations exhibited a low level of nucleotide diversity (<0.05). In addition, the intra-population genetic distance declined from F0 to F4, with significant genetic differentiation between F0 and F1, as well as between F0 and F4 (p < 0.05). In contrast, only the F0 and F4 population had multiple rrnL haplotypes, and no statistically significant genetic differentiations were observed based on rrnL fragments (p > 0.05). The AMOVA results showed that intra-population genetic variation exceeded inter-population variation, regardless of whether it was assessed using the cox1 gene or the rrnL gene, indicating that substantial genetic diversity persists within populations despite multiple generations of selection, and complete genetic differentiation across generations has not been achieved. These findings indicate that the selectively bred lines retain considerable genetic potential and can serve as a valuable resource for future breeding programs.

Glycogen is not only a critical energy storage molecule in oyster but also a key flavor-determining factor that affect their fatness, with glycogen content directly governing oyster quality. However, the molecular mechanisms underlying glycogen storage and metabolism in shellfish (including oyster) remain incompletely understood. In order to clarify the regulatory mechanisms of glycogen metabolism in Jinjiang oyster (C. ariakensis), we performed integrated transcriptomic and proteomic analyses on the mantle tissues with high glycogen content (HG) and low glycogen content (LG). The results identified 899 differentially expressed genes (DEGs) at the transcriptional level and 1294 differentially expressed proteins (DEPs) at the translational level, respectively. Functional enrichment analysis demonstrated that these DEGs and DEPs were mainly enriched in glycogen metabolism and energy metabolism-related pathways, including the insulin signaling pathway, starch and sucrose metabolism, and glycerolipid metabolism. In the HG, numerous key genes and proteins were significantly involved in glycogen synthesis, gluconeogenesis, glycolysis pathways and fatty acid metabolism were significantly upregulated. These findings indicate these multiple metabolic processes co-regulate the level of glycogen in the mantle, providing a theoretical basis for elucidating molecular mechanisms of glycogen metabolism and valuable insights for the breeding of high-glycogen oyster varieties.

Glutathione S-transferases (GSTs) constitute a superfamily of multifunctional detoxification isoenzymes that play essential roles in innate immunity. In this study, a μ-class GST gene was identified from Scapharca broughtonii (designated SbGSTμ) using the RACE approach. The full-length cDNA of SbGSTμ is 1040 bp and encodes a cytosolic protein of 215 amino acids. Sequence analysis revealed that SbGSTμ contains conserved structural features characteristic of the μ-class GST family, including an N-terminal thioredoxin-like domain with glutathione (GSH)-binding sites and a C-terminal domain harboring substrate-binding sites. Tissue distribution analysis showed that SbGSTμ is ubiquitously expressed across all examined tissues, with the highest expression level detected in the foot. Upon challenge with Staphylococcus aureus or Vibrio anguillarum, or exposure to Cu2+, SbGSTμ mRNA expression was significantly upregulated compared to controls. Recombinant SbGSTμ protein was successfully expressed in Escherichia coli, purified, and functionally characterized. The enzyme exhibited optimal activity at temperatures between 30 °C and 40 °C and at pH 7.4. Furthermore, benzo [a]pyrene exposure assays demonstrated the detoxification capacity of SbGSTμ through a significant reduction in 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. Collectively, these findings support the classical role of GSTs in xenobiotic detoxification while providing evidence for their involvement in immunological host defense mechanisms in the ark shell S. broughtonii.

