Effects of saline-alkali stress on the tissue structure, antioxidation, immunocompetence and metabolomics of Eriocheir sinensis

Dietary Melatonin Supplementation Improved Intestinal Health and Immune Function of Pacific White Shrimp (Litopenaeus vannamei) Under High Alkali Stress

The intestinal tract serves as a critical immune regulator in aquatic species, maintaining homeostasis and environmental stress resistance. This study evaluates the protective effects of melatonin (MT) on Litopenaeus vannamei (L. vannamei) under acute alkaline stress through a comprehensive analysis of intestinal morphology, antioxidant responses, apoptosis regulation, and microbial community dynamics. A total of six groups of melatonin treatment groups were designed. After another 2 months of breeding, a 96 h acute alkalinity stress experiment was conducted. Experimental supplementation revealed dose-dependent outcomes: 82.7 mg/kg MT significantly improved survival rates without affecting growth parameters, while higher concentrations (329.2 mg/kg) induced elevated apoptosis (p < 0.05). Histological examination demonstrated mitigated intestinal structural damage in MT-treated groups compared to non-supplemented controls under alkaline stress. Antioxidant capacity initially increased and then stabilized at optimal MT doses (82.7-165.1 mg/kg), accompanied by enhanced immune marker expression (p < 0.05). Microbial profiling indicated MT-mediated enrichment of commensal bacteria associated with polysaccharide metabolism, energy utilization, and intestinal immunity. This study establishes that melatonin exerts dose-dependent protection in L. vannamei under alkaline stress, balancing antioxidant enhancement, apoptosis modulation, and microbiome regulation to fortify intestinal health, with 82.7-165.1 mg/kg identified as the optimal therapeutic range for mitigating environmental stress without compromising physiological homeostasis. The results of this study establish an empirical framework for optimizing MT application in crustacean aquaculture, particularly highlighting its role in maintaining intestinal barrier integrity and microbial homeostasis under alkaline environmental challenges.

HIF1A Regulates Rhbg Expression to Enhance Ammonia Excretion in Amur Ide (Leuciscus waleckii) Under Extreme Alkaline Conditions

High-alkalinity water bodies can disrupt normal ammonia metabolism in fish, leading to ammonia poisoning. In China, there exists a highly tolerant group of Amur ide (Leuciscus waleckii) that can survive in extreme alkaline lakes with alkalinity up to 53.57 mM (pH 9.6), making it an excellent model for elucidating the high-alkalinity tolerance mechanism in fish. We have discovered that this species has evolved a special ammonia excretion mechanism to maintain ammonia efflux in high-alkalinity environments. Compared to the freshwater forms of Amur ide, the ammonia excretion protein RHBG plays a prominent role in the ammonia excretion process of the alkali forms of Amur ide; however, the regulatory mechanism of RHBG expression in fish remains unclear. Through DNA pull-down, RNA-Seq, qPCR, Western blotting, immunofluorescence, and dual-luciferase reporter assays, this study demonstrates that the transcription factor HIF1A can inversely regulate the expression of Rhbg by binding to its promoter region, thereby participating in the high-alkalinity adaptation process of fish. The findings of this study provide a theoretical basis for elucidating the ammonia excretion mechanism and revealing the alkalinity tolerance mechanism in fish.

Integration of microbiomics and metabolomics reveals energy metabolism imbalance in crucian carp (Carassius auratus) under saline-alkaline exposure

The ecological conditions of freshwater aquaculture are deteriorating by degrees in recent years. Consequently, the comprehensive utilization of saline-alkaline water has garnered increasing societal attention. Here, crucian carp (Carassius auratus) were exposed to 20, 40 mmol/L NaHCO3 for 30 days (T, F group). Metabolomic analyses were conducted using UPLC-QTOF/MS, complemented by biochemical and microbiology profiling to elucidate the damage of the saline environment to the intestinal microbial structure, which in turn interfered with the energy metabolism. It was observed that carbonate alkalinity (CA) exposure not only caused intestine oxidative stress but also changed the levels of several digestive enzymes, including α-amylase (AMS), chymotrypsin (CHY), lipase (LPS). Metabolomic analysis identified 22 different metabolites (DEMs) in T group and 77 DEMs in F group. MetaboAnalyst analysis indicated that these metabolites are primarily involved in energy-related pathways, including the citric acid cycle, galactose metabolism, and glycine, serine, and threonine metabolism. Intestinal microbial diversity and community composition were altered under carbonate alkalinity exposure, with increase in Proteobacteria abundance and decline in Firmicutes, abundance alongside enrichment of Sphingomonas. Herein, saline-alkaline stress disrupted the physiological homeostasis of the crucian carp intestine, leading to microbial dysbiosis and energy metabolic imbalance. This study provides a theoretical foundation for understanding the stress response of the crucian carp intestine and the role of the intestinal microbiome in host resilience under adverse environmental conditions.

