Physiological responses to heat stress in the liver of rainbow trout (Oncorhynchus mykiss) revealed by UPLC-QTOF-MS metabolomics and biochemical assays

Dietary vitamin B6 supplementation alleviates heat stress-induced intestinal barrier impairment by regulating the gut microbiota and metabolites in broilers

Heat stress (HS) brings great challenges to the poultry industry. Vitamin B6 (VB6) is an essential micro-nutrient for animals to maintain normal physiological functions and possesses antioxidant and anti-inflammatory properties. This study aimed to explore the effect of VB6 on alleviating HS-induced intestinal barrier impairment in broilers. A total of 250 broilers (609.76 ± 0.34 g) were randomly allocated to 5 groups with 5 replicate cages of 10 birds each. The broilers in thermoneutral (TN) group were raised in thermoneutral conditions (23 ± 1°C) and fed with a basal diet. The birds in other four groups were housed under cycle high temperature (34 ± 1°C for 8 h/d) from d 21 to 35 and fed with the basal diet (HS group) or basal diet supplemented with 6, 12, or 24 mg/kg VB6 (HB-6, HB-12, HB-24 groups). The results showed that HS reduced the growth performance, increased ileum inflammatory cytokines levels, and impaired the gut barrier function (P < 0.05). Compared to the HS group, final body weight, average daily gain, and average daily feed intake, and the feed conversion ratio were improved by VB6 supplementation. The diamine oxidase, interleukin (IL)-1β, tumor necrosis factor-α, IL-18, IL-10, and interferon-γ levels were reduced by VB6 supplementation (P < 0.05). Moreover, VB6 supplementation linearly or quadratically enhanced villus height and villus height-to-crypt depth ratio of duodenum and jejunum, and decreased crypt depth of duodenum and ileum. The mRNA expression of Occlaudin, ZO1, Mucin2, Mucin4, E-cadhein, and β-catenin were increased by VB6 treatment (P < 0.05). Furthermore, dietary VB6 altered the diversity and community of gut microbiota (P < 0.05). A total of 83 differential metabolites associated with the amelioration of VB6 were identified, which were primarily enriched in glycerophospholipid metabolism, caffeine metabolism, and glutathione metabolism pathway. Collectively, VB6 may improve the growth performance and intestinal barrier function of heat-stressed broilers by regulating the ileal microbiota and metabolic homeostasis.

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.

Long-term thermal acclimation enhances heat resistance of Hong Kong catfish (Clarias fuscus) by modulating gill tissue structure, antioxidant capacity and immune metabolic pathways

The rapid temperature changes caused by global warming significantly challenge fish survival by affecting various biological processes. Fish generally mitigate stress through physiological plasticity, but when temperature changes exceed their tolerance limits, even adaptable species like Siluriformes can experience internal disruptions. This study investigates the effects of extreme thermal climate on Hong Kong catfish (Clarias fuscus), native to tropical and subtropical regions. C. fuscus were exposed to normal temperature (NT, 26 ℃) or high temperature (HT, 34 ℃) condition for 90 days. Subsequently, histological, biochemical, and transcriptomic changes in gill tissue were observed after exposure to acute high temperatures (34 ℃) and subsequent temperature recovery (26 ℃). Histological analysis revealed that C. fuscus in the HT group exhibited less impact from sudden temperature shifts compared to the NT group, as they adapted by reducing the interlamellar cell mass (ILCM) and lamellae thickness (LT) of gill tissue, thereby mitigating the aftermath of acute heat shock. Biochemical analysis showed that catalase (CAT) activity in the high temperature group continued to increase, while malondialdehyde (MDA) levels decreased, suggesting establishment of a new oxidative balance and enhanced environmental adaptability. Transcriptome analysis identified 520 and 463 differentially expressed genes in the NT and HT groups, respectively, in response to acute temperature changes. Enrichment analysis highlighted that in response to acute temperature changes, the NT group inhibited apoptosis and ferroptosis by regulating the activity of alox12, gclc, and hmox1a, thereby attenuating the adverse effects of heat stress. Conversely, the HT group increased the activity of pfkma and pkma to provide sufficient energy for tissue repair. The higher degree of heat shock protein (Hsp) response in NT group also indicated more severe heat stress injury. These findings demonstrate alterations in gill tissue structure, regulation of oxidative balance, and the response of immune metabolic pathways to acute temperature fluctuations in C. fuscus following thermal exposure, suggesting potential avenues for further exploration into the thermal tolerance plasticity of fish adapting to global warming.

