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The mud crab (Scylla paramamosain) is an important species for seawater aquaculture, the utilization of saline-alkali water provides potential for the further development of the mud crab industry, but the adaptation mechanism of the antennal gland to chloride type low-salt saline-alkali water has not been fully studied. In this study, we evaluated the osmoregulatory enzyme activity (n=3) and metabolic changes (n = 5) of the antennal gland in S. paramamosain after a sudden drop in salinity from 23 ‰ of seawater to 2 ‰ of chloride type low-salt saline-alkali water. After the decrease in salinity, the activity of osmoregulatory enzymes in the antennal gland, including Na+/K+-ATPase, NKCC, carbonic anhydrase (CA), and V-ATPase showed a trend of first increasing and then decreasing. Through LC-MS technology, we identified 308 differential metabolites. In addition, KEGG enrichment analysis identified eight significant metabolic pathways (P

Salinity affects the growth and development of crustaceans by affecting their physiological functions such as respiration, metabolism, osmotic regulation and immune defense. Gill is the most important organ of osmotic regulation. The adaptation of Scylla paramamosain to low salt is a process of oxygen consumption and energy consumption, and the mitochondria in the cells are considered to be the synthesis site of energy. Therefore, in this study, GC-MS technology was used to conduct non-targeted metabolomics studies on the posterior gill mitochondria of S. paramamosain under acute hyposaline stress, revealing the key role of mitochondria in gill response to acute low salinity stress. We identified 196 metabolites, 21 of which were differentially expressed. Differential metabolite KEGG enrichment analysis identified 16 metabolic pathways. The results of this study suggest that mitochondria may maintain osmotic homeostasis by increasing the utilization of monosaccharides, and decreasing the synthesis of amino acids in crabs under acute low salt stress when they are in a state of oxygen and energy depletion. In addition, carbohydrates and organic acid metabolites may also play an important role. For the first time, we analyzed the metabolic mechanism of posterior gill mitochondria in response to acute low salt, aiming to provide effective technical support and theoretical reference for the cultivation of S. paramamosain.

Scylla paramamosain is an important mariculture animal. In the present study, we examined the physiological and biochemical characteristics of juvenile S. paramamosain under hypoosmotic stress and further verified the function of ABCC1, a key transport protein in gill tissue. The results showed that Na+/K+-ATPase, Ca2+-ATPase, and Na+/K+/2Cl- cotransporter in gill tissues increased first and then decreased. In addition, SOD and CAT activities also began to gradually increase, protecting gill tissues from oxidative damage. The hemolymph osmolarity decreased rapidly from 792 mOsm/kg to 560 mOsm/kg within 6 h, and then rose to 626.25 mOsm/kg at 48 h, and then remained stable. At the same time, Na+, Cl-, K+, and Ca2+ concentrations were decreased to varying degrees. There were significant changes in free amino acids such as aspartic acid, glutamic acid, and asparagine in hemolymph in response to acute salt depletion. By injection of ABCC1 inhibitor/activator, it was found that while ABCC1 transporter activity in the MK-571 group showed a decreasing trend at 9 h, Na+/K+ -ATPase activity began to increase and reached a peak at 48 h. Compared with the control group, the levels of aspartic acid, glutamic acid, asparagine, glycine, arginine, alanine, lysine, and proline in the MK-571 group showed significant differences at 6 h; Significant differences in glutamate, asparagine, arginine, alanine, lysine, and proline appeared at 12 h in the Thiethylperazine group. These results suggested that the dynamic changes of gill ion transport enzymes, antioxidant enzymes, inorganic ions, and free amino acids in hemolymph occurred in S. paramamosain under hypoosmotic stress, and the ABCC1 transporter played an important role in this regulatory process.

IntroductionThe mud crab, Scylla paramamosain, holds great commercial significance as a marine crustacean widely cultivated in the Indo-Pacific region. Understanding the core gut microbiota of aquatic animals is crucial for their overall health and growth, yet the core gut microbiota of mud crab remains poorly characterized.MethodsIn this study, we gathered gut samples from mud crabs across five locations within Sanmen Bay, China. Through the utilization of high-throughput sequencing, we delved into the composition of the gut microbial community and identified the core gut microbiome of mud crab.ResultsOur results demonstrate that the gut microbial diversity of mud crab did not exhibit significant variation among the five sampling sites, although there were some differences in community richness. At the phylum level, we identified 35 representative phyla, with Firmicutes, Proteobacteria, Bacteroidota, and Campilobacterota as the dominant phyla. Among the 815 representative genera, we discovered 19 core genera, which accounted for 65.45% of the total sequences. These core genera were distributed across 6 phyla, and among them, Photobacterium exhibited the highest average relative abundance.DiscussionPhotobacterium has probiotic activity and may play a crucial role in enhancing the immune response of the host and maintaining the diversity of the gut microbiota. Moreover, we observed a positive correlation between the relative abundance of core genera and the stability of the gut microbial community. Furthermore, our findings revealed distinct differences in gut microbial composition and specific taxa between the sexes of mud crab. These differences subsequently influenced the functionality of the gut microbial community. Overall, our investigation sheds light on the core gut microbiota of mud crab, emphasizing the importance of core gut microbial communities in maintaining the health and growth of these commercially significant marine crustaceans.

