Physiological and immunological responses to mass mortality in noble scallop Chlamys nobilis cultured in Nan'ao waters of Shantou, China

Assembly mechanism of microbial community under different seasons in Shantou sea area

Coastal areas are often affected by a variety of climates, and microbial composition patterns are conducive to adaptation to these environments. In this study, the composition and pattern of microbial communities in the Shantou sea from four seasons were analyzed. The diversity of microbial community was significant differences under different seasons (p < 0.01). Meanwhile, dissolved oxygen levels, temperature were key factors to shift microbial communities. The assembly mechanism of microbial communities was constructed by the iCAMP (Infer community assembly mechanism by the phylogenetic bin-based null). Interestingly, the analyses revealed that drift was the predominant driver of this process (44.5 %), suggesting that microbial community assembly in this setting was dominated by stochastic processes. For example, Vibrio was found to be particularly susceptible to stochastic processes, indicating that the pattern of bacterial community was governed by stochastic processes. Thus, these results offering novel insight into the regulation of microbial ecology in marine environments.

Positive effects of dietary Clostridium butyricum supplementation on growth performance, antioxidant capacity, immunity and viability against hypoxic stress in largemouth bass

The effects of dietary supplementation of Clostridium butyricum (CB) on growth performance, serum biochemistry, antioxidant activity, mRNA levels of immune-related genes and resistance to hypoxia stress were studied in largemouth bass. Feed with CB0 (control, 0 CFU/kg), CB1 (4.3×108 CFU/kg), CB2 (7.5×108 CFU/kg), CB3 (1.5×109 CFU/kg) and CB4 (3.2×109 CFU/kg) CB for 56 days, and then a 3 h hypoxic stress experiment was performed. The results showed that dietary CB significantly increased the WGR (weight gain rate), SGR (specific growth rate), PDR (protein deposition rate) and ISI (Intestosomatic index) of largemouth bass (P<0.05). Hepatic GH (growth hormone)/IGF-1 (insulin-like growth factor-1) gene expression was significantly upregulated in the CB3 and CB4 groups compared with the CB0 group (P<0.05), while the FC (feed conversion) was significantly decreased (P<0.05). Serum TP (total protein) and GLU (glucose) levels were significantly higher in the CB4 group than in the CB0 group (P<0.05), while the contents of serum AST (aspartate transaminase), ALT (alanine transaminase), AKP (alkline phosphatase) and UN (urea nitrogen) in CB4 were significantly lower than those in CB0 (P<0.05). T-AOC (total antioxidant capacity), SOD (superoxide dismutase), CAT (catalase), POD (peroxidase) and GSH-Px (glutathione peroxidase) activities were significantly higher in CB3 and CB4 groups than in CB0 group (P<0. 05). The liver MDA (malondialdehyde) content of CB1, CB2, CB3 and CB4 groups was significantly higher than that of CB0 group (P<0. 05). The relative expressions of IL-1β (interleukin 1β), TNF-α (tumor necrosis factor α) and TLR22 (toll-like receptor-22) genes in CB2, CB3 and CB4 groups were significantly lower than those in CB0 group (P<0.05). The relative expression of IL-8 (malondialdehyde) and MyD88 (Myeloid differentiation factor 88) genes in the CB4 group was significantly lower than that in the CB0 group (P<0.05). The liver LZM (lysozyme) content of CB2, CB3 and CB4 groups was significantly higher than that of CB0 group (P<0. 05). The relative expression of IL-10 (interleukin 10) and TGF-β (transforming growth factor β) genes in the CB4 group was significantly higher than that in the CB0 group (P<0.05). Under hypoxic stress for 3 h, the CMR of CB0 group was significantly higher than that of CB1, CB2, CB3 and CB4 groups (P<0.05). Dietary CB can improve the growth performance and resistance to hypoxic stress of largemouth bass by regulating the expression of GH/IGF-1 gene and inflammatory factors and inhibiting TLR22/MyD88 signaling pathway.