Mechanism of blocking the glutamate pathway to exacerbate oxidative stress, ammonia toxicity and metabolic disorders in crucian carp (Carassius auratus) under saline-alkaline exposure

Climate change and intensified human activities have accelerated the salinization and alkalinization of aquatic environments, further shrinking the space for freshwater aquaculture. One of the key survival mechanisms for fish in saline-alkaline habitats is the conversion of accumulated endogenous ammonia into less toxic glutamine. This study focuses on the freshwater teleost, crucian carp (Carassius auratus), using the liver as the target organ. Three groups were established: 0, 20, and 40 mmol/L NaHCO3 stress groups. After 30 days, methionine sulfoximine was injected to block the glutamate pathway, respectively. Through a combination of biochemical analysis and metabolomics, this study investigated the mechanisms by which blocking the glutamate pathway under different NaHCO3 stress concentrations affects metabolism in the liver of crucian carp. Biochemical results indicated that saline-alkaline stress led to oxidative stress and impaired ammonia excretion in crucian carp, and these effects were exacerbated after blocking the glutamate pathway. Metabolomic results revealed significant alterations in pathways such as glycerophospholipid metabolism, arachidonic acid metabolism, and purine metabolism. The study demonstrates that blocking the glutamate pathway exacerbates lipid and energy metabolism disorders under saline-alkaline stress, with crucian carp compensating by regulating glucose metabolism to mitigate energy deficiencies. In summary, this study elucidates the metabolic changes in crucian carp following the blockade of glutamate pathway under carbonate-alkaline stress, providing insight into the mechanisms leading to liver inflammation and metabolic dysregulation, and offers preliminary insights into the effects on ammonia excretion, which lay a scientific foundation for future research on freshwater teleosts in saline-alkaline environments.

Selenium-enriched Lactiplantibacillus plantarum alleviates alkalinity stress-induced selective hepatic insulin resistance in common carp

Carbonate alkalinity is one of the primary factors limiting saline-alkaline water aquaculture, and high alkalinity can lead to respiratory alkalosis, which is hazardous to fish health. Selenium (Se) and Lactiplantibacillus plantarum (L. plantarum) can be used for the biosynthesis of organic selenium (selenium-enriched Lactiplantibacillus plantarum: SL), which has low toxicity, high bioavailability, and the promotion of metabolism. Additionally, it can be used as a feed additive in aquaculture. In the present study, we established a model of chronic alkalinity stress in common carp and added SL to the feed. We found that alkalinity stress can cause severe hepatic dysfunction in common carp, as well as disrupt the intestinal barrier, further contributing to the translocation of enterogenous lipopolysaccharides through portal circulation and exacerbating liver injury. SL alleviated glucose-lipid metabolism abnormalities of the liver while reducing serum LPS levels and reduction of enterogenous LPS translocation to the liver, thus significantly reducing the degree of intestinal villi damage, hepatocyte vacuolisation, and nuclear damage. The significantly increased activities of SOD, GSH-Px, CAT, and T-AOC revealed that SL improved the antioxidant capacity of common carp. SL inhibited the alkalinity stress-induced overexpression of genes related to lipid synthesis and gluconeogenesis by modulating the P13K/Akt/FoxO1 signalling pathway, thus alleviating selective hepatic insulin resistance. SL attenuated the inflammatory response by modulating the mRNA expression levels of IL-7, IL-6, TNF-α and IL-10. In addition, apparent increase in the abundance of pathogenic bacteria (Brevinema, Bosea, Luteolibacter, and Vibrio) and apparent reduction in the abundance of beneficial bacteria (Cetobacterium, ZOR0006, and Shewanella) were closely related to the hepato-intestinal circulation process in carp exposed to alkalinity stress. SL regulated the hepato-intestinal circulation, reduced the abundance of Brevinema, Bosea, Luteolibacter, and Vibrio, increased the abundance of Cetobacterium, ZOR0006, and Shewanella, alleviated alkalinity stress-induced damage to intestinal microvilli (villus height and width), and significantly restored normal liver and intestinal functions. This study reveals the physiological regulatory mechanism by which Se-enriched L. plantarum through liver-intestinal axis alleviates alkalinity stress-induced hepatic insulin resistance and may provide new ideas and a theoretical basis for protecting against alkalosis and treating insulin resistance.

Osmoregulation and Physiological Response of Largemouth Bass (Micropterus salmoides) Juvenile to Different Salinity Stresses

The distribution of saline-alkali water is extensive and is increasing globally each year. Fully utilizing saline-alkali water for aquaculture can help alleviate the scarcity of freshwater resources in global fisheries. As a major economic fish species, the largemouth bass (Micropterus salmoides) holds significant potential for aquaculture in saline-alkali water. In the present study, we evaluated its tolerance to different salinities (0 ppt, 6 ppt, 9 ppt, 12 ppt, 15 ppt, and 18 ppt) and investigated tissue pathology, serum biochemical indicators, enzyme activities of osmolality and antioxidant, and the relative expression of Na-K-2Cl 1a cotransporter (NKCC1a) under different saline stress (0 ppt, 6 ppt, 9 ppt, and 12 ppt). The largemouth bass 96 h mortality rate increased with increasing salinity, and the LC50 for 96 h was 14.28 ppt based on the mortality results. High salinity group (12 ppt) caused gill and intestinal damage, including necrosis and cell shedding, while 6 ppt had no adverse effects, and the 9 ppt between the two salinities showed an adaptive change histologically. Serum osmolality, Na+, Cl-, and cortisol levels of the high salinity group were significantly higher than of the low salinities (p < 0.05). Similarly, Na+/K+-ATPase (NKA), Ca2+-Mg2+-ATPase (CMA), and superoxide dismutase (SOD) activities of 12 ppt peaked at 24 h (15.7 U/mgprot, 11.5 U/mgprot, and 243 U/mgprot), which is significantly different compared to the other three groups (p < 0.05). The expression of NKCC1a was significantly upregulated at 9 ppt and 12 ppt, suggesting its role in osmoregulation. Furthermore, the expression of NKCC1a in the gill is 2-4 times higher than that in the intestine. These results suggested that largemouth bass can be cultured at 6 ppt and selectively bred for tolerance at 9 ppt. NKA activity, cortisol levels, and NKCC1a expression can be used as a marker of salinity suitability. These findings provide insight into the adaptive mechanisms underlying the physiological responses to acute salinity stress and will contribute to improving aquaculture in saline waters.

Comparative analysis of crab growth performance, enzyme activity, and microbiota between rice-crab coculture and pond farming systems

Introduction

To support the sustainable development of rice and aquaculture industries, various rice-animal coculture systems have been developed. One such system, the rice-crab coculture system (RCC), has been practiced for decades in northern China. However, studies on the crab physiological status in RCC remain limited. Microorganisms play a crucial role in aquaculture by influencing animal nutrition, health, nutrient cycling, water quality, and environmental impact. Research on the gut and environmental microbiota in RCC is scarce.

Methods

This study compared the growth performance, immune and digestive enzyme activities of crabs between RCC and traditional pond farming system (PF). In addition, the microbiota in crab guts, water, and sediment from both systems was investigated using 16S rRNA gene sequencing.

Results

Crabs in RCC exhibited superior growth performance and higher enzymatic activities, including acid phosphatase (ACP), alkaline phosphatase (AKP), lipase (LPS), and trypsin (TRY). Significant differences were observed in microbiota composition across crab gut, water, and sediment samples, respectively. RCC crabs had a lower abundance of Bacteroidota and a higher abundance of Firmicutes in their gut microbiota. The RCC environment was enriched with beneficial bacteria such as Rhizobiales, Methylococcales, KD4-96, C39, Xanthomonadales, and Nitrosomonadaceae. Microbial function predictions confirmed enhanced methanotrophy and nitrogen fixation in the RCC.

Discussion

The RCC enhances the growth rate and immune capability of crabs. Crabs from RCC consume more animal-based nutrition, which results in distinct differences in gut microbiota composition and higher levels of LPS and TRY compared to those in PF. Additionally, RCC supports environmentally beneficial bacteria that contribute to greenhouse gas reduction, carbon and nitrogen fixation, organic matter decomposition, and ammonia oxidation, benefiting both the crabs and their ecosystem. These findings enhance our understanding of crab physiology and microbial communities in RCC and PF systems.

Integration of metabolomics and transcriptomics reveals the toxicological mechanism of deltamethrin exposure in Chinese mitten crab Eriocheir sinensis

This study investigated the toxicological mechanism of deltamethrin on Chinese mitten crab Eriocheir sinensis juveniles in fresh water. We first conducted an acute toxicity test, followed by laboratory methods to detect changes in immune-related indices in terms of antioxidant enzyme markers, lipid metabolism-related genes, and autophagy-related and apoptosis genes. The acute toxicity (96-h LC50) of deltamethrin to E. sinensis was 7.195 μg/L. After 48 h of exposure, serum showed elevated immune-related indices (P < 0.05) for alkaline phosphatase (AKP), acid phosphatase (ACP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), complement components C3 and C4, and the key pro-inflammatory cytokines interleukin-6, interleukin-1β, and tumor necrosis factor alpha (TNF-α). In hepatopancreas at 48 h, indicators related to the antioxidant system, namely superoxide dismutase (SOD) and glutathione (GSH), were significantly elevated, whereas nitric oxide and total antioxidant capacity (T-AOC) were decreased (P < 0.05). In contrast, lipid metabolism indices for triglyceride (TG), total cholesterol (TC), and malondialdehyde (MDA) were increased (P < 0.05). Transcriptomics and metabolomics revealed that exposure to deltamethrin disrupted the lipid metabolic process in the hepatopancreas mainly by altering fatty acid synthesis, amino acid metabolism, immune signaling, and autophagy activation, while the exposure increased the content of phospholipids and cholesterol but decreased the levels of amino acids and palmitoleic acid. Quantitative genetics revealed significantly aberrantly expressed (P < 0.05) lipid metabolism-related genes, including acc1, fasn, scd1, and pnpla2, all key genes involved in lipid accumulation. Deltamethrin exposure also significantly altered (P < 0.05) gene expression levels for Toll-like receptor (tlr), myeloid differentiation factor 88 (myd88), crustin1, anti-lipopolysaccharide factor isoform 3 (alf3), tumor necrosis factor alpha (tnf-α), and NF-κB transcription factor relish. Furthermore, deltamethrin activated the toll-like receptor/major myeloid differentiation response gene 88/nuclear factor kappa-light-chain-enhancer of activated B cells (TLR/MyD88/NF-kB) signaling pathway, which activates a nonspecific immune response in E. sinensis. Additionally, carnitine palmitoyltransferase 1 A (cpt1a), cytochrome c (cyt-c), adenosine 5'-monophosphate (amp)-activated protein kinase (ampk), the autophagosomal protein microtubule-associated protein 1 light chain 3c (lc3c), and the autophagy-related proteins beclin1, atg5, atg12 were significantly induced (P < 0.05) in the adenosine monophosphate-activated protein kinase/rapamycin (AMPK/mTOR) signaling pathway. These changes resulted in excess free radicals, causing oxidative stress in the mitochondrial membrane, promoting mitochondrial autophagy. The results confirm that deltamethrin exposure can induce hepatopancreatic injury by promoting mitochondrial autophagy, activating an immune response, and inhibiting lipid metabolism. Overall, this study provides multi-level information to reveal the toxic effects of deltamethrin on E. sinensis.

Characterization of the molecular, cellular, and behavioral changes caused by exposure to a saline-alkali environment in the Chinese mitten crab, Eriocheir sinensis

In the context of global warming, the accelerated evaporation of seawater will lead to a continuous expansion of saline-alkali land area. As an important economic freshwater crustacean, investigation on the mechanism of damage to Eriocheir sinensis (E. sinensis) under saline-alkali environment will provide a valuable precedent for understanding the detrimental effect of climate change on crustaceans. In this study, histopathological analysis and integrative omics analysis were employed to explore the injury mechanism on the cerebral nervous system of E. sinensis exposure to saline-alkali stress. Our findings revealed that under this stress E. sinensis exhibited behavioral disorders and damage to cerebral neurosecretory cells and key organelles. Additionally, several pathways related to detoxification metabolism, neurotransmitter synthesis, and antioxidant defense were significantly down-regulated. Collectively, these results show, for the first time, that saline-alkali stress can induce neurodegenerative disease-like symptoms in E. sinensis, and provide critical information for understanding the harmful effects of saline-alkali environments.