IntroductionThe intestinal microbiota acts as an additional “organ” that performs a variety of fu\nctions for the host’s health. However, the composition and role of the intestinal microbiota in Scylla paramamosain cultivated in inland low salinity saline-alkaline water are unknown.MethodsAccordingly, from the perspective of practical production, we explored the intestinal microbiota communities and the critical bacteria of S. paramamosain in normal salinity seawater (NS), coastal low salinity seawater (CS), acute low salinity seawater (AS) and inland low salinity saline-alkaline water (IS).ResultsResults showed that there were significant differences in the diversity composition of intestinal microbiota and the relative abundance of dominant taxa in each group of cultured crabs. Firmicutes, Proteobacteria, Bacteroidota and Campilobacterota were shown to be the major phyla shared by the four groups, with Bacteroidota having the highest relative abundance (27.10%) in the inland low salinity saline-alkaline water group (IS). Fusobacteriota had the highest proportion in IS group compared with other low salinity groups. A total of 284 indicator bacteria were identified, belonging to eight phyla, and their relative abundances were varied significantly (P < 0.05). Genus Carboxylicivirga, as the indicator bacterium of the IS group, may play a critical role in the adaptation of crab to saline-alkaline water environment. Moreover, salinity may exert considerable selective pressure on the entire microbial community.DiscussionThese findings revealed the features of the intestinal microbiome in S. paramamosain in multiple low salinity patterns, and provided candidate probiotics and basic information for crab farming in saline-alkaline water, which was conducive to the development and perfection of mud crab culturing technology in inland low salinity saline-alkaline water.

Scylla paramamosain is an important marine aquaculture crustacean on the southeastern coast of China. Given the difficulties of overcrowded coastal aquaculture space and insufficient production, inland saline-alkaline water culture has the potential to alleviate this bottleneck. This study separated 600 crabs into four groups: normal salinity (12-18 ppt, NS), coastal low salinity (3-5 ppt, CS), inland low salinity saline-alkaline (1.5 ppt, IS), and acute low salinity (23 ppt down to 3 ppt, AS), followed by a transcriptomic analysis of the gills. CS-vs-NS, IS-vs-NS, and AS-vs-NS obtained 1154, 1012, and 707 DEGs, respectively. GO analysis showed that the DEGs of the three comparison groups were mainly involved in cellular process, metabolic process, biological regulation, organelle, membrane, extracellular region, binding, and catalytic activity. The findings demonstrate that a significant number of genes are engaged in controlling metabolic processes in the osmoregulation process, and that cell membrane catalysis and different enzymes play a vital part in the environmental adaption process. KEGG enrichment analysis revealed that IS possesses a considerable number of signaling pathways that play important roles in osmoregulation when compared to NS. The cAMP signaling pathway increased the expression of CaM and Na+/K+-ATPase. These findings show that cations like Ca2+, Na+, and K+ are critical for S. paramamosain to adapt to inland low salinity saline-alkaline water, and that the cAMP signaling pathway regulates their levels. This research provides a theoretical foundation for improving the saline-alkaline aquaculture technology of S. paramamosain.

Scylla paramamosain is a high-quality cultivar for saline-alkaline water aquaculture as a euryhaline crustacean species. However, salinity impacts the respiratory metabolism, growth, and survival of marine crustaceans. The metabolic response of crabs adapting to multiple low salinity environments has not been thoroughly studied yet, especially in inland saline-alkaline water. In this study, we analyzed metabolites in the gill and hemolymph of crabs cultured in three different low salinity environments. The results showed that membrane composition (lipids and lipid molecules) and free amino acids played an essential role in the osmoregulation of crabs, and the energy consumption accompanied as well. Meanwhile, S. paramamosain relied on ion transport and energy metabolism under acute/short-term low salinity conditions for osmoregulation. In contrast, amino acids and energy metabolism occupied a leading position in long-term low salinity. Furthermore, taurine and hypotaurine play a vital role in crabs adapting to inland saline-alkaline water. This is the first study to identify the crucial metabolites and key pathways as biomarkers to differentiate the metabolic mechanisms of S. paramamosain under multiple low salinity stress modes based on GC-MS technology, which provided novel insight into the metabolic response of S. paramamosain adapting to inland low salinity saline-alkaline water, and provided theoretical guidance for the aquaculture of S. paramamosain in the inland saline-alkaline water.