The positive effects of dietary inositol on juvenile hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) fed high-lipid diets: Growthperformance, antioxidant capacity and immunity

The objective of the present research was to assess the influence of inositol supplementation on growth performance, histological morphology of liver, immunity and expression of immune-related genes in juvenile hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu). Hybrid grouper (initial weight 6.76 ± 0.34 g) were fed isonitrogenous and isolipidic diets (16%) with various inositol levels of 0.17 g/kg (J1, the control group), 0.62 g/kg (J2), 1.03 g/kg (J3), 1.78 g/kg (J4), 3.43 g/kg (J5), 6.59 g/kg (J6), respectively. The growth experiment lasted for 8 weeks. The results indicated that dietary inositol had a significant promoting effect on final mean body weight of the J5 and J6 groups and specific growth rate (SGR) of the J3, J4, J5 and J6 groups (P < 0.05). In the serum, superoxide dismutase (SOD) of the J4 group became significantly active compared with that of the control group (P < 0.05), while aspartate transaminase (AST), alanine transaminase (ALT) and alkaline phosphatase (AKP) activities in the inositol-treated groups showed distinctly decreased compared with those of the control group (P < 0.05). In the liver, dietary inositol could significantly increase the activities of SOD, catalase (CAT), lysozyme (LYZ) and the contents of total antioxidative capacity (T-AOC) and immunoglobulin M (IgM) (P < 0.05), and distinctly reduce the content of malondialdehyde (MDA) as well as reactive oxygen species (ROS) (P < 0.05). Compared with the control group, the damaged histological morphology of the liver was relieved and even returned to normal after an inositol increase (0.4-3.2 g/kg). In the liver, the remarkable up-regulation of SOD, CAT, glutathione peroxidase (GPX), heat shock protein70 (HSP70) and heat shock protein90 (HSP90) expression levels were stimulated by supply of inositol, while interleukin 6 (IL6), interleukin 8 (IL8) and transforming growth factor β (TGF-β) expression levels were down-regulated by supply of inositol. In head kidney, the mRNA of toll-like receptor 22 (TLR22), myeloid differentiation factor 88 (MyD88) and interleukin 1β (IL1β) expression levels were significantly down-regulated (P < 0.05), which could further lead to remarkable down-regulation of IL6 and tumor necrosis factor α (TNF-α) expression (P < 0.05). These results indicated that high-lipid diets with supply of inositol promoted growth, increased the antioxidant capacity, and suppressed the inflammation of the liver and head kidney by inhibiting the expression of pro-inflammation factors (IL6, IL8, TGF-β and TNF-α). In conclusion, these results indicated that dietary inositol promoted growth, improved antioxidant capacity and immunity of hybrid grouper fed high-lipid diets. Based on SGR, broken-line regression analysis showed that 1.66 g/kg inositol supply was recommended in high-lipid diets of juvenile grouper.

Gene Co-Expression Network Analysis Reveals the Correlation Patterns Among Genes in Different Temperature Stress Adaptation of Manila Clam

The Manila clam (Ruditapes philippinarum) is one of the most important aquaculture species and widely distributed along the coasts of China, Japan, and Korea. Due to its wide distribution, it can tolerate a wide range of temperature. Studying the gene expression profiles of clam gills had found differentially expressed genes (DEGs) and pathway involved in temperature stress tolerance. A systematic study of cellular response to temperature stress may provide insights into the mechanism of acquired tolerance. Here, weighted gene co-expression network analysis (WGCNA) was carried out using RNA-seq data from gill transcriptome in response to high and low temperature stress. There are a total 32 gene modules, of which 18 gene modules were identified as temperature-related modules. Blue module was one significantly correlated with temperature which was associated with cellular metabolism, apoptosis pathway, ER stress, and others.

Temporal Changes in Physiological Responses of Bay Scallop: Performance of Antioxidant Mechanism in Argopecten irradians in Response to Sudden Changes in Habitat Salinity

Changes to habitat salinity may induce oxidative stress in aquatic organisms. The effect of salinity on the antioxidant function of bay scallops was investigated at 55, 70, 85 and 120% of seawater salinity (SW), with 100% SW as the control. The scallops were sampled 0, 6, 12, 24, 48 and 72 h after the salinity change to measure superoxide dismutase (SOD), catalase (CAT), hydrogen peroxide (H₂O₂), and lipid peroxidation (LPO) levels, as well as apoptosis in the digestive diverticula and/or hemolymph. The SOD immunohistochemistry and apoptotic response were assessed at 55% and 120% SW at 12 h. Antioxidant expressions at 55% and 70% SW peaked at 24 h or 48 h, and then decreased. At 120% SW, they increased with exposure time. The H₂O₂ and LPO levels at each SW increased significantly with time. A comet assay also revealed that changes in salinity increased the rate of nuclear DNA damage in all the salinity groups. Thus, variations in salinity result in significant physiological responses in bay scallops. A change in habitat salinity of 15% or more produces oxidative stress that cannot be resolved by the body’s antioxidant mechanism, suggesting that excessive generation of reactive oxygen species can lead to cell death.