Study on the physiological responses and tolerance mechanisms to subchronic carbonate alkalinity exposure in the gills of Paramisgurnus dabryanus

Given the reduction of freshwater resources, saline-alkaline aquaculture has emerged as an effective approach to expand the fishery's accessible space. High carbonate alkalinity (CA) is a major stressor for aquatic organisms in saline-alkaline environments. Paramisgurnus dabryanus is a potential species for culture in saline-alkaline water, making it an ideal model for investigating the physiological responses and tolerance mechanisms to CA exposure in freshwater fishes. In the current study, P. dabryanus were exposed to 15 and 30 mmol/L NaHCO3, combining blood biochemical, gill histological, transcriptomic, and metabolomic methods for conjoint analysis of response mechanisms. After 28-d exposure, the gill ventilation frequency of P. dabryanus decreased significantly, gill lamellae twisted and atrophied, and gill filament epithelial cells proliferated, potentially limiting gas exchange, whereas the accessory air-breathing frequency increased significantly, possibly for greater oxygen uptake. Serum osmolality and blood pH remained relatively steady, while serum ammonia levels rose significantly. A total of 3718 differentially expressed genes (DEGs) and 205 differential metabolites (DMs) were identified between the control group and 30 mmol/L NaHCO3 group, involved in ion transport (Na+/K+-ATPase, V-type ATPase, carbonic anhydrase, and ABC transporters), ammonia transport (Rh glycoproteins and Aquaporins), amino acid metabolism, carbohydrate metabolism, and fatty acid metabolism. Furthermore, DEGs were significantly associated with cell-cell/ extracellular matrix interaction and protein synthesis. An integrated multi-omics analysis revealed the activation of carbon metabolism and TCA cycle. These results indicate that in response to CA exposure, P. dabryanus may facilitate carrier-mediated ion and ammonia transport to maintain the internal osmotic equilibrium and lessen the deleterious effects of blocked ammonia excretion. Meanwhile, amino acid metabolism and protein synthesis are disturbed, P. dabryanus can modulate carbohydrate catabolism to maintain energy homeostasis. The above findings provide novel insights into saline-alkaline adaptation in freshwater fishes, paving the way for future research and development of saline-alkaline-tolerant Cobitidae strains.

Effects of Diets With Different Carbohydrate to Lipid Ratios on the Growth Performance, Ion Transport, and Carbohydrate, Lipid and Ammonia Metabolism of Nile Tilapia (Oreochromis niloticus) Under Long-Term Saline-Alkali Stress

A 50-day test was adopted to compare the growth performance, liver histology, glucose metabolism, lipid (L) metabolism, ion transport, and ammonia metabolism of tilapia fed different carbohydrate-lipid (C:L) ratio diets under saline-alkaline water (salinity = 16 mmol/L and alkalinity = 35 mmol/L). The C and L levels of five isoenergetic (16.5 kJ/g) and isonitrogenous (32% protein) diets were C45%:L3% (L3), C38%:L6% (L6), C31%:L9% (L9), C24%:L12% (L12), and C17%:L15% (L15). This study found that the dietary C:L ratio did not affect the survival rate (SR), feed conversion ratio (FCR), or condition factor of tilapia in saline-alkali water, but fish in the L12 group had the highest weight gain (WG) rate and the lowest hepatosomatic index (HSI) compared with the other groups. Fish fed the higher C diet (L3 and L6) had a higher ion transport capacity and ammonia excretion capacity in gills. However, the highest mRNA expression of genes involved in glutamine metabolism and urea metabolism in the liver was found in the high-L diet groups (L12 and L15). In particular, a lower serum ammonia concentration was observed in the high-L diet groups (L12 and L15). In addition, biochemical indicators indicated that the L12 group had the highest liver pyruvic acid, lactic dehydrogenase (LDH), and lipase (LPS) and serum total cholesterol (T-CHO) contents. In summary, this study indicated that dietary Ls could promote glutamine metabolism and urea metabolism more than dietary Cs and then reduce the serum ammonia concentration of tilapia in saline-alkali water. A dietary C:L ratio of 2:1 was beneficial to the growth and ammonia excretion of tilapia in saline-alkali water in this study.

Effects of Alkalinity Stress on Amino Acid Metabolism Profiles and Oxidative-Stress-Mediated Apoptosis/Ferroptosis in Hybrid Sturgeon (Huso dauricus ♀ × Acipenser schrenckii ♂) Livers

Alkaline water is toxic to cultured aquatic animals that frequently live in pH-neutral freshwater. Overfishing and habitat destruction have contributed to the decline in the wild sturgeon population; consequently, the domestic hybrid sturgeon has become an increasingly important commercial species in China. Hybrid sturgeons are widely cultured in alkaline water, but little is known about the effects of alkalinity stress on hybrid sturgeon liver tissues. We exposed hybrid sturgeons to four alkaline concentrations (3.14 ± 0.02 mmol/L, 7.57 ± 0.08 mmol/L, 11.78 ± 0.24 mmol/L and 15.46 ± 0.48 mmol/L). Histopathology, biochemical index assessment, gene expression level detection and metabolomics analysis were used to investigate the negative effects on liver functions following exposure to NaHCO3. Livers exposed to alkaline stress exhibited severe tissue injury and clear apoptotic characteristics. With increased exposure concentrations, the hepatic superoxide dismutase, catalase, glutathione peroxidase and alkaline phosphatase activities significantly decreased in a dose-dependent manner. NaHCO3 exposure up-regulated the transcriptional levels of apoptosis/ferroptosis-related genes in livers. Similarly, the expression trends of interleukin-1β and heat shock protein genes also increased in high-alkalinity environments. However, the expression levels of complement protein 3 significantly decreased (p < 0.05). Hepatic untargeted metabolomics revealed the alteration conditions of various metabolites associated with the antioxidant response, the ferroptosis process and amino acid metabolism (such as beta-alanine metabolism; alanine, aspartate and glutamate metabolism; and glycine, serine and threonine metabolism). These data provided evidence that NaHCO3 impaired immune functions and the integrity of hybrid sturgeon liver tissues by mediating oxidative-stress-mediated apoptosis and ferroptosis. Our results shed light on the breeding welfare of domestic hybrid sturgeons and promote the economic development of fisheries in China.

Effects of Dietary Bio-Fermented Selenium Supplementation on Growth, Immune Performance, and Intestinal Microflora of Chinese Mitten Crabs, Eriocheir sinensis

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.

Exploration of Synergistic Regulation Mechanisms of Cerebral Ganglion and Muscle in Eriocheir sinensis Activated in Response to Alkalinity Stress

The cerebral ganglion and muscle are important regulatory tissues in Eriocheir sinensis. Therefore, it is of great significance to explore their synergistic roles in this organism's anti-stress response. In this study, proteomics, metabolomics, and combination analyses of the cerebral ganglion and muscle of E. sinensis under alkalinity stress were performed. The cerebral ganglion and muscle played a significant synergistic regulatory role in alkalinity adaptation. The key regulatory pathways involved were amino acid metabolism, energy metabolism, signal transduction, and the organismal system. They also played a modulatory role in the TCA cycle, nerve signal transduction, immune response, homeostasis maintenance, and ion channel function. In conclusion, the present study provides a theoretical reference for further research on the mechanisms regulating the growth and development of E. sinensis in saline-alkaline environments. In addition, it provides theoretical guidelines for promoting the vigorous development of the E. sinensis breeding industry in saline-alkaline environments in the future.

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.

Temporal Transcriptomic Profiling Reveals Dynamic Changes in Gene Expression of Giant Freshwater Prawn upon Acute Saline-Alkaline Stresses

Bicarbonate and sulfate are among two primary ion constituents of saline-alkaline water, with excessive levels potentially causing metabolic disorders in crustaceans, affecting their molting and interrupting development. As an economically important crustacean species, the molecular adaptive mechanism of giant freshwater prawn Macrobrachium rosenbergii in response to the stress of bicarbonate and sulfate remains unexplored. To investigate the mechanism underlying NaHCO3, Na2SO4, and mixed NaHCO3, Na2SO4 stresses, M. rosenbergii larvae were exposed to the above three stress conditions, followed by total RNA extraction and high-throughput sequencing at eight distinct time points (0, 4, 8, 12, 24, 48, 72, and 96 h). Subsequent analysis revealed 13, 16, and 13 consistently identified differentially expressed genes (DEGs) across eight time points under three stress conditions. These consistently identified DEGs were significantly involved in the Gene Ontology (GO) terms of chitin-based cuticle development, protein-carbohydrate complex, structural constituent of cuticle, carnitine biosynthetic process, extracellular matrix, and polysaccharide catabolic process, indicating that alkaline stresses might potentially impact the energy metabolism, growth, and molting of M. rosenbergii larvae. Particularly, the transcriptome data revealed that DEGs associated with energy metabolism, immunity, and amino acid metabolism were enriched across multiple time points under three stress conditions. These DEGs are linked to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including glycolysis/glucogenesis, amino sugar and nucleotide sugar metabolism, and lysine degradation. Consistent enrichment findings across the three stress conditions support conclusions above. Together, these insights are instrumental in enhancing our understanding of the molecular mechanisms underlying the alkaline response in M. rosenbergii larvae. Additionally, they offer valuable perspectives on the regulatory mechanisms of freshwater crustaceans amid saline-alkaline water development.

Response of the terrestrial isopod Porcellio scaber to lipopolysaccharide challenge after microplastic and insecticide exposure

The exposure of organisms to microplastics could compromise their ability to cope with other environmental stressors, such as infections. In this context, we investigated the effects of a 14-day exposure of the terrestrial isopod Porcellio scaber to tire particles in soil (1.5 % w w-1 dry weight) on the organisms' response to a secondary exposure, i.e., injection of the bacterial endotoxin lipopolysaccharide. In addition, the insecticide chlorpyrifos (2 mg kg-1 dry weight) was tested as a positive control. The survival and immune response of P. scaber was assessed at the end of the 7- and 14-day primary exposure and two days after the secondary exposure, by analyzing selected haemolymph immune parameters (total haemocyte count, differential haemocyte count, and haemocyte viability). No change in survival was observed after primary exposure of P. scaber to tire particles or chlorpyrifos. However, primary exposure to chlorpyrifos triggered a strong activation of the immune response, which was not the case following exposure to the tire particles. Further injection of lipopolysaccharide into the body did not affect the survival of animals exposed to tire particles or chlorpyrifos, while a strong immunomodulatory change was observed, particularly with chlorpyrifos, and to some extent, tire particles. Based on these results, we conclude that exposure of P. scaber to tire particles or chlorpyrifos has no significant effect on the susceptibility of the organism to lipopolysaccharide in terms of their mortality, but primary exposure to an insecticide significantly modulates the immune response of the organisms to a second stressor. We discuss the "stress on stress" approach for testing low-toxic substances, such as microplastics, where an environmentally realistic exposure is followed by a secondary exposure.

