Transcriptome analysis reveals the mechanism of alkalinity exposure on spleen oxidative stress, inflammation and immune function of Luciobarbus capito

The tricarboxylic acid cycle is inhibited under acute stress from carbonate alkalinity in the gills of Eriocheir sinensis

Owing to population growth and environmental pollution, freshwater aquaculture has been rapidly shrinking in recent years. Aquaculture in saline-alkaline waters is a crucial strategy to meet the increasing demand for aquatic products. The Chinese mitten crab is an important economic food in China, but the molecular mechanism by which it tolerates carbonate alkalinity (CA) in water remains unclear. Here, we found that enzyme activities of the tricarboxylic acid (TCA) cycle in the gills, such as citrate synthase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase, were markedly reduced under CA stress induced by 40 mM NaHCO3. Secondly, the TCA cycle in the gills is inhibited under acute CA stress, according to proteomic and metabolomic analyses. The expressions of six enzymes, namely aconitate hydratase, isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase, dihydrolipoyl dehydrogenase, succinate-CoA ligase, and malate dehydrogenase, were downregulated, resulting in the accumulation of phosphoenolpyruvic acid, citric acid, cis-aconitate, and α-ketoglutaric acid. Finally, we testified that if the TCA cycle is disturbed by malonate, the survival rate increases in CA water. To our knowledge, this is the first study to show that the TCA cycle in the gills is inhibited under CA stress. Overall, the results provide new insights into the molecular mechanism of tolerance to saline-alkaline water in crabs, which helped us expand the area for freshwater aquaculture and comprehensively understand the physiological characteristics of crab migration.

Identification of the effects of alkalinity exposure on the gills of oriental river prawns, Macrobrachium nipponense

Macrobrachium nipponense is an important commercial freshwater species in China. However, the ability of alkali tolerance of M. nipponense is insufficient to culture in the major saline-alkali water source in China. Thus, it is urgently needed to perform the genetic improvement of alkali tolerance in this species. In the present study, we aimed to analyse the effects of alkali treatment on gills in this species after 96 h alkalinity exposure under the alkali concentrations of 0 mmol/L, 4 mmol/L, 8 mmol/L, and 12 mmol/L through performing the histological observations, measurement of antioxidant enzymes, metabolic profiling analysis, and transcriptome profiling analysis. The results of the present study revealed that alkali treatment stimulated the contents of malondialdehyde, glutathione, glutathione peroxidase in gills, indicating these antioxidant enzymes plays essential roles in the protection of body from the damage, caused by the alkali treatment. In addition, high concentration of alkali treatment (> 8 mmol/L) resulted in the damage of gill membrane and haemolymph vessel, affecting the normal respiratory function of gill. Metabolic profiling analysis revealed that Metabolic pathways, Biosynthesis of secondary metabolites, Biosynthesis of plant secondary metabolites, Microbial metabolism in diverse environments, Biosynthesis of amino acids were identified as the main enriched metabolic pathways of differentially expressed metabolites, which are consistent with the previous publications, treated by the various environmental factors. Transcriptome profiling analyses revealed that the alkali concentration of 12 mmol/L has more regulatory effects on the changes of gene expression than the other alkali concentrations. KEGG analysis revealed that Phagosome, Lysosome, Glycolysis/Gluconeogenesis, Purine Metabolism, Amino sugar and nucleotide sugar metabolism, and Endocytosis were identified as the main enriched metabolic pathways in the present study, predicting these metabolic pathways may be involved in the adaption of alkali treatment in M. nipponense. Phagosome, Lysosome, Purine Metabolism, and Endocytosis are immune-related metabolic pathways, while Glycolysis/Gluconeogenesis, and Amino sugar and nucleotide sugar metabolism are energy metabolism-related metabolic pathways. Quantitative PCR analyses of differentially expressed genes (DEGs) verified the accuracy of the RNA-Seq. Alkali treatment significantly stimulated the expressions of DEGs from the metabolic pathways of Phagosome and Lysosome, suggesting Phagosome and Lysosome play essential roles in the regulation of alkali tolerance in this species, as well as the genes from these metabolic pathways. The present study identified the effects of alkali treatment on gills, providing valuable evidences for the genetic improvement of alkali tolerance in M. nipponense.

