Transciptomic and histological analysis of hepatopancreas, muscle and gill tissues of oriental river prawn (Macrobrachium nipponense) in response to chronic hypoxia

How water acidification influences the organism antioxidant capacity and gill structure of Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) at normoxia and hypoxia

The effect of water acidification in combination with normoxia or hypoxia on the antioxidant capacity and oxidative stress markers in gills and hemolymph of the Mediterranean mussel (Mytilus galloprovincialis), as well as on gill microstructure, has been evaluated through an in vivo experiment. Mussels were exposed to a low pH (7.3) under normal dissolved oxygen (DO) conditions (8 mg/L), and hypoxia (2 mg/L) for 8 days, and samples were collected on days 1, 3, 6, and 8 to evaluate dynamic changes of physiological responses. Cytoplasmic concentrations of reactive oxygen species (ROS) and levels of DNA damage were measured in hemocytes, while the activity of catalase (CAT) and superoxide dismutase (SOD) and histopathological changes were assessed in gills. The results revealed that while water acidification did not significantly affect the activity of SOD and CAT in gills under normoxic and hypoxic conditions, there was a trend towards suppression of CAT activity at the end of the experimental period (day 8). Similarly, we did not observe increased formation of ROS in hemocytes or changes in the levels of DNA damage during the experimental period. These results strongly suggest that the oxidative stress response system in mussels is relatively stable to experimental conditions of acidification and hypoxia. Experimental acidification under normoxia and hypoxia caused changes to the structure of the gills, leading to various histopathological alterations, including dilation, hemocyte infiltration into the hemal sinuses, intercellular edema, vacuolization of epithelial cells in gill filaments, lipofuscin accumulation, changes in the shape and adjacent gill filaments, hyperplasia, exfoliation of the epithelial layer, necrosis, swelling, and destruction of chitinous layers (chitinous rods). Most of these alterations were reversible, non-specific changes that represent a general inflammatory response and changes in the morphology of the gill filaments. The dynamics of histopathological alterations suggests an active adaptive response of gills to environmental stresses. Taken together, our data indicate that Mediterranean mussels have a relative tolerance to water acidification and hypoxia at tissue and cellular levels.

Molecular pathways of osmoregulation in response to salinity stress in the gills of the scalloped spiny lobster (Panulirus homarus) within survival salinity

Scalloped spiny lobster (Panulirus homarus) aquaculture is the preferred strategy to resolve the conflict between supply and demand for lobster. Environmental conditions, such as salinity, are key to the success of lobster aquaculture. However, physiological responses of P. homarus to salinity stress have not been well studied. This study investigated the gill histology, osmoregulation and gill transcriptome of the early juvenile P. homarus (weight 19.04 ± 3.95 g) cultured at salinity 28 (control), 18, and 38 for 6 weeks. The results showed that the gill filaments of P. homarus exposed to low salinity showed severe separation of the cuticle and epithelial cells due to water absorption and swelling, as well as the dissolution and thinning of the cuticle and the rupture of the septum that separates the afferent and efferent channels. The serum osmolarity of P. homarus varied proportionately with external medium salinity and remained consistently above ambient osmolarity. The serum Na+, Cl-, K+, and Mg2+ concentrations P. homarus exhibited a pattern similar to that of serum osmolality, while the concentration of Ca2+ remained unaffected at salinity 18 but significantly increased at salinity 38. Gill Na+/K+-ATPase activity of P. homarus increased (p < 0.05) under the both salinity stress. Salinity 18 significantly increased Glutamate dehydrogenase (GDH) and Glutamicpyruvic transaminase (GPT) activity in the hepatopancreas of P. homarus (p < 0.05). According to transcriptome analysis, versus control group (salinity 28), 929 and 1095 differentially expressed genes (DEGs) were obtained in the gills of P. homarus at salinity 18 and 38, respectively, with these DEGs were mainly involved in energy metabolism, transmembrane transport and oxidative stress and substance metabolism. In addition, the expression patterns of 8 key DEGs mainly related to amino acid metabolism, transmembrane transport and oxidative stress were verified by quantitative real-time PCR (RT-qPCR). The present study suggests that salinity 18 has a greater impact on P. homarus than salinity 38, and P. homarus demonstrates effective osmoregulation and handle with salinity fluctuations (18 to 38) through physiological and functional adaptations. This study provides an improved understanding of the physiological response strategies of P. homarus facing salinity stress, which is crucial for optimizing aquaculture practices for this species.

Identifying Relationships between Glutathione S-Transferase-2 Single Nucleotide Polymorphisms and Hypoxia Tolerance and Growth Traits in Macrobrachium nipponense

Investigating hypoxia tolerance and growth trait single nucleotide polymorphisms (SNPs) in Macrobrachium nipponense is conducive to cultivating prawns with hypoxia tolerance and good growth characteristics. The glutathione S-transferase-2 gene (GST-2) has been shown to regulate hypoxia responses in M. nipponense. In this study, we identified a single GST-2 SNP in M. nipponense, and analyzed its regulatory relationship with hypoxia tolerance and growth. The GST-2 sequence was amplified with a polymerase chain reaction from 197 "Taihu Lake No. 3", "Taihu Lake No. 2", and Pearl River population samples to identify SNP loci. The full-length Mn-GST2 sequence was 2317 bp, including three exons and two introns. In total, 38 candidate SNP loci were identified from GST-2 using Mega11.0 comparisons, with most loci moderately polymorphic in terms of genetic diversity. Locus genotypes were also analyzed, and basic genetic parameters for loci were calculated using Popgene32 and PIC_CALC. The expected heterozygosity of the 38 SNP loci ranged from 0.2334 to 0.4997, with an average of 0.4107, while observed heterozygosity ranged from 0.1929 to 0.4721, with an average of 0.3401. The polymorphic information content ranged from 0.21 to 0.37. From SPSS analyses, the G+256A locus was significantly correlated with hypoxia tolerance across all three M. nipponense populations, while the SNP loci A+261C, C+898T, A+1370C, and G+1373T were significantly associated with growth traits. Further analyses revealed that the T+2017C locus was significantly correlated with hypoxia tolerance in "Taihu Lake No. 2" populations, G+256A, A+808T, C+1032T, and A+1530G loci were significantly correlated with hypoxia tolerance in "Taihu Lake No. 3" populations, while no SNP loci were correlated with hypoxia tolerance in Pearl River populations. A+1370C and G+1373T loci, which were associated with growth traits, exhibited a high degree of linkage disequilibrium (r2 = 0.89 and r2 > 0.8), suggesting potential genetic linkage. Our data suggest associations between hypoxia tolerance and growth trait SNP loci in M. nipponense, and provide valuable evidence for the genetic improvement of growth and hypoxia tolerance in this prawn species.

Response of lipid metabolism, energy supply, and cell fate in yellowstripe goby (Mugilogobius chulae) exposed to environmentally relevant concentrations atorvastatin

The usage of typical pharmaceuticals and personal care products (PPCPs) such as cardiovascular and lipid-modulating drugs in clinical care accounts for the largest share of pharmaceutical consumption in most countries. Atorvastatin (ATV), one of the most commonly used lipid-lowering drugs, is frequently detected with lower concentrations in aquatic environments owing to its wide application, low removal, and degradation rates. However, the adverse effects of ATV on non-target aquatic organisms, especially the molecular mechanisms behind the toxic effects, still remain unclear. Therefore, this study investigated the potentially toxic effects of ATV exposure (including environmental concentrations) on yellowstripe goby (Mugilogobius chulae) and addressed the multi-dimensional responses. The results showed that ATV caused typical hepatotoxicity to M. chulae. ATV interfered with lipid metabolism by blocking fatty acid β-oxidation and led to the over-consumption of lipids. Thus, the exposed organism was obliged to alter the energy supply patterns and substrates utilization pathways to keep the normal energy supply. In addition, the higher concentration of ATV exposure caused oxidative stress to the organism. Subsequently, M. chulae triggered the autophagy and apoptosis processes with the help of key stress-related transcriptional regulators FOXOs and Sestrins to degrade the damaged organelles and proteins to maintain intracellular homeostasis.

Sex differences in antioxidant ability and energy metabolism level resulting in the difference of hypoxia tolerance in red swamp crayfish (Procambarus clarkii)

Sexual dimorphism widely exists in crustaceans. However, sex differences in the hypoxia tolerance of crayfish have rarely been reported. In this study, the differences in hypoxia tolerance between the two sexes of crayfish were assessed according to mortality, pathological features of hepatopancreas, antioxidant enzyme activity and differentially expressed genes (DEGs) analysis using transcriptome. The results showed that male crayfish displayed significantly higher mortality than the female under hypoxia stress (p < 0.05). Furthermore, female crayfish demonstrated higher levels of antioxidant enzyme activity. Hematoxylin-eosin staining analysis revealed that the damage of hepatopancreas was more severe in the male crayfish compared to the female crayfish. Additionally, there was higher expression level of the DEGs in hypoxia-inducible factor (HIF) pathway and higher energy metabolism level in the female compared to the male. Together, these findings suggest that the female crayfish with higher antioxidant ability and energy metabolism level exhibits stronger hypoxia tolerance than the male crayfish, providing the theoretical support for investigating sex differences in hypoxia tolerance among crustaceans.

