Crustacean hyperglycemic hormone (CHH) regulates the ammonia excretion and metabolism in white shrimp, Litopenaeus vannamei under ammonia-N stress

Transcriptional analysis reveals antioxidant, ion transport, and glycolysis mechanisms in Litopenaeus vannamei gills involved in the response to high alkali stress

Saline-alkali aquacultural systems have an important role in improving the economic output of the aquacultural industry. However, the survival rate of shrimp in intensive aquacultural systems is affected by alkalinity fluctuations. This study explored the ion transport and molecular responses of the whiteleg shrimp Litopenaeus vannamei to short-term high alkaline stress (96 h). The results showed that survival rate decreased significantly with time, hemolymph osmotic pressure and oxygen consumption dropped sharply after peaking at 48 h, and ammonia excretion followed a non-monotonic pattern, with an initial decline followed by a subsequent increase. Analysis of key physiological indicators revealed that urea nitrogen continued to accumulate, antioxidant (SOD and CAT) and glycolytic (PFK and LDH) enzymes were significantly activated, but ion regulatory enzymes (Na+/K+-ATPase) were severely suppressed. Gill histopathology showed typical injuries (such as gill filament shrinkage, vacuolation, and hemocytopenia). Furthermore, transcriptome analysis confirmed that high alkali stress activated insulin signaling pathway and glycolysis-related genes (e.g., upregulating PFK and GLUT expression). These results indicate that the high alkalinity causes an ion imbalance, changes the ammonia transport process, and activates the glycolysis pathway. These conclusions provide a theoretical basis for the subsequent development for the saline-alkaline aquacultural of Litopenaeus vannamei.

Epigenetic regulation of physiological resilience to ammonia nitrogen stress in the Pacific whiteleg shrimp Penaeus vannamei: Evidence from genome-wide DNA methylation dynamics

Although DNA methylation has emerged as an essential epigenetic mechanism modulating organismal responses to abiotic stresses, its involvement in the physiological resilience of marine invertebrates like shrimp to ammonia nitrogen toxicity remains enigmatic. Here, we performed the first comprehensive dissection of genome-wide DNA methylation dynamics in the Pacific whiteleg shrimp Penaeus vannamei exposed to ammonia nitrogen, based on whole-genome bisulfite sequencing and transcriptome analyses. In the genome of P. vannamei, three DNA methyltransferases (DNMT1, DNMT2 and DNMT3a), one DNA demethylase (TET2) and four methyl-CpG binding proteins (MBD2, MBD4, Kaiso, and UHRF1) were present. About 1.68-1.87 % of cytosine nucleotides were methylated, and higher percentages of cytosines in the CpG context (5.23 %-6.34 %) was methylated compared with the CHG and CHH contexts. Methylated cytosines were mostly enriched in the coding DNA sequence, and methylation peaks occurred near the transcription end sites. Following ammonia exposure, 4203 differentially expressed genes (DEGs) and 1100 differentially methylated genes (DMGs) were identified. The DMGs accounted for 4.4 % of the total gene reservoir in P. vannamei genome, and 212 shared genes were found between the DEGs and DMGs. Genes exhibiting significant methylation and expression changes were enriched in various pathways including the FoxO signaling pathway, autophagy and endocytosis. Among them was a group of genes related to energy metabolism, antioxidation response and detoxification metabolism, highlighting involvement of DNA methylation in fine-tuning these crucial physiological processes. These findings provide new insights into the regulatory roles of DNA methylation in the physiological resilience of marine invertebrates to aquatic stressors.

Key Neuropeptides Regulating Molting in Pacific White Shrimp (Penaeus vannamei): Insights from Transcriptomic Analysis

Molting is a vital physiological process essential for the growth and development of Penaeus vannamei, with significant implications for aquaculture productivity. This study aimed to identify neuropeptide-related genes involved in molting through transcriptomic analysis. RNA sequencing of pre-molt and post-molt samples revealed 1203 differentially expressed genes (DEGs). Functional enrichment analysis indicated that these genes play significant roles in cuticle formation and molting regulation. Among the DEGs, 243 were predicted to be neuropeptides based on the presence of signal peptides and the absence of transmembrane domains. Five key neuropeptide genes-PvCHH, PvMIH, PvEH I, PvCDA I, and PvCDA II-were identified as critical regulators of molting. Their role was further validated through RT-qPCR analysis, confirming their close association with the molting process. These genes were highlighted in this study as pivotal factors driving molting in P. vannamei. The neuropeptides identified in this research are anticipated to offer valuable insights into the regulation of molting. Additionally, their synthetic products hold promise for improving molting consistency in shrimp aquaculture.

Effects of ammonia exposure and post-exposure recovery in pacific white shrimp, Litopenaeus vannamei: Histological, physiological and molecular responses

The toxic effects of ammonia exposure on Litopenaeus vannamei have been widely reported, including tissue damage, oxidative stress, and metabolic disorders, but the ability of L. vannamei to recover from ammonia damage is still unclear. To further understand the adaptation mechanism of L. vannamei to ammonia, this study explored the effects of ammonia exposure and recovery on histopathology, physiological indicators, and transcriptomic responses. In the ammonia exposure (NH4+-N 25 mg/L) and recovery experiment, shrimp were sampled at 0 h, 24 h, 48 h of exposure, and 24 h, 48 h of recovery. The results showed that histopathological damage to the hepatopancreas and gills caused by short-term ammonia exposure could be alleviated after recovery. Ammonia exposure inhibited superoxide dismutase (SOD) and catalase (CAT) activities, decreased total antioxidant capacity (T-AOC), and increased malondialdehyde (MDA) in shrimp. Restoration of the antioxidant system after exposure mitigated oxidative damage and reduced MDA levels. The inhibition of acid phosphatase (ACP) and alkaline phosphatase (AKP) activities in shrimp caused by ammonia exposure was reversible. Ammonia excretion and metabolism attenuate ammonia toxicity and promote recovery in L. vannamei. Transcriptome analysis identified 1690, 1568, and 1463 differentially expressed genes (DEGs) in the hepatopancreas at 48 h of stress, 24 h, and 48 h of recovery, respectively. KEGG enrichment analysis revealed that ammonia exposure induced oxidative damage, resulting in apoptosis. Furthermore, activation of antioxidant-related pathways, such as glutathione metabolism and peroxisomes, helped reduce oxidative damage during the post-exposure recovery period. The addition of exogenous spermine and spermidine may contribute to post-exposure recovery and enhance ammonia acclimation in L. vannamei. Differential expression of the inflammatory gene STEAP4 in the ammonia stress and recovery phases, as screened by transcriptome analysis, may play a positive role in post-stress recovery. This study demonstrated the reversibility of the toxic effects of ammonia exposure on L. vannamei, complemented the knowledge of the mechanisms of adaptation of shrimp under ammonia exposure, and provided a basis for subsequent ammonia tolerance studies in crustaceans.

miR-8-3p regulates the antioxidant response and apoptosis in white shrimp, Litopenaeus vannamei under ammonia-N stress

Exposure to excess ammonia-N (NH3/NH4+) in aquaculture can disrupt physiological function in shrimp leading to enhanced oxidative stress and apoptosis, but little is known concerning the post-transcriptional regulation mechanism. In this study, the first miR-200 family member in crustacean was identified and characterized from Litopenaeus vannamei (designed as Lva-miR-8-3p). Lva-miR-8-3p was highly expressed in eyestalks, brainganglion, and gills. The expression of Lva-miR-8-3p in gills significantly decreased after ammonia-N stress, and Lva-miR-8-3p was confirmed to target IKKβ 3'UTR for negatively regulating IKKβ/NF-κB pathway. Overexpression of miR-8-3p promoted the hemolymph ammonia-N accumulation, total hemocyte count (THC) decrease, and gills tissue damage, thus resulting in a decreased survival rate of ammonia-exposed shrimp. Besides, Lva-miR-8-3p silencing could enhance the antioxidant enzymes activities and reduce the oxidative damage, whereas overexpression of Lva-miR-8-3p exerted the opposite effects. Furthermore, Lva-miR-8-3p overexpression was found to aggravate ammonia-N induced apoptosis in gills. In primarily cultured hemocytes, the cell viability decreased, the ROS content and caspase-3 activity increased after agomiR-8-3p transfection, while antagomiR-8-3p transfection caused the opposite change except the cell viability. These findings indicate that Lva-miR-8-3p acts as a post-transcriptional regulator in ammonia-N induced antioxidant response and apoptosis by negatively regulating IKKβ/NF-κB pathway.

Combined effects of hypoxia and ammonia-N exposure on the oxygen consumption, glucose metabolism and amino acid metabolism in hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂)

This study evaluated the influence of hypoxia and ammonia-N co-exposure on oxygen consumption, glucose metabolism and amino acid metabolism in hybrid grouper. The results showed that elevated expression of GLUT1, MCT1, PFK, HK and LDH were induced by co-exposure to hypoxia and ammonia. In addition, co-exposure to hypoxia and ammonia reduced the tolerance of hybrid grouper to ammonia-N. Furthermore, ammonia-N exposure caused an increase in oxygen consumption in hybrid grouper. After ammonia-N exposure for 96 h, 10 amino acids contents and activities of AST and ALT elevated in hybrid grouper muscle. The study revealed that combined exposure to hypoxia and ammonia-N significantly increased glucose metabolism, oxygen consumption and amino acid metabolism in hybrid grouper, and presented significant synergistic effects.

Difference in muscle metabolism caused by metabolism disorder of rainbow trout liver exposed to ammonia stress

Ammonia pollution is an important environmental stress factors in water eutrophication. The intrinsic effects of ammonia stress on liver toxicity and muscle quality of rainbow trout were still unclear. In this study, we focused on investigating difference in muscle metabolism caused by metabolism disorder of rainbow trout liver at exposure times of 0, 3, 6, 9 h at 30 mg/L concentrations. Liver transcriptomic analysis revealed that short-term (3 h) ammonia stress inhibited carbohydrate metabolism and glycerophospholipid production but long-term (9 h) ammonia stress inhibited the biosynthesis and degradation of fatty acids, activated pyrimidine metabolism and mismatch repair, lead to DNA strand breakage and cell death, and ultimately caused liver damage. Metabolomic analysis of muscle revealed that ammonia stress promoted the reaction of glutamic acid and ammonia to synthesize glutamine to alleviate ammonia toxicity, and long-term (9 h) ammonia stress inhibited urea cycle, hindering the alleviation of ammonia toxicity. Moreover, it accelerated the consumption of flavor amino acids such as arginine and aspartic acid, and increased the accumulation of bitter substances (xanthine) and odorous substances (histamine). These findings provide valuable insights into the potential risks and hazards of ammonia in eutrophic water bodies subject to rainbow trout.

Mechanisms of ammonotelism, epithelium damage, cellular apoptosis, and proliferation in gill of Litopenaeus vannamei under NH4Cl exposure

Excessive ammonia-N in coastal environment and aquaculture threatens the health of marine organisms. To explore the mechanism of gill damage induced by ammonia-N, transcriptome of Litopenaeus vannamei 's gill was carried out under 20 mg/L NH4Cl for 0, 6, and 48 h. K-means clustering analysis suggested that ammonia excretion and metabolism-related genes were elevated. GO and KEGG enrichment analysis suggested that glycosyltransferase activity and amino acid metabolism were affected by ammonia. Moreover, histological observation via three staining methods gave clues on the changes of gill after ammonia-N exposure. Increased mucus, hemocyte infiltration, and lifting of the lamellar epithelium suggested that gill epithelium was suffering damage under ammonia-N stress. Meanwhile, the composition of extracellular matrix (ECM) in connective tissue changed. Based on the findings of transcriptomic and histological analysis, we further investigated the molecular mechanism of gill damage under multiple concentrations of NH4Cl (0, 2, 10, 20 mg/L) for multiple timepoints (0, 3, 6, 12, 24, 48, 72 h). First, ammonia excretion was elevated via ion channel, transporter, and exocytosis pathways, but hemolymph ammonia still kept at a high level under 20 mg/L NH4Cl exposure. Second, we focused on glycosaminoglycan metabolism which was related to the dynamics of ECM. It turned out that the degradation and biosynthesis of chondroitin sulfate (CS) were elevated, suggesting that the structure of CS might be destructed under ammonia-N stress and CS played an important role in maintaining gill structure. It was enlightening that the destructions occurred in extracellular regions were vital to gill damage. Third, ammonia-N stress induced a series of cellular responses including enhanced apoptosis, active inflammation, and inhibited proliferation which were closely linked and jointly led to the impairment of gill. Our results provided some insights into the physiological changes induced by ammonia-N and enriched the understandings of gill damage under environmental stress.

The immunotoxicity mechanism of hemocytes in Chlamys farreri incubated with noradrenaline and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide alone or in combination

Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) is the active intermediate metabolite of benzo[a]pyrene (B[a]P) and is considered the ultimate immunotoxicant. The neuroendocrine immunoregulatory network of bivalves is affected under pollutant stress. Besides, bivalves are frequently affected by pollutants in marine environments, yet the combined effects of neuroendocrine factors and detoxification metabolites on bivalves under pollutant stress and the signal pathways that mediate this immunoregulation are not well understood. Therefore, we incubated the hemocytes of Chlamys farreri with the neuroendocrine factor noradrenaline (NA) and the B[a]P detoxification metabolite BPDE, alone or in combination, to examine the immunotoxic effects of NA and BPDE on the hemocytes in C. farreri. Furthermore, the effects of NA and BPDE on the hemocyte signal transduction pathway were investigated by assessing potential downstream targets. The results revealed that NA and BPDE, alone or in combination, resulted in a significant decrease in phagocytic activity, bacteriolytic activity and the total hemocyte count. In addition, the immunotoxicity induced by BPDE was further exacerbated by co-treatment with NA, and the two showed synergistic effects. Analysis of signaling pathway factors showed that NA activated G proteins by binding to α-AR, which transmitted information to the Ca2+-NF-κB signaling pathway to regulate the expression of phagocytosis-associated proteins and regulated cytokinesis through the cAMP signaling pathway. BPDE could activate PTK and affect phagocytosis and cytotoxicity proteins through Ca2+-NF-κB signal pathway, also affect the regulation of phagocytosis and cytotoxicity by inhibiting the AC-cAMP-PKA pathway to down-regulate the expression of NF-κB and CREB. In addition, BPDE and NA may affect the immunity of hemocytes by down-regulating phagocytosis-related proteins through inhibition of the lectin pathway, while regulating the expression of cytotoxicity-related proteins through the C-type lectin. In summary, immune parameters were suppressed through Ca2+ and cAMP dependent pathways exposed to BPDE and the immunosuppressive effects were enhanced by the neuroendocrine factor NA.

Potential pathway and mechanisms underlining the immunotoxicity of benzo[a]pyrene to Chlamys farreri

The long-distance migration of polycyclic aromatic hydrocarbons (PAHs) promotes their release into the marine environment, posing a serious threat to marine life. Studies have shown that PAHs have significant immunotoxicity effects on bivalves, but the exact mechanism of immunotoxicity remains unclear. This paper aims to investigate the effects of exposure to 0.4, 2, and 10 μg/L of benzo(a)pyrene (B[a]P) on the immunity of Chlamys farreri under environmental conditions, as well as the potential molecular mechanism. Multiple biomarkers, including phagocytosis rate, metabolites, neurotoxicity, oxidative stress, DNA damage, and apoptosis, were adopted to assess these effects. After exposure to 0.4, 2, and 10 μg/L B[a]P, obvious concentration-dependent immunotoxicity was observed, indicated by a decrease in the hemocyte index (total hemocyte count, phagocytosis rate, antibacterial and bacteriolytic activity). Analysis of the detoxification metabolic system in C. farreri revealed that B[a]P produced B[a]P-7,8-diol-9,10-epoxide (BPDE) through metabolism, which led to an increase in the expression of protein tyrosine kinase (PTK). In addition, the increased content of neurotransmitters (including acetylcholine, γ -aminobutyric acid, enkephalin, norepinephrine, dopamine, and serotonin) and related receptors implied that B[a]P might affect immunity through neuroendocrine system. The changes in signal pathway factors involved in immune regulation indicated that B[a]P interfered with Ca2+ and cAMP signal transduction via the BPDE-PTK pathway or neuroendocrine pathway, resulting in immunosuppression. Additionally, B[a]P induced the increase in reactive oxygen species (ROS) content and DNA damage, as well as an upregulation of key genes in the mitochondrial pathway and death receptor pathway, leading to the increase of apoptosis rate. Taken together, this study comprehensively investigated the detoxification metabolic system, neuroendocrine system, and cell apoptosis to explore the toxic mechanism of bivalves under B[a]P stress.