Modulation of liver metabolism and gut microbiota by Alhagi-honey alleviated heat stress-induced liver damage

Alhagi-honey (AH) is a well-established traditional ethnic medicine with advantageous effects against diarrhea and headaches. We aimed to explore the preventive effect of AH on liver damage induced by heat stress (HS) and its underlying mechanism. HS models were established by thermostat, and mice were treated at 39 ℃ for 10 h, lasting for 7 days. Hematoxylin-eosin (H&E) staining and Periodic Acid-Schiff (PAS) staining were used for histological observation, and transmission electron microscopy (TEM) was used for ultrastructure examination of hepatocytes. Gut microbiota (GM) composition and liver metabolites were respectively analyzed by 16S rRNA sequencing and non-targeted metabolome sequencing. AH pretreatment alleviated liver damage caused by heat stress in mice. The main manifestation was that AH alleviated serum aspartate transferase (AST) and aspartate transaminase (ALT). It was found that AH improved symptoms of hepatocyte damage. In addition, the relative abundance of f_Rikenellaceae, g_Incertae_Sedis and s_Staphylococcus_Orisratti, g_Lachnoclostridium, g_GCA-900066575, and s_Alistipes_inops were modified by AH and these bacterial genera showed association with 6 metabolites (2- (3,4-dihydroxyphenyl) acetamide, 3-hydroxy-3-methylpentanedioic acid, PC (17:0/17:1), Y-L-Glutamy-L-glutamic acid, L-Isoleucine, 5-Methyluridine, 8,8-dimethyl-2-phenyl-4H,8H-pyrano [2, 3-h] chromen-4-one). The Pearson analysis also showed a strong correlation between these microbes and 2 risk indicators (AST and ALT) of liver damage. AH alleviated HS-induced liver damage by regulating liver metabolism and maintaining normal GM. It demonstrated that AH held potential as a prophylactic drug for the prevention of HS-induced liver damage.

Black sand nanoparticles and heat stress impacts the neurological and oxidative stress indices and splenic-renal histology of Clarias gariepinus

In Egypt, while many studies have focused on the radiometry and mineralogy of black sands, research on their effects on nearby aquatic organisms is rare. This study aimed to assess the combined effects of heat stress (HS) and black sand nanoparticles (BS-NPs) on renal function, antioxidant responses (TAC, SOD, CAT), neuro-stress indicators (AchE, cortisol), and to conduct histopathological investigations in the kidney and spleen tissues of African catfish Clarias gariepinus over a 15-day period to exposure to control, HS (32 °C), BS (6.4 g/kg diet) and HS + BS groups. The outcomes revealed that thermal stress alone showed no significant difference from the control. However, creatinine and uric acid levels were significantly higher in the BS-NPs and HS + BS-NPs groups (p < 0.001). Antioxidant markers (TAC, SOD, and CAT) were substantially reduced across all treated groups (0.05 ≥ p < 0.0001). AchE levels were significantly elevated in BS-NPs and HS + BS-NPs (p < 0.001), while cortisol levels were higher in these groups but not significantly different in HS. Degeneration and necrosis in the white and red pulps, scattered lymphocytes, and increased collagen fiber surrounding blood vessels and the lining of the ellipsoid structure were all evident in the spleen, along with the enlargement of the melanomacrophage centers with big granular, irregular, and brown pigments (hemosiderin). Our study, therefore, provides new insights into how heat stress, an abiotic environmental factor, influences the toxicity of black sand nanoparticles in catfish.