Characterization of a Lipopolysaccharide- and Beta-1,3-Glucan Binding Protein (LGBP) from the Hepatopancreas of Freshwater Prawn, Macrobrachium rosenbergii, Possessing Lectin-Like Activity

The study focuses on the isolation, characterization, and expression analysis of a lectin from the hepatopancreas of Macrobrachium rosenbergii. The protein was isolated by affinity chromatography on a melibiose-agarose column. The molecular weight of the native protein was found to be ~120 kDa which consists of a single polypeptide of ~39.5 kDa. On mass spectrometric analysis, the protein was identified as lipopolysaccharide- and beta-1,3-glucan binding protein (LGBP). LGBP showed hemagglutination with rabbit RBC like a lectin and its carbohydrate-binding specificity was determined by the hemagglutination inhibition test. The protein also showed antibacterial activity against two Gram-negative bacteria Vibrio harveyi and Aeromonas sobria, and one Gram positive bacteria Bacillus cereus in the disc diffusion test. Rabbit antiserum was raised against the purified LGBP and used to develop a sandwich ELISA system for quantitation of the protein in hepatopancreas and serum samples of M. rosenbergii. The expression of the LGBP transcripts in muscle, hepatopancreas, and gill tissues from M. rosenbergii juveniles at 72 h post-challenge of V. harveyi was not modulated as noticed in qPCR analysis. However, significant increases in the concentrations of LGBP protein in hepatopancreas (5.23 ± 0.45 against 3.43 ± 0.43 mg/g tissue in control) and serum (1.08 ± 0.14 against 0.61 ± 0.08 µg/ml in control) were observed in the challenged group of prawns in ELISA suggesting its putative role against bacterial infections. The study for the first time characterized the native LGBP of M. rosenbergii showing a multifunctional role in immunity.

Effects of Low-Fish-Meal Diet Supplemented with Coenzyme Q10 on Growth Performance, Antioxidant Capacity, Intestinal Morphology, Immunity and Hypoxic Resistance of Litopenaeus vannamei

The aim of this study was to evaluate the effects of a low-fish-meal diet supplemented with coenzyme Q10 on the growth, antioxidant capacity, immunity, intestinal health and hypoxic resistance of Litopenaeus vannamei. L.vannamei with an initial weight of 0.66 g were fed with the experimental diets for 56 days. Diets D1 (20% FM level) and D2-D7 (15% FM level), supplemented with 0%, 0.002%, 0.004%, 0.006%, 0.008% and 0.01% coenzyme Q10 were formulated. In terms of growth performance, the weight gain and specific growth rate in the D2 diet were significantly lower than those in the D1 diet (p < 0.05). The final body weight, weight gain and specific growth rate in the D2-D7 diets had an upward trend, and the condition factor in the D2-D7 diets was lower than those in the D1 diet (p < 0.05). There were no significant differences in the crude protein and crude lipid levels in the whole body among all diet treatments (p > 0.05). In terms of hepatopancreas antioxidant parameters, the D5 and D6 diets significantly promoted the total antioxidant capacity and total superoxide dismutase activity, and significantly decreased the malondialdehyde content (p < 0.05). The expression levels of cat, mnsod and gpx in shrimp fed with the D5 and D6 diets were significantly higher than those of shrimp fed with the D2 diet (p < 0.05). In addition, the mRNA level of ProPO was increased in the D4 and D5 diets, and LZM expression was increased in the D6 diet compared with the D1 diet (p < 0.05). The villus height of shrimp fed with diets supplemented with coenzyme Q10 was significantly increased (p < 0.05), and the intestinal thickness and submucosal thickness of shrimp fed with the D6 diet were the highest (p < 0.05). After acute hypoxia stress, lethal dose 50 time in the D3-D7 diets was significantly increased compared with the D1 and D2 diets (p < 0.05), and the highest value was found in the D4 diet (p < 0.05). After stress, the expression levels of TLR pathway-related genes (Toll, Myd88, Pelle, TRAF6 and Dorsal) in the D4 and D6 diets were significantly increased compared with the D2 diet. In general, Litopenaeus vannamei fed with the D6 diet achieved the best growth, antioxidant capacity, immunity, and intestinal morphology among all low FM diets and D4-D6 diets improved hypoxic resistance.

Hypoxia in aquatic invertebrates: Occurrence and phenotypic and molecular responses

Global deoxygenation in aquatic systems is an increasing environmental problem, and substantial oxygen loss has been reported. Aquatic animals have been continuously exposed to hypoxic environments, so-called "dead zones," in which severe die-offs among organisms are driven by low-oxygen events. Multiple studies of hypoxia exposure have focused on in vivo endpoints, metabolism, oxidative stress, and immune responses in aquatic invertebrates such as molluscs, crustaceans, echinoderms, and cnidarians. They have shown that acute and chronic exposure to hypoxia induces significant decreases in locomotion, respiration, feeding, growth, and reproduction rates. Also, several studies have examined the molecular responses of aquatic invertebrates, such as anaerobic metabolism, reactive oxygen species induction, increased antioxidant enzymes, immune response mechanisms, regulation of hypoxia-inducible factor 1-alpha (HIF-1α) genes, and differently expressed hemoglobin/hemocyanin. The genetic basis of those molecular responses involves HIF-1α pathway genes, which are highly expressed in hypoxic conditions. However, the identification of HIF-1α-related genes and understanding of their applications in some aquatic invertebrates remain inadequate. Also, some species of crustaceans, rotifers, sponges, and ctenophores that lack HIF-1α are thought to have alternative defense mechanisms to cope with hypoxia, but those factors are still unclear. This review covers the formation of hypoxia in aquatic environments and the various adverse effects of hypoxia on aquatic invertebrates. The limitations of current hypoxia research and genetic information about the HIF-1α pathway are also discussed. Finally, this paper explains the underlying processes of the hypoxia response and presents an integrated program for research about the molecular mechanisms of hypoxic stresses in aquatic invertebrates.

Transcriptome Analysis Reveals the Effect of Stocking Density on Energy Metabolism in the Gills of Cherax quadricarinatus under Rice-Crayfish Co-Culture

Stocking density is a crucial factor affecting productivity in aquaculture, and high stocking density is a stressor for aquatic animals. In this study, we aimed to investigate the effects of stocking densities on oxidative stress and energy metabolism in the gills of Cherax quadricarinatus under rice-crayfish farming. The C. quadricarinatus were reared at low density (LD), medium density (MD), and high density (HD) for 90 days. The results showed that the superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and malondialdehyde (MDA) levels were higher in the HD group than those in the LD group. Transcriptomic analysis revealed 1944 upregulated and 1157 downregulated genes in the gills of the HD group compared to the LD group. Gene ontology (GO) enrichment analysis indicated that these differentially expressed genes (DEGs) were significantly associated with ATP metabolism. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis also showed that high stocking density resulted in the dysregulation of oxidative phosphorylation. Furthermore, high stocking density upregulated six lipid metabolism-related pathways. Overall, our findings, despite the limited number of samples, suggested that high stocking density led to oxidative stress and dysregulation of energy metabolism in the gills of C. quadricarinatus under rice-crayfish co-culture. Alteration in energy metabolism may be an adaptive response to adverse farming conditions.

Physiological and molecular responses to hypoxia stress in Manila clam Ruditapes philippinarum

Hypoxia has become one of the major environmental problems in the aquaculture industry. As one of the most commercially important bivalves, Manila clam Ruditapes philippinarum may be suffering substantial mortality attributable to hypoxia. The physiological and molecular responses to hypoxia stress in Manila clam were evaluated at two levels of low dissolved oxygen: 0.5 mg/L (DO 0.5 mg/L) and 2.0 mg/L (DO 2.0 mg/L). With the prolongation of hypoxia stress, the mortality rate was 100% at 156 h under DO 0.5 mg/L. In contrast, 50% of clams survived after 240 h of stress at DO 2.0 mg/L. After the hypoxia stress, some severe structural damages were observed in gill, axe foot, hepatopancreas tissues, such as cell rupture and mitochondrial vacuolization. For the hypoxia-stressed clams, the significant rise and decline of enzyme activity (LDH and T-AOC) was observed in gills, in contrast to the reduction of glycogen content. Furthermore, the expression levels of genes related to energy metabolism (SDH, PK, Na⁺/K⁺-ATPase, NF-κB and HIF-1α) was significantly affected by the hypoxia stress. It is therefore suggested that the short-term survival of clams under hypoxia may be dependent on stress protection by antioxidants, energy allocation, and tissue energy reserves (such as glycogen stores). Despite this, the prolongation of hypoxia stress at DO 2.0 mg/L may cause the irreversible damages of cellular structures in clam tissues, eventually leading to the death of clams. We therefore support the hypothesis that the extent of hypoxia impacts on marine bivalves may be underestimated in the coastal areas.

