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Molt is a critical developmental process in crustaceans. Recent studies have shown that the hepatopancreas is an important source of innate immune molecules, yet hepatopancreatic patterns of gene expression during the molt cycle which may underlie changes in immune mechanism are unknown. In this study, we performed Illumina sequencing for the hepatopancreas of the mud crab, Scylla paramamosain during molt cycle (pre-molt stage, post-molt stage, and inter-molt stage). A total of 44.55 Gb high-quality reads were obtained from the normalized cDNA of hepatopancreas. A total of 70,591 transcripts were assembled; 55,167 unigenes were identified. Transcriptomic comparison revealed 948 differentially expressed genes (DEGs) in the hepatopancreas from the three molt stages. We found that genes associated with immune response patterns changed in expression during the molt cycle. Antimicrobial peptide genes, inflammatory response genes, Toll signaling pathway factors, the phenoloxidase system, antioxidant enzymes, metal-binding proteins and other immune related genes are significantly up-regulated at the post-molt stage and inter-molt stage compared with the pre-molt stage, respectively. These genes are either not expressed or are expressed at low levels at the pre-molt stage. To our knowledge, this is the first systematic transcriptome analysis of genes capable of mobilizing a hepatopancreas immune response during the molt cycle in crustaceans, and this study will contribute to a better understanding of the hepatopancreas immune system and mud crab prophylactic immune mechanisms at the post-molt stage.

Selenium is a vital trace mineral that is crucial for maintaining regular biological processes in aquatic animals. In this study, a four-week dietary trial was carried out to assess the impact of bio-fermented selenium (Bio−Se) on the growth and immune response of Chinese mitten crabs, Eriocheir sinensis. The crabs were randomly allocated to five dietary treatment groups, each receiving a different dose of Bio−Se. The doses included 0, 0.3, 0.6, 1.5, and 3.0 mg/kg and were accurately measured in basal diet formulations. The results showed the weight gain rate (WGR), specific growth rate (SGR), and survival rate (SR) in the 1.5 mg/kg Bio−Se group were the highest, and 3.0 mg/kg of Bio−Se has an inhibitory effect on the WGR, SGR, and SR. The activities of the immune enzymes, including glutathione peroxidase (GPX), superoxide dismutase (SOD), and acid phosphatase (ACP), of the hepatopancreas were significantly (p < 0.05) increased in the 1.5 mg/kg Bio−Se group, while they decreased (p < 0.05) in the 3.0 mg/kg feeding group compared to the 0 mg/kg feeding group. The concentration of maleic dialdehyde (MDA) exhibited the opposite pattern. Similarly, the mRNA expression levels of antimicrobial peptides (ALF-1, Crus-1, and LYS), ERK, and Relish genes were also observed to be the highest in the 1.5 mg/kg Bio−Se group compared with the other groups. Furthermore, the administration of 1.5 mg/kg of Bio−Se resulted in an increase in the thickness of the intestinal plica and mucosal layer, as well as in alterations in the intestinal microbial profile and bacterial diversity compared to the dose of 0 mg/kg of Bio−Se. Notably, the population of the beneficial bacterial phylum Fusobacteria was increased after crabs were fed the 1.5 mg/kg Bio−Se diet. In conclusion, the oral administration of 1.5 mg/kg of Bio−Se improved the growth efficiency, antioxidant capabilities, immunity, and intestinal health of E. sinensis. Through a broken-line analysis of the WGR against dietary Bio−Se levels, optimal dietary Bio−Se levels were determined to be 1.1 mg/kg. These findings contribute valuable insights to the understanding of crab cultivation and nutrition.

