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We conducted a whole genome survey in the portunid crab Charybdis feriatus (Linnaeus, 1758) using Illumina sequencing platform and developed a set of polymorphic microsatellite loci. A total of 117.7 Gb of clean reads were generated, with 74× coverage of the estimated genome size of 1.4 Gb. The GC content, heterozygosity rate, and repeat sequence rate of the genome were estimated to be 40%, 1.1%, and 51%, respectively. A total of 3,779,209 microsatellites were identified from the genome. Sixty microsatellite loci were evaluated in a wild population of 40 individuals. As a result, 14 polymorphic microsatellite loci (23.3%) were obtained. The number of alleles (3 to 15), polymorphism information content (0.365 to 0.884), observed heterozygosity (0.050 to 0.975), and expected heterozygosity (0.450 to 0.907) per locus averaged 6.8, 0.652, 0.691, and 0.707, respectively. We show that the genome of C. feriatus has a high heterozygosity and repeat sequence rates, and provide a novel insight into the genome profile of marine crabs. The genetic markers developed in this study are potentially useful for studies on population dynamics and conservation genetics of C. feriatus and other species of brachyuran crabs.

To investigate the effects of salinity on early development of Chinese mitten crab (Eriocheir sinensis), and the salinity tolerance mechanism of embryos, different developmental stages of embryos (gastrula, eyespot and pre-hatching stage), and hatched stage I zoea and megalopa, were exposed to a range of salinities (1, 5, 10, 15 (control), 20, 25, 30, 35 and 40). Hatching, survival and molting were monitored. Effects of 24-hour hypersaline (35) and hyposaline (1) stress on egg diameter, water content, Na+/K+-ATPase (NKA) activity, and crustacean hyperglycemic hormone (CHH) gene mRNA expression in embryos and megalopa, are reported. Embryos are more tolerant of low (≤5) than high (≥25) salinities, with optimum ranges for gastrula and pre-hatching stage embryos being 5–20, and for eyespot embryo and stage I zoea, 10–20. Most megalopa can molt to the first juvenile instar by day 5 at salinities between 1 and 40, whereas molting of megalopa stages was delayed at 40. Hypersaline conditions resulted in a loss of moisture, reduction of egg volume, and a significant increase in NKA activity and CHH mRNA expression at some developmental stages. Hyposaline conditions did not affect moisture content or egg volume, but resulted in decreased NKA activity and CHH mRNA expression in embryos. For megalopa stages, NKA activity was significantly upregulated following both hypo- and hypersaline stress. Our results suggest high salinity will inhibit development and hatching of E. sinensis embryos, and low salinity will affect the survival of their stage I zoea. Increased NKA activity in embryos and megalopa stages might indicate a hyporegulation response under hypersaline conditions. These findings provide useful information for spawning ground protection of indigenous E. sinensis and enrich the knowledge of embryonic tolerance mechanisms of hyper-regulating crustaceans following osmotic stress.

Crustins, the main AMP family in Crustacea, are generated as isoforms in many species and implicated in innate immune responses, but their detailed molecular mechanisms on susceptible bacteria remain largely unclear. Type II and type I crustins are distinguished by glycine-rich region (GRR), which is a major marker motif, and some type II crustins exhibit stronger antibacterial activities than their GRR deletion mutants. In the present study, a novel crustin, namely, SpCrus5, was functionally characterized from a commercially valuable crab Scylla paramamosain. SpCrus5 contained a typical cysteine-rich domain at the N-terminus, a conserved WAP domain in the center, and a special GRR at the C-terminus, which is located in a site that differs from that of GRRs in typical type II crustins found between signal peptides and cysteine-rich domains. SpCrus5 shared high similarities with most type II crustins, and it was more closely related to type II crustins than to other retrieved crustins. SpCrus5 was predominantly expressed in gills and remarkably upregulated after the crabs were challenged with Vibrio parahemolyticus or Staphylococcus aureus, suggesting that SpCrus5 might participate in antibacterial immune responses. To further elucidate how this C-terminal GRR affects the function of SpCrus5, we harvested a GRR deletion mutant (SpCrus5-ΔGRR) by deleting the GRR. Liquid growth inhibition assays demonstrated that the antimicrobial activity of SpCrus5 was stronger than that of SpCrus5-ΔGRR, and the antibacterial spectrum of the former toward Gram-negative bacteria was broader than that of the latter. Binding assays revealed that the microorganism-binding ability and polysaccharide-binding activity of SpCrus5 were stronger than those of SpCrus5-ΔGRR. SpCrus5 or SpCrus5-ΔGRR agglutinated all tested Gram-positive bacteria. Therefore, the antibacterial activities of SpCrus5 were stronger and broader than those of SpCrus5-ΔGRR, and the binding ability and agglutination activity might contribute to the antimicrobial activity of SpCrus5. These results revealed that the C-terminal GRR was necessary to produce an efficient antibacterial activity of SpCrus5. SpCrus5 was highly identical with most type II crustins and it functioned as many type II crustins did, indicating that SpCrus5 was more likely an atypical type II crustin than a type I crustin. This study revealed that SpCrus5 participated as an essential antimicrobial effector in immune responses and provided new insights into the underlying mechanisms of the sequence and function diversity of crustins.