Isolation, identification and transcriptome analysis of triadimefon-degrading strain Enterobacter hormaechei TY18

Triadimefon, a type of triazole systemic fungicide, has been extensively used to control various fungal diseases. However, triadimefon could lead to severe environmental pollution, and even threatens human health. To eliminate triadimefon residues, a triadimefon-degrading bacterial strain TY18 was isolated from a long-term polluted site and was identified as Enterobacter hormaechei. Strain TY18 could grow well in a carbon salt medium with triadimefon as the sole nitrogen source, and could efficiently degrade triadimefon. Under triadimefon stress, a total of 430 differentially expressed genes (DEGs), including 197 up-regulated and 233 down-regulated DEGs, were identified in strain TY18 using transcriptome sequencing (RNA-Seq). Functional classification and enrichment analysis revealed that these DEGs were mainly related to amino acid transport and metabolism, carbohydrate transport and metabolism, small molecule and pyrimidine metabolism. Interestingly, the DEGs encoding monooxygenase and hydrolase activity acting on carbon-nitrogen were highly up-regulated, might be mainly responsible for the metabolism in triadimefon. Our findings in this work suggest that strain E. hormaechei TY18 could efficiently degrade triadimefon for the first time. They provide a great potential to manage triadimefon biodegradation in the environment successfully.

Analysis revealed the molecular mechanism of oxidative stress-autophagy-induced liver injury caused by high alkalinity: integrated whole hepatic transcriptome and metabolome

Introduction

High-alkalinity water is a serious health hazard for fish and can cause oxidative stress and metabolic dysregulation in fish livers. However, the molecular mechanism of liver damage caused by high alkalinity in fish is unclear.

Methods

In this study, 180 carp were randomly divided into a control (C) group and a high-alkalinity (A25) group and were cultured for 56 days. High-alkalinity-induced liver injury was analysed using histopathological, whole-transcriptome, and metabolomic analyses.

Results

Many autophagic bodies and abundant mitochondrial membrane damage were observed in the A25 group. High alkalinity decreased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activity and the total antioxidant capacity (T-AOC) and increased the malondialdehyde (MDA) content in liver tissues, causing oxidative stress in the liver. Transcriptome analysis revealed 61 differentially expressed microRNAs (miRNAs) and 4008 differentially expressed mRNAs. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that mammalian target of rapamycin (mTOR), forkhead box O (FoxO), mitogen-activated protein kinase (MAPK), and the autophagy signalling pathway were the molecular mechanisms involved. High alkalinity causes oxidative stress and autophagy and results in autophagic damage in the liver. Bioinformatic predictions indicated that Unc-51 Like Kinase 2 (ULK2) was a potential target gene for miR-140-5p, demonstrating that high alkalinity triggered autophagy through the miR-140-5p-ULK2 axis. Metabolomic analysis revealed that the concentrations of cortisol 21-sulfate and beta-aminopropionitrile were significantly increased, while those of creatine and uracil were significantly decreased.

Discussion

The effects of high alkalinity on oxidative stress and autophagy injury in the liver were analysed using whole-transcriptome miRNA-mRNA networks and metabolomics approaches. Our study provides new insights into liver injury caused by highly alkaline water.

The impact of dietary supplementation of polysaccharide derived from Polygonatum sibiricum on growth, antioxidant capacity, meat quality, digestive physiology, and gut microbiota in broiler chickens

Polygonatum sibiricum polysaccharide (PSP) has demonstrated diverse medicinal properties, extensively researched for human applications. Nonetheless, there is a lack of studies investigating the potential advantages of PSP in poultry farming. The present study investigated the impact of incorporating PSP into broiler diets on their growth performance, meat quality, blood metabolites, antioxidative status, and ileal histomorphology. Two hundred and forty-one-day-old male Ross-308 broiler chicks (44.98 ± 0.79 g) were randomly assigned to 3 experimental groups, with 8 replicates of 10 birds each. The birds were fed diets supplemented with PSP at 0, 400, and 800 mg/kg (control, PSP400, and PSP800, respectively). The results revealed a linear (P > 0.05) improvement in body weight gain, European production efficiency index, and feed conversion ratio during the grower (22-35 d) and overall periods (1-35 d). The pH levels in the ingluvies, ileum, and cecum exhibited a linear reduction (P > 0.05) in the PSP800 group at d 21 and d 35, respectively. Villus height and crypt depth were increased in the PSP400 and PSP800 groups compared to the control group. PSP400 and PSP800 groups exhibited decreased hydrogen peroxide (H2O2) levels and increased total antioxidant capacity (TAC) at 21 d, while at 35 d, TAC and sulfhydryl concentrations were elevated, and H2O2 was reduced only in the PSP800 group compared to the untreated one. No significant variations between the groups at the phylum and genus levels were observed, with Bacteroidetes and Firmicutes being the dominant phyla. However, PSP supplementation notably augmented Firmicutes and Verrucomicrobiota while reducing Euryarchaeota and Proteobacteria. At the genus level, there was an increase in Akkermansia, Alistipes, CHKCI001, Erysipelatoclostridium, and a decrease in Methanobrevibacter. Conclusively, incorporating PSP into broiler diets, particularly at a dosage of 800 mg/kg, improved growth performance, antioxidant capacity, and intestinal architecture and resulted in alterations in cecal microbiota without discernible impacts on digestive function and meat quality criteria.