Dynamic N6-methyladenosine RNA methylation landscapes reveal epi-transcriptomic modulation induced by ammonia nitrogen exposure in the Pacific whiteleg shrimp Litopenaeus vannamei

Despite the versatility of RNA m⁶A methylation in regulating various biological processes, its involvement in the physiological response to ammonia nitrogen toxicity in decapod crustaceans like shrimp remains enigmatic. Here, we provided the first characterization of dynamic RNA m⁶A methylation landscapes induced by toxic ammonia exposure in the Pacific whiteleg shrimp Litopenaeus vannamei. The global m⁶A methylation level showed significant decrease following ammonia exposure, and most of the m⁶A methyltransferases and m⁶A binding proteins were significantly repressed. Distinct from many well-studied model organisms, m⁶A methylated peaks in the transcriptome of L. vannamei were enriched not only near the termination codon and in the 3' untranslated region (UTR), but also around the start codon and in the 5' UTR. Upon ammonia exposure, 11,430 m⁶A peaks corresponding to 6113 genes were hypo-methylated, and 5660 m⁶A peaks from 3912 genes were hyper-methylated. The differentially methylated genes showing significant changes in expression were over-represented by genes associated with metabolism, cellular immune defense and apoptotic signaling pathways. Notably, the m⁶A-modified ammonia-responsive genes encompassed a subset of genes related to glutamine synthesis, purine conversion and urea production, implying that m⁶A methylation may modulate shrimp ammonia stress responses partly through these ammonia metabolic processes.

Toxicological mechanism of ammonia-N on haematopoiesis and apoptosis of haemocytes in Litopenaeus vannamei

Ammonia, as an important pollutant, contributed to the reduction of immunity, disruption of physiology in animals. RNA interference (RNAi) was performed to understand the function of astakine (AST) in haematopoiesis and apoptosis in Litopenaeus vannamei under ammonia-N exposure. Shrimps were exposed to 20 mg/L ammonia-N from 0 to 48 h with injection of 20 μg AST dsRNA. Further, shrimps were exposed to 0, 2, 10 and 20 mg/L ammonia-N also from 0 to 48 h. The results showed that the total haemocytes count (THC) decreased under ammonia-N stress and the knockdown of AST resulted in a further decrease of THC, suggesting that 1) the proliferation was decreased through the reduction of AST and Hedgehog, the differentiation was interfered by Wnt4, Wnt5 and Notch, and the migration was inhibited by the decrease of VEGF; 2) oxidative stress was induced under ammonia-N stress, leading to the increase of DNA damage with the up-regulated gene expression of death receptor, mitochondrial and endoplasmic reticulum stress pathways; 3) the changes of THC resulted from the decrease of proliferation, differentiation and migration of haematopoiesis cells and the increase of apoptosis of haemocytes. This study helps to deepen our understanding of risk management in shrimp aquaculture.

Eyestalk transcriptome and methyl farnesoate titers provide insight into the physiological changes in the male snow crab, Chionoecetes opilio, after its terminal molt

The snow crab, Chionoecetes opilio, is a giant deep-sea brachyuran. While several decapod crustaceans generally continue to molt and grow throughout their lifetime, the snow crab has a fixed number of molts. Adolescent males continue to molt proportionately to their previous size until the terminal molt at which time an allometric increase in chela size occurs and an alteration of behavioral activities occurs, ensuring breeding success. In this study, we investigated the circulating concentrations of methyl farnesoate (an innate juvenile hormone in decapods) (MF) before or after the terminal molt in males. We then conducted eyestalk RNAseq to obtain molecular insight into the regulation of physiological changes after the terminal molt. Our analyses revealed an increase in MF titers after the terminal molt. This MF surge may be caused by suppression of the genes that encode MF-degrading enzymes and mandibular organ-inhibiting hormone that negatively regulates MF biosynthesis. Moreover, our data suggests that behavioral changes after the terminal molt may be driven by the activation of biogenic amine-related pathways. These results are important not only for elucidating the physiological functions of MFs in decapod crustaceans, which are still largely unknown, but also for understanding the reproductive biology of the snow crab.

Impacts of ammonia stress on different Pacific whiteleg shrimp Litopenaeus vannamei families and the underlying adaptive mechanisms

Ammonia stress in aquaculture systems poses a great threat to the growth and survival of the Pacific whiteleg shrimp Litopenaeus vannamei. Although the ammonia stress tolerance capacity of L. vannamei has been found to vary significantly among different breeding families, the underneath mechanisms are still largely unknown. In this study, the ammonia tolerance capacity of different L. vannamei breeding families was compared. Results confirmed the significant differences in the ammonia adaptability among different families. To ascertain the underlying adaptive strategies, ATP status, ATP synthase activity, expression and activities of ammonia excretion and metabolism-related enzymes, and apoptosis in shrimp gills were analyzed. Furthermore, transcriptomic analyses were also performed to elucidate the molecular mechanisms. Our results indicated that ammonia-tolerant L. vannamei may possess (1) enhanced ability to excrete ammonia, (2) better capacity to convert ammonia into less toxic products, and (3) sufficient energy reserves for ammonia-compensating processes.