The capability of Scenedesmus obliquus to remove cations (K+, Na+, Ca2+, Mg2+) from saline-alkaline water was investigated at different salinities (0, 5, 10, 15, 20, 25) and carbonate alkalinities (0, 5, 10, 15, 20, 25, 30, 35 mmol/L). K+, Na+, Ca2+, and Mg2+ in saline-alkaline water were efficiently removed by S. obliquus. The maximum removal of the cations (29.37 mg for K+, 185.85 mg for Na+, 23.07 mg for Ca2+, 66.14 mg for Mg2+) occurred at salinity 25. The maximum removal of K+ (2.28 mg), Na+ (6.62 mg), Ca2+ (1.01 mg), and Mg2+ (0.62 mg) occurred at carbonate alkalinities of 25 mmol/L for K+, 35 mmol/L for Na+, 20 mmol/L for Ca2+, and 25 mmol/L for Mg2+, respectively. Under a salinity stress, the concentration of Na+ in S. obliquus increased significantly, while that of K+ decreased significantly. The concentrations of Ca2+ and Mg2+ decreased as well. The ratios of K+/Na+, Ca2+/Na+, and Mg2+/Na+ were significantly lower in all salinity treatments than those of the control. Under alkaline stress, the concentrations of Na+ and K+ in S. obliquus decreased significantly and the ratios of K+/Na+, Ca2+/Na+, and Mg2+/Na+ were significantly higher in all treatments than in the control. Moreover, the concentrations of Ca2+ and Mg2+ in S. obliquus at alkalinities of 5–10 mmol/L were significantly higher than those of the other treatments. The removal of Na+ by S. obliquus mainly occurs through biosorption, and Mg2+ and Ca2+ were removed through both biosorption and bioaccumulation.

In this study, the population genetic structure and historical demography of the blue swimming crab, Portunus pelagicus, from southeastern sea of China were investigated using cytochrome c oxidase subunit I (COI) gene of mitochondrion. A total of 889 bp segment of COI gene was sequenced, which showed a high haplotype diversity (0.6833-0.8142) and low nucleotide diversity (0.0021-0.0034). Among 30 haplotypes defined in this study, one (H1) was the most dominant (47.7%) and shared by each locality, while the majority (23) were rare and only existed in one individual. The AMOVA analysis revealed a limited population genetic structure, which suggested a high level of gene flow along the distribution areas of China. This conclusion was supported by the pairwise F

The complete mitochondrial genome of Charybdis natator (family Portunidae) was obtained using Illumina and Sanger dideoxy sequencing. This genome was a typically circular molecule with a length of 15,664 bp and encoded 13 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. The overall base composition of this mitogenome was 34.00% for A, 11.06% for G, 36.36% for T, and 18.58% for C, respectively, with a higher A + T content (70.36%). The gene composition and arrangement were accordant to the closely published species. The phylogenetic analysis suggested that C. natator had the closest relationship with C. japonica.

The red crab (Charybdis feriata) is one of most important fishery resources in China. In the present study, we first measured 17 morphological traits and body weight of C. feriata, characterized these 18 traits, and then estimated the effects of morphological traits on body weight by statistical methods including correlation coefficients, determination coefficients, path coefficients, and regression equation. All correlation coefficients between 17 morphological traits and body weight reached an extremely significant level (P8; meropodite length of pereopod 3, X16; meropodite length of pereopod 4, X17) and body weight that suggested these three traits were the key traits directly influence body weight. Multiple correlation index (R2) between above three morphological traits and body weight was of 0.977, which indicated that the main independent variables influencing body weight has been found. Finally a best-fit linear regression equation was established as Y = 13.078 X8 + 7.048 X16 - 4.902 X17 - 576.635, which provided an ideal model for better understanding the feature of morphological traits and body weight of C. feriata.

Carbonate alkalinity (CA) and pH are considered to be two important stress factors that determine the response of aquatic animals to sudden transfers into saline-alkaline water. To evaluate the potential for aquaculture production of Venus clams (Cyclina sinensis) farmed in saline-alkaline water, the combined effects of CA (2.5 (control), 10.0, 20.0 and 40.0 meq/l) and pH (8.0 (control), 8.5, 9.0 and 9.5) on survival rate was monitored every day for 10 days. Length gain rate (LGR) and weight gain rate (WGR) were also monitored for two months, and total haemocyte count (THC), phagocytic rate (PR) and haemocyte mortality (HM) were measured for 3, 6, 12 and 24 days under the same water temperature (20 °C) and salinity (15‰) conditions. The results showed that survival rates in treatments of CA ≤ 20.0, combined with pH ≤ 9.0, were 100%. LGR and WGR in treatments of CA 2.5pH 8.0 (control), CA 2.5pH 8.5 and CA 10.0pH 8.0 exhibited the largest values (P0.05), while in other treatments, they showed a decreasing trend with an increase in either CA or pH or both (P0.05). Similarly, for THC, PR and HM, no significant differences were observed among the fast growth treatments during the entire experimental period (P0.05), however, in other treatments, they presented significant differences, especially on day 3 and 6 (P0.05), most notably with increases in CA or pH, but returned to control levels on day 12. In conclusion, in this study, a strong interaction between CA and pH was observed. Additionally, it was ascertained that the Venus clam C. sinensis can withstand the stress of CA 20.0 combined pH 9.0, although individuals grows slowly and may take approximately 12 days to recover to the unstressed condition.