Rh proteins and H+ transporters involved in ammonia excretion in Amur Ide (Leuciscus waleckii) under high alkali exposure

High alkaline environment can lead to respiratory alkalosis and ammonia toxification to freshwater fish. However, the Amur ide (Leuciscus waleckii), which inhabits an extremely alkaline lake in China with titratable alkalinity up to 53.57 mM (pH 9.6) has developed special physiological and molecular mechanisms to adapt to such an environment. Nevertheless, how the Amur ide can maintain acid-base balance and perform ammonia detoxification effectively remains unclear. Therefore, this study was designed to study the ammonia excretion rate (Tamm), total nitrogen accumulation in blood and tissues, including identification, expression, and localization of ammonia-related transporters in gills of both the alkali and freshwater forms of the Amur ide. The results showed that the freshwater form Amur ide does not have a perfect ammonia excretion mechanism exposed to high-alkaline condition. Nevertheless, the alkali form of Amur ide was able to excrete ammonia better than freshwater from Amur ide, which was facilitated by the ionocytes transporters (Rhbg, Rhcg1, Na+/H+ exchanger 2 (NHE2), and V-type H+ ATPase (VHA)) in the gills. Converting ammonia into urea served as an ammonia detoxication strategy to reduced endogenous ammonia accumulation under high-alkaline environment.

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.

The Biochemical Composition and Quality of Adult Chinese Mitten Crab Eriocheir sinensis Reared in Carbonate-Alkalinity Water

Saline-alkaline aquaculture has become an important breakthrough in expanding the space available for aquaculture in China. However, the biochemical composition and quality of Eriocheir sinensis reared in carbonate alkalinity water are still unclear. Therefore, this study investigated the edible yield, coloration, and nutritional and flavor quality of Eriocheir sinensis. A significantly lower gonadosomatic index (GSI), meat yield (MY), and total edible yield (TEY) were detected in intensive pond (IP) samples than those in semi-intensive reed wetland (SIWR) (p < 0.05). Six color parameters in the hepatopancreas (p < 0.05) differed between IP and SIRW. The contents of crude protein and fat in the female hepatopancreas of IP were significantly higher than those in SIRW (p < 0.05). The concentrations of total monounsaturated fatty acids (∑MUFA), total essential fatty acids (∑EFA), and hypocholesterolaemic/hypercholesterolaemic ratio (h/H) in the female edible tissues checked were higher in IP than those in SIRW, with significant differences including ∑MUFA in the hepatopancreas and ovary, ∑EFA in the muscle, and h/H in the ovary (p < 0.05). Higher total free amino acid (∑FAA) contents of muscle were detected in SIRW than that in IP samples. Significantly higher K, Ca, Mg, Fe, and Zn contents in the ovary were detected in SIRW samples compared to IP (p < 0.05). Overall, Eriocheir sinensis reared in carbonate-alkalinity water is an important source of nutrients.