Nutrient sensing signaling and metabolic responses in shrimp Litopenaeus vannamei under acute ammonia stress

Ammonia is the primary environmental factor affecting the growth and health of crustaceans. It would induce oxidative stress and metabolic disorders. Extra amount of energy was demanded to maintain the physiological functions under ammonia stress. However, limited information was available on its effects on the main nutrient metabolism, as well as the nutrient sensing signaling pathways. In the present study, shrimp Litopenaeus vannamei were exposed to acute ammonia stress and injected with amino acid solution. The results showed that acute ammonia exposure resulted in lower free amino acid levels in hemolymph, incomplete activation of the mechanistic target of rapamycin (mTOR) signaling and cascaded less protein synthesis in muscle. It induced autophagy and activated the AMP-activated protein kinase (AMPK) pathway. Meanwhile, ammonia exposure enhanced glycolysis and lipogenesis, but inhibited lipolysis. The results characterized the integrated metabolic responses and nutrient signaling to ammonia stress. It provides critical clues to understand the growth performance and physiological responses in shrimp under ammonia stress.

Divergent responses in the gut microbiome and liver metabolome to ammonia stress in three freshwater turtles

Ammonia is a common pollutant in aquaculture system, and toxic to all aquatic animals. However, different aquatic animals exhibit diverse physiological responses to high-level ammonia exposure, potentially indicating their divergent resistance to ammonia stress. In this study, juveniles of three freshwater turtles (Mauremys reevesii, Pseudemys nelsoni and Trachemys scripta elegans) were exposed to different concentrations of ammonia (0, 0.3 and 3.0 mg/L) for 30 days, and their swimming, growth performance, gut microbiota, and hepatic metabolites were measured to evaluate the interspecific difference in physiological responses to ammonia stress. Despite no differences in swimming ability, growth rate, and gut microbial diversity, observable changes in microbial community composition and hepatic metabolite profiles were shown in ammonia-exposed turtles. A relatively higher abundance of potentially pathogenic bacteria was found in M. reevesii than in the other two species. Moreover, microbial compositions and metabolic responses differed significantly among the three species. M. reevesii was, out of the three tested species, the one in which exposure to ammonia had the greatest effect on changes in bacterial genera and hepatic metabolites. Conversely, only a few metabolites were significantly changed in T. scripta elegans. Integrating these findings, we speculated that native M. reevesii should be more vulnerable to ammonia stress compared to the invasive turtle species. Our results plausibly reflected divergent potential resistance to ammonia among these turtles, in view of differential physiological responses to ammonia exposure at environmentally relevant concentrations.

Application of proteomics and metabolomics to assess ammonia stress response and tolerance mechanisms of juvenile ornate rock lobster Panulirus ornatus

Ammonia is a common pollutant in the aquatic ecosystem and closed aquaculture systems. It may pose a threat to the lobster growth, reproduction and survival. However, there is lack of research of the mechanisms on the toxic effects ammonia at molecular levels. In this work, proteomics and metabolomics were integrated to analyze the proteome and metabolome responses in the ornate spiny lobster Panulirus ornatus treated with ammonia (20 mg L^-1) for 48 h. A total of 199 proteins and 176 metabolites were significantly altered in P. ornatus following ammonia treatment. The responsive proteins and metabolites were predominantly involved in immune response, phase I and phase II biotransformation, carbohydrate metabolism, amino acid metabolism, and lipid metabolism. Furthermore, an increase in urea levels was observed, and amino acid metabolism was induced, indicating that the urea cycle was utilized to biotransform ammonia so as to reduce endogenous ammonia content. Ammonia exposure also affected the antioxidant system and induced cellular apoptosis. Overall, our results provide comprehensive insights into the molecular mechanisms underlying the response of P. ornatus to ammonia stress. We believe that the data reported herein should contribute to the development of novel, efficient methods for P. ornatus aquaculture.

Genome-wide association study identified genes associated with ammonia nitrogen tolerance in Litopenaeus vannamei

Ammonia nitrogen tolerance is an economically important trait of the farmed penaeid shrimp Litopenaeus vannamei. To identify the genes associated with ammonia nitrogen tolerance, we performed an extreme phenotype genome-wide association study method (XP-GWAS) on a population of 200 individuals. The single nucleotide polymorphism (SNP) genotyping array method was used to construct the libraries and 36,048 SNPs were genotyped. Using the MLM, FarmCPU and Blink models, six different SNPs, located on SEQ3, SEQ4, SEQ5, SEQ7 and SEQ8, were determined to be significantly associated with ammonia nitrogen tolerance. By integrating the results of the GWAS and the biological functions of the genes, seven candidate genes (PDI, OZF, UPF2, VPS16, TMEM19, MYCBP2, and HOX7) were found to be associated with ammonia nitrogen tolerance in L. vannamei. These genes are involved in cell transcription, cell division, metabolism, and immunity, providing the basis for further study of the genetic mechanisms of ammonia nitrogen tolerance in L. vannamei. Further candidate gene association analysis in the offspring population revealed that the SNPs in the genes zinc finger protein OZF-like (OZF) and homeobox protein Hox-B7-like (HOX7) were significantly associated with ammonia nitrogen tolerance trait of L. vannamei. Our results provide fundamental genetic information that will be useful for further investigation of the molecular mechanisms of ammonia nitrogen tolerance. These associated SNPs may also be promising candidates for improving ammonia nitrogen tolerance in L. vannamei.

