Eriocheir Sinensis Research Articles

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.

Multi-omics characterization and identification of small non-coding RNAs in Spiroplasma eriocheiris

Spiroplasma eriocheiris is the major pathogen in the aquaculture shrimp and crab tremor disease; its infection causes heavy losses in aquaculture. Previous investigations concentrated on how the host responds to S. eriocheiris infection, with little known on the regulation of virulence and pathogenesis by the bacteria themselves. A body of increasing evidence shows that bacterial small noncoding RNAs (sRNAs) play a crucial part in regulating bacterial virulence and pathogenesis; however, whether there are some sRNAs in S. eriocheiris and how those sRNAs regulate virulence and pathogenesis are still unclear. This study analyzed multi-omics data integration to identify the potential sRNAs and their mediated regulatory network in S. eriocheiris. First, through an integration analysis of the public genomic and transcriptomic data, 54 potential sRNAs were identified in S. eriocheiris with a 50–250 nt length distribution and the base composition mainly AT. Next, sRNA profiling of the in vitro logarithmic and decline phase of S. eriocheiris, as well as the early and onset stage of infection in Eriocheir sinensis, was performed, showing that 4 sRNAs (SR01, SR05, SR08, and S04) were both down-regulated in the logarithmic and the onset stage of infection. Subsequently, integrated with sRNAs target gene prediction and target gene expression analysis, a regulatory network composed of four sRNAs and 96 target genes was constructed. Last, an RNA pull-down experiment was performed on the SR01, which exhibited the highest abundance and the highest number of target genes, resulting in 37 highly credible target genes with multiple genes related to bacterial virulence, such as GTPases and virulence factor coding genes. Collectively, this study identified the sRNAs in S. eriocheiris and revealed their mediated regulatory network for regulating virulence and pathogenesis, thus paving a new avenue for disease prevention and control in aquaculture.

Comparative study on growth performance and edible portion nutritional composition of male Eriocheir sinensis at different growth stages in rice-crab culture systems

Currently, there is a lack of data related to the growth and development regulations of male Eriocheir sinensis (E.sinensis) in rice field in northern China, which prevents timely adjustment of the nutritional structure of the feed. This has led to the poor quality of male E.sinensis, which has seriously constrained the cultivation of rice crab. Therefore, the purpose of this experiment was to study the growth, development and nutritional composition of male E.sinensis in rice field. Tissue samples from male E.sinensis were randomly collected on the 0, 15, 31, 46 and 62 days of culture for detection. The results showed that the growth performance of male E.sinensis was faster from 31 to 46 days. The levels of crude protein, crude lipid and EAA in hepatopancreas decreased from 46 to 62 days, whereas gonadal changes were not significant. The PUFA levels of muscle, hepatopancreas and gonad decreased in varying degrees from 46 to 62 days. To sum up, nutrients in hepatopancreas and gonads of male E.sinensis accumulated rapidly from July 15 to August 30. From August 30 to September 15, the nutritional quality of hepatopancreas and gonad of male E.sinensis decreased.

Involvement of Histone Acetyltransferase 1 (HAT1) in the Spermatogenesis of Non-Condensed Nuclear Sperm in Chinese Mitten Crab, Eriocheir sinensis.

Chinese mitten crab, Eriocheir sinensis, is a decapod crustacean with a special, non-condensated nucleus in the sperm. Studies have shown that the nuclear compact state of male germ cells during the spermatogenesis is closely related to histone modification. To explore the possible role of histone acetyltransferase 1 (HAT1) in the chromatin organization during the E. sinensis spermatogenesis, we took the testis tissues of both adult and juvenile crabs as the materials of study and analyzed the biological functions of HAT1 by whole transcriptome sequencing and bioinformatics, then further analyzed the expression and distribution of HAT1 using the methods of RT-qRCR, western blotting, and immunofluorescence location. The results showed that HAT1 is an alkaline-unstable hydrophilic protein. Itwaspredictedtointeractwith a variety of histones and chromosome assembly proteins, including Asf1b, Chaf1b, and Hist1h3f, and is involved in many biological functions pertaining to chromatin dynamics such as chromatin organization, DNAdependent nucleosome assembly, DNA conformational changes, and so on. HAT1 was up-regulated in the adult testes compared to the juvenile (n = 3, P < 0.05). HAT1 was mainly located in the nuclei of male germ cells of E. sinensis. As spermatogenesis proceeded, the expression of HAT1 decreased and evendisappearedinthenuclei (n = 3, P < 0.05). HAT1 is an important player in histone acetylation, which facilitates chromatin alteration in a three-dimensional conformation. The expression of HAT1 in different male germ cells might indicate the chromatin dynamics at the diversity stages of spermatogenesis. The high expression of HAT1 at the early stages of E. sinensis spermatogenesis hints the active involvement in chromatin organization, while its progressively reduced expression accompanied by the progression of spermatogenesis suggests a relatively gradual stabilization and stereotyping of chromatin. As for the disappearance of HAT1 in mature sperm with non-condensed nuclei, the reduction in histones targeted by HAT1 or histone acetylation may be an important initiator.

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.

KIF2A Upregulates PI3K/AKT Signaling through Polo-like Kinase 1 (PLK1) to Affect the Proliferation and Apoptosis Levels of Eriocheir sinensis Spermatogenic Cells.

E. sinensis is an animal model for studying the reproduction and development of crustaceans. In this study, we knocked down the Es-Kif2a gene by injecting dsRNA into E. sinensis and inhibited Es-Plk1 gene expression by injecting PLK1 inhibitor BI6727 into E. sinensis. Then, the cell proliferation level, apoptosis level, and PI3K/AKT signaling expression level were detected. Our results showed that the proliferation level of spermatogenic cells decreased, while the apoptosis level increased after Es-Kif2a knockdown or Es-Plk1 inhibition. In order to verify whether these changes are caused by regulating the PI3K/AKT pathway, we detected the expression of PI3K and AKT proteins after Es-Kif2a knockdown or Es-Plk1 inhibition. Western Blot showed that in both the Es-Kif2a knockdown group and the Es-Plk1 inhibition group, the expression of PI3K and AKT proteins decreased. In addition, immunofluorescence showed that Es-KIF2A and Es-PLK1 proteins were co-localized during E. sinensis spermatogenesis. To further explore the upstream and downstream relationship between Es-KIF2A and Es-PLK1, we detected the expression level of Es-PLK1 after Es-Kif2a knockdown as well as the expression level of Es-KIF2A after Es-Plk1 inhibition. Western Blot showed that the expression of Es-PLK1 decreased after Es-Kif2a knockdown, while there was no significant change of Es-KIF2A after Es-Plk1 inhibition, indicating that Es-PLK1 may be a downstream factor of Es-KIF2A. Taken together, these results suggest that Es-KIF2A upregulates the PI3K/AKT signaling pathway through Es-PLK1 during the spermatogenesis of E. sinensis, thereby affecting the proliferation and apoptosis levels of spermatogenic cells.

Effects of microcystin-LR on immune function, lipid metabolism and intestinal microbial structure in Eriocheir sinensis