Different reoxygenation rates induce different metabolic, apoptotic and immune responses in Golden Pompano (Trachinotus blochii) after hypoxic stress

Dissolved oxygen (DO) is essential for teleosts, and fluctuating environmental factors can result in hypoxic stress in the golden pompano (Trachinotus blochii). However, it is unknown whether different recovery speeds of DO concentration after hypoxia induce stress in T. blochii. In this study, T. blochii was subjected to hypoxic conditions (1.9 ± 0.2 mg/L) for 12 h followed by 12 h of reoxygenation at two different speeds (30 mg/L per hour and 1.7 mg/L per hour increasing). The gradual reoxygenation group (GRG), experienced DO recovery (1.9 ± 0.2 to 6.8 ± 0.2 mg/L) within 3 h, and the rapid reoxygenation group (RRG), experienced DO recovery (1.9 ± 0.2 to 6.8 ± 0.2 mg/L) within 10 min. Physiological and biochemical parameters of metabolism (glucose, glycegon, lactic acid (LD), lactate dehydrogenase (LDH), pyruvic acid (PA), phosphofructokinase (PFKA), and hexokinase (HK), triglyceride (TG), lipoprotein lipase (LPL), carnitine palmitoyltransferase 1 (CPT-1)) and transcriptome sequencing (RNA-seq of liver) were monitored to identify the effects of the two reoxygenation speeds. Increased LD content and increased activity of LDH, PA, PFKA, and HK suggested enhanced anaerobic glycolysis under hypoxic stress. LD and LDH levels remained significantly elevated during reoxygenation, indicating that the effects of hypoxia were not immediately alleviated during reoxygenation. The expressions of PGM2, PFKA, GAPDH, and PK were increased in the RRG, which suggests that glycolysis was enhanced. The same pattern was not observed in the GRG. Additionally, In the RRG, reoxygenation may promote glycolysis to guarantee energy supply. However, the GRG may through the lipid metabolism such as steroid biosynthesis at the later stage of reoxygenation. In the aspect of apoptosis, differentially expressed genes (DEGs) in the RRG were enriched in the p53 signaling pathway, which promoted cell apoptosis, while DEGs in the GRG seem to activate cell apoptosis at early stage of reoxygenation but was restrained latterly. DEGs in both the RRG and the GRG were enriched in the NF-kappa B and JAK-STAT signaling pathways, the RRG may induce cell survival by regulating the expression of IL-12B, COX2, and Bcl-XL, while in the GRG it may induce by regulating the expression of IL-8. Moreover, DEGs in the RRG were also enriched in the Toll-like receptor signaling pathway. This research revealed that at different velocity of reoxygenation after hypoxic stress, T. blochii would represent different metabolic, apoptotic and immune strategies, and this conclusion would provide new insight into the response to hypoxia and reoxygenation in teleosts.

Comparative Transcriptome Analysis of Head Kidney of Aeromonas hydrophila-infected Hypoxia-tolerant and Normal Large Yellow Croaker

The large yellow croaker (Larimichthys crocea) is one of the most economically important marine fish on the southeast coast of China and much of its yield is usually lost by hypoxia. To address this problem and lay a foundation for culturing a new strain of large yellow croaker with hypoxia tolerance, our research group screened a hypoxia-tolerant population of L. crocea. Surprisingly, we also found that hypoxia-tolerant population exhibited higher survival when infected with pathogens compared to the normal population during the farming operation. In order to understand the mechanism underlying the higher survival rate of the hypoxia-tolerant population and enrich the head kidney immune mechanism of L. crocea infected with pathogens, we compared and analyzed the head kidney transcriptome of the hypoxia-tolerant and normal individuals under Aeromonas hydrophila infection. We obtained 159.68 GB high-quality reads, of which more than 87.61% were successfully localized to the reference genome of L. crocea. KEGG analysis revealed differentially expressed genes in the signaling pathways involving immunity, cell growth and death, transport and catabolism, and metabolism. Among these, the toll-like receptor signaling pathway, Nod-like receptor signaling pathway, cytokine-cytokine receptor interaction, phagosome, apoptosis, and OXPHOS pathways were enriched in both groups after infection compared to before, and were enriched in infected tolerant individuals compared to normal individuals. In addition, we found that the expression of hif1α and its downstream genes were higher in the hypoxia-sensitive group of fish than in the normal group. In conclusion, our results showed some signaling pathways and hub genes, which may participate in A. hydrophila defense in the head kidney of two populations, and may contribute to the higher survival rate in the hypoxia-tolerant population. Overall, these findings increase our understanding of the defense mechanism within the head kidney of L. crocea under A. hydrophila infection, and suggest a preliminary hypothesis for why hypoxia-tolerant individuals may exhibit a higher survival rates after infection. Our study provides scientific evidence for the breeding of a new hypoxia-tolerant strain of L. crocea for aquaculture.

Glucose transporter GLUT1 expression is important for oriental river prawn (Macrobrachium nipponense) hemocyte adaptation to hypoxic conditions

Crustaceans have an open vascular system in which hemocytes freely circulate in hemolymph. Hemocytes are rich in hemocyanin, a specific oxygen-transport protein in crustaceans; therefore, understanding the response of hemocytes to hypoxia is crucial. Although hemocytes take up glucose during hypoxia, the molecular mechanism of glucose uptake in crustaceans remains unclear. Herein, we identified two highly conserved glucose transporters (GLUT1 and GLUT2) in Macrobrachium nipponense (oriental river prawn) and analyzed their tissue-specific expression patterns. Our immunofluorescence assays showed that GLUT1 and GLUT2 are located on the cell membrane, with a strong GLUT1 signal in primary hemocytes under hypoxia. We found that during acute hypoxia, hypoxia-inducible factor-1α-related metabolic alterations result in decreased mitochondrial cytochrome c oxidase activity, implying a classic glycolytic mechanism. As a proof of concept, we replicated these findings in insect S2 cells. Acute hypoxia significantly induced hypoxia-inducible factor-1α, GLUT1, and pyruvate dehydrogenase kinase isozyme 1 expression in primary hemocytes, and hypoxia-induced increases in glucose uptake and lactate secretion were observed. GLUT1 knockdown induced intracellular reactive oxygen species generation and apoptosis in vitro and in vivo, resulting in increased prawn mortality and more apoptotic cells in their brains, implying a vital function of GLUT1 in hypoxia adaptation. Taken together, our results suggest a close relationship between hypoxia-mediated glycolysis and GLUT1 in hemocytes. These results demonstrated that in crustaceans, adaptation to hypoxia involves glucose metabolic plasticity.

Optimal Niacin Requirement of Oriental River Prawn Macrobrachium nipponense as Determined by Growth, Energy Sensing, and Glycolipid Metabolism

Niacin is indispensable for the growth and development of aquatic animals. However, the correlations between dietary niacin supplementations and the intermediary metabolism of crustaceans are still poorly elucidated. This study explored the effects of different dietary niacin levels on the growth, feed utilization, energy sensing, and glycolipid metabolism of oriental river prawn Macrobrachium nipponense. Prawns were fed with different experimental diets containing graded niacin levels (15.75, 37.62, 56.62, 97.78, 176.32, and 339.28 mg/kg, respectively) for 8 weeks. Weight gain, protein efficiency, feed intake, and hepatopancreas niacin contents all maximized in the 176.32 mg/kg group with significance noted with the control group (P <0.05), whereas the opposite was true for feed conversion ratio. Hepatopancreas niacin concentrations increased significantly (P < 0.05) as dietary niacin levels increased, and peaked at the 339.28 mg/kg group. Hemolymph glucose, total cholesterol, and triglyceride concentrations all maximized in the 37.62 mg/kg group, while total protein concentration reached the highest value in the 176.32 mg/kg group. The hepatopancreas mRNA expression of AMP-activated protein kinase α and sirtuin 1 peaked at the 97.78 and 56.62 mg/kg group, respectively, and then both decreased as dietary niacin levels increased furtherly (P < 0.05). Hepatopancreas transcriptions of the genes related to glucose transportation, glycolysis, glycogenesis, and lipogenesis all increased with increasing niacin levels up to 176.32 mg/kg, but decreased significantly (P < 0.05) as dietary niacin levels increased furtherly. However, the transcriptions of the genes related to gluconeogenesis and fatty acid β-oxidation all decreased significantly (P < 0.05) as dietary niacin levels increased. Collectively, the optimum dietary niacin demand of oriental river prawn is 168.01-169.08 mg/kg. In addition, appropriate doses of niacin promoted the energy-sensing capability and glycolipid metabolism of this species.

RNA-seq Provides Novel Insights into Response to Acute Salinity Stress in Oriental River Prawn Macrobrachium nipponense

The oriental river prawn Macrobrachium nipponense is an important aquaculture species in China, Vietnam, and Japan. This species could survive in the salinity ranging from 7 to 20 ppt and accelerate growth in the salinity of 7 ppt. To identify the genes and pathways in response to acute high salinity stress, M. nipponense was exposed to the acute high salinity of 25 ppt. Total RNA from hepatopancreas, gills, and muscle tissues was isolated and then sequenced using high-throughput sequencing method. Differentially expressed genes (DGEs) were identified, and a total of 632, 836, and 1246 DEGs with a cutoff of significant twofold change were differentially expressed in the hepatopancreas, gills, and muscle tissues, respectively. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genome pathway enrichment analyses were conducted. These DEGs were involved in the GO terms of cellular process, metabolic process, membrane, organelle, binding, and catalytic activity. The DEGs of hepatopancreas and gill tissues were mainly enriched in PPAR signaling pathway, longevity regulating pathway, protein digestion and absorption, and the DEGs of muscle tissue in arginine biosynthesis, adrenergic signaling in cardiomyocytes, cardiac muscle contraction, and cGMP-PKG signaling pathway. Real-time PCR conducted with fifteen selected DEGs indicated high reliability of digital analysis using RNA-Seq. The results indicated that the M. nipponense may regulate essential mechanisms such as metabolism, oxidative stress, and ion exchange to adapt the alternation of environment, when exposed to acute high salinity stress. This work reveals the numbers of genes modified by salinity stress and some important pathways, which could provide a comprehensive insight into the molecular responses to high salinity stress in M. nipponense and further boost the understanding of the potential molecular mechanisms of adaptation to salinity stress for euryhaline crustaceans.