Impact of heatwaves and environmental ammonia on energy metabolism, nitrogen excretion, and mRNA expression of related genes in the indicator model system Daphnia magna

Due to increasing anthropogenic impacts, heatwaves and prolonged exposure to elevated concentrations of ammonia (HEA) may occur in aquatic environments as a single stressor or a combination thereof, potentially impacting the physiology of exposed animals. In the current study, common water fleas Daphnia magna were exposed for one week to either a 5°C increase in temperature, an increase of 300 µmol l^-1 total environmental ammonia, or to both of these stressors simultaneously. Exposure to elevated temperature caused a decrease in MO₂, ammonia excretion rates, a downregulation of mRNA coding for key Krebs cycle enzymes and the energy consuming Na⁺/K⁺-ATPase and V-type H⁺-ATPase, as well as the energy distributing crustacean hyperglycemic hormone Rh-protein. High environmental ammonia inflicted a lesser inhibitory effect on the energy metabolism of Daphnia, but initiated ammonia detoxification processes via urea synthesis evident by elevated urea excretion rates and a mRNA upregulation of arginase. Effects observed under the combined stressors resembled largely the effects seen after acclimation to elevated temperature alone, potentially due to the animals' capability to efficiently detoxify critical ammonia loads. The observed physiological effects and potential threats of the environmental stressor are discussed in detail.

Ammonia stress affects the structure and function of hemocyanin in Penaeus vannamei

Anthropogenic factors and climate change have serious effects on the aquatic ecosystem and aquaculture. Among water pollutants, ammonia has the greatest impact on aquaculture organisms such as penaeid shrimp because it makes them more susceptible to infections. In this study, we explored the effects of ammonia stress (0, 50, 100, and 150 mg/L) on the molecular structure and functions of the multifunctional respiratory protein hemocyanin (HMC) in Penaeus vannamei. While the mRNA expression of Penaeus vannamei hemocyanin (PvHMC) was up-regulated after ammonia stress, both plasma hemocyanin protein and oxyhemocyanin (OxyHMC) levels decreased. Moreover, ammonia stress changed the molecular structure of hemocyanin, modulated the expression of protein phosphatase 2 A (PP2A) and casein kinase 2α (CK2α) to regulate the phosphorylation modification of hemocyanin, and enhanced its degradation into fragments by trypsin. Under moderate ammonia stress conditions, hemocyanin also undergoes glycosylation to improve its in vitro antibacterial activity and binding with Gram-negative (Vibrio parahaemolyticus) and Gram-positive (Staphylococcus aureus) bacteria, albeit differently. The current findings indicate that P. vannamei hemocyanin undergoes adaptive molecular modifications under ammonia stress enabling the shrimp to survive and counteract the consequences of the stress.

Integrated Metabolomics and Transcriptomic Analysis of Hepatopancreas in Different Living Status Macrobrachium nipponense in Response to Hypoxia

As the basic element of aerobic animal life, oxygen participates in most physiological activities of animals. Hypoxia stress is often the subject of aquatic animal research. Macrobrachium nipponense, an economically important aquatic animal in southern China, has been affected by hypoxia for many years and this has resulted in a large amount of economic loss due to its sensitivity to hypoxia; Metabolism and transcriptome data were combined in the analysis of the hepatopancreas of M. nipponense in different physiological states under hypoxia; A total of 108, 86, and 48 differentially expressed metabolites (DEMs) were found in three different comparisons (survived, moribund, and dead shrimps), respectively. Thirty-two common DEMs were found by comparing the different physiological states of M. nipponense with the control group in response to hypoxia. Twelve hypoxia-related genes were identified by screening and analyzing common DEMs. GTP phosphoenolpyruvate carboxykinase (PEPCK) was the only differentially expressed gene that ranked highly in transcriptome analysis combined with metabolome analysis. PEPCK ranked highly both in transcriptome analysis and in combination with metabolism analysis; therefore, it was considered to have an important role in hypoxic response. This manuscript fills the one-sidedness of the gap in hypoxia transcriptome analysis and reversely deduces several new genes related to hypoxia from metabolites. This study contributes to the clarification of the molecular process associated with M. nipponense under hypoxic stress.

Integrated physiological, transcriptome and metabolome analyses of the hepatopancreas of the female swimming crab Portunus trituberculatus under ammonia exposure

Ammonia is a common environmental pollutant in aquatic ecosystem and is also a significant concern in closed aquaculture systems. The threat of ammonia has been increasing with rising anthropogenic activities including intensified aquaculture. In this study, we aimed to investigate ammonia toxicity and metabolism mechanisms in the hepatopancreas, a major organ for Vitellogenin (Vtg) synthesis and defending against ammonia stress, of female swimming crab Portunus trituberculatus which is an important fishery and aquaculture species, by integrating physiological, transcriptome and metabolome analyses. The results revealed that ammonia exposure (10 mg/L, an environmentally relevant concentration) resulted in a remarkable reduction in vtg expression and depression of multiple signaling pathways for reproductive regulators including methyl farnesoate, ecdysone and neuroparsin, demonstrating for the first time that ammonia impairs swimming crab female reproduction. In addition, a number of important genes and metabolites in glycolysis, the Krebs cycle, fatty acid β-oxidation and synthesis were significantly downregulated, indicating that changes in ammonia levels lead to a general depression of energy metabolism in hepatopancreas. After ammonia exposure, an increased level of urea and a reduction of amino acid catabolism were observed in hepatopancreas, suggesting that urea cycle was utilized to biotransform ammonia, and amino acid catabolism was decreased to reduce endogenous ammonia generation. Furthermore, antioxidant systems were altered following ammonia exposure, which was accompanied by proteins and lipid oxidations, as well as cellular apoptosis. These results indicate that ammonia leads to metabolic suppression, oxidative stress and apoptosis in P. trituberculatus hepatopancreas. The findings improve the understanding for the mechanisms of ammonia toxicity and metabolism in P. trituberculatus, and provide valuable information for assessing potential ecological risk of environmental ammonia and improving aquaculture management.