To investigate the potential toxic mechanism of Microcystin-LR (MC-LR) on juvenile Eriocheir sinensis (E. sinensis), a toxicity test was conducted by injecting MC-LR into the 3rd pereiopod. Following injection, we evaluated alterations in immune response biomarkers, antioxidant status, lipid metabolism-related genes expression, and intestinal microbiota composition in the hepatopancreas and intestinal tissues of E. sinensis. The results of immune response showed that after injection of MC-LR, the serum complement C3 level in E. sinensis significantly decreased at 48 hours (P < 0.05), whereas complement C4 level increased considerably from 12 to 96 hours (P < 0.01). The phenoloxidase system (PO) showed an increasing trend from 6 to 96 hours (P < 0.05 or P < 0.01). The levels of TNF-α, IL-6 significantly increased at 6 and 12 hours (P < 0.05 or P < 0.01). Gene expression analysis showed that FASN gene in the hepatopancreatic tissue displayed a higher expression at both 6 and 12 hours post-exposure (P < 0.01), while ALDH and ACAA2 gene exhibited a consistent downward trend from 6 to 48 hours (P < 0.05), Additionally, the mRNA levels of MECR and ACSL demonstrated a pattern of initial downregulation, followed by an upregulation, and subsequent downregulation. The antioxidant status results revealed that the levels GSH and CAT increased first and then decreased, while the activity of SOD decreased first and then increased. Meanwhile, the MDA content showed an increasing trend. 16 S rDNA analysis showed that the intestinal microbial diversity in MC-LR treatment group was significantly higher relative to the control group (P < 0.01). Compared with the control group, the MC-LR group had a significantly higher relative abundance of Proteobacteria, Fusobacteria, and Actinobacteria (P < 0.05) and a significantly lower relative abundance of Firmicutes (P < 0.01). At genus level, the relative abundance of Acinnetobacter, Flavobacterium, Acidovorax, Paracoccus, Cloacibacterium, Gemmobacter, Aeromonas, and Dechloromonas in the intestine of MC-LR-treated group was significantly increased relative to the control group (P < 0.05 or P < 0.01), but the relative abundance of Lachnospiraceae_NK4A136_group was significantly decreased (P < 0.01). The results of the study demonstrated that MC-LR could induced oxidative stress, hepatopancreas tissue damage, and intestinal microbial imbalance in E. sinensis.

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.

Effect of temperature on the occurrence of Metschnikowia bicuspidata disease in Eriocheir sinensis

Eriocheir sinensis aquaculture has been significantly impeded by “milky disease,” which is caused by Metschnikowia bicuspidata. This disease exhibits distinct seasonality and is closely associated with temperature fluctuations. The present study investigated the impact of temperature on the proliferation and pathogenicity of M. bicuspidata and the immune capacity of E. sinensis. We observed a significant temperature-dependent effect on the proliferation rate of M. bicuspidata in vitro and in vivo. Although low temperatures (4 °C) suppressed M. bicuspidata proliferation, different temperatures did not have a considerable influence on pathogenicity (P > 0.05). Cultivation at lower temperatures significantly reduced the proliferation rate of pathogens in infected E. sinensis and the time to death. Further, the bacteriostatic capacity of E. sinensis serum was significantly enhanced under high temperatures compared with that under low-temperature conditions (P < 0.01). Transcriptome analysis of hemocytes from E. sinensis at different breeding temperatures indicated that the host's metabolism and immunity were differentially affected at 4 °C compared to 32 °C, with pathways associated with growth and development primarily affected under low-temperature conditions and pathways related to energy supply predominantly influenced under high-temperature conditions. Notably, temperature also led to changes in the expression of genes closely linked to immunity and apoptosis, such as acid phosphatase, C-type lectin, glutathione peroxidase, caspase, and initiator caspase-8. The current findings have significant implications for understanding the effect of temperature on M. bicuspidata pathogenicity in E. sinensis and preventing milky disease infection during aquaculture.

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 effect of fermented feed (FF) on intestinal, surrounding water, and sediment microbiomes of the Chinese mitten crab Eriocheir sinensis