Regulation of the cell cycle under anoxia stress in tail muscle and hepatopancreas of the freshwater crayfish, Orconectes virilis

Regulation of the cell cycle is an understudied response to oxygen deprivation among crustaceans. The virile crayfish, Orconectes virilis, is a freshwater crustacean that when challenged by environmental oxygen limitation undergoes metabolic rate depression (to ~30% of normal levels) and switches to anaerobic metabolism to generate energy. To understand how crayfish regulate the cell cycle in response to anoxia, key proteins involved in cell cycle control were analyzed in muscle and hepatopancreas. At the G1/S barrier, an overall upregulation of positive regulators of cell cycle progression was indicated by the responses of G1 cyclins (cyclin D and cyclin E) and Cyclin dependent kinases (CDK4, CDK6 and CDK2) under anoxia. Although the levels of Cyclin kinase inhibitors (CKIs) at this juncture were also upregulated (P15/16 and P21 (T145) in muscle and P16 (S152) in hepatopancreas), levels of a major regulator of this phase and driver to S-phase, E2F1, were significantly higher in both tissues in conjunction with deactivation of its inhibitor, Retinoblastoma (Rb) protein. At the G2/M barrier, expression profiles of the G2 cyclin B suggested cell cycle progression despite overall trend of higher activities of checkpoint kinases, (Chk1 (S317) and Chk2 (S19)), that also negatively regulate the cyclin B-CDK1 complex via CdC25C (cell division cycle 25) whose levels remained unchanged. Overall, the present study suggests continued cell cycle progression, albeit with potential deceleration, as indicated by checkpoint kinases and kinase inhibitor profiles that might play a role in protecting tissues from apoptotic damage under chronic anoxic stress.

Transcriptome Analysis to Study the Molecular Response in the Gill and Hepatopancreas Tissues of Macrobrachium nipponense to Salinity Acclimation

Macrobrachium nipponense is an economically important prawn species and common in Chinese inland capture fisheries. During aquaculture, M. nipponense can survive under freshwater and low salinity conditions. The molecular mechanism underlying the response to salinity acclimation remains unclear in this species; thus, in this study, we used the Illumina RNA sequencing platform for transcriptome analyses of the gill and hepatopancreas tissues of M. nipponense exposed to salinity stress [0.4‰ (S0, control group), 6‰ (S6, low salinity group), and 12‰ (S12, high salinity group)]. Differentially expressed genes were identified, and several important salinity adaptation-related terms and signaling pathways were found to be enriched, such as "ion transport," "oxidative phosphorylation," and "glycometabolism." Quantitative real-time PCR demonstrated the participation of 12 key genes in osmotic pressure regulation in M. nipponense under acute salinity stress. Further, the role of carbonic anhydrase in response to salinity acclimation was investigated by subjecting the gill tissues of M. nipponense to in situ hybridization. Collectively, the results reported herein enhance our understanding of the mechanisms via which M. nipponense adapts to changes in salinity.

Neural excitotoxicity and the toxic mechanism induced by acute hypoxia in Chinese mitten crab (Eriocheir sinensis)

Hypoxia can induce neural excitotoxicity in mammals, but this adverse effect has not been investigated in aquatic animals to date, especially in crustaceans. This study explored the induction effect and toxic mechanism of acute hypoxia stress (1.0 ± 0.1 mg dissolved oxygen /L) for 24 h on neural excitotoxicity in juvenile Chinese mitten crab, Eriocheir sinensis. The results showed that hemolymph glucose and serum lactic acid content were significantly increased, and the mRNA expression of crustacean hyperglycemic hormone and hypoxia-inducible factor 1α were significantly up-regulated in the hypoxia group compared with control. RNA-Seq results confirmed that acute hypoxia stress had a more significant impact on carbohydrate metabolism than lipid and protein metabolism. In addition, the TUNEL assay showed that the apoptosis rate of nerve cells was significantly higher in the hypoxia group than in the control, and similar trends were observed in the expression of apoptosis-related genes. RNA-Seq results also showed that acute hypoxia stress-induced neuronal apoptosis by regulating multiple apoptosis-related pathways. Moreover, free glutamate and GABA contents in the nerve tissue of thoracic ganglia were significantly higher in the hypoxia group than in the control group. Furthermore, the mRNA expression of NMDA related receptors was significantly up-regulated in the hypoxia group compared with the control. Similar trends were observed in the expression of calcium-dependent degrading enzymes and endogenous antioxidant-related proteins or enzymes. Meanwhile, the mRNA expression level of high-affinity neuronal glutamate transporter in the hypoxia group was significantly up-regulated compared with the control, whereas the vesicular glutamate transporter was significantly down-regulated. Furthermore, NMDA-R antagonists (MK-801 and Ro25-6981) injection showed that NMDA-R served as the bridge and core position of glutamate-induced neural neurotoxicity. This study provides a new perspective and theoretical guidance for exploring the regulation of hypoxic tolerance in E. sinensis.

Genome-Wide Analyses of Heat Shock Protein Superfamily Provide New Insights on Adaptation to Sulfide-Rich Environments in Urechis unicinctus (Annelida, Echiura)

The intertidal zone is a transitional area of the land-sea continuum, in which physical and chemical properties vary during the tidal cycle and highly toxic sulfides are rich in sediments due to the dynamic regimes. As a typical species thriving in this habitat, Urechis unicinctus presents strong sulfide tolerance and is expected to be a model species for sulfide stress research. Heat shock proteins (HSPs) consist of a large group of highly conserved molecular chaperones, which play important roles in stress responses. In this study, we systematically analyzed the composition and expression of HSPs in U. unicinctus. A total of eighty-six HSP genes from seven families were identified, in which two families, including sHSP and HSP70, showed moderate expansion, and this variation may be related to the benthic habitat of the intertidal zone. Furthermore, expression analysis revealed that almost all the HSP genes in U. unicinctus were significantly induced under sulfide stress, suggesting that they may be involved in sulfide stress response. Weighted gene co-expression network analysis (WGCNA) showed that 12 HSPs, including 5 sHSP and 4 HSP70 family genes, were highly correlated with the sulfide stress response which was distributed in steelblue and green modules. Our data indicate that HSPs, especially sHSP and HSP70 families, may play significant roles in response to sulfide stress in U. unicinctus. This systematic analysis provides valuable information for further understanding of the function of the HSP gene family for sulfide adaptation in U. unicinctus and contributes a better understanding of the species adaptation strategies of marine benthos in the intertidal zone.

The transcriptomic responses of blunt snout bream (Megalobrama amblycephala) to acute hypoxia stress alone, and in combination with bortezomib

BACKGROUND

Blunt snout bream (Megalobrama amblycephala) is sensitive to hypoxia. A new blunt snout bream strain, "Pujiang No.2", was developed to overcome this shortcoming. As a proteasome inhibitor, bortezomib (PS-341) has been shown to affect the adaptation of cells to a hypoxic environment. In the present study, bortezomib was used to explore the hypoxia adaptation mechanism of "Pujiang No.2". We examined how acute hypoxia alone (hypoxia-treated, HN: 1.0 mg·L^- 1), and in combination with bortezomib (hypoxia-bortezomib-treated, HB: Use 1 mg bortezomib for 1 kg fish), impacted the hepatic ultrastructure and transcriptome expression compared to control fish (normoxia-treated, NN).

RESULTS

Hypoxia tolerance was significantly decreased in the bortezomib-treated group (LOE_crit, loss of equilibrium, 1.11 mg·L^- 1 and 1.32 mg·L^- 1) compared to the control group (LOE_crit, 0.73 mg·L^- 1 and 0.85 mg·L^- 1). The HB group had more severe liver injury than the HN group. Specifically, the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the HB group (52.16 U/gprot, 32 U/gprot) were significantly (p < 0.01) higher than those in the HN group (32.85 U/gprot, 21. 68 U/gprot). In addition, more severe liver damage such as vacuoles, nuclear atrophy, and nuclear lysis were observed in the HB group. RNA-seq was performed on livers from the HN, HB and NN groups. KEGG pathway analysis disclosed that many DEGs (differently expressed genes) were enriched in the HIF-1, FOXO, MAPK, PI3K-Akt and AMPK signaling pathway and their downstream.

CONCLUSION

We explored the adaptation mechanism of "Pujiang No.2" to hypoxia stress by using bortezomib, and combined with transcriptome analysis, accurately captured the genes related to hypoxia tolerance advantage.

cDNA Characterization and Expression of Selenium-Dependent CqGPx3 Isoforms in the Crayfish Cherax quadricarinatus under High Temperature and Hypoxia

Glutathione peroxidase 3 (GPx3) is the only extracellular selenoprotein (Sel) that enzymatically reduces H2O2 to H2O and O2. Two GPx3 (CqGPx3) cDNAs were characterized from crayfish Cherax quadricarinatus. The nerve cord CqGPx3a isoform encodes for a preprotein containing an N-terminal signal peptide of 32 amino acid residues, with the mature Sel region of 192 residues and a dispensable phosphorylation domain of 36 residues. In contrast, the pereiopods CqGPx3b codes for a precursor protein with 19 residues in the N-terminal signal peptide, then the mature 184 amino acid residues protein and finally a Pro-rich peptide of 42 residues. CqGPx3 are expressed in cerebral ganglia, pereiopods and nerve cord. CqGPx3a is expressed mainly in cerebral ganglia, antennulae and nerve cord, while CqGPx3b was detected mainly in pereiopods. CqGPx3a expression increases with high temperature and hypoxia; meanwhile, CqGPx3b is not affected. We report the presence and differential expression of GPx3 isoforms in crustacean tissues in normal conditions and under stress for high temperature and hypoxia. The two isoforms are tissue specific and condition specific, which could indicate an important role of CqGPx3a in the central nervous system and CqGPx3b in exposed tissues, both involved in different responses to environmental stressors.

