Chinese Mitten Crab Eriocheir Sinensis Research Articles

Analysis of food sources of Eriocheir sinensis in rice-crab integrated ecosystem based on stable isotopes in saline-alkali land of the Yellow River Delta

To explore food composition of Chinese mitten crab (Eriocheir sinensis) in rice-crab integrated ecosystem in saline-alkali land of the Yellow River Delta, we analyzed carbon and nitrogen stable isotope ratios (δ13C and δ15N) in the crab and that in food sources, including plants (Elodea, Potamogeton crispus, Ceratophyllum demersum, Lemna minor, Oryza sativa stem and leaf, rice grain), animals (benthos, zooplankton), organic debris and artificial feed (compound feed, corn meal) in Kenli District, Dongying, Shandong Province in June to October of 2020. Substantial differences in δ13C and δ15N were found among food sources. The δ13C and δ15N values of different food sources were in a range of -30.09‰--11.24‰ and 0.03‰-12.78‰, respectively, while those of the crab muscle were in range of -24.61‰--20.08‰ and 4.74‰-9.21‰, respectively, indicating diverse food sources for the crab. During the experiment, the contribution rate of different food sources followed the order: plant (46.7%-57.1%)>animal (21.5%-24.5%)>artificial feed (10.9%-21.3%)>organic detritus (7.1%-7.9%). It suggested that the natural bait of the paddy field could meet the feeding needs of Chinese mitten crabs in saline-alkali land. Even the crabs were fed with non-animal artificial feed, the contribution rates of the main food sources were not altered.

Taste Attributes of the “June Hairy Crab” Juveniles of Chinese Mitten Crab (Eriocheir sinensis) in Yangcheng Lake, China—A Pilot Study

This is the first report on the use of a taste sensing system to quantitatively evaluate the taste attributes of two groups of native “June hairy crab” juveniles (commonly referred to as “Liu-Yue-Huang”) of the Chinese mitten crab (Eriocheir Sinensis H. Milne Edwards, 1853) from a net enclosure culture area in Yangcheng Lake (lake culture) and aquaculture ponds near the lake (pond culture). We showed that umami was the predominant basic taste of steamed June hairy crabs, followed by bitterness and astringency. The intensity value of saltiness was aberrant and could not be determined using this system. The average values of aftertaste-U reached 8.7 and 10.7 in the male June hairy crabs from the lake and pond cultures, respectively, which was significantly higher than their respective aftertaste-B and aftertaste-A values (p < 0.01). Female crabs did not have aftertaste-B, while their aftertaste-U was significantly higher than aftertaste-A (p < 0.01). Although principal component analysis and linear discriminant analysis were not able to completely distinguish among crabs from different cultures, they could robustly distinguish between male and female crabs.

Determination of arsenic in Chinese mitten crabs (Eriocheir sinensis): Effects of cooking and gastrointestinal digestion on food safety

This study used the sexually mature Chinese mitten crabs as the research object, and the total arsenic and six major species were determined by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The influence of three common cooking methods on the forms of arsenic and content in different edible parts of crabs were explored. Furthermore, the bioavailability of arsenic and its different forms in the crabs were studied by in vitro gastrointestinal digestion. Based on the risk assessment of arsenic in gastrointestinal digestion, the results showed that the Target Hazard Quotient (THQ) of arsenic was less than 1, which did not pose a significant health risk, but the risk of carcinogenesis of arsenic can not be ignored. Considering the effects of cooking and gastrointestinal digestion into account, a more realistic estimate of the risk associated with the consumption of Chinese mitten crabs can be deciphered.

Molecular identification and functional analysis of a tumor necrosis factor superfamily gene from Chinese mitten crab (Eriocheir sinensis)