Response of antioxidation and immunity to combined influences of pH and ammonia nitrogen in the spotted babylon (Babylonia areolata)

Spotted babylon were exposed to three different pH levels (7.0, 8.0 and 9.0) and four different concentrations of ammonia nitrogen (0.02, 1.02, 5.10 and 10.20 mg/L) in seawater to determine their acute toxicity and physiological responses to environmental fluctuation. The study evaluated four antioxidant enzymes: catalase (CAT), alkaline, superoxide dismutase (SOD), peroxidase (POD) and glutathione peroxidase (GSH-PX), and two immunoenzymes: acid phosphatase (ACP) and phosphatase (AKP). Over time, the immunoenzyme activity was significantly affected by pH and ammonia nitrogen concentration. After being exposed to pH and ammonia nitrogen, the spotted babylon showed signs of unresponsiveness to external stimuli, reduced vitality, slow movement, and an inability to maintain an upright position. Over time, the spotted babylon exhibited a trend of increasing and then decreasing GSH-PX, CAT, and SOD activities to adapt to the changing environment and enhance its immunity. On the contrary, the POD and ACP activities exhibited a decreasing trend initially, followed by an increasing trend over time and the AKP activity showed a gradual increase with time. The combined effect of pH and ammonia was found to be stronger than the effect of either factor alone. The interaction between pH and ammonia increased the activity of the spotted babylon antioxidant enzymes, induced oxidative stress, and reduced the ability of the spotted babylon's non-specific immune system to reverse it. Thus, the reverse-back of the spotted babylon was higher when pH and ammonia stress were dual than when pH or ammonia were single-factor stresses. The study results will establish a theoretical basis for analyzing the risk of multiple factors to the spotted babylon, and also enrich the basic information about the shellfish immune system.

H2O2-Induced Oxidative Stress Responses in Eriocheir sinensis: Antioxidant Defense and Immune Gene Expression Dynamics

Eriocheir sinensis, a key species in China's freshwater aquaculture, is threatened by various diseases, which were verified to be closely associated with oxidative stress. This study aimed to investigate the response of E. sinensis to hydrogen peroxide (H2O2)-induced oxidative stress to understand the biological processes behind these diseases. Crabs were exposed to different concentrations of H2O2 and their antioxidant enzyme activities and gene expressions for defense and immunity were measured. Results showed that activities of antioxidant enzymes-specificallysuperoxide dismutase (SOD), catalase (CAT), total antioxidant capacity(T-AOC), glutathione (GSH), and glutathione peroxidase (GSH-Px)-varied with exposure concentration and duration, initially increasing then decreasing. Notably, SOD, GSH-Px, and T-AOC activities dropped below control levels at 96 h. Concurrently, oxidative damage markers, including malondialdehyde (MDA), H2O2, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, increased with exposure duration. The mRNA expression of SOD, CAT, and GSH-Px also showed an initial increase followed by a decrease, peaking at 72 h. The upregulation of phenoloxidaseloxidase (proPO) and peroxinectin (PX) was also detected, but proPO was suppressed under high levels of H2O2. Heat shock protein 70 (HSP70) expression gradually increased with higher H2O2 concentrations, whereas induced nitrogen monoxide synthase (iNOS) was upregulated but decreased at 96 h. These findings emphasize H2O2's significant impact on the crab's oxidative and immune responses, highlighting the importance of understanding cellular stress responses for disease prevention and therapy development.

Comparative Transcriptome Analysis of the Hepatopancreas from Macrobrachium rosenbergii Exposed to the Heavy Metal Copper

The contamination of aquatic ecosystems by the heavy metal copper (Cu) is an important environmental issue and poses significant risks to the physiological functions of aquatic organisms. Macrobrachium rosenbergii is one of the most important freshwater-cultured prawns in the world. The hepatopancreas of crustaceans is a key organ for immune defense, heavy metal accumulation, and detoxification, playing a pivotal role in toxicological research. However, research on the molecular response of the hepatopancreas in M. rosenbergii to Cu exposure is still lacking. In this study, the transcriptomic response in the hepatopancreas of M. rosenbergii was studied after Cu exposure for 3 and 48 h. Compared with the control group, 11,164 (7288 up-regulated and 3876 down-regulated genes) and 10,937 (6630 up-regulated and 4307 down-regulated genes) differentially expressed genes (DEGs) were identified after 3 and 48 h exposure, respectively. Most of these DEGs were up-regulated, implying that gene expressions were largely induced by Cu. Functional enrichment analysis of these DEGs revealed that immunity, copper homeostasis, detoxification, DNA damage repair, and apoptosis were differentially regulated by Cu. Seven genes involved in immunity, detoxification, and metabolism were selected for validation by qRT-PCR, and the results confirmed the reliability of RNA-Seq. All these findings suggest that M. rosenbergii attempts to resist the toxicity of Cu by up-regulating the expression of genes related to immunity, metabolism, and detoxification. However, with the excessive accumulation of reactive oxygen species (ROS), the antioxidant enzyme system was destroyed. As a result, DNA damage repair and the cellular stress response were inhibited, thereby exacerbating cell damage. In order to maintain the normal function of the hepatopancreas, M. rosenbergii removes damaged cells by activating the apoptosis mechanism. Our study not only facilitates an understanding of the molecular response mechanisms of M. rosenbergii underlying Cu toxicity effects but also helps us to identify potential biomarkers associated with the stress response in other crustaceans.