Differential immune and metabolic responses underlie differences in the resistance of Siganus oramin and Trachinotus blochii to Cryptocaryon irritans infection

Numerous studies have demonstrated that Cryptocaryon irritans can efficiently propagate in golden pompano (Trachinotus blochii), especially under intensive high-density culture, which can lead to large-scale infection, bacterial invasion, and major economic losses. By contrast, Siganus oramin is less susceptible to C. irritans infection. Here, we artificially infected S. oramin and T. blochii with C. irritans. We then used RNA-seq to characterize the expression of genes in the gills of S. oramin and T. blochii at different times after infection, conducted bioinformatics analysis of relevant pathways, and compared the differentially expressed genes in the two species. The aim of this study was to enhance our understanding of host-parasite interactions to aid the development of effective prevention and treatment strategies for C. irritans. Infection with C. irritans induced the differential expression of a large number of genes in the gills of S. oramin, indicating that S. oramin may respond to C. irritans infection by modifying the expression of genes at the transcriptional level. Our research showed that the Toll-like receptor signaling pathway, Antigen processing and presentation, Complement and coagulation cascades, and Cytosolic DNA-sensing pathway are involved in the immune response of S. oramin and T. blochii to C. irritans infection. However, T. blochii has a weak ability to mobilize neutrophils to participate in defense against C. irritans infection and differs from S. oramin in its ability to induce specific immune responses. Because of gill tissue damage during infection, dissolved oxygen intake is reduced, which increases physiological and metabolic stress. The metabolic pathways of S. oramin and T. blochii significantly differed; specifically, the main pathways in S. oramin were related to glucose and lipid metabolism, and the main pathways in T. blochii were related to amino acid metabolism. This may reduce the efficiency of ATP biosynthesis in T. blochii and result in dysfunctional energy metabolism. Therefore, differential immune and metabolic responses underlie differences in the resistance of S. oramin and T. blochii to C. irritans.

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.

Transcriptome analysis of hepatopancreas from different living states oriental river prawn (Macrobrachium nipponense) in response to hypoxia

As an important economical freshwater prawn, Macrobrachium nipponense has difficulty with adapting to hypoxia. In this study, comparative transcriptome analysis was used for the first time to explore the differences between different living states of Macrobrachium nipponense under hypoxia. A total of 94.22 Gb clean reads were obtained and assembled into 54,688 unigenes. A total of 224, 266, and 750 differently expressed genes were found in the comparison of the control and death groups, the control and moribund groups, and the control and survived groups, respectively. Three signal pathways closely related to hypoxia were found by enriching of the signal pathways in three comparison groups. In addition, much attention was focused on the differential genes in these pathways. Oxidative stress related genes, such as 70 kDa heat shock protein, phosphoenolpyruvate carboxykinase and cyclooxygenase were differentially expressed in different comparisons. After comparing with previous studies, cyclooxygenase was found to be an important hypoxia-related gene that is fully involved in the hypoxic response. Interestingly, two new genes with no Nr annotation were found in this manuscript. This manuscript will enrich our understanding of oxidative stress response to hypoxia and provide a theoretical basis for the subsequent solution of apoptosis caused by hypoxia.

Transcriptional changes revealed water acidification leads to the immune response and ovary maturation delay in the Chinese mitten crab Eriocheir sinensis

Nowadays, due to increasing carbon dioxide released, water acidification poses a series of serious impacts on aquatic organisms. To evaluate the effects of water acidification on crustaceans, we focused on the Chinese mitten crab Eriocheir sinensis, which is a spawning migration and farmed species in China. Based on histological and oocyte transparent liquid observation, we found that the acidified environment significantly delayed the ovarian maturation of E. sinensis. Moreover, RNA-seq was applied to obtain gene expression profile from the crab's gills and ovaries in response to acidified environment. Compared with control groups, a total of 5471 differentially expressed genes (DEGs) were identified in acidified gills and 485 DEGs were identified in acidified ovaries. Enrichment analysis indicated that some pathways also responded to the acidified environment, such as PI3K-Akt signaling pathway, Chemokine signaling pathway, apoptosis, and toll-like receptor signaling pathway. Subsequently, some DEGs involved in immune response (ALF, Cathepsin A, HSP70, HSP90, and catalase) and ovarian maturation (Cyclin B, Fem-1a, Fem-1b, and Fem-1c) were selected to further validate the influence of water acidification on gene expression by qRT-PCR. The results showed that the expression level of immune-related genes was significantly increased to response to the water acidification, while the ovarian maturation-related genes were significantly decreased. Overall, our data suggested that E. sinensis was sensitive to the reduced pH. This comparative transcriptome also provides valuable molecular information on the mechanisms of the crustaceans responding to acidified environment.

Analysis of transcriptome difference between rapid-growing and slow-growing in Penaeus vannamei

Penaeus vannamei is the principle cultured shrimp species in China. However, with the increase of culture density, the growth difference between individuals is also expanding. Here, we make use of RNA-seq to study the growth mechanisms of P. vannamei. After 120 days, we examined the transcriptomes of rapid-growing individuals (RG) and slow-growing individuals (SG). A total of 2116 and 176 differentially expressed genes (DEGs) were found in SG and RG, respectively. Moreover, the main DEGs are opsin, heat shock protein (HSP), actin, myosin, superoxide dismutase (SOD), cuticle protein, and chitinase. GO analysis further revealed that the DEGs were enriched in biological processes significantly, such as "sensory perception," "sensory perception of light stimulus," "response to stimulus," and "response to stress." Additionally, KEGG enrichment analysis showed that the DEGs were mainly enriched in "pentose and glucuronate interconversions," "amino sugar and nucleotide sugar metabolism," "glycophospholipid biosynthesis," and "glutathione metabolism." Interestingly, the upstream genes in the ecdysone signaling pathway, including molting inhibition hormone (MIH) and crustacean hyperglycemic hormone (CHH), did not differ significantly between RG and SG, which suggests that the cause for the inconsistent growth performance is due to the stress levels rather than the ecdysone signal pathway. In summary, this work provides data that will be useful for future studies on shrimp growth and development.

Comparative Phosphoproteomics Reveals a Role for AMPK in Hypoxia Signaling in Testes of Oriental River Prawn (Macrobrachium nipponense)

Hypoxia is one of the major stresses in aquaculture animals. Recently, we reported that hypoxia disrupts the endocrine system and inhibits testicular function of oriental river prawns (Macrobrachium nipponense), but the molecular mechanism of testes responded to hypoxia remains largely unknown. In the present study, we aimed to integrate whole phosphoproteomic profiles of hypoxia-treated testes of the oriental river prawn (Macrobrachium nipponense). We successfully isolated sperm cells and evaluated the mitochondrial morphology and function using laser confocal microscopy, flow cytometry, and biochemical analyses. Quantitative proteomics identified 117 differentially abundant phosphorylated proteins, and these proteins are mainly involved in the pathways related to cellular processes, including autophagy, apoptosis, and the FoxO signaling pathway. Protein-protein interaction analysis clustered these phosphoproteins into three groups, many of which have been suggested to impact carbohydrate metabolism, autophagy, and signal regulation in testes. Western blotting confirmed that phosphorylated proteins including AMPK, ULK1, and TP53 (of the AMPK pathway) may contribute to testicular dysfunction caused by hypoxia. Further, we investigated the potential roles of AMP-activated protein kinase (AMPK)'s in testes mitochondrial autophagy and apoptosis in M. nipponense as induced by hypoxia. Simultaneous knockdown of AMPKα in sperm cells led to a decrease in FOXO3a phosphorylation at Ser413, upregulation of caspase-3 and caspase-9 activities, and an increased apoptosis rate. These results improve our understanding of hypoxia-induced energy metabolism disorders in the testes of M. nipponense.

De novo assembly of the freshwater prawn Macrobrachium carcinus brain transcriptome for identification of potential targets for antibody development

Crustaceans are major constituents of aquatic ecosystems and, as such, changes in their behavior and the structure and function of their bodies can serve as indicators of alterations in their immediate environment, such as those associated with climate change and anthropogenic contamination. We have used bioinformatics and a de novo transcriptome assembly approach to identify potential targets for developing specific antibodies to serve as nervous system function markers for freshwater prawns of the Macrobrachium spp. Total RNA was extracted from brain ganglia of Macrobrachium carcinus freshwater prawns and Illumina Next Generation Sequencing was performed using an Eel Pond mRNA Seq Protocol to construct a de novo transcriptome. Sequencing yielded 97,202,662 sequences: 47,630,546 paired and 1,941,570 singletons. Assembly with Trinity resulted in 197,898 assembled contigs from which 30,576 were annotated: 9,600 by orthology, 17,197 by homology, and 3,779 by transcript families. We looked for glutamate receptors contigs, due to their main role in crustacean excitatory neurotransmission, and found 138 contigs related to ionotropic receptors, 32 related to metabotropic receptors, and 18 to unidentified receptors. After performing multiple sequence alignments within different biological organisms and antigenicity analysis, we were able to develop antibodies for prawn AMPA ionotropic glutamate receptor 1, metabotropic glutamate receptor 1 and 4, and ionotropic NMDA glutamate receptor subunit 2B, with the expectation that the availability of these antibodies will help broaden knowledge regarding the underlying structural and functional mechanisms involved in prawn behavioral responses to environmental impacts. The Macrobrachium carcinus brain transcriptome can be an important tool for examining changes in many other nervous system molecules as a function of developmental stages, or in response to particular conditions or treatments.