Global climate change poses a significant threat to coastal aquaculture, with rising seawater temperatures considerably affecting the survival and distribution of economically important shellfish species. As a key aquaculture species, the Manila clam (Ruditapes philippinarum) faces the risk of mass mortality during summer heatwaves. Conventional methods for assessing thermal tolerance, such as the median lethal temperature (LT₅₀), are often destructive and inefficient in clams. In this study, we evaluated thermal tolerance by monitoring heart rate (HR) as an indicator of cardiac performance and physiological status across different clam strains, including a heat-tolerant strain and other selective strains, under three temperature conditions (20 °C, 26 °C, and 32 °C). The results revealed that the heat-tolerant strain exhibited markedly higher survival under 32 °C thermal stress, with a 49% survival rate over 504 h, compared to less than 10% in other groups. At 32 °C, the oxygen consumption rate of the heat-tolerant strain increased to 0.60 mg/(g·h), significantly higher than that of other groups. Concurrently, its ammonia excretion rate decreased to 0.22 mg/(g·h), which was significantly lower. Notably, the heat-tolerant strain also showed significantly elevated activities of antioxidant enzymes (SOD and GSH). Importantly, heart rate monitoring indicated that the heat-tolerant strain maintained stable cardiac performance under thermal stress, with heart rates increasing significantly and no arrhythmic events observed, whereas the control group displayed severe cardiac impairment. This study demonstrates that heart rate monitoring serves as an effective non-invasive indicator of thermal tolerance in the Manila clam. Its integration with physiological and cellular molecular analyses provides a comprehensive assessment framework. This multi-level approach offers a robust strategy for selective breeding of heat-tolerant strains in clam aquaculture and other aquatic species.

The Manila clam (Ruditapes philippinarum) is a key aquaculture species in China's intertidal zones, where body size and growth rates strongly influence market preference and commercial value. Nevertheless, the genetic basis of shell traits and population structure of coastal stocks remain poorly understood. Here, we performed RAD-seq sequencing of 301 individuals from 10 populations along the Chinese coast to analyze population genetics and conduct a genome-wide association study (GWAS). Population genetic analyses revealed nucleotide diversity (π) ranging from 0.259 to 0.273, with the Haiyang population showing the highest diversity. The Hongdao population exhibited the highest inbreeding coefficient (FIS = 0.469) and lowest observed heterozygosity (Ho = 0.144), whereas the Sanya population had the lowest inbreeding (FIS = 0.235) and highest heterozygosity (Ho = 0.199). Genetic differentiation (FST) was greatest between the Rizhao and Donggang populations (FST = 0.0484). In contrast, unexpectedly low differentiation between the geographically distant Donggang and Beihai populations (FST = 0.0122) suggests the possible anthropogenic translocation and gene flow. Using a mixed linear model (MLM) for GWAS, we identified 142 significant SNPs associated with shell traits after Bonferroni correction. Notably, 139 SNPs distributed across chromosomes from 1 to 19 were linked to shell thickness, while only three SNPs on chromosome 13 were associated with shell width. Within 50 kb flanking regions of these loci, 453 candidate genes were annotated. Functional enrichment analyses (GO and KEGG) highlighted seven candidate genes (e.g., Calml3, MC1R, and TBXT) that may be associated with biomineralization, calcium signaling, and shell-related trait variation. Additionally, a selective sweep analysis comparing Beihai and Hongdao populations identified 118 candidate genes located in putative outlier regions (top 1% of FST and π ratio). Enrichment of these regions revealed three candidate genes (Acp5, SLC6A1, and FNTA) related to metabolism and cellular transport, potentially reflecting local adaptation or artificial selection. Together, these findings provide important insights into the germplasm resources of R. philippinarum and offer valuable genomic targets for marker-assisted selection to improve shell traits in aquaculture breeding programs.

Larval settlement and metamorphosis is a critical biological process governing the recruitment and population dynamics of bivalves, with profound implications for aquaculture sustainability. This study systematically assessed the effects of neurochemical inducers (Serotonin [5-HT], L-DOPA, acetylcholine, choline) and inorganic ions (K⁺, Ca²⁺, NH₄⁺, Mg²⁺) on larval settlement and metamorphosis in Manila clam Ruditapes philippinarum. Laboratory bioassays demonstrated that 5-HT acted as a potent settlement inducer, eliciting >65% settlement and metamorphosis at concentrations ranging from 10⁻² to 1 μM within 6-24 h. However, it exhibited acute toxicity at 10² μM, resulting in 100% mortality at 72 h. In contrast, L-DOPA showed transient efficacy, achieving 66.3% settlement and metamorphosis at 10 μM within 6 h but lack of induction effects at 48 h. Among ions, K⁺ (30 mM) and Ca²⁺ (30-50 mM) significantly enhanced larval settlement and metamorphosis, with the highest induction rates of 41% and 51% at 24 h, respectively, but the elevated concentrations resulted in increased larval mortality (≥ 37.7%). Ammonium chloride (which is usually present in both ionized and more toxic unionized forms, partly dependent on pH) displayed strong toxicity, causing 100% mortality at >20 mM concentrations within 48 h, while Mg²⁺ had the negligible effects on both settlement and survival. These findings highlight the inductive effects of chemical cues on larval settlement and metamorphosis in R.philippinarum, providing practical thresholds (e.g., 1 μM 5-HT with ≤24 h exposure) to optimize hatchery-rearing protocols in aquaculture.