Physiological Responses to Acute Heat Stress in Rohu, Labeo rohita: Insights from Liver Proteomics

Heat stress is a major problem in aquaculture species, causing changes in physiology such as decreased feed intake, growth rate, reproduction, and internal cellular damage, thereby affecting fish's health. The effects of an acute heat stress simulating a daily rise and fall in temperature on summer days were evaluated in the liver proteome of rohu (Labeo rohita) fingerlings in the present study. The fish maintained at 30 °C were gradually exposed to a higher temperature of 36 °C at an increment rate of 1 °C per 1.5 h, and after 3 h at that temperature, it was gradually reduced to 30 °C. The liver tissue samples were collected at 5 am, 5 pm, and 5 am the next day from the exposed and control fish. Protein samples were prepared from the liver tissues, and the extracted proteins were compared using 2-dimensional (2D) gel electrophoresis (2DGE) and mass spectrometry (MS) using a MALDI-TOF/TOF mass spectrometer. A total of 44 differentially expressed protein spots were visualized in 2D gel analysis from heat stress exposed fish at three time points, out of which 21 proteins including one hypothetical protein could be identified by MS. The abundance of five selected differentially expressed proteins (DEPs) was validated using qPCR. The majority of DEPs were found to be involved primarily in lipid, protein and energy metabolism, immune system regulation, cytoskeletal stability, and ROS management. The findings of this study would help in the development of strategies to mitigate heat stress in L. rohita.

Ribosome Profiling and RNA Sequencing Reveal Translation and Transcription Regulation under Acute Heat Stress in Rainbow Trout (Oncorhynchus mykiss, Walbaum, 1792) Liver

Rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) is an important economic cold-water fish that is susceptible to heat stress. To date, the heat stress response in rainbow trout is more widely understood at the transcriptional level, while little research has been conducted at the translational level. To reveal the translational regulation of heat stress in rainbow trout, in this study, we performed a ribosome profiling assay of rainbow trout liver under normal and heat stress conditions. Comparative analysis of the RNA-seq data with the ribosome profiling data showed that the folding changes in gene expression at the transcriptional level are moderately correlated with those at the translational level. In total, 1213 genes were significantly altered at the translational level. However, only 32.8% of the genes were common between both levels, demonstrating that heat stress is coordinated across both transcriptional and translational levels. Moreover, 809 genes exhibited significant differences in translational efficiency (TE), with the TE of these genes being considerably affected by factors such as the GC content, coding sequence length, and upstream open reading frame (uORF) presence. In addition, 3468 potential uORFs in 2676 genes were identified, which can potentially affect the TE of the main open reading frames. In this study, Ribo-seq and RNA-seq were used for the first time to elucidate the coordinated regulation of transcription and translation in rainbow trout under heat stress. These findings are expected to contribute novel data and theoretical insights to the international literature on the thermal stress response in fish.

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

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

Transcriptome analysis in hepatopancreases reveals the response of domesticated common carp to a high-temperature environment in the agricultural heritage rice-fish system