Comparison of growth performance and biochemical components between parent and hybrid offspring in the oriental river prawn, Macrobrachium nipponense

Macrobrachium nipponense, as one of the large-yield farmed shrimp, is facing germplasm degradation. Genetic improvement through hybridization is one of the effective methods to solve this problem. In this study, using a three-line hybrid strategy, two-hybrid F1 populations were obtained using three local populations of M. nipponense as parents for crossbreeding. Five populations were then cultured for 3 months. Growth rate performance was measured by the hepatosomatic index, weight gain, body length growth rate and special growth rate. Biochemical components were also assessed. The results showed that the survival rate and growth performance of the hybrid progeny were better than those of the parents. The levels of triglycerides, total cholesterol, glycogen and lactic acid of the hybrid population were higher than those of the parents. This was consistent with variation in the activity of four digestive enzymes. Compared with the results of the fatty acid and amino acid analysis, it was found that the contents of polyunsaturated fatty acids such as eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acid and eight essential amino acids in the hybrid populations were significantly higher than those of their parents, and the contents of flavor amino acids were higher. The expression level of molting genes related to the growth of the parent populations was lower than that of the hybrids. These results show that crossbreeding is effective for the genetic improvement of M. nipponense germplasm. Hybrids showed advantages in growth and nutrition and multigenerational breeding will be required to form a stable germplasm.

Evaluating environmental impact of STP effluents on receiving water in Beijing by the joint use of chemical analysis and biomonitoring

To evaluate the environmental impact of receiving water from the Qinghe River sewage treatment plant (STP) effluents in Beijing, we collected sediments and Bellamya aeruginosa (Up-site, Discharge-site, and Down-site) both in 2017 and 2018 and analyzed the samples via chemical analysis, biological responses and transcriptomics. In two years of data, our biological results showed that AChE activities presented different degrees of influence on B. aeruginosa captured at sampling points of the STP compared to control sites (P < 0.05). Additionally, indicators of the antioxidant system (e.g., SOD, CAT, GST, EROD activity) and MDA content were significantly increased in the whole tissue at the Up-site of the STP. Integration of the assessed biomarkers using the integrated biomarker response (IBR) index ranked the environmental impact at sites as Up-site > Discharge-site > Down-site. In terms of the transcriptome data, B. aeruginosa collected from the Discharge-site of the STP showed greater transcriptomic response than it did from all other sites. KEGG pathway analysis revealed that sewage significantly altered the expression of genes involved in xenobiotics by cytochrome P450, drug metabolism-cytochrome P450, glutathione metabolism, oxidative phosphorylation, citrate (TCA) cycle, glycolysis/gluconeogenesis, apoptotic and Parkinson's disease. The concentrations of 34 organic pollutants (17 PAHs, 10 PAEs, 7 EDCs) were measured. The chemical concentrations of pollutants decreased from Up-site to Down-site and were well correlated with enzyme activity, IBR, and transcriptomic results. Our results demonstrated that the combined use of chemical analysis, biological responses and transcriptome data is necessary to validate the efficacy of a battery of biomarkers chosen to detect environmental stress due to pollution.

Comparative transcriptome reveals the response of oriental river prawn (Macrobrachium nipponense) to sulfide toxicity at molecular level

Aquatic environmental pollutants have various impacts on aquaculture. Specifically, sulfide has been established as being toxic to aquatic animals including the oriental river prawn Macrobrachium nipponense. In response, the hepatopancreas has been broadly studied, as it plays a pivotal role in arthropod nutrient digestion and absorption, energy supply, and organ development as well as in crustacean immunity. However, the underlying molecular mechanisms of hepatopancreas's response to sulfide toxicity are still poorly understand. Herein, we used Nova-seq 6000 platform to conduct a comparative transcriptome analysis of gene expression profiles in the hepatopancreas of M. nipponense, while it was under the influence of a semi-lethal sulfide concentration (3.20 mg/L at 48 h). A total of 139 million raw reads were obtained, in which 67,602 transcripts were clustered into 37,041 unigenes for further analysis. After constant sulfide exposure for 48 h, 235 differentially expressed genes, i.e., DEGs (151 up-regulated and 84 down-regulated) were identified in the sulfide treatment group (TGHP) compared with the control group (CGHP). We used GO and KEGG databases to annotate all the DEGs into 1180 functions and 123 pathways, respectively. The metabolic pathways included proximal tubule bicarbonate reclamation, sulfur metabolism, glycolysis and gluconeogenesis, and the TCA cycle; while immune-related pathways contained Ras, Rap1, focal adhesion and platelet activation. Additionally, apoptosis-involved pathways e.g., lysosome, also exhibited remarkable alteration in the presence of sulfide stress. Notably, responses to external stimuli and detoxification genes- such as GSKIP, CRT2, APOD, TRET1, CYP4C3 and HR39- were significantly altered by the sulfide stress, indicating that significant toxicity was transferred through energy metabolism, growth, osmoregulatory processes and immunity. Finally, we demonstrated that in the present of sulfide stress, M. nipponense altered the expression of detoxification- and extracellular stimulation-related genes, and displayed positive resistance via tight junction activation and lysosome pathways. The results of these novel experiments shed light on the hepatopancreas's molecular response to sulfide stress resistance and the corresponding adaptation mechanism; and enable us to identify several potential biomarkers for further studies.

Aquatic hypoxia disturbs oriental river prawn (Macrobrachium nipponense) testicular development: A cross-generational study

Recently, we reported that hypoxia disrupts the endocrine system and causes metabolic abnormalities in prawns. Although transgenerational impairment effects of hypoxia have become a hot topic in vertebrate, it is unknown whether hypoxia could exert cross-generational effects on testicular function crustaceans. The present study aimed to investigate hypoxia's toxic effects on the testicular function of oriental river prawns (Macrobrachium nipponense) and offspring development. Hypoxia disrupted testicular germ cells quality, caused sex hormone imbalance (testosterone and estradiol), and delayed testicular development. The F1 generation derived from male prawns exposed to hypoxia showed retarded embryonic development, and reduced hatching success and larval development, despite not being exposed to hypoxia. Analysis of the transcriptome the F0 generation (exposed to hypoxia) showed that the impaired testicular functions were associated with changes to mitochondrial oxidative phosphorylation, apoptosis, and steroid biosynthesis. Interestingly, quantitative real-time PCR confirmed that hypoxia could significantly suppress the expression of antioxidant and gonad development-related genes in the testis of the F1 generations, with and without continued hypoxia exposures. In addition, paternal exposure to hypoxia could result in a higher production of reactive oxygen species in offspring testis tissue compared with those without hypoxia exposure. The cross-generational effects of testicular function implied that the sustainability of natural freshwater prawn populations would be threatened by chronic hypoxia.

Molecular characterization of p38 MAPK and tissue-specific expression under cadmium stress in red swamp crayfish (Procambarus clarkii)

Keeping harmful pollutants out of some crucial tissues as much as possible is a key trait for the organism to survive in adverse conditions, such as in heavy-metal contaminated aquatic environments. In the current study, it was hypothesized that the p38 Mitogen-activated Protein Kinase (MAPK) controls the distribution of cadmium (Cd) in red swamp crayfish (Procambarus clarkii) by regulating the accumulation of Cd in different tissues under Cd-stressed conditions. To test this hypothesis, this study analyzed the p38 MAPK gene and compared the differential expression levels in the heart, antennal gland, gill, hepatopancreas, and muscles. Differences in expression levels of p38 MAPK gene between different tissues were conducted under controlled Cd exposure. This study found that the expression of p38 MAPK is tissue-specific in all tested samples under non-stressed condition. Under Cd-stressed condition and with the prolongation of Cd exposure time, the content of Cd in all examined tissues of P. clarkii has substantially increased compared to the control, although the Cd contents in the heart, antennal gland, and muscle remained relatively lower than those observed in the hepatopancreas. Consequently, the levels of p38 MAPK in the heart, antennal gland, and muscle were higher than the level in the hepatopancreas. These results indicate that p38 MAPK regulates the distribution and accumulation of Cd in different tissues of P. clarkii under Cd-stressed condition. Furthermore, the results suggested that the higher expression of p38 MAPK played a crucial role in keeping Cd out of the tissues in the Cd-rich aquatic environment to maintain the normal physiological function of the red swamp crayfish, a process necessary for survival and growth.

Acute hypoxia changes the mode of glucose and lipid utilization in the liver of the largemouth bass (Micropterus salmoides)

Dissolved oxygen (DO) undountedly affects fish distribution, metabolism, and evern survival. Intensive aquaculture and environmental changes will inevitably lead to hypoxic stress for largemouth bass (Micropterus salmoides). The different metabolic responses and mechanism still remains relatively unknown during acute hypoxia exposure. In this study, largemouth bass were subjected to hypoxic stress (3.0 ± 0.2 mg/L and 1.2 ± 0.2 mg/L) for 24 h and 12 h reoxygenation to systemically evaluate indicators of glucose and lipid metabolism. A regulatory network was constructed using RNA-seq to further elucidate the transcriptional regulation of glucose and lipid metabolism. During hypoxia for 4 h, the liver glycogen, glucose and pyruvic acid contents significantly decreased, whereas plasma glucose content and liver lactic acid content increased significantly. The accumulation of liver triglycerides and non-esterified fatty acids was enhanced during hypoxia for 8 h. The activity of key enzymes revealed the different metabolic responses to hypoxia exposure for 4 h, including the enhancement of glycolysis, and inhibition of gluconeogenesis. Furthermore, hypoxia exposure for 8 h increased lipid mobilization, and inhibited the β-oxidation. In addition, an integrated regulatory network of 9 major pathways involved in the response to hypoxia exposure was constructed, including HIF signaling pathway, VEGF signaling pathway, AMPK signaling pathway, insulin signaling pathway and PPAR signaling pathway; glycolysis/gluconeogenesis, pyruvate metabolism, fatty acid degradation and fatty acid biosynthesis. Additionally, reoxygenation inhibited glycolysis, and promoted gluconeogenesis and lipid oxidation, but energy deficits persisted. In short, although the mobilization and activation of fatty acid in liver were enhanced in the early stage of hypoxia, glycolysis was the main energy source under acute hypoxia. The extent and duration of hypoxia determine the degree of change in energy metabolism.