All-trans retinoic acid (atRA) is known to regulate lipid metabolism, adipocyte differentiation, and the immune system in mammals and other aquatic species. However, studies on atRA in crustaceans, especially in , are still scarce. The present study aimed to investigate the regulatory effects of dietary or injected atRA on female crabs during the fattening period. In the dietary regulation experiment, 270 female crabs were fed diets containing different doses of atRA (0, 150, 300, 600, 1200, and 2400 mg/kg) for a total of 49 days. In the in vivo injection experiment, 90 females were divided into an experimental group (injected with a 0.3 μg/g dose of atRA) and a control group (injected with the same amount of DMSO solvent). Injections were given weekly throughout the 35-day experimental period. Results: Both dietary atRA and atRA injection promoted ovarian development, as evidenced by increased GSI, elevated serum Vg levels, decreased GIH, and upregulated expression of , , and genes. In terms of mechanism, dietary atRA promoted ovarian development via the upregulation of pyrimidine nucleotides and dehydroepiandrosterone, which supplied nucleic acid precursors and hormonal support. Furthermore, RXR was identified as a potential key target of atRA in inducing ovarian development, as molecular docking revealed that atRA could spontaneously bind to RXR. Moreover, following atRA injection, the expression of , along with key genes involved in ovarian development, lipid synthesis, and lipid transport, was significantly upregulated. In addition, the atRA diet created a favorable microenvironment for ovarian development by reducing pro-inflammatory lipid levels in the ovary. Transcriptomic and metabolomic analyses revealed that atRA modulates energy and lipid metabolism by activating the AMPK pathway. In terms of the bacterial community structure, the atRA diet significantly decreased abundance and enriched as the signature beneficial bacterium. In terms of nutritional quality, the atRA diet markedly reduced saturated and trans-fatty acids while increasing monounsaturated fatty acids and various key essential amino acids. Conclusions: This study revealed that atRA plays a key role in promoting ovarian development, improving nutritional quality, and modulating the structure of the microbiota, thereby providing theoretical support for healthy aquaculture of female crabs during the fattening period.

The intermolt crustacean Y-organ (YO) maintains a basal state mediated by pulsatile release of molt inhibiting hormone (MIH), a neuropeptide produced in the eyestalk ganglia, inhibiting YO ecdysteroidogenesis. Reduction of MIH results in YO activation and the animal enters premolt. In the crab, Gecarcinus lateralis , molting was induced by eyestalk ablation (ESA). ESA animals were injected with either rapamycin, an mTOR inhibitor, or DMSO vehicle at Day 0. YOs were harvested at 1, 3, and 7 days post-ESA and processed for high throughput RNA sequencing. ESA-induced increases in mRNA levels of mTOR signaling genes (e.g., mTOR , Rheb , TSC1 / 2 , Raptor , Akt , and S6 kinase ) declined following rapamycin treatment. In concert with mTOR inhibition, mRNA levels of ecdysteroid biosynthesis genes (e.g., Nvd , Spo , Sad , Dib , and Phm ) were decreased and accompanied by a decrease in hemolymph ecdysteroid titer. By contrast, rapamycin increased the mRNA level of FKBP12 , the rapamycin-binding protein, as well as the mRNA levels of genes associated with Wnt and insulin-like growth factor signaling pathways. Many MIH and transforming growth factor-β signaling genes were down regulated in ESA animals. These results indicate that mTOR activity either directly or indirectly controls transcription of genes that drive activation of the YO.

The sex-specific differences in the growth and population characteristics of the high-commercial-value sand crab Ovalipes punctatus were investigated in Korea. The estimated allometric growth between the sexes showed significant differences in all morphometric measurements. In the classification of growth types, carapace width-chela length exhibited positive and negative allometric growth in males and females, respectively. Carapace width-abdominal width showed positive relative growth in both sexes, and orbital spine width exhibited negative relative growth in both sexes. Consequently, sexual dimorphism was evident in all measured traits. Growth parameters estimated using the ELEFAN function of the FiSAT II program indicated higher values in males compared to females. Asymptotic length (CW ∞ ) for males was estimated at 139.2 mm, whereas for females it was 116.6 mm. Additionally, the growth coefficient (K) was higher in males (0.65) than in females (0.54), suggesting faster growth in males. The winter point (WP) was 1 for males and 0.7 for females, indicating slower growth in males during the colder December and slower growth in females during the spawning period in August. The modified von Bertalanffy growth curves indicated asymptotic growth in all sexes, and the growth performance index (φ') showed higher values in males (4.10) compared to females (3.87), reflecting differences in growth curves. The steady increase in recruitment rates from July to September was associated with the appearance of larvae and their subsequent growth into juveniles, leading to their recruitment into the population during this period. Therefore, O. punctatus exhibited sex-specific differences in growth parameters, suggesting distinct growth strategies between the sexes.