Ginger polysaccharide alleviates the effects of acute exposure to carbonate in crucian carp (Carassius auratus) by regulating immunity, intestinal microbiota, and intestinal metabolism

Alkaline stress poses a significant challenge to the healthy growth of fish. Ginger polysaccharide (GP) is one of the main active substances in ginger and has pharmacological effects, such as anti-oxidation and immune regulation. However, the physiological regulatory mechanism of GP addition to diet on alkalinity stress in crucian carp remains unclear. This study aimed to investigate the potential protective effects of dietary GP on antioxidant capacity, gene expression levels, intestinal microbiome, and metabolomics of crucian carp exposed to carbonate (NaHCO3). The CK group (no GP supplementation) and COG group (NaHCO3 stress and no GP supplementation) were set up. The GPCS group (NaHCO3 stress and 0.4% GP supplementation) was stressed for seven days. Based on these data, GP significantly increased the activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), acid phosphatase (ACP), and alkaline phosphatase (AKP) in carp under alkalinity stress (p < 0.05) and decreased the activity of malon dialdehyde (MDA) (p < 0.05). GP restored the activity of GSH-PX, ACP, and AKP to CK levels. The expression levels of tumor necrosis factor β (TGF-β), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and interleukin 8 (IL-8) genes were decreased, and the expression levels of determination factor kappa-B (NF-κB) and interleukin 10 (IL-10) genes were increased (p < 0.05). Based on 16 S rRNA high-throughput sequencing, GP improved the changes in the intestinal microbial diversity and structural composition of crucian carp caused by NaHCO3 exposure. In particular, GP increased the relative abundance of Proteobacteria and Bacteroidetes and decreased the relative abundance of Actinobacteria. The metabolic response of GP to NaHCO3 exposed crucian carp guts was studied using LC/MS. Compared to the COG group, the GPCS group had 64 different metabolites and enriched 10 metabolic pathways, including lipid metabolism, nucleotide metabolism, and carbohydrate metabolism. The addition of GP to feed can promote galactose metabolism and provide an energy supply to crucian carp, thus alleviating the damage induced by alkalinity stress. In conclusion, GP can mitigate the effects of NaHCO3 alkalinity stress by regulating immune function, intestinal flora, and intestinal metabolism in crucian carp. These findings provide a novel idea for studying the mechanism of salt-alkali tolerance in crucian carp by adding GP to feed.

Integrated characterizations of intestinal bacteria and transcriptomics revealed the acute stress response to carbonate alkalinity in white shrimp Penaeusvannamei

The impact of carbonate alkalinity in saline-alkaline water on aquatic organisms, particularly Penaeus vannamei, a significant species in aquaculture, remains a critical area of study. To elucidate the acute response mechanisms of P. vannamei to elevated carbonate alkalinity environments, we utilized 16S rRNA gene and transcriptome sequencing technologies to analyze intestinal bacteria and gene expressions within various tissues. Our investigation revealed notable changes in specific intestinal bacterial OTUs, whose abundances varied preceding the overall bacterial community, indicating the sensitivity to carbonate alkalinity exposure. These shifts are accompanied by a simplification in bacterial networks and alterations in pathogenic OTUs, notably Aeromonas OTU. Concurrently, gene expression variations were observed across the hepatopancreas, gills, muscles, and intestines, with decreasing numbers of DEGs in the mentioned order. Annotation of these DEGs revealed enrichments in pathways related to transport, catabolism, immune responses, circulatory functions, and lipid metabolism. Notably, correlations between specific intestinal bacterial OTUs and gene expression shifts were identified across these tissues. Several OTUs, attributed to Rhizobiales, Saccharimonadales, Acidovora, and Aeromona, exhibited a correlation with DEGs in all four tissues, primarily associated with amino acid metabolism, signal transduction, and transport and catabolism pathways. Our study provides comprehensive insights into the dynamic responses of P. vannamei to elevated carbonate alkalinity stress. These findings contribute crucial knowledge for effective P. vannamei cultivation in saline-alkaline water, advancing our understanding in this field.

The effects of bisphenol S exposure on the growth, physiological and biochemical indices, and ecdysteroid receptor gene expression in red swamp crayfish, Procambarus clarkii

The experiment was conducted to investigate the effects of Bisphenol S (BPS) on growth, physiological and biochemical indices, and the expression of ecdysteroid receptor (ECR) of the red swamp crayfish (Procambarus clarkii). The gene encoding ECR was isolated from red swamp crayfish by homologous cloning and rapid amplification of cDNA ends (RACE). The ECR transcripts were 1757 bp long and encoded proteins of 576 amino acids. The quantitative real-time PCR (qRT-PCR) analysis showed that the ECR gene was expressed in various tissues under normal conditions, and the highest level was observed in the ovary and the lowest level was observed in the muscle (P < 0.05). Then, the experiment was designed with four different BPS concentrations (0, 1, 10, and 100 μg/L), BPS exposure for 14 days, three parallel groups, and a total of 240 red swamp crayfish. At 100 μg/L BPS, the survival rate, weight gain rate, and relative length rate were decreased significantly (P < 0.05). Malonaldehyde (MDA) content reached the highest level at 100 μg/L BPS. When BPS concentration was higher than 10 μg/L, the activities of superoxide dismutase (SOD) and catalase (CAT) were significantly lower than those of the control group (P < 0.05). The expression levels of the ECR gene in ovary, intestinal, gill, and hepatopancreas tissues were significantly increased after BPS exposure (P < 0.05). The ECR gene expression in ovaries and Y-organs was significantly higher than other groups in 10 μg/L BPS (P < 0.05). The expressions of the tumor necrosis factor -α (TNF-α) and interleukin-6 (IL-6) genes in the hepatopancreas gradually increased, and the highest expression was observed exposed in 100 μg/L BPS (P < 0.05). This research will provide novel insights into the health risk assessment of BPS in aquatic organisms.