Heavy metal concentrations in tissues of marine fish and crab collected from the middle coast of Zhejiang Province, China

Concentrations of the heavy metals As, Cd, Cu, Hg, Pb, and Zn in various tissues of five marine fish species and one crab species collected from the middle coast of Zhejiang Province of China were investigated in this study. The results indicated considerable variation in heavy metal concentrations in different tissues and species. Elevated concentrations of most heavy metals were identified in fish gills and crab gills and hepatopancreas, with some differences by heavy metal type. In addition, carnivorous and benthivorous fish species generally contained relatively high concentrations of heavy metals due to feeding habits and habitats. Geographical variations of heavy metal concentrations in muscle may be attributable to species-dependent differences and terrigenous contamination. The potential health risk assessment suggested that exposure doses of most heavy metals were safe for human consumption, with the exception of As.

Transcriptome and physiology analysis identify key metabolic changes in the liver of the large yellow croaker (Larimichthys crocea) in response to acute hypoxia

The large yellow croaker (Larimichthys crocea) is one of the most important marine economic fish in the southeast coast of China. However, hypoxia stress become a major obstacle to the benign development of L. crocea industry. To understand the energy metabolism mechanism adapted to hypoxia, we analyzed the transcriptome and physiology of L. crocea liver in response to hypoxia stress for different durations. We obtained 243,756,080 clean reads, of which 83.38% were successfully mapped to the reference genome of L. crocea. The heat map analysis showed that genes encoding enzymes involved in glycolysis/gluconeogenesis were significantly upregulated at various time points. Moreover, genes encoding enzymes related to the citrate cycle, oxidative phosphorylation, and amino acid metabolism were significantly downregulated at 6 and 24 h, but upregulated at 48 and 96 h. The change of liver in physiology processes, including respiratory metabolism, and activities of the carbohydrate metabolism enzymes showed a similar trend. The results revealed that the respiratory metabolism of L. crocea was mainly anaerobic within 24 h of hypoxia stress, and aerobic metabolism was dominant after 24 h. Carbohydrate metabolism plays a crucial role in energy supply and amino acid metabolism is an important supporting character to cope with acute hypoxia stress. There was no significant change in lipid utilization under short-term acute stress. This study increases our understanding of the energy metabolism mechanism of the hypoxia response in fish and provides a useful resource for L. crocea genetics and breeding.

Antiviral activity of cathelicidin 5, a peptide from Alligator sinensis, against WSSV in caridean shrimp Exopalaemon modestus

White spot disease caused by white spot syndrome virus (WSSV) is responsible for harming shrimp aquaculture industry and results in a pandemic throughout the world. Cathelicidin 5 treatment enhanced immune parameters including antioxidant enzyme activity and immune-related genes expression in shrimp Exopalaemon modestus. Shrimp treated with cathelicidin 5 and inoculated with white spot syndrome virus (WSSV) exhibited a significantly lower mortality rate and lower viral VP28 amplification and expression than control. This study addresses the role of cathelicidin 5 in immune stimulatory and antiviral activities that could protect E. modestus from WSSV infection.

Transcriptional responses to starvation stress in the hepatopancreas of oriental river prawn Macrobrachium nipponense

Various crustaceans are farmed using aquaculture, and food deprivation or fasting can occur due to changing of environmental or management strategies. However, the molecular mechanisms underlying responses to starvation in crustaceans remain unclear. To address this, 12 hepatopancreas transcriptomes were compared for oriental river prawn (Macrobrachium nipponense) from four fasting stages (0, 7, 14 and 21 d). Gene Ontology functional annotation and Kyoto Encyclopaedia of Genes and Genomes pathway enrichment analysis of differentially expressed genes were subsequently performed. During the early stages of starvation (0-7 d), drug metabolism via the cytochrome P450 pathway and metabolism of xenobiotics by the cytochrome P450 pathway were enriched, suggesting that they metabolised compounds generated under starvation stress. As starvation proceeded (7-14 d), the retinol (vitamin A) metabolism pathway was activated, based on three up-regulated genes (CYP3, ADH and UGT), along with the two p450 pathways. Meanwhile, vitamin A was gradually consumed. As acute starvation was reached (14-21 d), vitamin A deficiency decreased the mRNA expression levels of IGF-I that is involved in the mTOR signalling pathway, which ultimately affected the growth and development of M. nipponense. Our results implicate drug/xenobiotic metabolism by cytochrome P450s in adaptation to starvation stress. Furthermore, metabolic cascades (CYP and retinol pathways) and growth (mTOR signalling) pathways are clearly triggered in crustaceans during starvation. The findings expand our understanding of the genes associated with hepatopancreas functioning in M. nipponense, and the underlying molecular mechanisms that govern the responses of crustaceans to starvation stress.

Changes in growth performance, haematological parameters, hepatopancreas histopathology and antioxidant status of pacific white shrimp (Litopenaeus vannamei) fed oxidized fish oil: Regulation by dietary myo-inositol

A 58-day feeding trial was conducted to evaluate the effects of dietary myo-inositol (MI) supplementation on growth performance, haematological parameters, hepatopancreas histopathology and antioxidant status of Litopenaeus vannamei fed with oxidized fish oil (OFO). Control diet contained fresh fish oil (FFO) without MI supplementation. The other four diets contained two oxidation levels of OFO (peroxide value: 133.2 and 268.7 meq kg^-1) with or without 200 mg MI kg^-1 diets (MI0+L, MI0+H, MI200 + L and MI200 + H). Results showed that OFO-supplemented groups (without MI supplementation) showed better growth performance and lower whole-body inositol content when opposed to control group. MI supplementation significantly improved whole-body inositol content in high-oxidized fish oil (HOFO) groups, and also reduced whole-body lipid in low-oxidized fish oil (LOFO) groups. Moreover, Supplementation of OFO and MI markedly hit the fatty acid profile of muscle. HOFO caused severe histopathological changes in hepatopancreas of shrimp, which slightly alleviated by MI supplementation. MI supplementation also grew the total protein (TP) content and alkaline phosphatase (AKP) activity and decreased the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of serum in OFO-supplemented groups. Ingestion of OFO increased levels of lipid peroxidation and protein oxidation in serum or hepatopancreas, which partly ameliorated by MI supplementation. Activities of antioxidant enzymes exhibited different expression patterns because of OFO and MI. In addition, HOFO markedly increased mRNA expression levels of antioxidant genes including ferritin (FT), thioredoxin (Trx), GPX, glutathione S-transferase (GST) and catalase (CAT) and decreased peroxiredoxin (Prx) expression, in which expression of GPX and Prx were increased owing to MI supplementation. Therefore, it suggested that dietary OFO stimulated growth performance, but also induced oxidative stress and caused impairment to hepatopancreas in L. vannamei. The negative impact brought about by OFO was partially mitigated by dietary MI supplementation.

Evaluating expression of autophagy-related genes in oriental river prawn Macrobrachium nipponense as potential biomarkers for hypoxia exposure

Autophagy, a crucial process for maintaining cellular homeostasis, is under the control of several autophagy-related (ATG) proteins, and is highly conserved in most animals, but its response to adverse environmental conditions is poorly understood in crustaceans. Herein, we hypothesised that autophagy acts as a protective response to hypoxia, and Beclin 1, ATG7 and ATG8 in oriental river prawn (Macrobrachium nipponense) were chosen as potential biomarkers under hypoxia exposure; thus, their full-length cDNA sequences were cloned and characterised. Open reading frames (ORFs) of 1281, 2076 and 360 bp, encoding proteins of 427, 692 and 120 amino acid residues, respectively, were obtained. Phylogenetic analysis demonstrated the three M. nipponense proteins do not form a clade with vertebrate homologs. Protein and mRNA levels were investigated in different tissues and developmental stages, and all three were significantly upregulated in a time-dependent manner in the hepatopancreas following hypoxia stress. Biochemical and morphological analysis of hepatocytes revealed that hypoxia increased the abundance of hepatic autophagic vacuoles and stimulated anaerobic metabolism. RNA interference-mediated silencing of ATG8 significantly increased the death rate of M. nipponense juveniles under hypoxia stress conditions. Together, these results suggest that Beclin 1, ATG7 and ATG8 contribute to autophagy-based responses against hypoxia in M. nipponense. The findings also expand our understanding of the potential role of autophagy as an adaptive response against hypoxia toxicity in crustaceans. The results showed that hepatic ATG8 levels may be directly indicative of acute hypoxia in prawns, and provide insight into the time at which hypoxia exposure occurs. Autophagy-related genes expression pattern seems to be sensitive and good biomarkers of acute hypoxia exposure.