Background Evolutionary adaptation drives organismal adjustments to environmental pressures, exemplified in the diverse morphological and ecological adaptations seen in Decapoda crustaceans, particularly brachyuran crabs. Crabs thrive in diverse ecosystems, from coral reefs to hydrothermal vents and terrestrial habitats. Despite their ecological importance, the genetic mechanisms underpinning their developmental processes, reproductive strategies, and nutrient acquisition remain poorly understood. Results Here, we report a comprehensive genomic analysis of the green mud crab  Scylla paramamosain using ultralong sequencing technologies, achieving a high-quality chromosome-level assembly. The refined 1.21 Gb genome, with an impressive contig N50 of 11.45 Mb, offers a valuable genomic resource. The genome exhibits 33,662 protein-coding genes, enriched in various pathways related to development and environmental adaptation. Gene family analysis shows expansion in development-related pathways and contraction in metabolic pathways, indicating niche adaptations. Notably, investigation into Hox gene regulation sheds light on their role in pleopod development, with the Abd-A gene identified as a linchpin. Post-transcriptional regulation involving novel-miR1317 negatively regulates Abd-A levels. Furthermore, the potential role of fru gene in ovarian development and the identification of novel-miR35 as a regulator of Spfru2 add complexity to gene regulatory networks. Comparative functional analysis across Decapoda species reveals neo-functionalization of the elovl6 gene in the synthesis of long-chain polyunsaturated fatty acids (LC-PUFA), suggesting its importance in environmental adaptation. Conclusions Our findings shed light on various aspects of crab biology, including genome sequencing, assembly, and annotation, as well as gene family expansion, contraction, and regulatory mechanisms governing crucial developmental processes such as metamorphosis, reproductive strategies, and fatty acid metabolism.

The crustacean hepatopancreas has different functions including absorption, storage of nutrients and vitellogenesis during growth, and ovarian development. However, genetic information on the biological functions of the crustacean hepatopancreas during such processes is limited. The swimming crab, Portunus trituberculatus, is a commercially important species for both aquaculture and fisheries in the Asia-Pacific region. This study compared the transcriptome in the hepatopancreas of female P. trituberculatus during the growth and ovarian maturation stages by 454 high-throughput pyrosequencing and bioinformatics. The goal was to discover genes in the hepatopancreas involved in food digestion, nutrition metabolism and ovarian development, and to identify patterns of gene expression during growth and ovarian maturation. Our transcriptome produced 303,450 reads with an average length of 351 bp, and the high quality reads were assembled into 21,635 contigs and 31,844 singlets. Based on BLASTP searches of the deduced protein sequences, there were 7,762 contigs and 4,098 singlets with functional annotation. Further analysis revealed 33,427 unigenes with ORFs, including 17,388 contigs and 16,039 singlets in the hepatopancreas, while only 7,954 unigenes (5,691 contigs and 2,263 singlets) with the predicted protein sequences were annotated with biological functions. The deduced protein sequences were assigned to 3,734 GO terms, 25 COG categories and 294 specific pathways. Furthermore, there were 14, 534, and 22 identified unigenes involved in food digestion, nutrition metabolism and ovarian development, respectively. 212 differentially expressed genes (DEGs) were found between the growth and endogenous stage of the hepatopancreas, while there were 382 DEGs between the endogenous and exogenous stage hepatopancreas. Our results not only enhance the understanding of crustacean hepatopancreatic functions during growth and ovarian development, but also represent a basis for further research on new genes and functional genomics of P. trituberculatus or closely related species.