The Manila clam (Ruditapes philippinarum), as one of the most economically significant shellfish species in China, faces major challenges in seed production due to the high mortality during larval settlement and metamorphosis. 5-Hydroxytryptamine (5-HT) has been identified as a crucial neurotransmitter involved in regulating larval settlement and metamorphosis in molluscs. However, the underlying signaling mechanisms of its receptor (5-HTR) in molluscs remain poorly understood. In this study, the full-length cDNA sequence of 5-HT1R gene (1343 bp) is successfully cloned, encoding a protein of 393 amino acids. Bioinformatics analysis results reveal that the encoded protein has the typical characteristics of G protein-coupled receptors, including seven trans-membrane domains and a molecular weight of 45.61 kDa. Quantitative real-time PCR (qPCR) results show that 5-HT1R expression in gill tissue of adult clams is significantly higher than that in other tissues, followed by adductor muscle and foot tissues. Whole-mount in situ hybridization illustrates its dynamic expression pattern throughout larval development, especially during larval settlement and metamorphosis. Prior to larval settlement and metamorphosis, 5-HT1R is predominantly localized in the apical sensory organ (ASO) of the larva, while the positive signals are progressively diminished during metamorphosis and eventually disappear after metamorphosis. Moreover, chemical induction experiments of larval settlement and metamorphosis using 5-HT agonists and antagonists have proved that 1 mu M 5-HT treatment significantly enhances larval settlement and metamorphosis (60.9 %), whereas antagonists (clozapine) markedly suppress this process. These evidences indicate that 5-HT1R exerts the crucial regulatory function during larval settlement and metamorphosis of R. philippinarum. This study not only provides a theoretical foundation for elucidating the molecular mechanism underlying larval settlement and metamorphosis, but also offers potential targets for further investigation of 5-HT signaling pathway in bivalves.