Effects of Alkalinity Exposure on Antioxidant Status, Metabolic Function, and Immune Response in the Hepatopancreas of Macrobrachium nipponense

The oriental river prawn Macrobrachium nipponense is an important freshwater economic species in China, producing huge economic benefits. However, M. nipponense shows lower alkali tolerance than fish species, thus genetic selection is urgently needed in order to improve alkali tolerance in this species. In the present study, the effects of alkalinity exposure on the hepatopancreas of M. nipponense were measured under the alkali concentrations of 0 (control), 4, 8, and 12 mmol/L with the exposure time of 96 h through histological observations, measurement of antioxidant enzymes, metabolic profiling analysis, and transcriptome profiling analysis. The present study identified that the low concentration of alkali treatment (<4 mmol/L) did not result in morphological changes in the hepatopancreas and activity changes in antioxidant enzymes, while high-alkali treatment (>8 mmol/L) damaged the normal structures of the lumen and vacuoles and significantly stimulated the levels of superoxide dismutase, catalase, and total antioxidant capacity, indicating these antioxidant enzymes play essential roles in the protection of the body from the damage caused by the alkali treatment. Metabolic profiling analysis revealed that the main enriched metabolic pathways of differentially expressed metabolites in the present study were consistent with the metabolic pathways caused by environmental stress in plants and other aquatic animals. Transcriptome profiling analysis revealed that the alkali concentration of <8 mmol/L did not lead to significant changes in gene expression. The main enriched metabolic pathways were selected from the comparison between 0 mmol/L vs. 12 mmol/L, and some significantly up-regulated genes were selected from these metabolic pathways, predicting these selected metabolic pathways and genes are involved in the adaptation to alkali treatment in M. nipponense. The expressions of Ras-like GTP-binding protein, Doublesex and mab-3 related transcription factor 1a, and Hypothetical protein JAY84 are sensitive to changes in alkali concentrations, suggesting these three genes participated in the process of alkali adaptation in M. nipponense. The present study identified the effects of alkalinity exposure on the hepatopancreas of M. nipponense, including the changes in antioxidant status and the expressions of metabolites and genes, contributing to further studies of alkali tolerance in this species.

Tissue-specific accumulation of DEHP and involvement of endogenous arachidonic acid in DEHP-induced spleen information and injury

The plasticizer Diethylhexyl phthalate (DEHP), one of the most common contaminants, is widely detected in environmental and biological samples. However, the accumulation of DEHP in tissue and the molecular mechanisms underlying its physiological damage in the spleen of aquatic organisms have not yet been reported. In this study, gas chromatography-mass spectrometry (GC-MS), histology and multi-omics analysis were used to investigate DEHP exposure-induced alterations in transcriptomic profiles and metabolic network of zebrafish model. After exposure to DEHP, higher concentrations of DEHP were found in the intestine, liver and spleen. Anatomical and histological analyses showed that the zebrafish spleen index was significantly increased and inflammatory damage was observed. Increased splenic neutrophil counts indicate inflammation and tissue damage. Transcriptomic filtering showed that 3579 genes were significantly altered. Metabolomic analysis detected 543 differential metabolites. Multi-omics annotation results indicated that arachidonic acid and 12-Hydroperoxyicosatetraenoic acid (HPETE) are involved in the key inflammatory pathway "Inflammatory mediator regulation of TRP channels". This study demonstrated the accumulation characteristics of DEHP in aquatic zebrafish and the mechanisms of inflammation and tissue damage in the spleen which involve endogenous arachidonic acid. This will provide theoretical basis and data support for health risk assessments and tissue damage of DEHP.

Effects of chloride, sulfate, and bicarbonate stress on mortality rate, gill tissue morphology, and gene expression in mandarin fish (Siniperca chuatsi)

The mandarin fish Siniperca chuatsi is a freshwater fish that is endemic to East Asia. To study the different damages and molecular mechanisms caused by different salt (NaCl, Na2SO4, and NaHCO3) on Siniperca chuatsi, the fish were subjected to NaCl, Na2SO4, and NaHCO3 stresses with different concentration for 96 h for mortality assessment, moreover, the fish were exposed to these salt stresses with equal sodium ion concentration (Na+ = 210 mmol/L), then gill morphological changes were observed and gene expression was analyzed by high-throughput transcriptome sequencing and real-time quantitative PCR (qRT-PCR). The results showed that mandarin fish tolerated NaCl and Na2SO4 better than NaHCO3. NaHCO3 stress caused more damage to gill than NaCl and Na2SO4 stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that differentially expressed genes were enriched in damage and apoptosis upon NaHCO3 stress, whereas they were enriched in energy and immune-related pathways upon NaCl and Na2SO4 stress. Hub genes were different under all three stresses. MAPK pathway genes showed a trend in up-regulated expression under all salt stresses, but the expression patterns varied with time during salt exposure and freshwater recovery stage. Taken together, this study demonstrated the variation in the effects of NaCl, Na2SO4, and NaHCO3 stress on mandarin fish. The MAPK signaling pathway is important for regulating the response to salt stress.