Background The yellow oil crab is a highly valuable aquatic species, with the accumulation of nutritional and flavor compounds closely linked to the degree of gonadal degeneration. However, the molecular mechanisms of gonadal degeneration remain unclear. In this study, we analyzed the differences in gene expression and metabolite accumulation across three gonadal degeneration stages (QX, GX, and TSX) in yellow oil crab using transcriptome and non-targeted metabolomics approaches, and identified key genes and metabolites involved. Results A total of 240 differential accumulated metabolites (DAMs) were identified, most of which were significantly more highly accumulated in GX and TSX than in QX. K-means clustering analysis of DAMs and gene expression data revealed distinct stage-specific expression patterns from QX to TSX stage. Moreover, the “steroid hormone biosynthesis” pathway was significantly enriched, with 15 highly expressed steroid hormones and their derivatives in GX and TSX. 7 types of key genes involved in steroid hormone biosynthesis (such as UGT , HSD17B12 , STS , HSD3B , SULT1E1 , SRD5A1 , and CYP1A1 ) showed a trend of upregulation in GX and TSX stages. Gene-metabolite regulatory network analysis revealed significant correlations between 14 steroid hormones and 13 structural genes related to their biosynthesis (|r| > 0.8, p  < 0.05). Conclusions Therefore, the identified differential steroid hormones and seven key genes were positively associated with gonadal degeneration in yellow oil crab. These results offer a theoretical basis for understanding the formation and aquaculture of the yellow oil crab.

Background Arthropods require periodic molting (ecdysis) for growth. While the neuroendocrine orchestration of ecdysis is well characterized in insects, it remains comparatively poorly understood in crustaceans. In insects, ecdysis-triggering hormone (ETH) from epitracheal cells and eclosion hormone (EH) from the brain initiate and coordinate ecdysis. ETH triggers pre-ecdysis behaviors, while EH amplifies ETH release and promotes neuropeptide secretion of crustacean cardioactive peptide (CCAP), myoinhibitory peptide (MIP) for exuviation. Definitive evidence for functional ETH and EH in crustaceans is lacking. Here, we investigate ETH and EH in the crab Carcinus maenas by functionally characterizing the ETH receptor, comprehensively mapping transcript and peptide localization of ETH and EH, and quantifying ETH neurohormone and transcript throughout the molt cycle. Results We identified a single CamETH GPCR with high specificity for arthropod ETHs, signaling via calcium and cAMP. ETHR mRNA is expressed in multiple tissues, but ETH is restricted to the central nervous system (CNS) with a complex neuroarchitecture in pericardial organs, adjacent to the branchiocardiac veins. EH is limited to CNS, notably in the eyestalk ganglia. Of note, complex EH immunopositive fibers in the abdominal ganglion, adjacent to CCAP/allatostatin-C (AST-C)/bursicon cells, represent a novel putative neurohemal site. Measurements of ETH mRNA and peptide through the molt cycle showed that transcription peaks in late premolt, while peptide is released during active ecdysis, later than observed in insects. Conclusions While crustacean and insect ecdysis share neuroendocrine components, reflecting common ancestry, there is clear divergence in terms of functionality. We propose a new crustacean ecdysis cascade: ETH released from pericardial organs may stimulate EH to initiate CCAP/AST-C and bursicon release from adjacent neurons.

Ring Box Protein-1 (RBX1) is an essential component of the Skp1-cullin-F-box protein (SCF) E3 ubiquitin ligase, which is involved in the regulation of oocyte maturation in the form of ubiquitination substrate modification. In this study, a sequence of RBX1 (Sp-RBX1) was identified and analyzed using bioinformatics methods from the transcriptome data of Scylla paramamosain. The length of Sp-RBX1 cDNA sequence was 1247 bp, consisting of a 336 bp open reading frame (ORF). Sequence analysis revealed that the protein contained a C-terminal modified RING-H2 finger domain, with two zinc binding sites and a Cullin binding site, classifying it as a member of the RBX1 superfamily. The results of real-time fluorescence quantitative PCR (RT-qPCR) showed that Sp-RBX1 expression in the ovary was low at stages I and II, then significantly increased from stage III to V (p < 0.05), which indicated that it might be closely related to the maturation of oocytes. It also peaked at stage II in the hepatopancreas, then sharply declined from stages III to V. The expression pattern might be related to the accumulation of fat in the early development of hepatopancreas. Furthermore, we characterized the expression of Sp-RBX1 induced by follicle-stimulating hormone (FSH) and estradiol (E2) hormones. The results showed that the expression in the ovary was up-regulated by FSH and significantly inhibited by E2. The expression in the hepatopancreas increased only at 0.5 µmol/L concentration of FSH, and decreased in other groups. Conversely, it was up-regulated by E2. Thus, the expression of Sp-RBX1 was influenced by FSH in a concentration-dependent manner. These findings could offer valuable insights for further research on ovarian maturation in crustaceans.