The exploration of neuroendocrine regulation of crustacean hyperglycemic hormone (CHH) on innate immunity of Litopenaeus vannamei under ammonia-N stress

To unveil the neuroendocrine-immune (NEI) mechanism of crustaceans under high ambient ammonia-N, crustacean hyperglycemic hormone (CHH) in L. vannamei was knocked down under 20 mg/L ammonia-N exposure. The results showed that the expression of CHH in the eyestalks decreased significantly when CHH was silenced. After CHH was knocked down, the levels of CHH, ACh, DA, NE, and 5-HT in the haemolymph decreased significantly. Correspondingly, the expressions of GC, ACh₇R, DM1, DA₁R, and 5-HT₇R in haemocytes down-regulated significantly, while DA₄R and α₂AR up-regulated significantly. Besides, the expression of Toll3 reduced significantly. And significantly changes occurred in the levels of G protein effectors (AC and PLC), second messengers (cAMP, cGMP, CaM, and DAG), protein kinases (PKA, PKC and PKG), and nuclear transcription factors (CREB, Dorsal, Relish and NKRF). Furthermore, immune defense proteins (BGBP and PPO3, Crustin A, ALF, LYC, TNFα, and IL-16), phagocytosis-related proteins (Cubilin, Integrin, Peroxinectin, Mas-like protein, and Dynamin-1) and exocytosis-related proteins (SNAP-25, VAMP-2 and Syntaxin) changed significantly. Eventually, a significant decrease in the levels of THC, haemocytes phagocytosis rate, plasma PO, antibacterial and bacteriolytic activities was detected. Therefore, these results indicate that under ammonia-N stress, the combination of CHH and GC mainly affects exocytosis of shrimp through the cGMP-PKG-CREB pathway. Simultaneously, CHH stimulates the release of biogenic amines, and then activate G protein effectors after binding to their specific receptors, to regulate exocytosis mainly via the cAMP-PKA-CREB pathway and influence phagocytosis primarily by the cAMP-PKA-NF-κB pathway. CHH can enhance ACh, and then activate G protein effectors after binding to the receptors, and finally regulate exocytosis mainly through the cAMP-PKA-CREB pathway and regulate phagocytosis by the cAMP-PKA-NF-κB pathway. CHH can also promote Toll3-NF-κB pathway, thereby affecting the expressions of immune defense factors. This study contributes to a further understanding of the NEI mechanism of crustacean in response to environmental stress.

A new insight to characterize immunomodulation based on hepatopancreatic transcriptome and humoral immune factor analysis of the Cherax quadricarinatus infected with Aeromonas veronii

Cherax quadricarinatus is a type of large freshwater crayfish that is characterized by rapid growth and formidable adaptability. It has also been widely cultured and studied as a model organism. Aeromonas veronii is the dominant pathogen in aquatic environments and the primary threat to aquaculture's economic stability. To better understand the interactions between C. quadricarinatus and A. veronii, high-throughput RNA sequencing of the C. quadricarinatus hepatopancreas was carried out on a control group, susceptible group (6 h after infection), and resistant group (48 h after infection). A total of 65,850,929 genes were obtained. Compared with the control group, 2616 genes were up-regulated and 1551 genes were down-regulated in the susceptible group; while 1488 genes were up-regulated and 1712 genes were down-regulated in the resistant group. GO and KEGG analysis showed that these differentially expressed genes (DEGs) were associated with multiple immune pathways, including Toll-like receptors (TLRs), antigen processing and presentation, NOD-like receptor signaling pathway, phagosome, lysosome, JAK-STAT signaling pathway. qRT-PCR showed that infection by A. veronii changed the expression pattern of the serine proteinase inhibitor (SPI), crustacean hyperglycemic hormone (CHH), anti-lipopolysaccharide factor (ALF), and extracellular copper/zinc superoxide dismutase (SOD1), all of which were significantly higher than in the control group up to 48 h after infection. In addition, detection of superoxide dismutase (SOD), catalase (CAT), lysozyme (LZM), and phenoloxidase (PO) activity, as well as ceruloplasmin (CP) concentration at different times after infection showed diverse trends. Furthermore, pathological sections obtained 24 h after infection show lesions on the hepatopancreas and intestinal tissues caused by A. veronii. The results of this study provide a foundation for analyzing the immune mechanism of C. quadricarinatus infected with A. veronii at the transcriptional level and a theoretical basis for screening disease-resistant individuals to ensure healthy economic development of the aquatic industry.