Integration of transcriptomic and metabolomic reveals carbonate alkalinity stress responses in the hepatopancreas of Litopenaeus vannamei

Carbonate alkalinity (CA) is one of the environmental factors affecting the survival and growth of aquatic animals. However, the toxic effects of CA stress on Pacific white shrimp Litopenaeus vannamei at the molecular level are completely unclear. In this study, we investigated the changes of the survival and growth, and hepatopancreas histology of L. vannamei under different levels of CA stress, and integrated transcriptomics and metabolomics to explore major functional changes in the hepatopancreas and identify biomarkers. After CA exposure for 14 days, the survival and growth of the shrimp were reduced, and the hepatopancreas showed obvious histological damage. A total of 253 genes were differentially expressed in the three CA stress groups, and immune-related genes such as pattern recognition receptors, phenoloxidase system and detoxification metabolism were affected; substance transport-related regulators and transporters were mostly downregulated. Furthermore, the metabolic pattern of the shrimp was also altered by CA stress, especially amino acids, arachidonic acid and B-vitamin metabolites. The integration analysis of differential metabolites and genes further showed that the functions of ABC transporters, protein digestion and absorption, and amino acid biosynthesis and metabolism were highly altered by CA stress. The results of this study revealed that CA stress caused immune, substance transport, and amino acid metabolic variations in L. vannamei, and identified several potential biomarkers related to stress response.

Stress response and tolerance mechanisms of NaHCO3 exposure based on biochemical assays and multi-omics approach in the liver of crucian carp (Carassius auratus)

The development and utilization of saline-alkaline water, an important backup resource, has received widespread attention. However, the underuse of saline-alkaline water, threatened by the single species of saline-alkaline aquaculture, seriously affects the development of the fishery economy. In this work, a 30-day NaHCO₃ stress experimental study combined with analyses of untargeted metabolomics, transcriptome, and biochemical approaches was conducted on crucian carp to provide a better understanding of the saline-alkaline stress response mechanism in freshwater fish. This work revealed the relationships among the biochemical parameters, endogenous differentially expressed metabolites (DEMs), and differentially expressed genes (DEGs) in the crucian carp livers. The biochemical analysis showed that NaHCO₃ exposure changed the levels of several physiological parameters associated with the liver, including antioxidant enzymes (SOD, CAT, GSH-Px), MDA, AKP, and CPS. According to the metabolomics study, 90 DEMs are involved in various metabolic pathways such as ketone synthesis and degradation metabolism, glycerophospholipid metabolism, arachidonic acid metabolism, and linoleic acid metabolism. In addition, transcriptomics data analysis showed that a total of 301 DEGs were screened between the control group and the high NaHCO₃ concentration group, of which 129 up-regulated genes and 172 down-regulated genes. Overall, NaHCO₃ exposure could cause lipid metabolism disorders and induce energy metabolism imbalance in the crucian carp liver. Simultaneously, crucian carp might regulate its saline-alkaline resistance mechanism by enhancing the synthesis of glycerophospholipid metabolism, ketone bodies, and degradation metabolism, at the same time increasing the vitality of antioxidant enzymes (SOD, CAT, GSH-Px) and nonspecific immune enzyme (AKP). Herein, all results will provide new insights into the molecular mechanisms underlying the stress responses and tolerance to saline-alkaline exposure in crucian carp.

Effects of Saline-Alkaline Stress on Metabolome, Biochemical Parameters, and Histopathology in the Kidney of Crucian Carp (Carassius auratus)