Tumor necrosis factor (TNF) is one of the most important cytokines involved in various biological processes in vertebrates and invertebrates. In the present study, a new member of the TNF superfamily (named EsTNFSF) was identified from the Chinese mitten crab (Eriocheir sinensis). The full-length cDNA of EsTNFSF is 2462 bp and encodes a polypeptide with 499 amino acids. The deduced EsTNFSF protein contained a transmembrane region and a conserved extracellular C-terminal TNF domain. Phylogenetic analysis indicated that EsTNFSF was closely related to other TNFSFs from crustaceans. Quantitative real-time PCR analysis showed that EsTNFSF was expressed in all the tissues examined, and the highest expression was found in the hepatopancreas. The mRNA levels of EsTNFSF in hemocytes underwent a time-dependent and variable degree of enhancement after stimulation with lipopolysaccharide, peptidoglycan, Staphylococcus aureus, and Vibrio parahaemolyticus. Functionally, EsTNFSF knockdown by siRNA suppressed the transcriptional levels of c-Jun N-terminal kinase and two antimicrobial peptides, anti-lipopolysaccharide factor and crustin. Furthermore, purified recombinant EsTNFSF protein accelerated the bacterial clearance in vivo and inhibited the growth of V. parahaemolyticus and S. aureus in vitro. The results revealed that EsTNFSF, as an inducible immune response gene, plays a crucial role in the antibacterial immune defense of E. sinensis.

Glyphosate-based herbicide causes spermatogenesis disorder and spermatozoa damage of the Chinese mitten crab (Eriocheir sinensis) by affecting testes characteristic enzymes, antioxidant capacities and inducing apoptosis

Glyphosate-based herbicide (GBH) is a popular herbicide, which may contaminate the water environment and affect aquatic animals. In this study, testes morphology, physiology function, apoptosis pathway, and spermatozoa quality of Chinese mitten crab (Eriocheir sinensis) were evaluated after 7 days of GBH exposure (48.945 mg/l,1/2 of the 96 h LC50 value of GBH). Results showed that GBH induced spermatogenesis disorder by H.E. staining. The obvious vacuolar degenerations and fewer spermatids of the testes accompanied by decreased primary spermatocytes-type seminiferous tubules (PSc-STs) were observed. The extensive apoptosis of spermatids by TUNEL staining was visible. Meanwhile, testes’' characteristic enzyme activities associated with spermatogenesis, including lactate dehydrogenase (LDH) and acid phosphatase (ACP) were significantly decreased. Testes suffered oxidative damage as reflected by the significant decrease in superoxide dismutase (SOD) activities, the significant increase in malondialdehyde (MDA) contents, and heat shock proteins (HSP-70) mRNA expression. Further studies demonstrated that GBH induced apoptosis of testes through the mitochondrial apoptotic pathway by upregulating the relative mRNA expression of cysteinyl aspartate specific proteinase 3 (Caspase-3), Bcl-2-associated X protein (Bax), and downregulating B-cell lymphoma 2 (Bcl-2). Oxidative damage may be one of the causes of GBH-induced apoptosis in testes. After GBH exposure, the morphology of spermatophores was changed. The survival and the acrosome reaction (AR) ratio of spermatozoa was significantly decreased. Altogether, these results demonstrated that GBH affects spermatogenesis, spermatophore and spermatozoa quality of E.sinensis, which provides novel knowledge about the toxic effects of GBH on the reproductive system of crustaceans.

Comparative Transcriptome Analysis Reveals the Process of Ovarian Development and Nutrition Metabolism in Chinese Mitten Crab, Eriocheir Sinensis.

Ovarian development is a key physiological process that holds great significance in the reproduction of the Chinese mitten crab (Eriocheir sinensis), which is an economically important crab species for aquaculture. However, there is limited knowledge for the regulatory mechanisms of ovarian development. To study the molecular mechanisms of its ovarian development, transcriptome analysis was performed in the ovary and hepatopancreas of E. sinensis during ovarian stages I (oogonium proliferation), II (endogenous vitellogenesis), and III (exogenous vitellogenesis). The results showed that 5,520 and 226 genes were differentially expressed in the ovary and hepatopancreas, respectively. For KEGG enrichment analysis, the differentially expressed genes in the ovary were significantly clustered in phototransduction-fly, phagosome, and ECM-receptor interaction. Significantly enriched pathways in the hepatopancreas included fatty acid biosynthesis, fatty acid metabolism, and riboflavin metabolism. Further analysis showed that 25 genes and several pathways were mainly involved in oogenesis, including the ubiquitin-proteasome pathway, cyclic AMP-protein kinase A signaling pathway, and mitogen-activated protein kinase signaling pathway. Twenty-five candidate genes involved in vitellogenesis and endocrine regulation were identified, such as vitellogenin, vitellogenin receptor, estrogen sulfotransferase, ecdysone receptor, prostaglandin reductase 1, hematopoietic prostaglandin D synthase and juvenile hormone acid O-methyltransferase. Fifty-six genes related to nutritional metabolism were identified, such as fatty acid synthase, long-chain-fatty-acid-CoA ligase 4, 1-acyl-sn-glycerol-3-phosphate acyltransferase 4, fatty acid-binding protein, and glycerol-3-phosphate acyltransferase 1. These results highlight the genes involved in ovarian development and nutrition deposition, which enhance our understanding of the regulatory pathways and physiological processes of crustacean ovarian development.

Effect of Dietary Cholesterol on Growth Performance, Cholesterol Deposition, and Lipid Metabolism in Adult Chinese Mitten Crab (Eriocheir sinensis)

This research investigated the effects of dietary cholesterol (CHO) on growth, molting performance, CHO deposition, and lipid metabolism of Chinese mitten crab (Eriocheir sinensis). Six diets were formulated to contain 0% (control), 0.1%, 0.2%, 0.4%, 0.8%, and 1.6% CHO and were administered to E. sinensis 43.35 ± 0.05 g , for 16 weeks. From our results, crabs fed with 0.2% and 0.4% CHO diet, the final body weight (FBW), and weight gain ratio (WGR) increased significantly and the feed conversion ratio (FCR) decreased significantly compared with that of the control group. Furthermore, the molting performance of E. sinensis was significantly improved in crabs fed 0.2% CHO. Meanwhile, 0.2% CHO tends to upregulate molt-promoting genes and downregulate the expression of molt-inhibiting genes. It indicated that CHO might improve the molting performance of crabs by regulating ecdysteroid signal pathway transduction. In addition, dietary CHO can significantly increase the content of CHO in the hepatopancreas, muscle, and hemolymph. Moreover, dietary CHO increases the content of triglyceride (TG) in the hepatopancreas and hemolymph. The gene-related lipid metabolism shows that CHO may increase the lipid content by promoting lipid synthesis and inhibiting lipolysis. According to the results of this study, the dietary CHO requirement of E. sinensis is 0.27% for growth requirement and 0.45% for tissue CHO deposition based on the broken-line model.

New insights into the transfer and accumulation of dioxins and dioxin-like PCBs in the food web of farmed Chinese mitten crabs: A typical case from the Yangtze River area

Dioxins and dioxin-like polychlorinated biphenyls (DL-PCBs) transfer and accumulation behavior remains poorly understood in the farmed Chinese mitten crab (Eriocheir sinensis). In this study, dioxins and DL-PCBs concentration in 48 farming crabs in lower reaches of the Yangtze River was monitored and controlled field design was conducted in a typical farm to dissect the dioxins and DL-PCBs contamination in crab food web (crab, feeds, and environment). Results showed that dioxins and DL-PCBs were ubiquitous in farmed crabs with concentrations ranging from 0.390 to 37.2 pg toxic equivalents (TEQ) g−1 ww and do not present a health risk to general consumers. Of the total dioxins TEQ found in crab in treated farms, 45.6% was attributed to direct transfer from the aquaculture environment and 46.5% to the consumption of snails. Consumption of feed material accounted for nearly all of the total DL-PCBs TEQ, divided as 58.2% from feed and 41.8% from snails. These results demonstrated that dominant routes of dioxins accumulation in crabs were transferred for the sediment-snail-crab and sediment-crab chains, whereas DL-PCBs is mainly transferred through consumption of feeds and snails. To our knowledge, this work is the first report of snails serving as a biomagnification medium that promotes accumulation of dioxins in mitten crabs. This observation provided crucial insight to prevent and reduce contamination of crab by dioxins and DL-PCBs.

Effect of Vitamin A Supplementation on Growth Performance, Lipid Deposition, Antioxidant Ability, and Immunity in Juvenile Chinese Mitten Crab Eriocheir sinensis Fed Diet with Fish Oil Totally Replaced by Palm Oil

This research evaluated the protective effect of vitamin A (VA) on the adverse effect of fish oil (FO) substitution with palm oil (PO) in an economical crab Eriocheir sinensis. Three diets of FO, PO, and PO + 8000 IU / kg VA as the main lipid sources were fed to crabs, respectively, for 8 weeks. Compared to crabs fed FO diet, crabs fed PO diet showed reduced hemolymph VA concentration, feed utilization efficiency, and growth performance. Besides, crabs fed PO diet showed elevated lipid content in hepatopancreas and body and triglyceride content in hepatopancreas, leading to decreased antioxidant enzyme and immune parameters activities from biochemical analysis, enzymatic determination, and quantitative polymerase chain reaction. In contrast, compared to crabs fed PO only, VA supplementation in PO improved the growth performance and utilization of fatty acids and reduced lipid deposition in the hepatopancreas. In addition, VA supplementation suppressed gene expression related to triglyceride synthesis (dgat1) and positively affected gene expression related to lipid catabolism (cpt1a, cpt1b, cpt2, and caat). Furthermore, VA supplementation upregulated antioxidant genes (CuZnSOD and CAT) through downregulating gene expression of upstream regulator Keap1. Furthermore, VA supplementation upregulated immune genes (Lzm and proPO) expression and reduced proinflammatory genes (LITAF, ADAM17, and IL-16) expression related to Toll2/MyD88/Relish signaling pathway. This study shows the necessity of VA addition in the feed with FO totally replaced by PO because it can relieve PO’s adverse effects and improve the growth of crabs.

Multi-mineral fingerprinting analysis of the Chinese mitten crab (Eriocheir sinensis) in Yangcheng Lake during the year-round culture period

Chinese mitten crabs (Eriocheir sinensis), originating from Yangcheng Lake, are valuable aquatic products in China. To characterize changes in nutrients in this species in Yangcheng Lake during the year-round culture period, the contents of ten mineral elements in the third pereiopod were evaluated. Principal component analysis revealed that mineral elements changed substantially in the first three months. Thereafter, the elemental “fingerprint” stabilized, and samples could not be accurately distinguished. This pattern was supported by linear discriminant analysis and self-organizing map analysis. These results demonstrate that a long period of time is required for element characteristics to stabilize, suggesting that short-term breeding is insufficient to obtain the natural elemental “fingerprint.” In addition, our findings provide a basis for verifying the origin of Chinese mitten crab and other aquatic taxa in Yangcheng Lake.

Occurrence of the chinese mitten crab Eriocheir sinensis (H. Milne Edwards) in South Iraq

The distribution of the invasive Chinese mitten crab Eriocheir sinensis in Shatt Al-Basrah Canal and Shatt Al-Arab River was investigated. The earlier published record of this species was in 2006 where only a single specimen was obtained from Shatt Al-Basrah Canal, but the species has long been observed in the region. The present work monitored the recent occurrence of the species where living and non living specimens were captured in large numbers. Although the species migrate to the sea for reproduction, it was not yet recorded from the North West Arabian Gulf region. Detailed description of the captured crabs is provided. Carapace width ranged from 53.4 to 56.6 mm and carapace length ranged from 56 to 62.4 mm. Recent rise in salinity or the change in water chemistry of south Iraq may play vital role in increasing the population of the mitten crab.

Acute toxic effects of thiamethoxam on Chinese mitten crab Eriocheir sinensis.

The information about toxic effects of thiamethoxam on non-target aquatic organisms is still incomplete. The semi-static toxicity test method was used to investigate the acute toxic effects of thiamethoxam on Eriocheir sinensis. The results showed that the median lethal concentration (LC50) of thiamethoxam to E. sinensis at 96h was 510μg/L, and the safety concentration (SC) was 51μg/L. After 96h exposure to thiamethoxam, the survival rates of crabs at concentrations of 0, 151.11, 226.67, 340, and 510μg/L were 100%, 76.19%, 64.29%, 61.91%, and 46.43%, respectively. A significant (P < 0.05) decrease of the number of hemocytes was observed in thiamethoxam groups. With the increase of thiamethoxam concentration, the phagocytic activity of hemocytes, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and the activities of protease, amylase, and lipase of crabs increased firstly and then decreased, and the above indexes reached the maximum in 151.11μg/L thiamethoxam group. Collectively, a high concentration of thiamethoxam (510μg/L) had a great effect on the gene expression of immune metabolism-related factors in hepatopancreas and gill of crabs. These findings indicated that thiamethoxam exposure had the ability to impair immune and metabolic systems and resulted in the reduction of survival rate of crabs.

Dietary DHA Oil Supplementation Promotes Ovarian Development and Astaxanthin Deposition during the Ovarian Maturation of Chinese Mitten Crab Eriocheir sinensis

Astaxanthin (Axn) is an essential carotenoid for crustacean pigmentation, and docosahexaenoic acid (DHA) is an important fatty acid; both play key roles in maintaining the health of many aquaculture species. The present study explored the combined effect of dietary Axn and DHA on gonadal development and carotenoid deposition in adult females of the Chinese mitten crab, Eriocheir sinensis. A 2 × 3 factorial design of experimental diets was created to contain two levels of Axn (0 mg/kg and 100 mg/kg) and three levels of DHA oil (0%, 0.33%, and 0.67%). The results showed as follows: (1) For the culture performance, dietary DHA oil significantly increased the gonadosomatic index (GSI), and Diet 2 (Axn 0% + DHA oil 0.33%) had the highest GSI among all treatments. (2) For the enzymatic indicators in the hepatopancreas and hemolymph, supplementation with 0.33% DHA oil significantly improved the antioxidant capacity (T-AOC and MDA), immunity (AKP and ACP), and health status (e.g., GPT and GOT) of E. sinensis. (3) Supplementation with 100 mg/kg Axn significantly increased redness (a ∗ ) and Axn concentration in both the ovaries and hepatopancreas, and supplementation with 0.33% or 0.67% DHA oil produced a further significant improvement in Axn concentration when the diets were supplemented with 100 mg/kg of Axn. (4) As for proximate composition, dietary Axn and DHA significantly increased the deposition of total lipids and triacylglycerol in the hepatopancreas. As expected, the crabs fed diets with DHA supplementation showed an increase in the DHA percentage and DHA/EPA ratio in the ovaries and hepatopancreas. In conclusion, dietary Axn and DHA oil had positive effects on ovarian development in E. sinensis females. The optimal combination of dietary Axn and DHA oil was determined to be approximately 100 mg/kg and 0.33%, respectively, for this species during ovarian maturation.

16S rRNA gene sequencing analysis reveals an imbalance in the intestinal flora of Eriocheir sinensis with hepatopancreatic necrosis disease

Hepatopancreas necrosis disease (HPND) is a highly fatal disease that first appeared in Jiangsu Province, China, in 2015, and later spread to many other provinces, which had a severe impact on the culture of Chinese mitten crab (Eriocheir sinensis). Here, changes in the intestinal flora of healthy and HPND-affected Chinese mitten crabs were compared via 16S rRNA sequencing. Our findings indicated that Firmicutes, Bacteroidota, and Proteobacteria were the three dominant phyla in both healthy and HPND-affected crabs and exhibited no significant differences in α-diversity (richness p = 0.0892; evenness and diversity p = 0.0630). Furthermore, there were no significant changes in the abundance of Proteobacteria between the experimental groups. However, the abundance of Bacteroidota in the HPND group was significantly higher than that of the control group (HPND: 30.12%, Control: 16.60%), whereas the abundance of Firmicutes was significantly lower (HPND: 29.90%, Control: 50.55%). At the genus level, the abundance of Candidatus Bacilloplasma, Desulfovibrio, Bacteroides, and Aeromonas also differed significantly between groups (P < 0.05). Collectively, our study confirms an imbalance in the gut microbiota of Chinese mitten crabs with HPND and we speculate that this alteration may affect the metabolism and immune function of these organisms. Furthermore, we suspect that the structural changes in the intestinal flora of sick crabs observed in our study may be related to HPND.

Preference for Shelters at Different Developmental Stages of Chinese Mitten Crab (Eriocheir sinensis).

Simple SummaryShelter is closely correlated with growth and development of aquatic crustaceans. Aquatic crustaceans often prefer to live in shelters to forage and avoid predators. In this study, Chinese Mitten Crabs (Eriocheir sinensis) at different developmental stages were selected to analyze preference for shelters. These results indicated that juvenile crabs had a significant preference for grass; button-sized crabs preferred to hide in mud; and the favorite shelters for parent crabs were rocks. Moreover, light, size, feeding habit, predation and molting were critical factors that affect the preference for shelters of E. sinensis.A shelter is a good habitat for aquatic organisms, which could aid in avoiding cannibalism and facilitate predation. Chinese Mitten Crab (Eriocheir sinensis) is an important aquaculture species with troglodytism and nocturnal habit. To clarify the preference for shelters at different developmental stages of E. sinensis, different shelters (mud, sand, grass and rocks) were selected for comparison. These results indicated that juvenile crabs had a significant preference for grass; button-sized crabs preferred to hide in mud; and the favorite shelters for parent crabs were rocks, followed by mud. E. sinensis in three stages all showed concealing behavior. The concealing behavior of juvenile crabs was the most significant, followed by button-sized and parent crabs. Additionally, E. sinensis held a low hiding rate at night but a high hiding rate during the daytime due to nocturnal habits. These findings will help to better understand the habits of E. sinensis and provide a reference for resource restoration, habitat construction and the restoration of E. sinensis.

Shift and interaction of intestinal bacterial community in juvenile Chinese mitten crab Eriocheir sinensis upon astaxanthin feeding

Intestinal bacterial communities of juvenile Chinese mitten crab Eriocheir sinensis are investigated for the effects of dietary supplementation with different amounts of micro-algal astaxanthin (0, 30, 60, 90, and 120 mg/kg dry diet) and for the correlation to crab hemolymph antioxidant capacity and immunity. Comprehensively analyzing of bacterial 16S rRNA gene amplicons showed that astaxanthin supplement, particularly of 90 mg/kg, appeared to enrich especially the number of Bacteroidetes members, albeit not significantly, increased the relative abundance of Dysgonomonas sp. (OTU1156), and significantly decreased the relative abundance of Jinshanibacter sp. (OTU1324) (P < 0.05). Both Dysgonomonas sp. (OTU1156) and Jinshanibacter sp. (OTU1324) are dominant and native bacterial lineages, present in neither the farming water nor feed. The Dysgonomonas sp. (OTU1156) are probably probiotics involving the digesting of food rich in plant matter, while the Jinshanibacter sp. (OTU1324) are potential parasitic/pathogenic bacteria. Intestinal bacterial communities were improved for the metabolic capacity by astaxanthin, such as the ability to digest xenobiotics, which significantly correlates with the total antioxidant capacity (P < 0.05) of crab hemolymph. These findings contribute to better understanding of the mutual-interaction among astaxanthin, gut bacterial community structure, and hemolymph antioxidant capability and immunity, and shed light on the health and disease-resistance aquaculture of crabs.

Lipid metabolism, immune and apoptosis transcriptomic responses of the hepatopancreas of Chinese mitten crab to the exposure to microcystin-LR

Global warming is favouring the incidence, intensity and duration of harmful cyanobacterial blooms. Microcystin-LR (MC-LR), a hepatotoxic agent, is produced during cyanobacterial blooms. To understand the molecular mechanisms of acute hepatotoxic effect of low doses of MC-LR in crab, we examined differentially expressed genes in samples of the hepatopancreas of Chinese mitten crab (Eriocheir sinensis) collected in 48 h after injections of MC-LR at doses of 0, 25, 50, and 75 µg/kg. The results revealed that MC-LR induced changes in corresponding gene led to the accumulation of triglycerides. MC-LR exposure affected sterol metabolism. Apoptosis-related genes such as Fas-L, Bcl-XL, Cytc, AiF, p53, PERK, calpain, CASP2, CASP7, α-tubulin, PARP, GF, G12, and PKC were upregulated. Conversely, expression levels of CASP10 and ASK1 were downregulated. Genes related to the regulation of actin cytoskeleton (Rho, ROCK, MLCP, MLC, PAK, and PFN) were upregulated. Further, expression levels of genes encoding fatty acid elongation-related enzymes were upregulated, but the expression of genes related to fatty acid synthesis was slightly down regulated. Taken together, these results demonstrated the hepatic toxicity and molecular mechanisms of changes in lipid metabolism, immune and apoptosis in Chinese mitten crab under the MC-LR-induced stress, which is the first report on crabs and performs a comprehensive analysis and a new insight of the molecular toxicological responses in crabs.

Gut Microbiome Succession in Chinese Mitten Crab Eriocheir sinensis During Seawater-Freshwater Migration.