Trace metal distribution in crab organs and human health risk assessment on consumption of crabs collected from coastal water of South East coast of India

The concentrations of nine heavy metals accumulated in different organs of two crab species collected from the South East coast of India were estimated. The order of trace metal concentration in different organs of Portunus pelagicus was Cu > Mn > Cd > Ni > Pb > Co > Hg = Cr = U in gills, Cu > Mn > Cd > Ni > Pb = Co > Hg > Cr = U in hepatopancreas, and Cu > Cr > Ni > Mn > Cd > Pb > Co > Hg > U in muscles, whereas that for Portunus sanguinolentus was Cu > Mn > Cd > Ni > Pb > Co > Hg > Cr = U in gills, Cu > Mn > Cd > Ni > Pb = Co > U > Cr = Hg in hepatopancreas, and Cr > Cu > Ni > Mn > Cd > Co > Pb > Hg = U in muscles. The order of trace metal uptake for different organs was gills > hepatopancreas > muscles. Individual mean bioaccumulation index (IMBI) values varied between 0.0 and 0.52, 0.0 and 0.28, and 0.06 and 0.30 for gills, hepatopancreas, and muscles, respectively. Cr in muscles of P. sanguinolentus and Cu and Cd in all organs of both the species were found to be higher than the maximum permitted concentration recommended by food safety guidelines. Target hazard quotient (THQ) results suggested that there is a potential risk due to Co, Cd, and Cr, particularly for children, if the crab consumption frequency is more than once a month.

Integrated metabolomic and transcriptomic analysis of brain energy metabolism in the male Oriental river prawn (Macrobrachium nipponense) in response to hypoxia and reoxygenation

Hypoxia is as an endocrine disruptor, and, in crustaceans, the energy metabolic consequences of hypoxia in the brain tissue are still poorly understood. We combined gas chromatography-mass spectrometry (GC-MS)-based metabolomic analysis and high-throughput RNA sequencing to evaluate the metabolic effects and subjacent regulatory pathways in the brain tissue of the male Oriental river prawn (Macrobrachium nipponense) in response to hypoxia and reoxygenation. We recorded LC₅₀ and heartbeats per minute of male M. nipponense juveniles. Hypoxia resulted in the generation of reactive oxygen species in the brain cells and alterations in gene expression and metabolite concentrations in the prawn brain tissue in a time-dependent manner. The transcriptomic analyses revealed specific changes in the expression of genes associated with metabolism pathways, which was consistent with the changes in energy metabolism indicated by the GC-MS metabolomic analysis. Quantitative real-time polymerase chain reaction and western blot confirmed the transcriptional induction of these genes because of hypoxia. The lactate levels increased significantly during hypoxia and decreased to normal after reoxygenation; this is consistent with a shift towards anaerobic metabolism, which may cause metabolic abnormalities in the brain tissue of M. nipponense. Overall, these results are consistent with metabolic disruption in the brain of M. nipponense exposed to hypoxia and will help in understanding how crustacean brain tissue adapts and responds to hypoxia and reoxygenation.

A transcriptome study on Macrobrachium nipponense hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

White spot syndrome virus (WSSV) is one of the most devastating pathogens of cultured shrimp, responsible for massive loss of its commercial products worldwide. The oriental river prawn Macrobrachium nipponense is an economically important species that is widely farmed in China and adult prawns can be infected by WSSV. However, the molecular mechanisms of the host pathogen interaction remain unknown. There is an urgent need to learn the host pathogen interaction between M. nipponense and WSSV which will be able to offer a solution in controlling the spread of WSSV. Next Generation Sequencing (NGS) was used in this study to determin the transcriptome differences by the comparison of control and WSSV-challenged moribund samples, control and WSSV-challenged survived samples of hepatopancreas in M. nipponense. A total of 64,049 predicted unigenes were obtained and classified into 63 functional groups. Approximately, 4,311 differential expression genes were identified with 3,308 genes were up-regulated when comparing the survived samples with the control. In the comparison of moribund samples with control, 1,960 differential expression genes were identified with 764 genes were up-regulated. In the contrast of two comparison libraries, 300 mutual DEGs with 95 up-regulated genes and 205 down-regulated genes. All the DEGs were performed GO and KEGG analysis, overall a total of 85 immune-related genes were obtained and these gene were groups into 13 functions and 4 KEGG pathways, such as protease inhibitors, heat shock proteins, oxidative stress, pathogen recognition immune receptors, PI3K/AKT/mTOR pathway, MAPK signaling pathway and Ubiquitin Proteasome Pathway. Ten genes that valuable in immune responses against WSSV were selected from those DEGs to furture discuss the response of host to WSSV. Results from this study contribute to a better understanding of the immune response of M. nipponense to WSSV, provide information for identifying novel genes in the absence of genome of M. nipponense. Furthermore, large number of transcripts obtained from this study could provide a strong basis for future genomic research on M. nipponense.

Identification of SNPs potentially related to immune responses and growth performance in Litopenaeus vannamei by RNA-seq analyses

Litopenaeus vannamei is one of the most important shrimp species for worldwide aquaculture. Despite this, little genomic information is available for this penaeid and other closely related taxonomic crustaceans. Consequently, genes, proteins and their respective polymorphisms are poorly known for these species. In this work, we used the RNA sequencing technology (RNA-seq) in L. vannamei shrimp evaluated for growth performance, and exposed to the White Spot Syndrome Virus (WSSV), in order to investigate the presence of Single Nucleotide Polymorphisms (SNPs) within genes related to innate immunity and growth, both features of great interest for aquaculture activity. We analyzed individuals with higher and lower growth rates; and infected (unhealthy) and non-infected (healthy), after exposure to WSSV. Approximately 7,000 SNPs were detected in the samples evaluated for growth, being 3,186 and 3,978 exclusive for individuals with higher and lower growth rates, respectively. In the animals exposed to WSSV we found about 16,300 unique SNPs, in which 9,338 were specific to non-infected shrimp, and 7,008 were exclusive to individuals infected with WSSV and symptomatic. In total, we describe 4,312 unigenes containing SNPs. About 60% of these unigenes returned GO blastX hits for Biological Process, Molecular Function and Cellular Component ontologies. We identified 512 KEGG unique KOs distributed among 275 pathways, elucidating the majority of metabolism roles related to high protein metabolism, growth and immunity. These polymorphisms are all located in coding regions, and certainly can be applied in further studies involving phenotype expression of complex traits, such as growth and immunity. Overall, the set of variants raised herein enriches the genomic databases available for shrimp, given that SNPs originated from nextgen are still rare for this relevant crustacean group, despite their huge potential of use in genomic selection approaches.

Hypoxia Induces Changes in AMP-Activated Protein Kinase Activity and Energy Metabolism in Muscle Tissue of the Oriental River Prawn Macrobrachium nipponense

Hypoxia has important effects on biological activity in crustaceans, and modulation of energy metabolism is a crucial aspect of crustaceans’ ability to respond to hypoxia. The adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK) enzyme is very important in cellular energy homeostasis; however, little information is known about the role of AMPK in the response of prawns to acute hypoxia. In the present study, three subunits of AMPK were cloned from the oriental river prawn, Macrobrachium nipponense. The full-length cDNAs of the α, β, and γ AMPK subunits were 1,837, 3,174, and 3,773 bp long, with open reading frames of 529, 289, and 961 amino acids, respectively. Primary amino acid sequence alignment of these three subunits revealed conserved similarity between the functional domains of the M. nipponense AMPK protein with AMPK proteins of other animals. The expression of the three AMPK subunits was higher in muscle tissue than in other tissues. Furthermore, the mRNA expression of AMPKα, AMPKβ, and AMPKγ were significantly up-regulated in M. nipponense muscle tissue after acute hypoxia. Probing with a phospho-AMPKα antibody revealed that AMPK is phosphorylated following hypoxia; this phosphorylation event was found to be essential for AMPK activation. Levels of glucose and lactic acid in hemolymph and muscle tissue were significantly changed over the course of hypoxia and recovery, indicating dynamic changes in energy metabolism in response to hypoxic stress. The activation of AMPK by hypoxic stress in M. nipponense was compared to levels of muscular AMP, ADP, and ATP, as determined by HPLC; it was found that activation of AMPK may not completely correlate with AMP:ATP ratios in prawns under hypoxic conditions. These findings confirm that the α, β, and γ subunits of the prawn AMPK protein are regulated at the transcriptional and protein levels during hypoxic stress to facilitate maintenance of energy homeostasis.

Based on the Metabolomic Approach the Energy Metabolism Responses of Oriental River Prawn Macrobrachium nipponense Hepatopancreas to Acute Hypoxia and Reoxygenation

Hypoxia represents a major physiological challenge for prawns and is a problem in aquaculture. Therefore, an understanding of the metabolic response mechanism of economically important prawn species to hypoxia and re-oxygenation is essential. However, little is known about the intrinsic mechanisms by which the oriental river prawn Macrobrachium nipponense copes with hypoxia at the metabolic level. In this study, we conducted gas chromatography-mass spectrometry-based metabolomics studies and assays of energy metabolism-related parameters to investigate the metabolic mechanisms in the hepatopancreas of M. nipponense in response to 2.0 O₂/L hypoxia for 6 and 24 h, and reoxygenation for 6 h following hypoxia for 24 h. Prawns under hypoxic stress displayed higher glycolysis-related enzyme activities and lower mRNA expression levels of aerobic respiratory enzymes than those in the normoxic control group, and those parameters returned to control levels in the reoxygenated group. Our results showed that hypoxia induced significant metabolomic alterations in the prawn hepatopancreas within 24 h. The main metabolic alterations were depletion of amino acids and 2-hydroxybutanoic acid and accumulation of lactate. Further, the findings indicated that hypoxia disturbed energy metabolism and induced antioxidant defense regulation in prawns. Surprisingly, recovery from hypoxia (i.e., reoxygenation) significantly affected 25 metabolites. Some amino acids (valine, leucine, isoleucine, lysine, glutamate, and methionine) were markedly decreased compared to the control group, suggesting that increased degradation of amino acids occurred to provide energy in prawns at reoxygenation conditions. This study describes the acute metabolomic alterations that occur in prawns in response to hypoxia and demonstrates the potential of the altered metabolites as biomarkers of hypoxia.