Potential causative factors of noble scallop Chlamys nobilis mass mortality in Nan'ao Island, Shantou, China in 2017

Noble scallop Chlamys nobilis is an important marine bivalve that has been extensively cultured in the south coast of China since the 1980s. Unfortunately, since the late 1990s, the farmed scallops often suffered from regional mass mortality, which results in enormous economic losses to farmers and industries. In 2017, another mass mortality event occurred in Nan'ao Island, Shantou, China. In this study, the cause of C. nobilis mass mortality in 2017 was first investigated in the field, and then validated in a laboratory experiment. In the field, three sampling sites were selected according to the scallop mortality rate: Hunter Bay (90% mortality), Baisha Bay (67% mortality) and Longhai (6% mortality). Meanwhile, environmental parameters (temperature, salinity, DO, pH and chlorophyll a) of each site were also measured in situ. Then, water and scallop samples were collected randomly for the analysis of phytoplankton diversity and algal toxin activity using 18S rDNA and PP2A inhibition assay, respectively. In laboratory, healthy scallops were challenged with Karenia mikimotoi (1 × 10³ cells/mL) for 30 h. The field results showed that no significant difference in those environmental parameters existed among the three sites, but the relative abundance of K. mikimotoi in seawater and scallops' intestines in Hunter Bay and Baisha Bay was significantly higher than that in Longhai, and sick scallops contained significantly higher algal toxin activity than healthy ones. Laboratory results revealed that challenged scallops with K. mikimotoi showed significantly higher mortality rate and algal toxin activity than healthy ones, and low density of K. mikimotoi (1 × 10³ cells/mL) was sufficient to cause >50% scallops' mortality within 26 h. This study provides the first evidence that low K. mikimotoi cell density can cause massive mortality in C. nobilis, and provides useful information as guide to prevent scallop mass mortality in the future.

Effects of the Maillard reaction on the epitopes and immunoreactivity of tropomyosin, a major allergen in Chlamys nobilis

Scallop (Chlamys nobilis) causes an IgE-mediated food allergy; however, studies of the allergens in its musculus are not sufficiently comprehensive. In this context, the target protein was purified from scallops and confirmed to be the major allergen tropomyosin (TM) using proteomic technology and serological testing. Subsequently, seven potential IgE epitopes of TM were obtained using phage display technology with IgE enrichment from the serum of scallop-sensitized patients and identified via inhibition enzyme-linked immunosorbent assays. A method for the Maillard reaction of TM and xylose was established, and Maillard-reacted TM (MR-TM) showed significantly decreased immunobinding activity and CD63 and CD203c expression in basophils compared with TM. Furthermore, shotgun proteomics analysis showed that eleven specific amino acids (K12, R15, K28, K76, R125, R127, K128, R133, R140, K146, and K189) of the six IgE epitopes of TM were modified after the Maillard reaction. Overall, the immunoactivity of MR-TM was reduced, which provides a theoretical reference for the development of hypoallergenic foods.

Enzymes and non-enzymatic antioxidants responses to sequential cold stress in polymorphic noble scallop Chlamys nobilis with different total carotenoids content

Noble scallop, an economically important edible marine bivalve displays polymorphism in shells (golden and brown) and flesh colors (orange and white). Mass mortality of noble scallops usually occurs during the winter months. Interestingly, carotenoid-rich golden scallops demonstrated much higher survival rates than brown scallops in winter. In order to understand the response of polymorphic noble scallops to sequential cold stress, the present study aimed to investigate the enzyme and non-enzymatic antioxidant responses of golden and brown scallops under sequential cold stress. Parameters evaluated included total carotenoid content (TCC), fatty acid composition, total antioxidant capacity (TAC), methylenedioxyamphetamine (MDA) content, catalase (CAT) activity, and superoxide dismutase (SOD) enzyme activity. The results of the present study revealed that golden scallops have higher cold tolerance than brown scallops. Golden and brown scallops are well adapted to low water temperature of above 12 °C, but in areas where winter water temperatures are below 12 °C, golden scallops are more suitable for aquaculture than brown scallops. The findings of this study are crucial to understanding the physiological responses of polymorphic scallops to cold stress and identify suitable candidates for winter aquaculture.

Climate Change and Bivalve Mass Mortality in Temperate Regions

One of the fastest-growing global food sectors is the bivalve aquaculture industry. Bivalves particularly oysters, mussels and clams are important sources of animal protein (Tan and Ransangan 2016a, b). Bivalve aquaculture represents 14-16% of the average per capita animal protein for 1.5 billion people and supports over 200,000 livelihoods, mostly in developing countries (FAO 2018). Most of the bivalves produced around the world (89%) are from aquaculture (FAO 2016). To date, mollusc aquaculture have accounted for 21.42% (17.14 million tonnes) of the total aquaculture production, with Asia being the largest contributor (92.27%) (FAO 2018).

Oxidative stress responses of golden and brown noble scallops Chlamys nobilis to acute cold stress

The noble scallop Chlamys nobilis is an important edible marine bivalve that is widely cultivated in the sea of southern China. Unfortunately, the mass mortality of noble scallops frequently occurs during the winter months. The present study investigated the effects of acute cold stress (8 °C) to the physiological responses of polymorphic noble scallops, by assessing the HSP70 gene expression, total carotenoid content (TCC), total antioxidant capacity (TAC), malondialdehyde (MDA) content, catalase (CAT) activity and superoxide dismutase (SOD) enzymatic activity in different tissues of golden and brown scallops. The results of the present study revealed that MDA, TCC and CAT increased drastically in most tissues in the early stage of acute cold stress (0-3 h), but TCC, SOD and CAT generally showed a downward trend. Within 3-6 h of acute cold stress, MDA content decreased in most tissues and the SOD content increased significantly in most tissues, while TCC and CAT remained at peak. After 6 h of acute cold stress, MDA content continued to increase in most tissues, while TCC, CAT, SOD and TAC decreased or remained at a lower level. For HSP70 expression, up-regulation of the HSP70 gene was observed only in mantle of brown scallops and hemolymph of golden scallops at 3 h and 24 h, respectively. The findings of the present study can better understand the physiological response of noble scallops to acute cold stress.

Effects of stocking density on the growth performance, bacterial load and antioxidant response systems of noble scallop Chlamys nobilis

Stocking density is a crucial factor in shellfish aquaculture that affects overall growth performance and health status. Present study analyzes the effects of stocking densities on growth, survival and hemolymph immune status of noble scallop Chlamys nobilis. The scallops with the same size were separately placed in the lantern cages (10 layers per cage) using high stocking density (500 scallops per cage) and low stocking density (100 scallops per cage) and cultivated in the same location for 60 days. The results indicated that the scallops cultivated at high stocking density had significantly higher mortality and slower growth than those cultivated at low stocking density. Moreover, the hemolymph of scallops cultivated at high density showed significantly higher bacterial load, higher reactive oxygen species (ROS), higher expression level of Nrf2 and lower expression level of Keap1, as well as lower antibacterial ability of Vibrio parahemolyticus than that of scallops cultivated at low density. The present results demonstrated that long-term overcrowding is detrimental for the scallops, which can not only lead to high mortality and slow growth, but also cause more vulnerable to pathogenic bacteria. Therefore, we speculated that high stocking density culture practice of scallops in China might be the root of infectious bacteria outbreaks.

A carotenoid oxygenase is responsible for muscle coloration in scallop

As lipid microconstituents mainly of plant origin, carotenoids are essential nutrients for humans and animals, and carotenoid coloration represents an important meat quality parameter for many farmed animals. Currently, the mechanism of carotenoid bioavailability in animals is largely unknown mainly due to the limited approaches applied, the shortage of suitable model systems and the restricted taxonomic focus. The mollusk Yesso scallop (Patinopecten yessoensis) possessing orange adductor muscle with carotenoid deposition, provides a unique opportunity to research the mechanism underlying carotenoid utilization in animals. Herein, through family construction and analysis, we found that carotenoid coloration in scallop muscle is inherited as a recessive Mendelian trait. Using a combination of genomic approaches, we mapped this trait onto chromosome 8, where PyBCO-like 1 encoding carotenoid oxygenase was the only differentially expressed gene between the white and orange muscles (FDR = 2.75E-21), with 11.28-fold downregulation in the orange muscle. Further functional assays showed that PyBCO-like 1 is capable of degrading β-carotene, and inhibiting PyBCO-like 1 expression in the white muscle resulted in muscle coloration and carotenoid deposition. In the hepatopancreas, which is the organ for digestion and absorption, neither the scallop carotenoid concentration nor PyBCO-like 1 expression were significantly different between the two scallops. These results indicate that carotenoids could be taken up in both white- and orange-muscle scallops and then degraded by PyBCO-like 1 in the white muscle. Our data suggest that PyBCO-like 1 is the essential gene for carotenoid metabolism in scallop muscle, and its downregulation leads to carotenoid deposition and muscle coloration.