Qingtian paddy field carp (PF-carp) is a local carp cultivated in the paddy field of Qingtian, Zhejiang. This rice-fish co-culture system has been recognized as one of the Globally Important Agriculture Heritage Systems (GIAHS). PF-carp has been acclimatized to the high-temperature environment of shallow paddy fields after several centuries of domestication. To reveal the physiological and molecular regulatory mechanisms of PF-carp, we chose to use 28°C as the control group and 34°C as the treatment group. We measured biochemical parameters in their serum and hepatopancreases and also performed transcriptome sequencing analysis. Compared with the control group, the serum levels of malondialdehyde (MDA), glucose (GLU), glutathione peroxidase (GSH-Px), catalase (CAT), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) show no significant change. In addition, superoxide dismutase (SOD), GSH-Px, and CAT also show no significant change in hepatopancreases. We identified 1,253 differentially expressed genes (DEGs), and their pathway analysis revealed that heat stress affected AMPK signaling pathway, protein export, and other biological processes. It is worth noting that protein processing in the endoplasmic reticulum (ER) was the most significantly enriched pathway identified by the Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene set enrichment analysis (GSEA). Significantly higher levels of HSP40, HSP70, HSP90, and other ubiquitin ligase-related genes were upregulated. In summary, heat stress did not lead to tissue damage, inflammation, oxidative stress, and ER stress in the hepatopancreases of PF-carp. This study provides valuable insights into the adaptation mechanism of this species to the high-temperature environment of paddy fields.

Stress responses to warming in Japanese flounder (Paralichthys olivaceus) from different environmental scenarios

Japanese flounder (Paralichthys olivaceus) is one of cold-water species widely farmed in Asia. In recent years, the increased frequency of extreme weather events caused by global warming has led to serious impact on Japanese flounder. Therefore, it is crucial to understand the effects of representative coastal economic fish under increasing water temperature. In this study, we investigated the histological and apoptosis responses, oxidative stress and transcriptomic profile in the liver of Japanese flounder exposed to gradual temperature rise (GTR) and abrupt temperature rise (ATR). The histological results showed liver cells in ATR group were the most serious in all three groups including vacuolar degeneration and inflammatory infiltration, and had more apoptosis cells than GTR group detected by TUNEL staining. These further indicated ATR stress caused more severe damage than GTR stress. Compared with control group, the biochemical analysis showed significantly changes in two kinds of heat stress, including GPT, GOT and D-Glc in serum, ATPase, Glycogen, TG, TC, ROS, SOD and CAT in liver. In addition, the RNA-Seq was used to analyze the response mechanism in Japanese flounder liver after heat stress. A total of 313 and 644 differentially expressed genes (DEGs) were identified in GTR and ATR groups, respectively. Further pathway enrichment of these DEGs revealed that heat stress affected cell cycle, protein processing and transportation, DNA replication and other biological processes. Notably, protein processing pathway in the endoplasmic reticulum (ER) was enriched significantly in KEGG and GSEA enrichment analysis, and the expression of ATF4 and JNK was significantly up-regulated in both GTR and ATR groups, while CHOP and TRAF2 were high expressed in GTR and ATR groups, respectively. In conclusion, heat stress could cause tissue damage, inflammation, oxidative stress and ER stress in the liver of Japanese flounder. The present study would provide insight into the reference for the adaptive mechanisms of economic fish in face of increasing water temperature caused by global warming.

FoxO signaling and mitochondria-related apoptosis pathways mediate tsinling lenok trout (Brachymystax lenok tsinlingensis) liver injury under high temperature stress

Tsinling lenok trout (Brachymystax lenok tsinlingensis) is a typical cold water fish. High temperature has been shown to damage the liver of fish. However, few studies have investigated the liver apoptosis induced by high temperature stress in fish from the perspective of gene expression and metabolic function. Therefore, we investigated the changes caused by high temperature stress (24 °C) on the liver tissue structure, antioxidant capacity, liver gene expression, and the metabolome of tsinling lenok trout. The transcriptomic results showed that genes associated with apoptosis, such as CASP8, CASP3, PERK, Bcl-6 and TRAIL, were upregulated under high temperature stress. Metabolomic analysis showed that the metabolic pathway of nucleotide synthesis was significantly downregulated, while that of oxygen radical synthesis was significantly upregulated. Integrated analysis showed that after high temperature stress, immune-related signaling pathways in trout were activated and their apoptosis level increased, which might be related to hepatopancreas injury. In addition, abnormalities in the tricarboxylic acid cycle and mitochondrial function were observed, suggesting that functional hypoxia caused by high temperature might be involved fish cell apoptosis. These results provide new insights into the process of cell apoptosis in fish under high temperature stress.