Reducing Dietary Protein Content by Increasing Carbohydrates Is More Beneficial to the Growth, Antioxidative Capacity, Ion Transport, and Ammonia Excretion of Nile Tilapia (Oreochromis niloticus) under Long-Term Alkalinity Stress

Alkalinity stress is the main stress experienced by aquatic animals in saline-alkali water, which hinders the aquaculture development and the utilization of water resources. The two-factor (2 × 3) test was adopted to study the influence of dietary protein to carbohydrate ratios on the energy metabolism of Nile tilapia (Oreochromis niloticus) under different alkalinity stress levels. Three diets with different protein-carbohydrate ratios (P27/C35, P35/C25, and P42/C15) were fed to fish cultured in freshwater (FW, 1.3 mmol/L carbonate alkalinity) or alkaline water (AW, 35.7 mmol/L carbonate alkalinity) for 50 days. Ambient alkalinity decreased tilapia growth performance. Although ambient alkalinity caused oxidative stress and enhanced ion transport and ammonia metabolism in tilapia, tilapia fed the P27/C35 diet showed better adaptability than fish fed the other two diets in alkaline water. Further metabolomic analysis showed that tilapia upregulated all the pathways enriched in this study to cope with alkalinity stress. Under alkalinity stress, tilapia fed the P27/C35 diet exhibited enhanced pyruvate metabolism and purine metabolism compared with tilapia fed the P42/C15 diet. This study indicated that ambient alkalinity could significantly decrease growth performance and cause oxidative stress and osmotic regulation. However, reducing dietary protein content by increasing carbohydrates could weaken stress and improve growth performance, ion transport, and ammonia metabolism in tilapia under long-term hyperalkaline exposure.

α-Lipoic acid improves mitochondrial biogenesis and dynamics by enhancing antioxidant and inhibiting Wnt/Ca2+ pathway to relieve fluoride-induced hepatotoxic injury

Fluoride (F), widely present in water and food, poses a serious threat to liver health, and oxidative damage and mitochondrial damage are its main causes. As a natural mitochondrial protector and antioxidant, α-lipoic acid (ALA)'s alleviating effect on fluorosis liver injury and its underlying mechanism are still unclear. Therefore, this study established a fluorosis ALA intervention mice model to explore the mechanism of mitochondrial biogenesis, mitochondrial dynamics, and Wnt/Ca2+ pathway in ALA attenuating fluorosis liver injury. The results showed that ALA mitigated F-induced weight loss, hepatic structural and functional damage, hepatocytes mitochondrial damage, and decreased antioxidant levels. However, ALA did not reduce F accumulation in the femur. Further mRNA and protein detection results showed that F increased the expression levels of key genes in the mitochondrial fission (Drp1, Mff, and Fis1), mitophagy (Parkin, Pink1, and Prdx3), Wnt/Ca2+ pathway (Wnt5a and CaMK2), and rised the number and intensity of fluorescent spots of Drp1, but decreased the expression levels of key genes in the mitochondrial biogenesis (Sirt1, Sirt3, and PGC-1α) and fusion (OPA1, Mfn2, and Mfn1), and reduced the number and intensity of fluorescent spots of PGC-1α in the liver. However, the intervention of ALA relieved the F-induced changes in the expressions of the above genes. In conclusion, ALA mitigated F-induced hepatic injury through enhancing antioxidant capacity and inhibiting Wnt/Ca2+ pathway to improve mitochondrial biogenesis and dynamics disturbance. This study further reveals the hepatotoxic mechanism of F and the protective mechanism of ALA, and provides a theoretical basis for ALA as a potential preventive and palliative agent for F-induced hepatotoxic injury.

Effects of prometryn on oxidative stress, immune response and apoptosis in the hepatopancreas of Eriocheir sinensis (Crustacea: Decapoda)

Prometryn, a triazine pesticide product used to control weed growth, poses a high risk to aquatic organisms in the environment. Several toxicological evaluations have been performed on bony fish and shrimp exposed to prometryn. However, there have been no reports conducted on the toxic mechanism of prometryn with regard to Eriocheir sinensis. In this study, our research evaluated the toxic effects of prometryn via in vitro and in vivo toxicity tests on E. sinensis. Firstly, we estimated the exposure toxicity of prometryn to E. sinensis, and then we constructed a 6 h transcriptional profile and conducted an enrichment analysis. To further reveal the toxicity of prometryn, the hepatopancreas (hepatopancreatic cells) was analyzed for antioxidant, immune and lipid-metabolism-related enzymes, antioxidant- and apoptosis-related gene expression, histopathology and TUNEL. From the results, we determined that the 96 h-LD50 was 70.059 mg/kg, and using RNA-seq, we identified 933 differentially expressed genes (DEGs), which were mainly enriched in the amino and fatty acid metabolism and the cell-fate-determination-related signaling pathway. The results of the biochemical assays showed that prometryn could significantly decrease the activities/levels of CAT, SOD, GSH, AKP and ACP, reduce the levels of T-AOC, TG, TCH, C3 and C4, and increase the MDA content. In addition, the expression levels of Nrf2, GSTs and HO-1 were first upregulated and then downregulated with increasing time. Histopathology showed that prometryn damaged the structure of the hepatopancreas cells and induced apoptosis, suggesting that the PI3K-Akt signaling pathway may be involved in the damage process of hepatopancreas cells (PI3K, PDK and Akt were downregulated whereas Bax was upregulated), leading to their apoptosis. The above results indicated that prometryn could cause injury of the hepatopancreas through oxidative stress, induce cell apoptosis, disrupt the lipid metabolism and cause immune damage. This study provided useful data for understanding and evaluating the toxicity of prometryn to aquatic crustacea.