The global aquaculture product industry is undergoing a strategic shift from “quality-driven” to “efficiency-driven” development, with consumer demand increasingly focused on premium seafood characterized by superior flavor and nutritional value. As the most productive marine shellfish in China, oyster yield reached 7.252 million tons in 2024. Glycogen content is a crucial determinant of oyster sweetness, flavor, and texture, and plays vital roles in energy metabolism and stress tolerance. Consequently, it has emerged as a key target trait for oyster germplasm innovation. Substantial genetic breeding research has been conducted on the Pacific oyster (Crassostrea gigas) with established heritability estimates for both growth traits and glycogen content, demonstrating significant potential for genetic improvement. In contrast, the Jinjiang oyster (Crassostrea ariakensis), an economically and ecologically important estuarine species in China, lags considerably behind. Although valued for their large size, attractive shell morphology, and sweet flavor, particularly in high-end markets, systematic data on the heritability of their growth traits are scarce, and crucially, no genetic parameter estimates for glycogen content have been reported to date. This knowledge gap severely impedes the development of high-quality fast-growing C. ariakensis strains through scientific breeding. To enable the effective selective breeding of high-quality, fast-growing strains, this study aimed to systematically estimate the genetic parameters of shell height, shell length, and glycogen content in C. ariakensis. A nested mating design (one male × four females) was used to create 72 full-sib families. All families were reared in a common pond environment to minimize non-genetic effects. Twenty families (600 individuals) were sampled at 330 days of age. Shell height and length were measured using a Vernier caliper. The glycogen content of dry soft tissues was determined using near-infrared spectroscopy (NIRS). Data were analyzed using ANOVA and Tukey's multiple range test to examine family differences. Genetic parameters were estimated in a reduced individual animal model using the ASReml package in R. Descriptive statistics for the 600 individuals revealed a mean shell height of (77.58±13.38) mm, shell length of (63.02±12.41) mm, and glycogen content of (208.10±67.61) mg/g. Glycogen content exhibited the highest variability among the traits, with a coefficient of variation (CV) of 0.32, compared to 0.17 and 0.20 for shell height and shell length, respectively. Substantial phenotypic variation within a population is a prerequisite for successful selective breeding. Analysis of variance indicated significant differences (P<0.05) in all three traits among the half-sib families, but not among full-sib families within the same half-sib group. Regarding growth traits, families F53 and F55 (sired by male 14) achieved the highest shell height (86.79 mm), and families F66 and F68 (sired by male 17) achieved the longest shell length (70.02 mm). Pronounced variation in glycogen content was observed among families. Families F36 and F34 (sired by male 9) displayed the highest glycogen levels, at 270.64 mg/g and 260.08 mg/g, respectively, representing an increase of 30.05% and 24.97% over the population mean. In contrast, families F09 and F10 (sired by male three) had the lowest glycogen content, averaging 145.94 mg/g. Clear stratification of family performance underscores the potential for identifying and selecting superior genetic lines. Heritability estimates derived from individual animal models were moderate to high for all traits. Shell height heritability was 0.37±0.12, shell length was 0.48±0.14, and glycogen content was 0.45±0.13. The bivariate animal model revealed significant positive genetic (rg=0.74±0.12) and phenotypic (rp=0.62±0.04) correlations between shell height and shell length. The results demonstrate that key growth and quality traits in C. ariakensis are under moderate to strong additive genetic control. The heritability estimates for shell height and shell length were consistent with those of previous reports on C. gigas, confirming their suitability for selective breeding. The strong genetic correlation between these growth traits suggests that they are influenced by a shared set of genes or closely linked genetic loci, allowing for concurrent genetic improvements and simplifying breeding objectives. Most significantly, this study provided the first estimate of glycogen content heritability in C. ariakensis. The value of 0.45 falls within the range reported for C. gigas (0.29–0.61), firmly establishing glycogen content as a heritable trait in Jinjiang oysters. The identification of high-glycogen families, such as F34 and F36, which significantly outperformed the population average, provides invaluable core breeding material for establishing elite lines. This study represents the first systematic assessment of genetic parameters for growth and glycogen content in C. ariakensis, filling a critical knowledge gap. In conclusion, our findings provide crucial genetic parameters necessary to launch scientific breeding programs for C. ariakensis. Moderate to high heritability indicates that significant genetic gain can be achieved through family- or individual-based selection. The identified high-glycogen families provide valuable core breeding materials. Collectively, these findings fill a critical gap in the genetic knowledge of C. ariakensis and provide the essential parameters required to initiate a formal breeding program aimed at developing new high-quality varieties that meet the evolving demands of the premium seafood market.

Human activities have profound impacts on the plankton communities and diversity in the sea. The Yellow River Water-Sediment Regulation Scheme (WSRS), diverting large volumes of freshwater and sediment into the sea, may influence the plankton community spatially and temporally in the Yellow River estuary and adjacent regions. To understand the potential ecological effects of WSRS on plankton community and diversity, 18 S rDNA sequencing was performed for the plankton samples collected in the Yellow River estuary during the period of WSRS. A total of 268 plankton genera were identified in 15 field samples from three sections (North, Middle, and South) of the Yellow River estuary and adjacent regions. For the spatial scale, Arthropoda was the predominant phylum consistently detected in the North, Middle, and South sections. For the time scale, Arthropoda was identified to be the predominant phylum during June (pre-WSRS) and July (inter-WSRS), accounting for 76.74 % and 78.99 %, respectively. In contrast, the proportion of Arthropoda during August (post-WSRS) was decreased to 23.89 %, respectively. The relative abundance of Chlorophyta increased to 31.11 % during August (postWSRS). Beta diversity analysis (PCoA, ANOSIM) revealed distinct separation in plankton community structure between post-WSRS and pre/inter-WSRS periods. Our findings suggest that the WSRS, as a massive humaninduced disturbance, likely acts as a key driver in reshaping the planktonic community in the Yellow River estuary. This study provides critical insights for evaluating the ecological impacts of the WSRS and informing sustainable management strategies for large river deltas. These findings underscore the necessity of integrating ecological monitoring into the WSRS to balance sediment management and ecosystem sustainability in the Yellow River estuary and beyond.

Manila clam (Ruditapes philippinarum) inhabits environments in which dissolved oxygen (DO) concentrations are prone to changes. Hemocytes are important participants in shellfish immune responses and are sensitive to environmental changes. To investigate the effect of DO concentration changes on the ultrastructure of R. philippinarum hemocytes and provide parameters for healthy breeding and management of this species, three DO concentration change modes were designed: normoxia C treatment; normoxia followed by acute hypoxia for 24 h and acute reoxygenation for 4 h, and normoxia followed by chronic hypoxia for 48 h and then chronic reoxygenation for 8 h. Hemocytes were classified as amoebocytes (AMCs), secretory cells (SECs), thrombocytes (THCs), spherical cells (SPCs), and macrophage-like cells (MACs). Granules were present in AMC, SEC, and SPC cytoplasm, and were rarely observed in THCs and MACs. The granule function and number and morphology of various organelles differed among hemocyte types. SPCs lost their spherical structure and their intracellular ultrastructure was severely damaged, leading to apoptosis. AMCs and SECs also suffered ultrastructural damage and apoptosis. AMCs exhibited weak deformability, decreased ability to engulf and remove foreign substances, and decreased secretion ability of SECs. Acute hypoxia damaged the THC ultrastructure and acute reoxygenation triggered coagulation reactions. Chronic hypoxia and reoxygenation severely affected MAC morphology and ultrastructure. Effects of DO concentration changes on the ultrastructure and function of five hemocyte types in Manila clams were clarified, providing a cellular basis for revealing the response of Manila clams to DO concentration changes.

Oysters are keystone species in marine ecosystems and essential for restoring ecological function and maintaining biodiversity maintenance.However,global climate change and increasing human activities have intensified environmental fluctuations in marine habitats,which greatly affect the growth and physiological functions of oysters and other marine organisms.Organisms in these environments have developed adaptive regulatory mechanisms.Crassostrea ariakensis is an economically important bivalve that inhabits estuarine areas along the coast of China and crucial for delivering essential ecological services.However,a lack of research exists on the physiological responses of C.ariakensis to frequent and substantial salinity variations in these estuaries. In this study,we investigated the physiological responses and key gene alterations in C.ariakensis under salinity stress by analyzing changes in respiration,ammonia excretion,ingestion,and clearance rates under various salinity conditions.The findings provide valuable data and insights for a comprehensive understanding of the physiological and metabolic responses of oysters to salinity stress.This study had different salinity gradients(5,15,25,35,and 45),whereas a salinity of 25 served as the control group.Seawater,freshwater,and seawater crystals were used to establish environments with different salinities,and oyster individuals were randomly assigned to different salinity groups,with three individuals per group.Following 4 h of salinity stress treatment,the gills,adductor muscle,mantle tissue,and labial palps of the oysters were individually removed and promptly frozen in liquid nitrogen at-80 ℃for subsequent analysis.The respiration,ammonia excretion,ingestion,and clearance rates of the oysters were measured using the static water method.Based on the β-actin gene as a reference,the expressions of the CarHsp70,CarHyou1,and CarDANJC2 genes were detected using RT-qPCR.The reaction system(10 μL)comprised the following:0.2 μL each of upstream and downstream primers,1 μL of template cDNA,5 μL of 2× ChamQ SYBR Color qPCR Master Mix,and 3.6 μL of diethyl pyrocarbonate water.The reaction conditions were as follows:pre-denaturation at 95 ℃ for 10 min,denaturation at 95 ℃ for 10 s,and annealing at 60 ℃ for 30 s,for 40 cycles.Each group included six biological replicates,with each biological replicate conducted in triplicate.The results demonstrated that within a salinity range of 5-45,the respiration and ammonia excretion rates of C.ariakensis initially increased and subsequently decreased,with peak values observed at a salinity of 35.Similarly,the ingestion and clearance rates of C.ariakensis exhibited an initial increase,followed by a decrease within the same salinity range,with the maximum clearance rate observed at a salinity of 15 and the minimum value observed at a salinity of 45.In addition,the research revealed substantial effects of salinity stress on gene expression,particularly for CarHsp70.The RT-qPCR results showed that the three genes(CarHsp70,CarHyou1,and CarDANJC2)were expressed in the gills,mantle tissue,adductor muscle,and lip tissue of C.ariakensis,with the highest expression level observed in the adductor muscle.Changes in salinity significantly affected the expression of the three genes in the HSP family of C.ariakensis.Following salinity stress,the expression levels of the three genes in gill tissues exhibited an upward trend.Upon a 10-unit rise in salinity,the expression levels of CarHsp70,CarHyou1,and CarDANJC2 were upregulated by 4.36-,3.58-,and 2.08-fold,respectively,compared to the control group.Conversely,a 10-unit drop in salinity resulted in adjustments to 3.62-,2.97-,and 2.05-fold,respectively.Upon a 20-unit rise in salinity,the expression levels of the three genes were 7.13-,4.68-,and 2.72-higher than those of the control group,respectively.Conversely,with a 20-unit drop in salinity,the expression levels were 5.92-,6.04-,and 2.54-higher than those of the control group,respectively. This study elucidates the physiological and molecular responses of C.ariakensis to different salinity conditions,including respiration,ammonia excretion,ingestion,and clearance rates,and the expression changes of HSP family genes in response to salinity stress.Within a defined salinity range,the respiratory metabolic activities of shellfish progressively increased with rising salinity;however,beyond a specific threshold,these activities were inhibited.The three genes(CarHsp70,CarHyou1,and CarDANJC2)are essential for physiological functions in different shellfish tissues and may exhibit synergistic effects in response to environmental stress.Their expression patterns provide insights into the mechanisms underlying the adaptation of organisms to environmental changes.This research enhances our scientific understanding of the adaptability of C.ariakensis to salinity variations and offers substantial guidance for the sustainable development of the oyster farming industry and genetic improvement.Additionally,it provides reference material for further investigations into the adaptability of oysters to salinity changes.

To explore optimal large-scale breeding conditions of artificial Manila clam(Ruditapes philippinarum)seedlings,the effects of different stocking density and diet species on the growth,survival,and attachment metamorphosis of R.philippinarum larvae were investigated.Four cultivation density gradients(5,10,15 and 20 ind./mL)and four groups of diets(Group A Lsochrysis galbana,Group B Chaetocerossp,Group C Lsochrysis galbana+Chaetocerossp 1∶2,Group D Lsochrysis galbana+Chaetocerossp 2∶1)were set up.The larval shell length and survival rates were measured on the 3rd,9th,18th,and 27th days.The larval settlement and metamorphosis rates were evaluated on the 27th day.The results indicated that the larval shell length of(0.968±0.002)mm in diet group A was the largest on day 3.The shell length of(0.102±0.013)mm in the medium density group(10 ind./mL)was the largest,which was significantly higher than that of other density groups(P＜0.05).The survival rate of bait group A(26.67％)on the 18th day was the lowest,which was significantly lower than that of the other groups.There was no significant difference in the survival rates between group C and group D,but the survival rates of group C and group B were significantly higher than those of group A and group B.There was no significant difference in the survival rate between the density groups of 5 ind./mL and 20 ind./mL;however,they were significantly lower than those of density groups of 10 and 15 ind./mL.In terms of settlement and metamorphosis,the mixed diets groups of C and D were significantly higher than those of diet groups of A and B.The density group of 15 ind./mL had the highest settlement and metamorphosis rate(17.38％),followed by 16.65％in density group of 10 ind./mL.For larval settlement and metamorphosis rates,there was no significant difference between density groups of 15 and 10 ind./mL,but significantly higher than those in density groups of 5 and 20 ind./mL.The results showed that larvae fed at early opening with Lsochrysis galbana had the highest survival rate,and larvae fed with the mixed diets showed the highest growth and metamorphosis rates.Therefore,the culture density of larvae should be maintained between 10-15 ind./mL.In summary,artificial seedling rearing of R.philippinarum,larval density should be maintained at 10-15 ind./mL.To obtain the most suitable condition for larval growth and survival,a Lsochrysis galbana diet should be selected for the early development stage and mixed diets should be adopted for the late development stage.These results provide the necessary scientific basis for the environmental factors of R.philippinarum larval growth and development and have important guiding significance and application value for improving the seed yield per water unit and stable production of seedlings of clams.

The coloration of shellfish significantly influences both environmental adaptability and economic value. In the Jinjiang oyster (Crassostrea ariakensis), soft-body color varies between individuals, with an orange-yellow phenotype distinct from the milky white coloration of the wild type. To elucidate the compositional differences and molecular mechanisms underlying orange-yellow (designated as CaR) versus milky white (CaW) soft-body color in C. ariakensis, we conducted comparative ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) non-targeted and transcriptomic analyses. A total of 280 differential accumulation metabolites (DAMs) and 691 differentially expressed genes (DEGs) were detected between the CaR and CaW groups. The metabolite set enrichment analysis (MSEA) revealed that DAMs were significantly enriched in pigment metabolism pathways, including tyrosine metabolism, porphyrin metabolism, and lipid metabolism. Furthermore, genes associated with melanin synthesis and carotenoids conversions or transports were upregulated in the CaR vs. CaW group. These genes included Cyp4z1, Cyp4f22, Cyp17a1, Cyp1a5, Cyp2d28a, Lrp4, Aldh, and Tyr-3, potentially driving the accumulation of pheomelanin and carotenoids. This study demonstrates the vital roles of melanin and carotenoid metabolism in Jinjiang oyster body color formation, providing key insights into the molecular mechanisms of color determination in shellfish.

Background/Objectives: The Pacific abalone Haliotis discus hannai originated in cold waters and is an economically important aquaculture shellfish in China. Our goal was to clarify the current status of the genetic structure of Pacific abalone in China. Methods: In this study, eighteen polymorphic EST-SSR loci were successfully developed based on the hemolymph transcriptome data of Pacific abalone, and thirteen highly polymorphic EST-SSR loci were selected for the genetic variation analysis of the six populations collected. Results: The results showed that the average number of observed alleles was 8.0769 (RC)-11.3848 (DQ) in each population. The number of observed alleles in the DQ, NH, and TJ populations was significantly higher than that in the RC population. The cultivated population outside the Changshan Islands has experienced a 22.79% reduction in allele diversity compared to the wild population of DQ. The pairwise Fst values and analysis of molecular variance (AMOVA) revealed significant population differentiation among all populations except DQ and NH populations, with RC and ZZ cultured populations exhibiting the largest population differentiation (Fst = 0.1334). The phylogenetic tree and structural analysis divided the six populations into two groups (group 1: NH, DQ, and ZZ; group 2: DL, TJ, and RC), and there was no relationship between geographical distance and genetic distance. Conclusions: These results may reflect the large-scale culture from different populations in China and the exchange of juveniles between hatcheries. Different breeding conditions have led to a higher degree of genetic differentiation between the RC and ZZ populations. This study enables a better understanding of the genetic diversity and structure of current Pacific abalone populations.

Elucidating the molecular regulatory mechanisms underlying muscle growth and development is of profound significance in aquaculture. Yesso scallop is a cold-water bivalve of considerable economic importance, having its primary edible component of adductor muscle. In this study, comparative transcriptomics and histological analysis at different sampling times after Myostatin (MSTN) interference were performed to identify the potential candidate genes potentially involved in muscle growth and development. The comparative transcriptomics revealed that growth factors and cytokines, extracellular matrix proteins and ubiquitin-proteasome system are potentially involved in muscle hypertrophy and hyperplasia. After MSTN interference, striated adductor muscle displays significant muscle hypertrophy (51.77 % increase on day 7 and 59.83 % increase on day 21) and muscle hyperplasia (59.36 % increase on day 7 and 61.83 % increase on day 21). WGCNA identifies the key darkolivegreen module, which may play crucial roles in muscle hyperplasia and hypertrophy within the striated muscle of the scallop. Five key transcription factors (zf-CCCH, zf-C2H2, PPP1R10, LRRFIP2, and Gon4) are identified by analyzing the co-expression patterns of core genes within the module. These findings will aid in understanding the regulatory mechanisms of muscle growth in scallops and provide a basis for genetic improvement in shellfish aquaculture.

Thermal stress in marine environments is likely to become more widespread in marine environments. Understanding age-related physiological adaptations to thermal stress is critically important for predicting the impacts of global climate change on marine biodiversity. The typical burrowing bivalve, Manila clam Ruditapes philippinarum, was selected to explore molecular and physiological responses to thermal stress and how the effects varied with ages (juvenile VS. adults). When the temperature increased to 30.6 °C, the significantly higher rates of burrowing behavior was found in juvenile clams than that of adult clams (60 % VS. 26.7 %). As the thermal stress increased to 44.6 °C, the survival rate was found to be 49.7 % in juvenile clams, compared to 100 % mortality in adult clams. According to the comparative transcriptomics, the significant up-regulation of genes related to neuropeptide and extracellular matrix (ECM) were potentially involved in active muscle contractility and wound healing ability in juveniles. This may be responsible for their high rates of burrowing behavior in response to the thermal stress. In contrast to juveniles, multiple down-regulated genes involved in antioxidant and energy metabolism were detected in adults, which may be associated with disruption of their energy homeostasis, cell damage and dysfunction, resulting in less capability of adult clams to resist the thermal conditions. The present study will provide new evidences on age differences of clams in response to thermal stress, suggesting clam age or body size constrains their thermal tolerance. These findings will not only shed lights on the molecular mechanism of clams with different ages or sizes in response to thermal stress, but also provide insights into the prediction of future biodiversity and sustainable aquaculture production in a warming world.

This study elucidates the role of the steroidogenic acute regulatory protein (StAR) in sex steroid hormone dynamics and the gonadal development of the commercially important marine bivalve ark shell Scapharca broughtonii. The sequence of the StAR gene was obtained and verified from the transcriptome of ark shell, then the tissue localization and expression pattern during the gonad development of the StAR gene were detected by in situ hybridization and quantitative real-time PCR, respectively. Additionally, the concentrations of three critical sex steroid hormones (progesterone, testosterone, and estradiol) were measured throughout gonadal development using enzyme-linked immunosorbent assay (ELISA). The results showed that the length of the coding region of StAR was 1446 bp, encoding 481 amino acids. The results of qRT-PCR showed that the expression of the StAR gene varied with gonadal development, increased from the early active stage to the development stage, and decreased from the mature stage to the spent stage. Notably, the expression level in ovaries was higher than that in testes, suggesting the potential involvement of StAR in sex differentiation and gonadal development. Additionally, the results indicated that progesterone, testosterone, and estradiol accounted for 80%, 10%, and 10% of the total hormone content in the gonads, respectively. Correlation analysis revealed a highly significant strong positive correlation between progesterone/estradiol levels and StAR gene expression, demonstrating that StAR serves as a key regulator in sex steroid hormone biosynthesis. These findings provide crucial molecular evidence for StAR-mediated steroidogenesis in bivalve reproduction, offering fundamental insights into invertebrate endocrinology.

The environmental problems brought about by factory-based aquaculture have become increasingly prominent. Reducing nitrogen and phosphorus concentrations in tailwater has become the key to tailwater management. In order to assess the potential of microalgae in removing nitrogen and phosphorus ions from aquaculture wastewater, four microalgae species, i.e., Chlorella sp., Dicrateria zhanjiangensis, Nitzschia closterium minutissima, and Platymonas subcordiformis, were used in this study, and their growth and nitrogen and phosphorus removal rates in four nutrient concentrations of simulated aquaculture wastewater were systematically evaluated. After 15 days of cultivation, the cell counts of all four types of microalgae increased. Three species, i.e., Chlorella sp., N. closterium minutissima, and P. subcordiformis, grew best in high PO43- and low NH4+ medium, whereas D. zhanjiangensis possessed best growth in low PO43- and high NH4+ medium. The removal rate of PO43-, NH4+, NO3-, and NO2- by four microalgae species exceeded 82.64%, 89.06%, 59.27%, and 42.15%, respectively, even though the four microalgae had different performance in the removal of nitrogen and phosphorus. All microalgae in the low-phosphorus groups removed PO43- at significantly lower rates than those in the high-phosphorus groups, while high NH4+ removal rates were observed in all four microalgae groups. Moreover, in phosphorus-limited conditions, four microalgae exhibit lower removal rates of NO3- when nitrogen content was high. The chlorophyll a contents of microalgae in four culture media strictly corresponded to their final cell densities. P. subcordiformis exhibited the highest intracellular polysaccharide accumulation in high PO43- and low NH4+ type medium, whereas D. zhanjiangensis demonstrated the strongest protein synthesis capacity in high PO43- and low NH4+ medium. The activities of acid phosphatase in all microalgae were higher under phosphorus-deficient conditions than phosphorus-sufficient conditions. Our results might provide useful references for microalgae selection in the treatment of different aquaculture wastewater conditions.