Comparative responses of Sinopotamon henanense to acute and sub-chronic Cd exposure

Studies on the freshwater crab Sinopotamon henanense have shown that acute and sub-chronic Cd²⁺ exposure induced differential alterations in the respiratory physiology and gill morphology. To elucidate Cd²⁺ toxicity under these two exposure conditions, crabs were acutely exposed to 7.14, 14.28, and 28.55 mg/L Cd²⁺ for 96 h and sub-chronically exposed to 0.71, 1.43, and 2.86 mg/L Cd²⁺ for 3 weeks. The Cd²⁺ accumulation, total metallothionein (MT), superoxide dismutase, and malondialdehyde (MDA) contents in the gill tissues were detected. Moreover, the glucose-6-phosphate dehydrogenase (G6PDH) activity, NADPH content, reduced glutathione (GSH), oxidized glutathione (GSSG), and GSH/GSSG ratio in the hepatopancreas were determined. The morphology of the X-organ-sinus gland complex was also observed. The results showed that sub-chronical Cd²⁺ exposure induced lower MT content and higher MDA level in the gills than in the acute exposure. In the hepatopancreas, acute Cd²⁺ exposure decreased the pentose phosphate pathway activity and NADPH content; however, an increased G6PDH activity and NADPH content were detected in sub-chronic Cd²⁺ exposure (2.86 mg/L). Morphological changes occurred in the sinus gland in crabs exposed to 2.86 mg/L Cd²⁺ for 3 weeks. The tightly packed structure composed by the axons, enlarged terminals, and glial cells, became loose and porous. Ultra-structurally, a large number of vacuoles and few neurosecretory granules were observed in the axon terminal. These effects added to our understanding of the toxic effects of Cd²⁺ and provide biochemical and histopathological evidence for S. henanense as a biomarker of acute or long-term waterborne Cd²⁺ pollution.

Effects of crustacean hyperglycaemic hormone RNA interference on regulation of glucose metabolism in Litopenaeus vannamei after ammonia-nitrogen exposure

To unveil the adaptation of Litopenaeus vannamei to elevated ambient ammonia-N, crustacean hyperglycaemic hormone (CHH) was knocked down to investigate its function in glucose metabolism pathway under ammonia-N exposure. When CHH was silenced, haemolymph glucose increased significantly during 3-6 h, decreased significantly during 12-48 h and recovered to the control groups' level at 72 h. After CHH knock-down, dopamine (DA) contents reduced significantly during 3-24 h, which recovered after 48 h. Besides, the expressions of guanylyl cyclase (GC) and DA1R in the hepatopancreas decreased significantly, while DA4R increased significantly. Correspondingly, the contents of cyclic AMP (cAMP), cyclic GMP (cGMP) and diacylglycerol (DAG) and the expressions of protein kinase A (PKA), protein kinase G (PKG), AMP active protein kinase α (AMPKα) and AMPKγ were significantly down-regulated, while the levels of protein kinase C (PKC) and AMPKβ were significantly up-regulated. The expressions of cyclic AMP response element-binding protein (CREB) and GLUT2 decreased significantly, while GLUT1 increased significantly. Moreover, glycogen content, glycogen synthase and glycogen phosphorylase activities in hepatopancreas and muscle were significantly increased. Furthermore, the levels of key enzymes hexokinase, pyruvate kinase and phosphofructokinase in glycolysis (GLY), rate-limiting enzymes citrate synthase in tricarboxylic acid and critical enzymes phosphoenolpyruvate carboxykinase, fructose diphosphate and glucose-6-phosphatase in gluconeogenesis (GNG) were significantly decreased in hepatopancreas. These results suggest that CHH affects DA and then they affect their receptors to transmit glucose metabolism signals into the hepatopancreas of L. vannamei under ammonia-N stress. CHH acts on the cGMP-PKG-AMPKα-CREB pathway through GC, and CHH affects DA to influence cAMP-PKA-AMPKγ-CREB and DAG-PKC-AMPKβ-CREB pathways, thereby regulating GLUT, inhibiting glycogen metabolism and promoting GLY and GNG. This study contributes to further understand glucose metabolism mechanism of crustacean in response to environmental stress.

The razor clam Sinonovacula constricta uses the strategy of conversion of toxic ammonia to glutamine in response to high environmental ammonia exposure

High ammonia can inhibit the survival and growth, and even cause mortality of razor clam (S. constricta). The accumulation of ammonia to lethal concentrations in some invertebrates may be partially prevented by converting some of the ammonia into glutamine (Gln). Glutamine dehydrogenase (GDH) and glutamine synthetase (GS) have been widely implicated a central role in response to ammonia stress. However, the molecular and physiological response of GDH and GS to ammonia alterations has not yet been determined in clams. To investigate the possible participatory role of GDH and GS genes in altered ammonia conditions, we have cloned their gene sequences and examined the mRNA expression and western blotting under ammonia exposure in S. constricta (ScGDH and ScGS), and detected the levels of GS and GDH, and the content of glutamate (Glu) and Gln. The full-length cDNA of ScGDH was 3924 bp, with a 1629 bp open reading frame (ORF) encoding a 542 amino-acid polypeptide. The complete cDNA sequence for ScGS had 2739 bp with an ORF of 1110 bp encoding 369 amino acids. To investigate ammonia detoxification strategies, the clams were exposed to ammonia for 96 h at four different concentrations (0, 100, 140, and 180 mg/L). Exposure to ammonia resulted in a significant increase of glutamate concentration and Gln in the haemocytes. GDH activity, GDH relative mRNA and protein expression, GS activity, GS relative mRNA and protein expression increased significantly and showed a pronounced time and dosage interaction in the liver. The results suggested that the protective strategies of Gln formation existed in S. constricta, which could convert ammonia to non- or less toxic nitrogenous compounds on the exposure of ammonia. Glutamate content in the haemocytes increased significantly, which is to ensure sufficient Glu to meet the needs for GS to catalyze the conversion of ammonia to Gln. We proposed that the induction of Glu synthesis-related genes and the subsequent formation of the active protein occurred in preparation for the increased capacity of the body to convert ammonia, into Gln. The results of this study suggested that GDH and GS play an important role in the synthesis of Gln, emphasizing, the protective strategies of Gln formation in S. constricta convert ammonia to nontoxic or less toxic nitrogenous compounds upon exposure to ammonia.