Chinese Mitten Crab Eriocheir Sinensis Research Articles

Untargeted LC–MS metabolomics reveals the metabolic responses in the Eriocheir sinensis gills exposed to salinity and alkalinity stress

In recent years, saline–alkaline aquaculture development has become an important measure for China to expand its fishery development space to ensure food safety. Previous studies have verified that salinity and alkalinity positively influence the quality of Chinese mitten crabs (Eriocheir sinensis). However, the regulatory mechanism of E. sinensis endures saline–alkaline stress which remains obscure. This study investigated the metabolic changes in puberty-molting E. sinensis gills exposed to freshwater (FW), sodium chloride salinity of 5 ppt (SW), and carbonate alkalinity 10.00 mmol/L (AW) for 50 days using untargeted liquid chromatography-mass spectrometry metabolomics (LC–MS). A total of 5802 (positive-ion mode) and 6520 (negative-ion mode) peaks were extracted by LC–MS, respectively. A total of 188 (50 upregulated and 138 downregulated), 141 (94 upregulated and 47 downregulated), and 130 (87 upregulated and 43 downregulated) significantly regulated metabolites (SRMs) were observed in the FW–SW, FW–AW, and SW–AW treatments, respectively, wherein 42 generic SRMs were also found by Venn diagram analysis. Seven of the top 10 SRMs with the highest (variable importance in projection) VIP values were similarly identified in FW–SW and SW–AW. Integrated analysis of key metabolic pathways revealed glycerophospholipid, choline in cancer, phenylalanine, and butanoate metabolism. Overall, significant differences were observed in the metabolites and key metabolic pathways of E. sinensis gill exposed to salinity and alkalinity stress. These results will be helpful in understanding the environmental adaptability of aquatic crustaceans to saline–alkaline water.

Effects of dietary methionine and taurine interaction on growth performance, the profiles of amino acids, and protein metabolism of Chinese mitten crab, Eriocheir sinensis

The purpose of this study is to explore the interaction between dietary methionine and taurine levels on growth performance, the profiles of amino acids, protein metabolism, and how taurine spares methionine of Chinese mitten crab (Eriocheir sinensis). The crabs were divided into six groups which were fed six diets formulated with two Tau levels (0 and 0.4%) and three Met levels (0.6%, 0.9% and 1.2%). The results showed that the weight gain rate and specific growth rate were the highest in the crabs fed 0.4% Tau and 0.6% Met. Crabs fed 1.2% Met had the highest survival rate and lowest feed conversion ratio. Furthermore, the hepatopancreas and muscle amino acid content were significantly influenced by the interactive effects of Met and Tau (P < 0.05). Moreover, interactive effects of dietary methionine and taurine were significantly observed in the expressions of amino acid metabolism-related genes (P < 0.05). Additionally, crabs fed 1.2% Met and 0% Tau had the highest activities of cysteine decarboxylase (CSD) and cysteine dioxygenase (CDO). In conclusion, the addition of appropriate amount of taurine to the diet can reduce the requirement of methionine for Chinese mitten crab by regulating the activities of CSD and CDO. At the same time, the addition of methionine and taurine could affect the amino acids metabolism. Therefore, the diet formula of Chinese mitten crab needs to consider the metabolism of sulfur-containing amino acids.

Comparison of Body Characteristics, Carotenoid Composition, and Nutritional Quality of Chinese Mitten Crab (Eriocheir sinensis) with Different Hepatopancreas Redness.

In this study, we investigated the body characteristics, carotenoid composition, and nutritional quality of Eriocheir sinensis with different hepatopancreas redness (a*). We distributed the crabs into two groups based on the hepatopancreas a* values and compared their body characteristics, chroma, carotenoid composition, and protein, lipid, total sugar, amino acid, and fatty acid content via paired t-test. The results revealed that the relationships between hepatopancreas a* values and crab quality are sex specific. In female crabs, the differences in nutritional characteristics were evident mainly in the hepatopancreases and ovaries. In the redder hepatopancreases, the content of zeaxanthin and β-carotene increased, and the levels of C22:6n3 and C20:5n3 decreased (p < 0.05). In the ovaries, the content of astaxanthin, canthaxanthin, β-carotene, umami, and sweet amino acids were lower in the redder hepatopancreas crabs (p < 0.05). In male crabs, there were positive relationships between hepatopancreas a* and amino acid and fatty acid content. The content of leucine, arginine, and total umami amino acids in muscles and of unsaturated fatty acids and n-6 polyunsaturated fatty acids in hepatopancreases and testicles increased with increasing hepatopancreas a* values (p < 0.05). Therefore, the redder the hepatopancreas, the higher the nutritional quality of male crabs.

Protein and lipid nutrition in crabs

AbstractUnderstanding the nutrition of crabs has a key role in ensuring the success and sustainability of their culture, as providing a well‐balanced, cost‐effective and sustainable diet that ensures the survival, growth and health of crabs is crucial. The present review is the first to focus primarily on the current state of knowledge of the nutrient requirements and related nutritional aspects in farmed crab species. The most common farmed and studied crabs are the Chinese mitten crab (Eriocheir sinensis Milne‐Edwards, 1853), giant mud crab (Scylla serrata Forsskal, 1775), green mud crab (Scylla paramamosain Estampador, 1949) and swimming crab (Portunus trituberculatus Miers, 1876). The article reviews how levels of dietary protein and lipid, the two most important and expensive macronutrient ingredients for most marine animals, directly affect reproduction, growth performance and survival of crabs, and the important impacts they have on immune response and antioxidant capacity. Furthermore, essential amino acids, and essential fatty acids, especially the long‐chain polyunsaturated fatty acids, as well as key lipid classes such as cholesterol and phospholipid will be discussed in terms of dietary requirements. Nutrient digestibility is a crucial method to determine protein quality, and studies on this topic in crabs were covered. The replacement of fishmeal and fish oil, as the predominant ingredients traditionally used in aquafeeds for marine animals, with more sustainable alternatives in diet formulations for crabs are also discussed. Modern ‘omics’ studies and high‐throughput technologies as fast‐growing approaches in protein and lipid research are also covered. Crabs generally require approximately 35%–50% protein, 5%–10% lipid, ~2.5% arginine, ~2.5% lysine, 1.5%–2.5% phenylalanine, 2.2% leucine, 0.7% tryptophan, 0.7% taurine, 1%–2% each of eicosapentaenoic acid, docosahexaenoic acid and arachidonic acid, 1% cholesterol and ~2% phospholipid in their diets.

Cardiac Transcriptome and Histology of the Heart of the Male Chinese Mitten Crab (Eriocheir sinensis) under High-Temperature Stress

High temperatures are important environmental stressors affecting the metabolism, growth, immunity, and mortality of Chinese mitten crabs (Eriocheir sinensis). In this study, Chinese mitten crabs were divided into two groups and exposed to temperatures of 35 °C (thermal stress group) or 25 °C (control group) for 24 h, and the transcriptome of the heart was analyzed. There were 4007 differentially expressed genes (DEGs) between the thermal stress and the control groups, including 2660 upregulated and 1347 downregulated genes. Heat shock proteins (HSPs) and transcription factors (TFs) were temperature-sensitive DEGs in Chinese mitten crabs. DEGs mainly focused on protein processing in the endoplasmic reticulum, ribosome biogenesis, glycine, serine, and threonine metabolism, protein export, and insect hormone biosynthesis pathways. A total of 28,916 SSRs and 59 TF families, including 851 TFs, were detected among all unigenes of E. sinensis transcripts. The qRT-PCR results for the HSPs and apoptotic DEGs from the heart exhibited the same trends as those in the E. sinensis transcriptome data. Results of light microscopy analyzing histological sections of the heart indicated that most myocardial fibers were lysed, and the number of nuclei and the connective tissue contents between the myocardial layers were both reduced following 35 °C exposure for 24 h.

Effects of dietary L-tryptophan supplementation on agonistic behavior, feeding behavior, growth performance, and nutritional composition of the Chinese mitten crab (Eriocheir sinensis)

In the pond culture of Chinese mitten crabs (Eriocheir sinensis), high stocking densities usually increase the frequency of agonistic behavior, which can directly impact crab integrity, survival, and growth and result in economic losses. We hoped to reduce agonistic behavior by adding additives to feed. In this study, we first observed the agonistic behavior of E. sinensis in 5 molting periods (from first molting to puberty molting) during the adult grow-out stage. Then, we assessed the effects of L-TRP as a feed additive on the agonistic behavior of juvenile, precocious, subadult, and adult crabs. Finally, we performed 106 days of cage culture to assess the effects of L-TRP on feeding behavior, animal vitality, growth performance, and nutritional composition. The results showed that the intensity of agonistic behavior was significantly higher after puberty molting than in other molting periods during the adult grow-out stage. Moreover, L-TRP supplementation inhibited the agonistic behavior of juvenile, subadult, and adult crabs, but it did not affect the precocious crabs. During cage culture, L-TRP significantly improved crab vitality after 3 weeks but not after 6 and 9 weeks, but it reduced the ingestion rate after 9 weeks. Moreover, the L-TRP group showed a significant increase in the weight gain rate and specific growth rate after the fourth molting. After 106 days of culture, the content of proline and fatty acids in the muscle decreased significantly after L-TRP diet supplementation. Some long-chain polyunsaturated fatty acids also decreased significantly in the hepatopancreas. However, we must focus on the adverse effects of L-TRP on Pro and fatty acid composition. Further research is required on the balance between inhibition of agonistic behavior and effects of L-TRP on the nutritional quality of E. sinensis.

Exposure to nanopolystyrene and phoxim at ambient concentrations causes oxidative stress and inflammation in the intestines of the Chinese mitten crab (Eriocheir sinensis)

Nanopolystyrene (NP) and phoxim (PHO) are common environmental pollutants in aquatic systems. We evaluated the toxic effects of exposure to ambient concentrations of NP and/or PHO in the intestines of the Chinese mitten crab (Eriocheir sinensis). Our study showed that histopathological changes were observed in the intestines. Specifically, NP and/or PHO exposure increased intraepithelial lymphocytes. Furthermore, NP and/or PHO exposure induced oxidative stress, as evidenced by a significant decrease in superoxide dismutase activity (SOD), peroxidase activity (POD), and total antioxidant capacity (T-AOC). Pro-inflammatory gene expression and transcriptome analysis demonstrated that NP and/or PHO exposure induced the intestinal inflammatory response. Transcriptome results showed that NP and/or PHO exposure upregulated the NF-κB signaling pathway, which is considered a key pathway in the inflammatory response. Additionally, the expression of pro-inflammatory genes significantly increased after a single exposure to NP or PHO, but it exhibited a significant decrease after the co-exposure. The downregulation of these genes in the co-exposure group likely suggested that the co-exposure mitigated intestinal inflammation response in E. sinensis. Collectively, our findings mainly showed that NP and/or PHO exposure at ambient concentrations induces oxidative stress and inflammatory response in the intestines of E. sinensis.

The interaction between lipid and vitamin D3 impacts lipid metabolism and innate immunity in Chinese mitten crabs Eriocheir sinensis

As a fat-soluble vitamin, vitamin D3 relies on fat to perform its biological function, affecting lipid metabolism and innate immunity. This study used different percentages of lipid and vitamin D3 diets to evaluate the synergistic effects on the growth, lipid metabolism and immunity of juvenile Eriocheir sinensis (5.83 ± 0.01 g) for 56 days, including low lipid (LL, 1.5%) and normal lipid (NL, 7.5%) and three levels of vitamin D3: low (LVD, 0 IU/kg), medium (MVD, 9000 IU/kg) and high (HVD, 27,000, IU/kg). The synergistic effect of lipid and vitamin D3 was not significant on growth but significant on ash content, total protein, hepatopancreas lipid content, hemolymph 1α,25-hydroxy vitamin D3 [1α,25(OH)2D3] content, hepatopancreas lipolysis and synthesis genes. Crabs fed normal lipid (7.5%) and medium vitamin D3 (9000 IU/kg) had the highest hepatopancreas index, hemolymph 1α,25(OH)2D3 content, antibacterial ability, immune-related genes and hepatopancreatic lipid synthesis genes expression, but down-regulated the lipolysis genes expression. In contrast, crabs fed diets with low lipid percentage (1.5%) had low growth performance, hemolymph 1α,25(OH)2D3, mRNA levels of lipid synthesis genes, antibacterial ability and immune-related gene expression. At the 1.5% lipid level, excessive or insufficient vitamin D3 supplementation led to the obstruction of ash and protein deposition, reduced growth and molting, aggravated the reduction in antioxidant capacity, hindered antimicrobial peptide gene expression and reduced innate immunity, and resulted in abnormal lipid accumulation and the risk of oxidative stress. This study suggests that diets' lipid and vitamin D3 percentage can enhance antioxidant capacity, lipid metabolism and innate immunity in E. sinensis. A low lipid diet can cause growth retardation, reduce antioxidant capacity and innate immunity, and enhance lipid metabolism disorder.

The P4' Peptide-Carrying Bacillus subtilis in Cottonseed Meal Improves the Chinese Mitten Crab Eriocheir sinensis Innate Immunity, Redox Defense, and Growth Performance.

This study developed a recombinant Bacillus subtilis to carry the LGSPDVIVIR peptide (cmP4) isolated from the hydrolyzed products of cottonseed meal with excellent antioxidant and immune-enhancing properties in vitro. It was carried as a tandem of five cmP4 peptides (cmP4') to be stably expressed on a large scale. Then, its effectiveness was evaluated in Chinese mitten crab (Eriocheir sinensis) based on growth performance, redox defense, and innate immunity. A total of 280 crabs (mean body weight: 41.40 ± 0.14) were randomly assigned to seven diets including a control one (without B. subtilis) and six experimental ones with different doses (107,108, and 109 CFU/kg) of unmodified and recombinant B. subtilis, respectively, for 12 weeks. Each diet was tested in four tanks of crabs (10/tank). In terms of bacterial dosages, the final weight (FW), weight gain (WG), hemolymph and hepatopancreatic activities of superoxide dismutase (SOD), catalase (CAT), lysosome (LZM), acid phosphatase (ACP) and alkaline phosphatase (AKP), and hepatopancreatic transcriptions of cat, mitochondrial manganese superoxide dismutase (mtmnsod), thioredoxin-1 (trx1), and prophenoloxidase (propo) all increased significantly with increasing B. subtilis dosages, while hemolymph and hepatopancreatic malondialdehyde (MDA) content and the transcriptions of toll like receptors (tlrs), NF-κB-like transcription factor (relish), and lipopolysaccharide-induced TNF-α factor (litaf) all decreased remarkably. In terms of bacterial species, the recombinant B. subtilis group obtained significantly high values of FW, WG, hemolymph, and hepatopancreatic activities of SOD, CAT, LZM, ACP, and AKP, and the transcriptions of mtmnsod, peroxiredoxin 6 (prx6), and propo compared with the unmodified B. subtilis, while opposite results were noted in hemolymph and hepatopancreatic MDA content and the transcriptions of tlrs, relish, and litaf. These results indicated that dietary supplementation with 109 CFU/kg of recombinant B. subtilis can improve the growth performance, redox defense, and nonspecific immunity of E. sinensis.

Assessing the ecotoxicity of florfenicol exposure at environmental levels: A case study of histology, apoptosis and microbiota in hepatopancreas of Eriocheir sinensis

The intensification of production practices in the aquaculture industry has led to the indiscriminate use of antibiotics to combat diseases and reduce costs, which has resulted in environmental pollution, posing serious threats to aquaculture sustainability and food safety. However, the toxic effect of florfenicol (FF) exposure on the hepatopancreas of crustaceans remains unclear. Herein, by employing Chinese mitten crab (Eriocheir sinensis) as subjects to investigate the toxic effects on histopathology, oxidative stress, apoptosis and microbiota of hepatopancreas under environment-relevant (0.5 and 5 μg/L), and extreme concentrations (50 μg/L) of FF. Our results revealed that the damage of hepatopancreas tissue structure caused by FF exposure in a dose-and time-dependent manner. Combined with the increased expression of apoptosis-related genes (Caspase 3, Caspase 8, p53, Bax and Bcl-2) at mRNA and protein levels, activation of catalase (CAT) and superoxide dismutase (SOD), and malondialdehyde (MDA) accumulation, FF exposure also induced oxidative stress, and apoptosis in hepatopancreas. Interestingly, 7 days exposure triggered more pronounced toxic effect in crabs than 14 days under environment-relevant FF concentration. Integrated biomarker response version 2 (IBRv2) index indicated that 14 days FF exposure under extreme concentration has serious toxicity effect on crabs. Furthermore, 14 days exposure to FF changed the diversity and composition of hepatopancreas microbiota leading remarkable increase of pathogenic microorganism Spirochaetes following exposure to 50 μg/L of FF. Taken together, our study explained potential mechanism of FF toxicity on hepatopancreas of crustaceans, and provided a reference for the concentration of FF to be used in culture of Chinese mitten crab.