The salinization of the water environment caused by human activities and global warming has increased which has brought great survival challenges to aquatic animals. Crucian carp (Carassius auratus) is an essential freshwater economic fish with superior adaptability to saline-alkali water. However, the physiological regulation mechanism of crucian carp adapting to saline-alkali stress remains still unclear. In this study, crucian carp were exposed to freshwater or 20, 40, and 60 mmol/L NaHCO₃ water environments for 30 days, the effects of saline-alkali stress on the kidney were evaluated by histopathology, biochemical assays and metabolomics analysis from renal function, antioxidant capacity and metabolites level. Our results showed different degrees of kidney damage at different exposure concentrations, which were characterized by glomerular atrophy and swelling, renal tubular degranulation, obstruction and degeneration, renal interstitial edema, renal cell proliferation and necrosis. Saline-alkali stress could change the levels of several physiological parameters with renal function and antioxidant capacity, including creatinine (CREA), urea nitrogen (BUN), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA). In addition, metabolomics analysis showed that differential metabolites (DMs) were involved in various metabolic pathways, including phenylalanine, tyrosine, and tryptophan biosynthesis, aminoacyl-tRNA biosynthesis, purine metabolism, glycerophospholipid metabolism, sphingolipid metabolism, glycolysis/gluconeogenesis and the TCA cycle. In general, our study revealed that saline-alkaline stress could cause significant changes in renal function and metabolic profiles, and induce severe damage in the crucian carp kidney through destroying the anti-oxidant system and energy homeostasis, inhibiting protein and amino acid catabolism, as well as disordering purine metabolism and lipid metabolism. This study could contribute to a deeper understanding the adverse effects of saline-alkali stress on crucian carp kidney and the regulatory mechanism in the crucian carp of saline-alkali adaptation at the metabolic level.

Transcriptome analysis of the spleen provides insight into the immunoregulation of Scortum barcoo under Streptococcus agalactiae infection

Jade perch (Scortum barcoo) is a freshwater fish with substantial economic value, which has been widely cultivated all over the world. However, with the intensification and expansion of farming, several bacterial and viral diseases have occurred in jade perch. To understand the immune response of jade perch against Streptococcus agalactiae (Group B Streptococcus, GBS), we performed a histopathological examination and transcriptome sequencing of jade perch spleen after artificial bacterial infection. GBS infection can cause structural changes and even necrosis of the jade perch spleen, which may affect the survival of infected individuals. A total of 144,458 unigenes were obtained through de novo assembly of spleen transcriptome. Among them, 1821 unigenes were identified as DEGs, including 1415 up-regulated and 406 down-regulated unigenes in the infection group. Moreover, the analysis of GO and KEGG revealed that many GO terms and pathways were involved in the host immune response, such as Toll-like receptor signaling pathway, Cytokine-cytokine receptor interaction, and TNF signaling pathway. In addition, according to transcriptome data and qRT-PCR analysis, the expression levels of many cytokines that participate in the inflammatory response changed a lot after GBS infection. Overall, this transcriptomic analysis provided valuable information for studying the immune response of jade perch against bacterial infection.

Integrated application of multi-omics approach and biochemical assays provides insights into physiological responses to saline-alkaline stress in the gills of crucian carp (Carassius auratus)

Given the decline of freshwater resources in recent years, the accessible space for freshwater aquaculture is rapidly shrinking, and aquaculture in saline-alkaline water has become a critical approach to meet the rising demand. However, the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance remains unclear. Here, adult crucian carp (Carassius auratus) were exposed to 60 mmol/L NaHCO₃ for 30 days. It was observed that long-term carbonate alkalinity (CA) exposure not only caused gill oxidative stress but also changed the levels of several physiological parameters associated with ammonia transport, including blood ammonia, urea nitrogen (BUN), glutamine (Gln), and glutamine synthetase (GS). According to the metabolomics study, differential metabolites (DMs) engaged in various metabolic pathways, such as glycerophospholipid metabolism, sphingolipid metabolism, and arachidonic acid metabolism. In addition, transcriptomics data showed that differentially expressed genes (DEGs) were closely related to ammonia transport, apoptosis, and immunological response. In general, comprehensive multi-omics and biochemical analysis revealed that crucian carp might adopt Rh glycoprotein as a carrier to mediate ammonia transport and increase glutamine and urea synthesis under long-term high saline-alkaline stress to mitigate the adverse effects of blocked ammonia excretion. Simultaneously, saline-alkaline stress caused the destruction of the antioxidant system and the disorder of lipid metabolism in the crucian carp gills, which induced apoptosis and immunological response. To our knowledge, this is the first study to investigate fish's molecular and metabolic mechanisms under saline-alkaline stress using integrated metabolomics, transcriptomics, and biochemical assays. Overall, the results of this study provided new insights into the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance.