The impact of acute thermal stress on the metabolome of the black rockfish (Sebastes schlegelii)

Proteomics and metabolomics analysis of American shad (Alosa sapidissima) liver responses to heat stress

The dramatic changes in the global climate pose a major threat to the survival of many organisms, including fish. To date, the regulatory mechanisms behind the physiological responses of fish to temperature changes have been studied, and a comprehensive analysis of the regulatory mechanisms of temperature tolerance will help to propose effective strategies for fish to cope with global warming. In this study, we investigated the expression profiles of proteins and metabolites in liver tissues of American shad (Alosa sapidissima) corresponding to different water temperatures (24 °C, 27 °C and 30 °C) at various times (1-month intervals) under natural culture conditions. Proteomic analysis showed that the expression levels of the heat shock protein family (e.g. HSPE1, HSP70, HSPA5 and HSPA.1) increase significantly with temperature and that many differentially expressed proteins were highly enriched especially in pathways related to the endoplasmic reticulum, oxidative phosphorylation and glycolysis/gluconeogenesis processes. In addition, the results of conjoint metabolomics and proteomics analysis suggested that the contents of several important amino acids and chemical compounds, including L-serine, L-isoleucine, L-cystine, choline and betaine, changed significantly under high-temperature environmental stress, affecting the metabolic levels of starch, amino acid and glucose, which is thought to represent a possible energy conservation method for A. sapidissima to cope with rapid changes in external temperature. In summary, our findings demonstrate that living under high temperatures for a long period of time leads to different physiological defense responses in A. sapidissima, which provides some new ideas for analyzing the molecular regulatory patterns of adaptation to high temperature and also provides a theoretical basis for the subsequent improvement of fish culture in response to global warming.

Effects of cold acclimation on serum biochemical parameters and metabolite profiles in Schizothorax prenanti

BACKGROUND

Environmental temperature is critical in regulating biological functions in fish. S. prenanti is a kind of cold-water fish, but of which we have little knowledge about the metabolic adaptation and physiological responses to long-term cold acclimation.

RESULTS

In this study, we determined the physiological responses of S. prenanti serum after 30 days of exposure to 6℃. Compared with the control group, the levels of TC, TG, and LDL-C in the serum were significantly (P < 0.05) increased, and the level of glucose was significantly (P < 0.05) decreased under cold acclimation. Cold acclimation had no effect on the gene expression of pro-inflammatory factors and anti-inflammatory factors of S. prenanti. Metabolomics analysis by LC-MS showed that a total of 60 differential expressed metabolites were identified after cold acclimation, which involved in biosynthesis of amino acids, biosynthesis of unsaturated fatty acids, steroid degradation, purine metabolism, and citrate cycle pathways.

CONCLUSION

The results indicate that cold acclimation can alter serum metabolites and metabolic pathways to alter energy metabolism and provide insights for the physiological regulation of cold-water fish in response to cold acclimation.

Comprehensive analysis of histophysiology, transcriptome and metabolome tolerance mechanisms in black porgy (Acanthopagrus schlegelii) under low temperature stress

Low temperature stress has adverse effects on fish growth and reproduction, causing huge economic losses to the aquaculture industry. Especially, black porgy (Acanthopagrus schlegelii) farming industry in north of Yangtze River has been severely affected by low temperature for a long time. To explore the tolerance mechanism of black porgy to low temperature stress, the experiment was designed. The liver and gill tissues of black porgy were taken from the water temperature point of 15 °C (control group named as CG), 3.8 °C (cold sensitive group named as CS) and 2.8 °C (cold tolerant group named as CT) with a cooling rate of 3 °C/d from 15 °C for histophysiology, transcriptomics and metabolomics analysis. After cold stress, the histological results showed that the nucleus of the black porgy liver tissue appeared swelling, the cell arrangement was disordered; meanwhile the gill lamellae were twisted and broken, the epidermis was detached and aneurysm appeared. In addition, the expression of antioxidant, glucose metabolism and immune-related enzymes in the liver and gill of black porgy also changed significantly after low temperature stress. By analyzing the transcriptome and metabolome dates of black porgy liver, 3474 differentially expressed genes (DEGs) and 689 differentially expressed metabolites (DEMs) involved in low temperature stress were identified, respectively. The results of the transcriptome and metabolome combined analysis showed that individuals in the CS group mainly supplied energy to the body through lipid metabolism and amino acid metabolism, and meanwhile the apoptosis pathway was activated. While, individuals in the CT group mainly through glucose metabolism and steroid hormone biosynthesis to supply energy for the body. The validation results of qPCR on eight functional genes further demonstrated the reliability of RNA-Seq data. In summary, the results provide molecular information about adaptation to climate change and genetic selection of black porgy.

Effects of Dietary Supplementation of Bile Acids on Growth, Glucose Metabolism, and Intestinal Health of Spotted Seabass (Lateolabrax maculatus)

An 8-week feeding trial was performed to investigate the effects of dietary bile acids on growth, glucose metabolism, and intestinal health in spotted seabass (Lateolabrax maculatus) reared at high temperatures (33 °C). The fish (20.09 ± 1.12 g) were fed diets supplemented with bile acids: 0 (Con), 400 (BA400), 800 (BA800), and 1200 (BA1200) mg/kg, respectively. The results showed that the growth was promoted in fish at the BA800 treatment compared with the control (p < 0.05). Increased enzyme activities and transcripts of gluconeogenesis in the liver were observed, whereas decreased enzyme activities and transcripts of glycolysis, as well as glycogen content, were shown in the BA800 treatment (p < 0.05). The transcripts of bile acid receptors fxr in the liver were up-regulated in the BA800 treatment (p < 0.05). A bile acid supplementation of 800 mg/kg improved the morphological structure in the intestine. Meanwhile, intestinal antioxidant physiology and activities of lipase and trypsin were enhanced in the BA800 treatment. The transcripts of genes and immunofluorescence intensity related to pro-inflammation cytokines (il-1β, il-8, and tnf-α) were inhibited, while those of genes related to anti-inflammation (il-10 and tgf-β) were induced in the BA800 treatment. Furthermore, transcripts of genes related to the NF-κB pathway in the intestine (nfκb, ikkα, ikkβ, and ikbα1) were down-regulated in the BA800 treatment. This study demonstrates that a dietary bile acid supplementation of 800 mg/kg could promote growth, improve glucose metabolism in the liver, and enhance intestinal health by increasing digestive enzyme activity and antioxidant capacity and inhibiting inflammatory response in L. maculatus.

Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions

BACKGROUND

Mutualistic interactions, which constitute some of the most advantageous interactions among fish species, are highly vulnerable to environmental changes. A key mutualistic interaction is the cleaning service rendered by the cleaner wrasse, Labroides dimidiatus, which involves intricate processes of social behaviour to remove ectoparasites from client fish and can be altered in near-future environmental conditions. Here, we evaluated the neuromolecular mechanisms behind the behavioural disruption of cleaning interactions in response to future environments. We subjected cleaner wrasses and surgeonfish (Acanthurus leucosternon, serving as clients) to elevated temperature (warming, 32 °C), increased levels of CO2 (high CO2, 1000 ppm), and a combined condition of elevated CO2 and temperature (warming and high CO2, 32 °C, and 1000 ppm) for 28 days.

RESULTS

Each of these conditions resulted in behavioural disruptions concerning the motivation to interact and the quality of interaction (high CO2 - 80.7%, warming - 92.6%, warming and high CO2 - 79.5%, p < 0.001). Using transcriptomics of the fore-, mid-, and hindbrain, we discovered that most transcriptional reprogramming in both species under warming conditions occurred primarily in the hind- and forebrain. The associated functions under warming were linked to stress, heat shock proteins, hypoxia, and behaviour. In contrast, elevated CO2 exposure affected a range of functions associated with GABA, behaviour, visual perception, thyroid hormones and circadian rhythm. Interestingly, in the combined warming and high CO2 condition, we did not observe any expression changes of behaviour. However, we did find signs of endoplasmic reticulum stress and apoptosis, suggesting not only an additive effect of the environmental conditions but also a trade-off between physiological performance and behaviour in the cleaner wrasse.

CONCLUSIONS

We show that impending environmental shifts can affect the behaviour and molecular processes that sustain mutualistic interactions between L. dimidiatus and its clients, which could have a cascading effect on their adaptation potential and possibly cause large-scale impacts on coral reef ecosystems.

Physiological, metabolomic, and transcriptomic reveal metabolic pathway alterations in Gymnocypris przewalskii due to cold exposure

Teleost fish have evolved various adaptations that allow them to tolerate cold water conditions. However, the underlying mechanism of this adaptation is poorly understood in Tibetan Plateau fish. RNA-seq combined with liquid chromatography‒mass spectrometry (LC‒MS/MS) metabolomics was used to investigate the physiological responses of a Tibetan Plateau-specific teleost, Gymnocypris przewalskii, under cold conditions. The 8-month G. przewalskii juvenile fish were exposed to cold (4 ℃, cold acclimation, CA) and warm (17 ℃, normal temperature, NT) temperature water for 15 days. Then, the transcript profiles of eight tissues, including the brain, gill, heart, intestine, hepatopancreas, kidney, muscle, and skin, were evaluated by transcriptome sequencing. The metabolites of the intestine, hepatopancreas, and muscle were identified by LC‒MS/MS. A total of 5,745 differentially expressed genes (DEGs) were obtained in the CA group. The key DEGs were annotated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. The DEGs from the eight tissues were significantly enriched in spliceosome pathways, indicating that activated alternative splicing is a critical biological process that occurs in the tissues to help fish cope with cold stress. Additionally, 82, 97, and 66 differentially expressed metabolites were identified in the intestine, hepatopancreas, and muscle, respectively. Glutathione metabolism was the only overlapping significant pathway between the transcriptome and metabolome analyses in these three tissues, indicating that an activated antioxidative process was triggered during cold stress. In combination with the multitissue transcriptome and metabolome, we established a physiology-gene‒metabolite interaction network related to energy metabolism during cold stress and found that gluconeogenesis and long-chain fatty acid metabolism played critical roles in glucose homeostasis and energy supply.

Molecular mechanisms of physiological change under acute total dissolved gas supersaturation stress in yellow catfish (Pelteobagrus fulvidraco)

During the dam discharging period, the strong aeration of high-speed water leads to the supersaturation of total dissolved gas (TDG) in the downstream water, which causes gas bubble disease (GBD) in fish and threatens their survival. TDG supersaturation has now become an ecological and environmental issue of global concern; however, the molecular mechanism underlying the physiological effect of TDG supersaturation on fish is poorly known. Here, we comprehensively investigated the effect of TDG supersaturation on Pelteobagrus fulvidraco at the histopathological, biochemical, transcriptomic, and metabolomic levels. After exposure to 116% TDG, P. fulvidraco exhibited classic GBD symptoms and pathological changes in gills. The level of superoxide dismutase was highly significantly decreased. Transcriptomic results revealed that heat shock proteins (HSPs) and a large number of genes involved in immunity were increased by TDG stress. A key environmental sensor PI3K/Akt/mTOR pathway was significantly stimulated for defence against stress. Integrated transcriptomic and metabolomic analyses revealed that key metabolites and genes were upregulated in the triacylglycerol synthesis pathway and that amino acid levels decreased, which might be associated with TDG supersaturation stress. The present study demonstrated that TDG supersaturation could cause severe physiological damage in fish. HSP genes, immune functions, and energy metabolic pathways were enhanced to counteract the adverse effects.

Metabolite Changes of Perna canaliculus Following a Laboratory Marine Heatwave Exposure: Insights from Metabolomic Analyses

Temperature is considered to be a major abiotic factor influencing aquatic life. Marine heatwaves are emerging as threats to sustainable shellfish aquaculture, affecting the farming of New Zealand's green-lipped mussel [Perna canaliculus (Gmelin, 1791)]. In this study, P. canaliculus were gradually exposed to high-temperature stress, mimicking a five-day marine heatwave event, to better understand the effects of heat stress on the metabolome of mussels. Following liquid chromatography-tandem mass spectrometry analyses of haemolymph samples, key sugar-based metabolites supported energy production via the glycolysis pathway and TCA cycle by 24 h and 48 h of heat stress. Anaerobic metabolism also fulfilled the role of energy production. Antioxidant molecules acted within thermally stressed mussels to mitigate oxidative stress. Purine metabolism supported tissue protection and energy replenishment. Pyrimidine metabolism supported the protection of nucleic acids and protein synthesis. Amino acids ensured balanced intracellular osmolality at 24 h and ammonia detoxification at 48 h. Altogether, this work provides evidence that P. canaliculus has the potential to adapt to heat stress up to 24 °C by regulating its energy metabolism, balancing nucleotide production, and implementing oxidative stress mechanisms over time. The data reported herein can also be used to evaluate the risks of heatwaves and improve mitigation strategies for aquaculture.

Effects of heat stress on the chemical composition, oxidative stability, muscle metabolism, and meat quality of Nile tilapia (Oreochromis niloticus)

The present study investigated the effects of chronic heat stress (HS) on the chemical composition, oxidative stability, muscle metabolism, and meat quality of Nile tilapia (Oreochromis niloticus). Compared with the control (26 °C), chronic HS (32 °C) lowered growth performance, the contents of whole-body lipid, muscle protein, and muscle lipid. Also, HS significantly increased the contents of reactive oxygen species (ROS) and decreased antioxidative status, causing a decline in meat quality, including increased lipid and protein oxidation, the centrifugal water loss, and cooking loss as well as decreased the fragmentation index and pH at 24 h, which may be attributed to induced apoptosis by excessive ROS in Nile tilapia meat. Moreover, metabolomic analysis showed HS lowered flavor and nutritional value by affecting amino acid, lipid, and nucleotide metabolism. These results reveal that HS adversely affects oxidative stability, meat quality, flavor, and nutrition, warranting its recognition and prevention.

Heat induces multiomic and phenotypic stress propagation in zebrafish embryos

Heat alters biology from molecular to ecological levels, but may also have unknown indirect effects. This includes the concept that animals exposed to abiotic stress can induce stress in naive receivers. Here, we provide a comprehensive picture of the molecular signatures of this process, by integrating multiomic and phenotypic data. In individual zebrafish embryos, repeated heat peaks elicited both a molecular response and a burst of accelerated growth followed by a growth slowdown in concert with reduced responses to novel stimuli. Metabolomes of the media of heat treated vs. untreated embryos revealed candidate stress metabolites including sulfur-containing compounds and lipids. These stress metabolites elicited transcriptomic changes in naive receivers related to immune response, extracellular signaling, glycosaminoglycan/keratan sulfate, and lipid metabolism. Consequently, non-heat-exposed receivers (exposed to stress metabolites only) experienced accelerated catch-up growth in concert with reduced swimming performance. The combination of heat and stress metabolites accelerated development the most, mediated by apelin signaling. Our results prove the concept of indirect heat-induced stress propagation toward naive receivers, inducing phenotypes comparable with those resulting from direct heat exposure, but utilizing distinct molecular pathways. Group-exposing a nonlaboratory zebrafish line, we independently confirm that the glycosaminoglycan biosynthesis-related gene chs1 and the mucus glycoprotein gene prg4a, functionally connected to the candidate stress metabolite classes sugars and phosphocholine, are differentially expressed in receivers. This hints at the production of Schreckstoff-like cues in receivers, leading to further stress propagation within groups, which may have ecological and animal welfare implications for aquatic populations in a changing climate.

Genome-wide identification of olive flounder (Paralichthys olivaceus) SOCS genes: Involvement in immune response regulation to temperature stress and Edwardsiella tarda infection

The suppressors of cytokine signaling (SOCS) gene family participates in development and immunity through negative regulation of cytokine signaling pathways. Although the immune response of SOCS gene family members has been extensively characterized in teleost, no similar study has been reported in olive flounder yet. In our present study, a total of 13 SOCSs in olive flounder were identified and characterized systematically. By querying the SOCS sequences of ten teleost fish species, we found there were exactly more members of SOCSs in fish than mammals, which indicated that there were more duplication events occurred in fish than in higher vertebrates. Phylogenetic analysis clearly illuminated that SOCS genes were highly conserved. The analysis of gene structure and motif showed SOCS proteins of olive flounder shared a high level of sequence similarity strikingly. The expression profiles of tissues and developmental stages indicated that SOCS members had a kind of specificity in temporality and spatiality. RNA-Seq analysis of temperature stress and E. Tarda infection demonstrated SOCS members were involved in inflammatory response. In a word, our results would provide a further reference for understanding the mechanism of SOCS genes in olive flounder.

Effects of Thermal Stress on the Antioxidant Capacity, Blood Biochemistry, Intestinal Microbiota and Metabolomic Responses of Luciobarbus capito

The rise in water temperature caused by global warming is seriously threatening the development of aquatic animals. However, the physiological response mechanism behind the adverse effects of thermal conditions on L. capito remains unclear. In this study, we investigated the physiological responses of L. capito exposed to thermal stress via biochemical analyses and intestinal microbiota and liver LC-MS metabolomics. The results show that the superoxide dismutase (SOD) and catalase (CAT) activities significantly decrease, while the malondialdehyde (MDA) content, aspartate aminotransferase (AST), acid phosphatase (ACP), alanine aminotransferase (ALT), and albumin (ALB) activities, and glucose (Glu) level significantly increase. Obvious variations in the intestinal microbiota were observed after stress exposure, with increased levels of Proteobacteria and Bacteroidota and decreased levels of Firmicutes, Fusobacteriota, and Actinobacteriota, while levels of several genera of pathogenic bacteria increased. Liver metabolomic analysis showed that stress exposure disturbed metabolic processes, especially of amino acids and lipids. The results of this study indicated that thermal stress caused oxidative stress, disturbed blood biological functioning and intestinal microbiota balance, and damaged amino acids and lipids metabolism of liver in L. capito.

Biochemical, transcriptomic and metabolomic responses to total dissolved gas supersaturation and their underlying molecular mechanisms in Yangtze sturgeon (Acipenser dabryanus)

With the rapid development of hydropower facility construction, the total dissolved gas (TDG) generated by dam discharge is seriously threatening the survival of fish and has become an ecological environmental issue of global concern. However, how TDG affects fish physiology and the underlying molecular mechanism remain poorly known. In this study, Acipenser dabryanus, an ancient living fossil that is a flagship species of the Yangtze River, was exposed to water supersaturated with TDG at a level of 116% for 48 h. A comprehensive analysis was performed to study the effect of TDG supersaturation stress on A. dabryanus, including histopathological, biochemical, transcriptomic and metabolomic analyses. The histopathological results showed that mucosal-associated lymphoid tissues were seriously damaged after TDG supersaturation stress. Plasma catalase levels increased significantly under TDG supersaturation stress, while superoxide dismutase levels decreased significantly. Transcriptomic analysis revealed 289 upregulated genes and 162 downregulated genes in gill tissue and 535 upregulated and 104 downregulated genes in liver tissue. Metabolomic analysis revealed 63 and 164 differentially abundant metabolites between the control group and TDG group in gill and liver, respectively. The majority of heat shock proteins and genes related to ubiquitin and various immune-related pathways were significantly upregulated by TDG supersaturation stress. Integrated transcriptomic and metabolomic analyses revealed the upregulation of amino acid metabolism and glycometabolism pathways under TDG supersaturation stress. Glycerophospholipid metabolism was increased which might be associated with maintaining cell membrane integrity. This is the first study revealing the underlying molecular mechanisms of effects of TDG supersaturation on fish. Our results suggested that acute TDG supersaturation stress could enhance immune and antioxidative functions and activate energy metabolic pathways as an adaptive mechanism in A. dabryanus.

Integrated biochemical, transcriptomic and metabolomic analyses provide insight into heat stress response in Yangtze sturgeon (Acipenser dabryanus)

Temperature fluctuations caused by climate change and global warming pose a great threat to various species. Most fish are particularly vulnerable to elevated temperatures. Understanding the mechanism of high-temperature tolerance in fish can be beneficial for proposing effective strategies to help fish cope with global warming. In this study, we systematically studied the effects of high temperature on Acipenser dabryanus, an ancient living fossil and flagship species of the Yangtze River, at the histological, biochemical, transcriptomic and metabolomic levels. Intestinal and liver tissues from the control groups (18 °C) and acute heat stress groups (30 °C) of A. dabryanus were sampled for histological observation and liver tissues were assessed for transcriptomic and metabolomic profiling. Histopathological analysis showed that the intestine and liver tissues were damaged after heat stress. The plasma cortisol content and the levels of oxidative stress markers (catalase/glutathione reductase) and two aminotransferases (aspartate aminotransferase/alanine aminotransferase) increased significantly in response to acute heat stress. Transcriptomic and metabolomic methods showed 6707 upregulated and 4189 downregulated genes and 64 upregulated and 78 downregulated metabolites in the heat stress group. Heat shock protein (HSP) genes showed striking changes in expression under heat stress, with 21 genes belonging to the HSP30, HSP40, HSP60, HSP70 and HSP90 families significantly upregulated by short-term heat stress. The majority of genes associated with ubiquitin and various immune-related pathways were also markedly upregulated in the heat stress group. In addition, the combined analysis of metabolites and gene profiles suggested an enhancement of amino acid metabolism and glycometabolism and the suppression of fatty acid metabolism during heat stress, which could be a potential energy conservation strategy for A. dabryanus. To the best of our knowledge, the present study represents the first attempt to reveal the mechanisms of heat stress responses in A. dabryanus, which can provide insights into improved cultivation of fish in response to global warming.

Thermal Stress Induces Metabolic Responses in Juvenile Qingtian Paddy Field Carp Cyprinus carpio var qingtianensis

Extreme fluctuations in water temperature lead to significant economic losses for the aquaculture industry. Cyprinus carpio var qingtianensis (locally called Qingtian paddy field carp), is a local variety commonly found in Zhejiang province, China. Unlike traditional aquaculture environments, the water temperature range between day and night in the rice field environment is much larger, and the high temperature in summer may exceed the growth threshold of fish because there is no manual intervention; therefore, the study of how the Qingtian paddy field carp (PF carp) adapts to high-temperature conditions can shed light how the species adapt to the rice field environment. To investigate the molecular mechanisms of this fish under thermal stress, the liver metabolomics of Qiangtian paddy field carp (PF carp) were analyzed. In this study, metabolomics was used to examine the metabolic reaction of PF carp (102 days old, 104.69 ± 3.08 g in weight, 14.65 ± 0.46 cm in length) at water temperatures of 28 °C (control group, CG), 34 °C (experimental group (EG) 34), and 38 °C (EG38). The results show that 175 expression profile metabolites (DEMs), including 115 upregulated and 60 downregulated metabolites, were found in the CG vs. EG34. A total of 354 DEMs were inspected in CG vs. EG38, with 85 metabolites downregulated and 269 metabolites upregulated. According to the pathway enrichment study, various pathways were altered by thermal stress, including those of lipid, amino-acid, and carbohydrate metabolism. Our study presents a potential metabolic profile for PF carp under thermal stress. It also demonstrates how the host responds to thermal stress on a metabolic and molecular level.

Understanding the Function and Mechanism of Zebrafish Tmem39b in Regulating Cold Resistance

Autophagy and endoplasmic reticulum (ER) stress response are among the key pathways regulating cold resistance of fish through eliminating damaged cellular components and facilitating the restoration of cell homeostasis upon exposure to acute cold stress. The transmembrane protein 39A (TMEM39A) was reported to regulate both autophagy and ER stress response, but its vertebrate-specific paralog, the transmembrane protein 39B (TMEM39B), has not been characterized. In the current study, we generate tmem39b-knockout zebrafish lines and characterize their survival ability under acute cold stress. We observed that the dysfunction of Tmem39b remarkably decreased the cold resilience of both the larval and adult zebrafish. Gene transcription in the larvae exposed to cold stress and rewarming were characterized by RNA sequencing (RNA-seq) to explore the mechanisms underlying functions of Tmem39b in regulating cold resistance. The results indicate that the deficiency of Tmem39b attenuates the up-regulation of both cold- and rewarming-induced genes. The cold-induced transcription factor genes bif1.2, fosab, and egr1, and the rewarming-activated immune genes c3a.3, il11a, and sting1 are the representatives influenced by Tmem39b dysfunction. However, the loss of tmem39b has little effect on the transcription of the ER stress response- and autophagy-related genes. The measurements of the phosphorylated H2A histone family member X (at Ser 139, abbreviated as γH2AX) demonstrate that zebrafish Tmem39b protects the cells against DNA damage caused by exposure to the cold-warming stress and facilitates tissue damage repair during the recovery phase. The gene modules underlying the functions of Tmem39b in zebrafish are highly enriched in biological processes associated with immune response. The dysfunction of Tmem39b also attenuates the up-regulation of tissue C-reactive protein (CRP) content upon rewarming. Together, our data shed new light on the function and mechanism of Tmem39b in regulating the cold resistance of fish.

Metabonomic Analysis Provides New Insights into the Response of Zhikong Scallop (Chlamys farreri) to Heat Stress by Improving Energy Metabolism and Antioxidant Capacity

Temperature is an important factor affecting the growth, development and survival of marine organisms. A short episode of high temperature has been proven to be a severe threat to sustainable shellfish culture. Zhikong scallop (Chlamys farreri), a shellfish with broad economic and biological value in North China, has frequently experienced heat stress in summer in recent years. To understand the effects of heat stress on shellfish, the metabolism of C. farreri was analyzed after exposure to 27 °C for either 6 h or 30 d. After 6 h of heat stress exposure, a total of 326 and 264 significantly different metabolites (SDMs) were identified in gill and mantle tissues, respectively. After 30 d of heat stress exposure, a total of 381 and 341 SDMs were found in the gill and mantle tissues, respectively. These SDMs were mainly related to the metabolism of amino acids, carbohydrates, lipids and nucleotides. A decline in pyruvic acid, and an increase in citric acid and fumaric acid in the gills and mantle of C. farreri indicated an alteration in energy metabolism, which may be attributed to increased ATP production in order to overcome the heat stress. Among the SDMs, 33 metabolites, including pyruvic acid, glycine and citric acid, were selected as potential biomarkers for heat stress response in C. farreri. In addition, a decline in glutamine and β-Alanine levels indicated oxidative stress in C. farreri exposed to heat, as well as an increase in the total antioxidant capacity (T-AOC). Our findings suggested C. farreri have the potential to adapt to heat stress by regulating energy metabolism and antioxidant capacity.

An updated review of cold shock and cold stress in fish

Temperature is critical in regulating virtually all biological functions in fish. Low temperature stress (cold shock/stress) is an often-overlooked challenge that many fish face as a result of both natural events and anthropogenic activities. In this study, we present an updated review of the cold shock literature based on a comprehensive literature search, following an initial review on the subject by M.R. Donaldson and colleagues, published in a 2008 volume of this journal. We focus on how knowledge on cold shock and fish has evolved over the past decade, describing advances in the understanding of the generalized stress response in fish under cold stress, what metrics may be used to quantify cold stress and what knowledge gaps remain to be addressed in future research. We also describe the relevance of cold shock as it pertains to environmental managers, policymakers and industry professionals, including practical applications of cold shock. Although substantial progress has been made in addressing some of the knowledge gaps identified a decade ago, other topics (e.g., population-level effects and interactions between primary, secondary and tertiary stress responses) have received little or no attention despite their significance to fish biology and thermal stress. Approaches using combinations of primary, secondary and tertiary stress responses are crucial as a research priority to better understand the mechanisms underlying cold shock responses, from short-term physiological changes to individual- and population-level effects, thereby providing researchers with better means of quantifying cold shock in laboratory and field settings.

Non-targeted Metabolomics Analysis Based on LC–MS to Assess the Effects of Different Cold Exposure Times on Piglets

Pigs are susceptible to low temperature conditions, and cold stress causes metabolic changes in the body to increase heat production as an adaption to adverse environments. To characterize and validate different metabolites in piglet livers at different cold exposure times, sixteen 30-day-old male weaned piglets with similar weights were randomly divided into four groups: the normal temperature group (24 ± 2°C, NT) and cold exposure (4 ± 2°C) 2-h group (CS2), 6-h group (CS6), and 12-h group (CS12). At the end of the experiment, the liver samples were analyzed using systemic non-targeted metabolomics. Eight known differentially abundant metabolites (farnesyl pyrophosphate, isocitrate, triethanolamine, phenylethylamine, deoxynosine, citric acid, maltotriose, and epinephrine) were observed between the CS groups and the control group in positive and negative ion modes. The eight main differentially abundant metabolites involved in seven metabolite classifications. Metabolic pathways and enrichment analyses revealed that the pathways involved three KEGG pathway classifications. Most of the pathways were related to amino acid or energy metabolism. Moreover, the metabolic pathways were not identical under different cold exposure times, with those following 2 and 6 h of cold exposure more related to carbohydrates and energy production and those following 12 h of cold exposure more related to the metabolism connected with epinephrine. Thus, under different cold exposure times, the metabolite profiles and metabolic pathways differed.

Integrated analysis about the effects of heat stress on physiological responses and energy metabolism in Gymnocypris chilianensis

The temperature of the rivers in the Qilian Mountains, China varies widely from day to night, and Gymnocypris chilianensis living in these rivers may experience a change of 10 °C to 20 °C within a day. To explore the mechanisms underlying G. chilianensis responses to heat stress, we conducted an acute temperature stress experiment. In response to heat stress, levels of antioxidant enzymes (SOD\CAT\MDA) first increased and then decreased with time, but T-AOC levels only decreased. The activities of key glycolytic enzymes HK and PFK in the liver also first increased and then decreased and transaminase (AST/ALT) activity increased significantly. We obtained 5350 significantly different genes through transcriptome sequencing with enrichment pathways including primarily glycine, serine and threonine metabolism, cysteine and methionine metabolism, tryptophan metabolism, fructose and mannose metabolism, steroid hormone biosynthesis, and fatty acid degradation. A total of 457 differential metabolites were identified in the liver under thermal stress, most of which are involved in biochemical pathways of amino acid metabolism. Biosynthesis of amino acids indicated that G. chilianensis maintained physiological homeostasis by enhancing glucose metabolism and regulating lipid and amino acid metabolism pathways under thermal stress. We also randomly selected 12 key response genes for validation using qRT-PCR. This is the first study describing the mechanisms underlying responses to thermal stress in G. chilianensis, and may also provide reference data for the study of environmental mutations in indigenous fish in the Qinghai-Tibet Plateau and Qilian Mountains.

Metabolism and Sex Differentiation in Animals from a Starvation Perspective

Animals determine their sex genetically (GSD: genetic sex determination) and/or environmentally (ESD: environmental sex determination). Medaka (Oryzias latipes) employ a XX/XY GSD system, however, they display female-to-male sex reversal in response to various environmental changes such as temperature, hypoxia, and green light. Interestingly, we found that 5 days of starvation during sex differentiation caused female-to-male sex reversal. In this situation, the metabolism of pantothenate and fatty acid synthesis plays an important role in sex reversal. Metabolism is associated with other biological factors such as germ cells, HPG axis, lipids, and epigenetics, and supplys substances and acts as signal transducers. In this review, we discuss the importance of metabolism during sex differentiation and how metabolism contributes to sex differentiation.

Metabolomics analysis of the effects of temperature on the growth and development of juvenile European seabass (Dicentrarchus labrax)

Temperature variations have significant impacts on the growth and development of fish. In this study, the effects of temperature on the growth and development of European seabass (Dicentrarchus labrax) were investigated using ultra-performance liquid chromatography-tandem mass spectrometry-based metabolomics. Three groups of fish were exposed to various temperatures for 60 days: T1-E (10 °C), T2-E (15 °C), and T3-E (20 °C). Afterward, the temperature of all groups was increased to 20 °C and maintained for 62 days (T1-S, T2-S, T3-S). The livers were extracted for subsequent analysis. In the first stage of the experiment, the growth rate was highest in the T3-E group, followed by the T1-E and T2-E groups. The following metabolites identified by comparative analysis were found to be elevated: L-thyroxine, cysteamine, uridine diphosphate (UDP)-glucose, α-ketoglutaric acid, carbamoyl phosphate, and guanidine acetic acid of the T1-E group. Pathway analysis of the altered metabolites suggested changes in glucose metabolism, arginine and proline metabolism, the tricarboxylic acid cycle, the ornithine cycle, histidine metabolism, and taurine metabolism, which were involved with growth and development. Meanwhile, partial compensatory growth was observed in fish in the T1-S and T2-S groups. Metabolites identified as potential markers of growth included L-cysteine, taurocholic acid, UDP-glucose, and L-thyroxine. The significantly changed metabolic pathways were cysteine and methionine metabolism, bile secretion, tyrosine metabolism, and hypotaurine metabolism. We screened out the marker metabolites and metabolic pathway could provide important insights into the potential mechanisms of temperature affects the growth and development of European seabass. All in all, our research can provide theoretical basis and technical guidance for efficiently culturing European seabass.

Integrated transcriptomic and metabolomic responses in the hepatopancreas of kuruma shrimp (Marsupenaeus japonicus) under cold stress

In aquatic ecosystems, the temperature of the water is an important ecological factor that modulates aquatic organisms' metabolism, growth, development, and reproduction. In this study, the morphological, transcriptomic, and metabolomic analyses of response of Marsupeneus japonicus to acute cold stress was investigated. The results revealed that low temperature caused profound morphological damage to the hepatopancreas. Transcriptomic responses suggested that energy and primary metabolism, cytoskeleton structure, and apoptosis signaling were altered. The metabolic responses to cold stress included changes of multiple amino acids and unsaturated fatty acids. Combined transcriptomic and metabolomic data indicated that energy metabolism pathways were downregulated in the hepatopancreas under cold stress. However, M. japonicus increased ATP and unsaturated fatty acids production to ameliorate. Moreover, cold stress caused significant attenuation of macrophage apoptosis. This study provides key information to increase our understanding of low-temperature tolerance in shrimp.

Multi-Omics Analysis Provides Novel Insight into Immuno-Physiological Pathways and Development of Thermal Resistance in Rainbow Trout Exposed to Acute Thermal Stress

In recent years, poikilothermic animals such as fish have increasingly been exposed to stressful high-temperature environments due to global warming. However, systemic changes in fish under thermal stress are not fully understood yet at both the transcriptome and proteome level. Therefore, the objective of this study was to investigate the immuno-physiological responses of fish under extreme thermal stress through integrated multi-omics analysis. Trout were exposed to acute thermal stress by raising water temperature from 15 to 25 °C within 30 min. Head-kidney and plasma samples were collected and used for RNA sequencing and two-dimensional gel electrophoresis. Gene enrichment analysis was performed: differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were identified to interpret the multi-omics results and identify the relevant biological processes through pathway analysis. Thousands of DEGs and 49 DEPs were identified in fish exposed to thermal stress. Most of these genes and proteins were highly linked to DNA replication, protein processing in the endoplasmic reticulum, cell signaling and structure, glycolysis activation, complement-associated hemolysis, processing of released free hemoglobin, and thrombosis and hypertension/vasoconstriction. Notably, we found that immune disorders mediated by the complement system may trigger hemolysis in thermally stressed fish, which could have serious consequences such as ferroptosis and thrombosis. However, antagonistic activities that decrease cell-free hemoglobin, heme, and iron might be involved in alleviating the side effects of thermally induced immuno-physiological disorders. These factors may represent the major thermal resistance traits that allow fish to overcome extreme thermal stress. Our findings, based on integration of multi-omics data from transcriptomics and proteomics analyses, provide novel insight into the pathogenesis of acute thermal stress and temperature-linked epizootics.

Metabolomics investigation of summer mortality in New Zealand Greenshell™ mussels (Perna canaliculus)

Increasing water temperatures due to climate change have resulted in more frequent high mortality events of New Zealand Greenshell™ mussels (Perna canaliculus Gmelin 1791). These events have significant impacts within mussel farms which support a major shellfish industry for New Zealand. The present study investigates metabolic responses of farmed mussels during a summer mortality event in order to identify health impacts and elucidate mechanistic effects of external stressors on mussels. A gas chromatography-mass spectrometry (GC-MS)-based metabolomics approach was used to identify metabolic perturbations and flow cytometry assays were used to assess viability, oxidative stress and apoptosis of haemocytes from healthy and unhealthy mussels during a summer mortality event. The results showed significantly higher mortality and apoptosis of haemocytes in unhealthy mussels compared to healthy mussels. Reactive oxygen species (ROS) production, which is an indicator of oxidative stress was very high in both mussel groups, but no differences were observed between the two mussel groups. Metabolomics revealed alterations of many metabolites in both haemolymph and hepatopancreas (digestive gland) of unhealthy mussels compared to healthy mussels, reflecting perturbations in several molecular pathways, including energy metabolism, amino acid metabolism, protein degradation/tissue damage and oxidative stress. An increased level of itaconic acid which is an antimicrobial metabolite and biomarker of pathogen infection was observed in haemolymph, but not in hepatopancreas samples. This investigation provides the first detailed metabolic characterization of mussel immune responses to a summer mortality event and illustrates the benefits of using an integrated metabolomics and flow cytometry workflow for mussel health assessment and biomarker identification for summer mortality early detection.

The effects of solid-state fermentation on the content, composition and in vitro antioxidant activity of flavonoids from dandelion

Dandelion (Taraxacum officinale), a common plant worldwide, is used as both a medicine and food. Fermentation is a food processing technology that has many advantages, such as low energy cost, changes in product characteristics, and enhanced product quality. The purpose of this study was to investigate the effect of solid-state fermentation (SSF) on the content, composition and antioxidant activity of dandelion flavonoids. Response surface methodology was used to optimize dandelion fermentation conditions. Under optimized conditions, the maximum flavone concentration was 66.05 ± 1.89 mg/g. The flavonoid content of the crude extract from fermented dandelion (FDF) was 183.72 ± 2.24 mg/g. The flavonoid compounds in the crude extracts were further identified by UPLC-ESI-MS/MS. A total of 229 flavonoid compounds were identified, and 57 differential flavonoids (including 27 upregulated and 30 downregulated flavonoids) between FDF and the crude extract of unfermented dandelion (DF) were observed, of which 25 were annotated to metabolic pathways. FDF displayed superior antioxidant activity to that of DF in in vitro DPPH radical-scavenging and reducing power assays. The favorable results of our investigation could provide a new way for the exploitation and utilization of dandelion, which could be promising for its application as an antioxidant and functional food additive with flavonoids as ingredients.

Physiological responses to cold and starvation stresses in the liver of yellow drum (Nibea albiflora) revealed by LC-MS metabolomics

As global climate changes, mass mortality in farmed fish associated with the severely cold weather has aroused growing concerns. Yellow drum (Nibea albiflora) is an important maricultured fish in China, whereby its aquaculture suffered from overwinter mortality associated with cold and cold-induced-fasting stresses. Here, by using LC-MS metabolomics combined with transcriptomics, we investigated the physiological responses of yellow drum liver to cold and starvation stresses. The experiment involved four groups: 16 °C fed group (CG1), 16 °C unfed group (CG2), 8 °C fed group (EG1), and 8 °C unfed group (EG2). Under cold stress, a total of 308 and 257 differential metabolites were identified in EG1 vs. CG1 and EG2 vs. CG2, respectively, showing 5 overlapping significant pathways: glutathione metabolism, biosynthesis of unsaturated fatty acids, galactose metabolism, arginine and proline metabolism, and ABC transporters. Intersection analysis identified that glutamate, oxidized glutathione (GSSG), and eicosenoic acid were the common metabolites induced by cold stress. Under starvation stress, a total of 300 and 215 differential metabolites were identified in CG2 vs. CG1 and EG2 vs. EG1, respectively, showing 2 overlapping significant pathways: glutathione metabolism and galactose metabolism. Intersection analysis revealed that glutamate and GSSG were the common metabolites caused by fasting. Under cold and starvation combined stresses, 286 differential metabolites were identified in EG2 vs. CG1, showing 7 influenced pathways: glycerophospholipid metabolism, biosynthesis of unsaturated fatty acids, glutathione metabolism, sphingolipid metabolism, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, autophagy, and purine metabolism. Interestingly, the glutamate and GSSG were induced by both single and combined stresses of cold and starvation treatments. These findings suggest that glutathione metabolism and its related metabolites (glutamate and GSSG) could be potential biomarkers of cold and starvation stresses in yellow drum. Overall, the results of this study provided insights into the physiological regulation in response to cold and starvation stresses in this fish.