Effects of dietary supplementation with Haematococcus pluvialis on the growth, antioxidantase activities, and gut microbiota of Chinese mitten crab (Eriocheir sinensis)

AbstractThe Chinese mitten crab (Eriocheir sinensis) is bred extensively in Eastern and Northern China and faces a series of problems such as frequent diseases, germplasm degradation, and declining benefits, which have appeared to seriously affect the sustainable development of the cultivation industry. Haematococcus pluvialis, a type of unicellular green algae, have been proven to be the suitable dietary supplementation in crustacean feeds. After 14 days of feeding with 5% dietary supplementation with Haematococcus pluvialis powder, the growth, antioxidantase activities, and gut microbiota of E. sinensis were analyzed. The results indicated that H. pluvialis powder could significantly improve growth indicators including weight gain rate (WGR) and specific growth rate (SGR) of E. sinensis (p &lt; 0.05). The levels of superoxide dismutase (SOD) and catalase (CAT) declined, while that of phenoloxidase (PO) kept rising under the treatment of H. pluvialis powder. Moreover, alkaline phosphatase (AKP) activity dropped initially and then increased. No significant differences in the Simpson index and Chao1 index in the control and H. pluvialis powder treatment were observed (p &gt; 0.05). Although the dominant microbiota in the crab gut were not affected significantly by H. pluvialis powder, significant differences in the relative abundance of the dominant phyla between the control and H. pluvialis powder treatment groups were observed (p &lt; 0.05). Furthermore, the relative abundance of Firmicutes and Candidatus_Bacilloplasma, which play an important role in the life activities of E. sinensis, were significantly higher in the group treated by H. pluvialis powder than in the control (p &lt; 0.05). Therefore, the H. pluvialis powder could be potentially used not only as a rapid fattening regulator, but also to improve the immunity and metabolic capacity of E. sinensis.

Effects of feed protein levels on Chinese mitten crabs (Eriocheir sinensis) under the rice-crab co-culture model: Performance, nutrient composition, antioxidant capacity and immunity

The Chinese mitten crab is an important aquaculture product in China. Currently, rice-crab co-culture is a novel model that can realize positive interactions. The feed for Chinese mitten crabs cultured in rice fields should be distinguished from other modes, since their culture environment is unique. Therefore, this study designed three experimental groups that were fed 15% (RC1), 25% (RC2), and 35% (RC3) protein, with a natural bait group (RC0) without artificial feeding as the control. The protein nutritional requirements of Chinese mitten crabs in a rice-crab co-culture model were investigated by exploring the indicators of growth performance, nutrient composition, immunity, antioxidant capacity, and economic benefits of different groups. Through a comprehensive discussion of one-way analysis of variance and regression analysis of the data, we obtained the following results: feeds with high-level protein improved the growth performance, quality, and economic benefits of Chinese mitten crabs and reduced their exposure to oxidative stress. Specifically, the contents of major nutrients and flavor-presenting substances, such as free amino acids (FAA), nucleotides, and essential amino acids (EAA), in the edible parts of female crabs in the 35% protein group were significantly higher than those in all other groups. Male crabs fed 25% − 28.08% protein diets showed higher production performance and FAA content. In conclusion, the optimal dietary protein levels for male and female crabs reared in rice fields are different: they are 35% for females, and at least 25% for males. Therefore, for actual crab production, male and female crabs could be cultured separately using different protein baits to reduce bait costs and achieve green and sustainable development.

Dietary N-carbamylglutamate (NCG) supplementation improves the survival, digestive and immunological parameters by promoting ammonia excretion in Chinese mitten crab (Eriocheir sinensis), under ammonia nitrogen stress

Ammonia nitrogen is one of the most common environmental stress factors in aquaculture. The aim of this experiment was to evaluate the effects of ammonia nitrogen stress on ammonia metabolism, digestion and immune function as well as the protective effects of dietary N-carbamylglutamate (NCG) in the Chinese mitten crab (Eriocheir sinensis). Two feeds were used, namely a control feed (regular commercial feed) and an NCG feed (NCG (302.96 ± 4.07) mg/kg added). Subsequently, animals fed by these two feeds were exposed to 30 mg/L or 60 mg/L ammonia nitrogen stress (named A30 or A60) for 21 days, respectively. The rate of hemolymph ammonia excretion was significantly increased in NCG group compared to C (control) group (P < 0.05). Hemolymph ammonia levels were significantly lower in NCG A30 (NCG feed and A30) and NCG A60 (NCG feed and A60) groups compared to A30 (control feed and A30) and A60 (control feed and A60) groups (P < 0.05). Glutamate dehydrogenase and glutamine synthetase activities in the gills and hepatopancreas of NCG A60 group were significantly increased compared with the A60 group, which promoted glutamine synthesis (P < 0.05). The cumulative mortality rate of Eriocheir sinensis in NCG A30 and NCG A60 groups were effectively reduced (P < 0.05). The arginine levels of hepatopancreas were significantly increased in NCG A60 group (P < 0.05). Under ammonia nitrogen stress, NCG significantly increased the activities of trypsin, pepsin, lipase and α-Amylase in NCG feed group, and promoted feeding (P < 0.05). In hemolymph, hepatopancreas and intestine, NCG significantly increased nitric oxide synthase activity, lysozyme and phenol oxidase activities compared to the ammonia nitrogen stress group (P < 0.05). The results indicated that, NCG added in feed could decelerate the toxic effects of ammonia on Eriocheir sinensis by promoting ammonia excretion and accelerating glutamine and endogenous arginine synthesis by metabolism. Moreover, the activity of digestive enzymes and immune-related enzymes is improved.

Replacement of fish meal with cottonseed protein concentrate in Chinese mitten crab (Eriocheir sinensis): nutrient digestibility, growth performance, free amino acid profile, and expression of genes related to nutrient metabolism

This study aimed to investigate the application of cottonseed protein concentrate (CPC) in Chinese mitten crabs (Eriocheir sinensis). First, the apparent digestibility coefficient (ADC) of CPC, fish meal and soybean meal were compared in crabs (21.72 ± 0.33 g). The protein ADC of CPC was 90.42%, which was significantly higher than that of soybean meal (83.16%) (P < 0.05). The ADC of Phe, Cys and Glu of CPC were significantly higher than those of fish meal, while the ADC of Ile, Leu, Lys, Met, Thr and Ala of CPC were significantly lower (P < 0.05). Second, we investigated the effects of fish meal substitution by CPC on growth performance, free amino acid profile, and expression of genes related to nutrient metabolism in crabs. Six diets were formulated by replacing 0%, 15%, 30%, 45%, 60% and 75% fish meal with CPC, namely FM, CPC15, CPC30, CPC45, CPC60, and CPC75. A total of 630 crabs (1.68 ± 0.00 g) were randomly divided into 18 tanks (3 tanks per group) and fed 3 times daily for 9 weeks. Results showed that CPC75 group significantly reduced growth performance, feed conversion efficiency, and free Ile, Leu, Lys, Met, and Thr contents in muscle (P < 0.05). The contents of free amino acids (Arg, His, Ile, Leu, Lys, Met, Phe, Thr, Val, Ala, Cys, Glu, Gly, Ser and Tyr) in hepatopancreas decreased linearly with the increase of dietary CPC level (P < 0.05). The substitution of more than 45% fish meal with CPC significantly decreased the concentration of delicious amino acids (Ala, Glu and Gly) in hepatopancreas (P < 0.05), which might adversely affect crab flavor. The expression of genes related to antioxidant capacity, protein transport, TOR pathway and lipid metabolism was significantly downregulated by increasing dietary CPC level (P < 0.05). In conclusion, based on the quadratic regression analysis of FCR and PER, the optimal replacement levels of fish meal with CPC in crab diet containing 35% fish meal were 32.36% and 35.38%, respectively. It is recommended that Ile, Leu and Thr be supplemented in addition to Met and Lys in the application of CPC.

Impact Analysis of Photoperiodic Disorder on the Eyestalk of Chinese Mitten Crab (Eriocheir sinensis) through High-Throughput Sequencing Technology.

Light is an indispensable factor in the healthy growth of living organisms, and alterations in the photoperiod can have consequences for body homeostasis. The eyestalk is a photosensitive organ that secretes various hormones to regulate the Chinese mitten crab (Eriocheir sinensis). However, the photoperiod-dependent eyestalk patterns of gene expression that may underlie changes in body homeostasis are unknown. In this study, we investigated the molecular mechanisms involved in eyestalk transcriptomic responses in E. sinensis under different photoperiod regimes on days 2, 4, and 6. The photoperiods tested were 12, 24, and 0 h light/day. In total, we obtained 110, 958, 348 clean datasets and detected 1809 differentially expressed genes (DEGs). Genes involved in the crustacean hyperglycemic hormone superfamily and juvenile hormones were observed, which play important roles in gonadal development, growth, and immunity in E. sinensis and may also be involved in photoperiod adaptation. In addition, the MAPK signaling pathway was the only signaling pathway identified in the continuous light group but was absent in the continuous darkness group. We suggest that the MAPK pathway is highly responsive to light input during the subjective night and insensitive to light during the middle of the subjective day. These results provide insight into the molecular mechanisms underlying the effects of photoperiod on the immune regulation of E. sinensis.

The Biochemical Composition and Quality of Adult Chinese Mitten Crab Eriocheir sinensis Reared in Carbonate-Alkalinity Water

Saline–alkaline aquaculture has become an important breakthrough in expanding the space available for aquaculture in China. However, the biochemical composition and quality of Eriocheir sinensis reared in carbonate alkalinity water are still unclear. Therefore, this study investigated the edible yield, coloration, and nutritional and flavor quality of Eriocheir sinensis. A significantly lower gonadosomatic index (GSI), meat yield (MY), and total edible yield (TEY) were detected in intensive pond (IP) samples than those in semi-intensive reed wetland (SIWR) (p &lt; 0.05). Six color parameters in the hepatopancreas (p &lt; 0.05) differed between IP and SIRW. The contents of crude protein and fat in the female hepatopancreas of IP were significantly higher than those in SIRW (p &lt; 0.05). The concentrations of total monounsaturated fatty acids (∑MUFA), total essential fatty acids (∑EFA), and hypocholesterolaemic/hypercholesterolaemic ratio (h/H) in the female edible tissues checked were higher in IP than those in SIRW, with significant differences including ∑MUFA in the hepatopancreas and ovary, ∑EFA in the muscle, and h/H in the ovary (p &lt; 0.05). Higher total free amino acid (∑FAA) contents of muscle were detected in SIRW than that in IP samples. Significantly higher K, Ca, Mg, Fe, and Zn contents in the ovary were detected in SIRW samples compared to IP (p &lt; 0.05). Overall, Eriocheir sinensis reared in carbonate-alkalinity water is an important source of nutrients.

Transcriptome analysis of Chinese mitten crabs (Eriocheir sinensis) gills in response to ammonia stress.

The Chinese mitten crab (Eriocheir sinensis) is an important commercial species in China. E. sinensis is typically farmed in rice-crab symbiosis, as an important ecological farming model. However, E. sinensis is often exposed to a high ammonia environment due to the application of nitrogen fertilizers essential for rice growth. We investigated the molecular mechanisms in the gills of E. sinensis exposed to high ammonia at transcriptional and histological levels. We randomly assigned E. sinensis to two groups (control group, CG; ammonia stress group, AG), and gill samples were excised from the CG and AG groups for histopathological and transcriptome analyses. The histopathological evaluation revealed that ammonia stress damaged the gills of E. sinensis. The transcriptome analysis showed that some essential genes, including Xanthine dehydrogenase (XDH), Ubiquitin C-terminal hydrolase-L3 (UCHL3), O-linked N-acetylglucosamine transferase (OGT), Cathepsin B (CTSB), and Ubiquitin-conjugating enzyme E2 W (UBE2W) changed significantly during ammonia exposure. These genes are related to ammonia detoxification, the immune response, and apoptosis. This study demonstrated the molecular response mechanism of E. sinensis gills to ammonia stress at the transcriptional and histological levels. This study provides insight for further study on the molecular mechanism of ammonia stress in crustaceans and supplies technical support for rice crab symbiosis.

Total body burden of neurotoxicant Hg in Chinese mitten crab (Eriocheir sinensis) - Considerations of distribution and human risk assessment

The Chinese mitten crab (Eriocheir sinensis) is considered one of the 100 most invasive alien species in the world. Despite this, its role in ecosystems, among others, in the trophodynamics of pollutants including mercury, is still not fully understood. Becoming an increasingly important and widespread element of the trophic chain in new areas arouses interest from humans as consumers. Hence it is important to determine the level of contaminants (including Hg) in alien species. In the present study, great attention was paid separately to the soft tissues and hard tissues of the exoskeleton, which may play an important role in the detoxification of the crab's body from toxic Hg. The study was conducted on crabs collected in 2011–2021 in the Vistula Lagoon. Concentrations of total mercury and its forms were carried out using a Direct Mercury Analyzer, DMA-80 (Milestone, Italy). The present study showed that mercury accumulation of the crab's body largely occurred through the gills, followed by the oral route. The distribution of Hg in the crab's organs was related to the trophic origin of the mercury, while halide-bound mercury and semilabile forms from the respiration (filtration) process were redistributed into the crab's exoskeleton. Male crabs, compared to females, had a higher Hg burden on internal organs such as their hepatopancreas and gonads. Hg concentration in hard tissues was closely related to the type of mineralization of the carapace. The elimination of Hg from the muscles and from the hepatopancreas into the carapace was one of the important detoxification processes of the crab's body. Thus, moulting crabs effectively remove Hg protecting its body from the neurotoxin. As a result, a smaller Hg load is biomagnified, making the crab's muscle tissue fit for human consumption. The observed decrease in Hg concentrations from 2011 to 2021, as well as the spatial variability of Hg in the crab's muscles, testify that the crab can serve as a biomonitor for ecosystem changes.

Proteome and gut microbiota analysis of Chinese mitten crab (Eriocheir sinensis) in response to Hepatospora eriocheir infection

In recent years, the Chinese mitten crab (Eriocheir sinensis), which is widely farmed in China, has been frequently affected by Hepatospora eriocheir. The gut response of mitten crabs to H. eriocheir infection is not yet known. The aim of this study was to evaluate the effects of H. eriocheir infection on the gut microbiota and proteome of E. sinensis. In this study, E. sinensis was divided into two groups based on whether it was infected with H. eriocheir using PCR and Calcofluor white staining. Calcofluor white staining revealed that H. eriocheir was massively aggregated in the gut. Proteomic results showed that 3959 proteins were identified. Under a 1.2-fold change threshold, 420 differentially expressed proteins (DEPs) were screened, including 292 upregulated DEPs and 128 downregulated DEPs. Differential protein expression related to apoptosis and energy metabolism increased, while protein expression related to immune and inflammatory responses and cell motility decreased. In addition, the microbiota results showed that alpha diversity tended to increase, and beta diversity indicated significant differences in gut microbiota between the two groups. Bacteroidetes, Proteobacteria, and Firmicutes were the dominant phyla in the E. sinensis gut. Compared with the control group, Bacteroidetes were significantly reduced in the infected group, while Firmicutes and Tenericutes were significantly increased. At the genus level, the abundance of Bacteroides, Flavobacterium, Shewanella and Aeromonas decreased significantly, while Candidatus Bacilloplasma, Dysgonomonas, Tyzzerella_3 and Lactovum increased significantly. Microbial function prediction found that most differentially abundant bacteria were related to metabolism. At the same time, correlation analysis between the proteome and gut microbiota found potential roles of differential bacteria and proteins involved in metabolism and immunity. These findings suggest that H. eriocheir infection can alter the gut microbiota composition and proteome of E. sinensis.

The effects of dietary L-theanine on the growth performance, non-specific immunity, antioxidant status, and intestinal microflora of female Chinese mitten crabs (Eriocheir sinensis)

L-theanine, a non-protein amino acid in tea, has been widely studied as an immune enhancer in poultry, livestock, and rodents. However, no studies have been performed on the application of L-theanine in aquaculture feed. To fill this research gap, we investigated the effects of L-theanine as a feed additive on the growth performance, immune function, antioxidant capacity, and intestinal flora of female Chinese mitten crab (Eriocheir sinensis) using biochemical assays, real-time polymerase chain reaction, and 16 S rRNA gene sequencing. In total, 300 one-year-old female Chinese mitten crabs were randomly divided into treatment groups supplemented with 0 (control), 0.5%, 1.0%, 1.5%, and 2.0% L-theanine (L0–L4, respectively; n = 4 replicates per group with 15 crabs per replicate). After eight weeks, the total edible yield was significantly higher in all treatment groups than in the L0 group (P < 0.05). Furthermore, the muscle yield (both P < 0.01) and hepatopancreas index (P < 0.01 and P < 0.05, respectively) were significantly higher in the L2 and L3 groups than in the L0 group. The gonadosomatic index was also significantly higher in the L2 group than in the L0 group (P < 0.01). Moreover, the hepatopancreas superoxide dismutase, acid phosphatase, total antioxidant capacity, and glutathione peroxidase activities increased, and the malondialdehyde content decreased in the L3 group compared to the L0 group (P < 0.05). Anti-lipopolysaccharide factor (ALF) 2 (i.e., ALF2), Toll-like receptor (i.e., TLR), and myeloid differentiation primary response gene 88 (i.e., Myd88) expression were also significantly up-regulated in the L2, L3, and L4 groups (P <0.01), and ALF1 and mammalian target of rapamycin (i.e., mTOR) expression were significantly up-regulated in the L3 group (P <0.01) compared to the L0 group. Overall, these results suggest that supplementation with 0.5–1.0% L-theanine positively affected the gut microbiota composition of female Chinese mitten crabs, improving their edible fraction, antioxidant capacity, immunity, and gut microbiota abundance.