Biological migration is usually associated with disturbances and environmental changes that are key drivers in determining the diversity, community compositions, and function of gut microbiome. However, little is known about how gut microbiome is affected by disturbance such as salinity changes during migration from seawater to freshwater. Here, we tracked the gut microbiome succession of Chinese mitten crabs (Eriocheir sinensis) during their migrations from seawater to freshwater and afterward using 16S rDNA sequencing for 127 days, and explored the temporal patterns in microbial diversity and the underlying environmental factors. The species richness of gut microbiome showed a hump-shaped trend over time during seawater–freshwater migration. The community dissimilarities of gut microbiome increased significantly with day change. The turnover rate of gut microbiome community was higher during seawater–freshwater transition (1–5 days) than that in later freshwater conditions. Salinity was the major factor leading to the alpha diversity and community dissimilarity of gut microbiome during seawater–freshwater transition, while the host selection showed dominant effects during freshwater stage. The transitivity, connectivity, and average clustering coefficient of gut microbial co-occurrence networks showed decreased trends, while modularity increased during seawater–freshwater migration. For metabolic pathways, “Amino Acid Metabolism” and “Lipid Metabolism” were higher during seawater–freshwater transition than in freshwater. This study advances our mechanistic understanding of the assembly and succession of gut microbiota, which provides new insights into the gut ecology of other aquatic animals.

Concentrations and health risk assessment of 24 residual heavy metals in Chinese mitten crab (Eriocheir sinensis)

In this study, a total of 135 Chinese mitten crab (Eriocheir sinensis) samples were collected from four major crab-producing provinces (Jiangsu, Hubei, Anhui, and Liaoning) in China. The content of 24 trace elements in the edible parts of mitten crabs was determined by inductively coupled plasma mass spectrometry (ICP-MS). In addition, the content of trace elements in crab samples collected from different provinces was compared, and the heavy metal levels exceeding the standard were evaluated. Twenty four trace metallic elements were determined in Chinese mitten crab samples. The single factor pollution index (Pi), percentage of provisionally tolerable weekly intake (PTWI), and target hazard quotients (THQ) were used to evaluate the pollution level and food safety of Chinese mitten crabs. The final assessment results of dietary risks led to the health risk assessment accompanying food safety recommendations on Chinese mitten crabs. The overall finding of this study established that Chinese mitten crab aquatic products can be eaten for nutrition; however, attention should be paid on the potential food safety risks of some heavy metals. Moreover, efforts on developing the industrial economy by the local government and peoples’ safety from food risks may also increase the awareness of environmental protection.

Role of peroxinectin in the antibacterial immune response of the Chinese mitten crab, Eriocheir sinensis

To elucidate the antibacterial role of peroxinectin (referred to as PXN) and its molecular mechanism in Chinese mitten crab Eriocheir sinensis, we analyzed the bacterial binding and removal of the peroxinectin recombinant protein in vitro and the interaction of peroxinectin with integrin and CuZn-SOD through GST-pulldown and bimolecular fluorescence complementation methods. Concurrently, the effect of peroxinectin interference on the expression of other immune-related genes was studied using RNA interference. The results showed that the recombinant peroxinectin protein could bind to Bacillus subtilis, Staphylococcus aureus, Aeromonas hydrophila, and Vibrio parahaemolyticus with different affinities in vitro and could eliminate Vibrio parahaemolyticus in vivo. The findings also indicated that peroxinectin could establish interactions with integrin and CuZn-SOD in vitro. Furthermore, 48 h after the injection of the peroxinectin gene siRNA in vivo, the expression of peroxinectin mRNA decreased significantly (P < 0.05), integrin mRNA expression decreased by 16.8%, and CuZn-SOD mRNA expression decreased by 62.84% (P < 0.01). The expression levels of Dorsal, GPx, GST, PPAF, and Relish (P < 0.01), as well as that of lectin (P < 0.001) were significantly decreased. When peroxinectin siRNA was injected in vivo for 48 h and Aeromonas hydrophila was injected into mitten crabs, the expression of immune-related genes significantly increased. All data indicate that the recombinant peroxinectin protein in Chinese mitten crabs can recognize and bind different bacteria and promote the elimination of Vibrio parahaemolyticus from the body. Furthermore, peroxinectin may establish interactions with integrin and CuZn-SOD to activate the expression of related immune genes to elicit responses to bacterial infections and achieve immune protection.