Sex-specific metabolic dysregulation in digestive glands of green mussels following exposure to triazophos

As a ubiquitous environmental pollutant in China, triazophos (TP) is known to have neurotoxicity, oxidative stress, and reproductive toxicity to mussels. To investigate the molecular mechanisms of TP toxicity, metabolic changes in the digestive glands of Perna viridis in different sexes were examined after treated with 35 μg/L TP. Notably, 158 significant different metabolites (SDMs) were detected in TP-treated mussels and more than half of the SDMs were lipids and lipid-like molecules, which suggested that TP disturbed the lipid metabolism of P. viridis. In addition, metabolites associated with neurotoxicity and reproductive disturbance were also detected in female and male mussels. Moreover, a larger number of SDMs were found in male mussels (120 SDMs) than females (99 SDMs), and 60 common metabolites exhibited consistent variation tendency and similar magnitude in both sexes. The metabolic alternations in female and male mussels displayed similar protective mechanisms and also sex-specific responses, male mussels were more sensitive to TP exposure. This research provided new data about the molecular mechanisms of TP toxicity and the gender specific changes in mussels after treated by chemicals.

Transcriptomic Response of the Liver Tissue in Trachinotus ovatus to Acute Heat Stress

Trachinotus ovatus is a major economically important cultured marine fish in the South China Sea. However, extreme weather and increased culture density result in uncontrollable problems, such as increases in water temperature and a decline in dissolved oxygen (DO), hindering the high-quality development of aquaculture. In this study, liver transcriptional profiles of T. ovatus were investigated under acute high-temperature stress (31 °C and 34 °C) and normal water temperature (27 °C) using RNA sequencing (RNA-Seq) technology. Differential expression analysis and STEM analysis showed that 1347 differentially expressed genes (DEGs) and four significant profiles (profiles 0, 3, 4, and 7) were screened, respectively. Of these DEGs, some genes involved in heat shock protein (HSPs), hypoxic adaptation, and glycolysis were up-regulated, while some genes involved in the ubiquitin-proteasome system (UPS) and fatty acid metabolism were down-regulated. Our results suggest that protein dynamic balance and function, hypoxia adaptation, and energy metabolism transformation are crucial in response to acute high-temperature stress. Our findings contribute to understanding the molecular response mechanism of T. ovatus under acute heat stress, which may provide some reference for studying the molecular mechanisms of other fish in response to heat stress.

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.

Chronic hypoxia and hyperoxia alter tissue-specific fatty acid profile and FD6D and elongase gene expression levels in rainbow trout (Oncorhynchus mykiss)

Commercially important trout species, especially rainbow trout, are under great threat due to several negative factors affecting oxygen levels in water such as global warming and eutrophication. In our study, rainbow trout (Oncorhynchus mykiss) was exposed to chronic (for 28 days) hypoxia (4.0 ± 0.5 mg/L) and hyperoxia (12 ± 1.2 mg/L) in order to evaluate the alteration of fatty acid profiles in muscle, liver and gill tissues. In addition, delta-6-desaturase and elongase gene expression profiles were measured in liver, kidney and gill tissues. The amount of saturated fatty acids increased by oxygen applications in the liver, while it decreased in the muscle and gill tissues compared to normoxia (p < 0.05). Monounsaturated fatty acids levels increased in muscle and gill (p < 0.05). Although n-3 polyunsaturated fatty acid (PUFA) decreased in muscle tissue, n-6 PUFA increased (p < 0.05). The n-3/n-6 ratio decreased in muscle tissue in response to the both exposures (p < 0.05) as well as eicosapentaenoic acid/docosahexaenoic acid ratio (p < 0.05). Hypoxia exposure generally increased delta-6-desaturase and elongase mRNA levels in all tissues (p < 0.05). However, gene expression profiles were variable in fish exposed to hyperoxia. As a result of oxygen exposures, the lipid profile of muscle tissue, which stores dense fat, was negatively affected more than that of liver and gill tissues. We determined that the change in expression levels was tissue specific.

Redox state and metabolic responses to severe heat stress in lenok Brachymystax lenok (Salmonidae)

In order to provide new insights into the physiological responses of lenok (Brachymystax lenok: Salmonidae) to acute and severe heat stress (25°C, 48 h), dynamic changes in redox state and metabolic responses are studied combined biochemical index and non-targeted metabolome. Nicotinamide adenine dinucleotide (NAD⁺) consumption causes significant increases in ratio of reduced NADH to NAD⁺ and ratio of reduced nicotinamide adenine dinucleotide phosphate (NADPH) to NADP⁺, which induced the redox imbalance in heat stressed lenok. Lowered reduced glutathione/oxidized glutathione (GSH/GSSG) ratios suggested that more oxidized conditions occurred in heat-stressed lenok, leading to membrane lipid oxidation. The first few hours of heat stress promoted the activity of enzymes involved in anaerobic glycolysis (hexokinase, pyruvate kinase, lactic dehydrogenase) and glutamicpyruvic transaminase and glutamic oxaloacetic transaminase, which might lead to consumption of many carbohydrates and amino acid catabolism. These enzyme activities decreased with time in a possible compensatory strategy to manage anabolic and catabolic metabolism, maintaining the redox homeostasis. After 48 h of recovery, NAD⁺, carbohydrate levels and enzyme activities had returned to control levels, whereas many amino acids were consumed for repair and new synthesis. GSH remained at levels lower than controls, and the more oxidized conditions had not recovered, aggravating oxidative damage. Glutamic acid, glutamine, lysine and arginine may play important roles in survival of heat-stressed lenok.

Comprehensive Analysis of Microbiome, Metabolome, and Transcriptome Revealed the Mechanisms of Intestinal Injury in Rainbow Trout under Heat Stress

Global warming is one of the most common environmental challenges faced by cold-water fish farming. Intestinal barrier function, gut microbiota, and gut microbial metabolites are significantly altered under heat stress, posing serious obstacles to the healthy artificial culture of rainbow trout. However, the molecular mechanisms underlying intestinal injury in rainbow trout under heat stress remain unclear. In the present study, the optimal growth temperature for rainbow trout (16 °C) was used for the control group, and the maximum temperature tolerated by rainbow trout (24 °C) was used for the heat stress group, which was subjected to heat stress for 21 days. The mechanism of intestinal injury in rainbow trout under heat stress was explored by combining animal histology, 16S rRNA gene amplicon sequencing, ultra-high performance liquid chromatography-mass spectrometry, and transcriptome sequencing. The results showed that the antioxidant capacity of rainbow trout was enhanced under heat stress, the levels of stress-related hormones were significantly increased, and the relative expression of genes related to heat stress proteins was significantly increased, indicating that the heat stress model of rainbow trout was successfully established. Secondly, the intestinal tract of rainbow trout showed inflammatory pathological characteristics under heat stress, with increased permeability, activation of the inflammatory factor signaling pathway, and increased relative expression of inflammatory factor genes, suggesting that the intestinal barrier function was impaired. Thirdly, heat stress caused an imbalance of intestinal commensal microbiota and changes in intestinal metabolites in rainbow trout, which participated in the stress response mainly by affecting lipid metabolism and amino acid metabolism. Finally, heat stress promoted intestinal injury in rainbow trout by activating the peroxisome proliferator-activated receptor-α signaling pathway. These results not only expand the understanding of fish stress physiology and regulation mechanisms, but also provide a scientific basis for healthy artificial culture and the reduction of rainbow trout production costs.

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.

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.