AbstractObjectiveFermented feed (FF) has several significant advantages in aquaculture. However, little is known about the characteristics of intestinal and environmental microbiota in the Chinese mitten crab Eriocheir sinensis.MethodsThis study was conducted to elucidate the relationship between bacterial communities in the intestine of Chinese mitten crabs and the surrounding environment and to compare the bacterial communities in FF and non‐FF diet modes by using 16S ribosomal RNA high‐throughput sequencing technology.ResultFermented feed diets mainly influenced the alpha diversity of intestinal microbiomes but could affect microbial community structures of beta diversity in water and sediment. Compared to water and sediment, crab intestines had the lowest operational taxonomic unit (OTU) richness and bacterial community diversity. The OTU richness and Chao richness index values were lower in the intestines of crabs that received FF than in crabs that were given non‐FF. No significant differences were observed in the bacterial diversity and OTU richness of water and sediment between the two feeding modes. The bacterial community structures were significantly different among the three environments. Tenericutes, Proteobacteria, and Actinobacteria were the most abundant phyla in the crab intestine, sediment, and water, respectively. Bacterial functions were also different among the three environments. Proportions of nitrate reduction and fermentation in the crab intestine, proportions of nitrification and sulfate respiration in the sediment, and proportions of chemoheterotrophy and aerobic chemoheterotrophy in the water were higher for the FF feeding mode than for the non‐FF mode.ConclusionThe bacterial community structures were significantly different among the three environments. The microbiome of the crab intestine was partially shared with that of the ambient environment. Additionally, the FF mainly influenced the alpha diversity of intestinal microbiomes but also affected the community structures of beta diversity in water and sediment. These results will help us to devise dietary strategies to influence the crab intestinal microbiota and provide guidance for sustainable crab culture practices.

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.

Effect of dietary β-carotene supplementation on growth and antioxidant capability of pre-adult male Chinese mitten crab, Eriocheir sinensis

β-carotene has been shown to be beneficial for the color formulation, survival, antioxidation, immunity and stress resistance of many crustaceans. This study was conducted to investigate the effects of dietary supplementation of synthetic β-carotene on growth, antioxidant status, high pH resistance, color parameters, and carotenoids composition of pre-adult Chinese mitten crab Eriocheir sinensis. Three diets were formulated to contain 3.06, 52.40 and 103.59 mg/kg dry diets of synthetic β-carotene (defined as Diet 1 - 3). The results showed that: (1) There were no marked differences in body weights or feed utilization, suggesting that β-carotene was not particularly efficient in enhancing the growth of pre-adult E. sinensis. (2) Indicators of antioxidant capacity (T-AOC, MDA) and immunity (AKP, ACP) both got improved in the hepatopancreas and hemolymph with the supplementation of 50–100 mg/kg β-carotene in the diets. (3) The stress test with high pH indicated Diet 1 treatment had the highest mortality among all treatments, and the lowest mortality was found in Diet 3 treatment. (4) For color enhancement, the redness of the carapace and hepatopancreas increased significantly with the increase of dietary β-carotene supplementation at Day 30. Combined, the inclusion of β-carotene in the diet could enhance the antioxidative capability, non-specific immunity, stress resistance to high pH and tissue carotenoid contents, and the optimal level of dietary synthetic β-carotene supplementation was suggested to be around 50 mg/kg for pre-adult male E. sinensis.

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.

Different types of dietary carotenoids improve the color and odor quality of Eriocheir sinensis ovaries

Chinese mitten crab, Eriocheir sinensis, is a commercially ecological crab species in China. Ovaries are one of the major edible parts for female E. sinensis, and their color and flavor primarily affect consumer acceptance. This study investigated the effects of different dietary carotenoids on the color and odor quality of adult female E. sinensis ovaries. The crab was fed the experiment diets with supplementation of 100 ×10−6 of β-carotene, astaxanthin, lutein, canthaxanthin and zeaxanthin, respectively, for 70 days, while the control diet without the supplementation of carotenoids. The results showed that different carotenoids generated an orange-red coloration on crab ovaries, and astaxanthin and canthaxanthin significantly increased the redness (P < 0.05). All carotenoid groups had higher total carotenoids and fatty acid contents than the control group. Moreover, β-carotene significantly promoted ovarian carotenoid deposition, and lutein predominantly affected fatty acid accumulation (P < 0.05). β-carotene and lutein groups accumulated more aroma components (alcohols, ketones, and aldehydes) by regulating the metabolism of carotenoid and fatty acids in ovaries. These results show that canthaxanthin is a potential astaxanthin substitute for promoting coloration, while β-carotene and lutein can improve the odor quality of the ovaries of adult female E. sinensis.