H2O2-Induced Oxidative Stress Responses in Eriocheir sinensis: Antioxidant Defense and Immune Gene Expression Dynamics.

Eriocheir sinensis, a key species in China's freshwater aquaculture, is threatened by various diseases, which were verified to be closely associated with oxidative stress. This study aimed to investigate the response of E. sinensis to hydrogen peroxide (H2O2)-induced oxidative stress to understand the biological processes behind these diseases. Crabs were exposed to different concentrations of H2O2 and their antioxidant enzyme activities and gene expressions for defense and immunity were measured. Results showed that activities of antioxidant enzymes-specificallysuperoxide dismutase (SOD), catalase (CAT), total antioxidant capacity(T-AOC), glutathione (GSH), and glutathione peroxidase (GSH-Px)-varied with exposure concentration and duration, initially increasing then decreasing. Notably, SOD, GSH-Px, and T-AOC activities dropped below control levels at 96 h. Concurrently, oxidative damage markers, including malondialdehyde (MDA), H2O2, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, increased with exposure duration. The mRNA expression of SOD, CAT, and GSH-Px also showed an initial increase followed by a decrease, peaking at 72 h. The upregulation of phenoloxidaseloxidase (proPO) and peroxinectin (PX) was also detected, but proPO was suppressed under high levels of H2O2. Heat shock protein 70 (HSP70) expression gradually increased with higher H2O2 concentrations, whereas induced nitrogen monoxide synthase (iNOS) was upregulated but decreased at 96 h. These findings emphasize H2O2's significant impact on the crab's oxidative and immune responses, highlighting the importance of understanding cellular stress responses for disease prevention and therapy development.

Integrative analysis of miRNA-mRNA expression in the brain during high temperature-induced masculinization of female Nile tilapia (Oreochromis niloticus).

Temperature is one of the most important non-genetic sex differentiation factors for fish. The technique of high temperature-induced sex reversal is commonly used in Nile tilapia (Oreochromis niloticus) culture, although the molecular regulatory mechanisms involved in this process remain unclear. The brain is an essential organ for the regulation of neural signals involved in germ cell differentiation and gonad development. To investigate the regulatory roles of miRNAs-mRNAs in the conversion of female to male Nile tilapia gender under high-temperature stress, we compared RNA-Seq data from brain tissues between a control group (28 °C) and a high temperature-treated group (36 °C). The result showed that a total of 123,432,984 miRNA valid reads, 288,202,524 mRNA clean reads, 1128 miRNAs, and 32,918 mRNAs were obtained. Among them, there were 222 significant differentially expressed miRNAs (DE miRNAs) and 810 differentially expressed mRNAs (DE mRNAs) between the two groups. Eight DE miRNAs and eight DE mRNAs were randomly selected, and their expression patterns were validated by qRT-PCR. The miRNA-mRNA co-expression network demonstrated that 40 DE miRNAs targeted 136 protein-coding genes. Functional enrichment analysis demonstrated that these genes were involved in several gonadal differentiation pathways, including the oocyte meiosis signaling pathway, progesterone-mediated oocyte maturation signaling pathway, cell cycle signaling pathway and GnRH signaling pathway. Then, an interaction network was constructed for 8 miRNAs (mir-137-5p, let-7d, mir-1388-5p, mir-124-4-5p, mir-1306, mir-99, mir-130b and mir-21) and 10 mRNAs (smc1al, itpr2, mapk1, ints8, cpeb1b, bub1, fbxo5, mmp14b, cdk1 and hrasb) involved in the oocyte meiosis signaling pathway. These findings provide novel information about the mechanisms underlying miRNA-mediated sex reversal in female Nile tilapia.

Silencing the fatty acid elongase gene elovl6 induces reprogramming of nutrient metabolism in male Oreochromis niloticus.

Elongation of very long-chain fatty acids protein 6 (ELOVL6) plays a pivotal role in the synthesis of endogenous fatty acids, influencing energy balance and metabolic diseases. The primary objective of this study was to discover the molecular attributes and regulatory roles of ELOVL6 in male Nile tilapia, Oreochromis niloticus. The full-length cDNA of elovl6 was cloned from male Nile tilapia, and was determined to be 2255-bp long, including a 5'-untranslated region of 193 bp, a 3'-untranslated region of 1252 bp, and an open reading frame of 810 bp encoding 269 amino acids. The putative protein had typical features of ELOVL proteins. The transcript levels of elovl6 differed among various tissues and among fish fed with different dietary lipid sources. Knockdown of elovl6 in Nile tilapia using antisense RNA technology resulted in significant alterations in hepatic morphology, long-chain fatty acid synthesis, and fatty acid oxidation, and led to increased fat deposition in the liver and disrupted glucose/lipid metabolism. A comparative transcriptomic analysis (elovl6 knockdown vs. the negative control) identified 5877 differentially expressed genes with significant involvement in key signaling pathways including the peroxisome proliferator-activated receptor signaling pathway, fatty acid degradation, glycolysis/gluconeogenesis, and the insulin signaling pathway, all of which are crucial for lipid and glucose metabolism. qRT-PCR analyses verified the transcript levels of 13 differentially expressed genes within these pathways. Our findings indicate that elovl6 knockdown in male tilapia impedes oleic acid synthesis, culminating in aberrant nutrient metabolism.

Geographical traceability of flavor compounds in Chinese mitten crab (Eriocheir sinensis): Implications for quality differentiation, authenticity assessment, and mechanism research.

Geographical traceability plays a crucial role in ensuring quality assurance, brand establishment, and the sustainable development of the crab industry. In this study, we examined the possibility of using gas chromatography-ion mobility spectrometry with multivariate statistical authenticity analysis to identify the origin of crabs from five sites downstream of the Yangtze River. Significant variations were observed in the levels of alcoholic flavor compounds in the hepatopancreas and muscles of crabs from different geographical locations, and a support vector machine exhibited discriminant ability with 100% accuracy. These flavor variations exhibited significant correlations with the types and concentrations of elements within the crabs, as well as with free amino acids. This study offers a practical approach for determining the geographical traceability of Chinese mitten crabs and elucidates the role of elements in flavor modulation, thereby providing innovative strategies to enhance the efficiency of crab farming.

Integrative analysis of metagenome and metabolome provides new insights into intestinal health protection in Coilia nasus larvae via probiotic intervention.

With the development of large-scale intensive feeding, growth performance and animal welfare have attracted more and more attention. Exogenous probiotics can promote the growth performance of fish through improving intestinal microbiota; however, it remains unclear whether intestinal microbiota influence physiological biomarkers. Therefore, we performed metagenomic and metabolomic analysis to investigate the effects of a 90-day Lactiplantibacillus plantarum supplementation to a basal diet (1.0 × 108 CFU/g) on the growth performance, intestinal microbiota and their metabolites, and physiological biomarkers in Coilia nasus larvae. The results showed that the probiotic supplementation could significantly increase weight and body length. Moreover, it could also enhance digestive enzymes and tight junctions, and inhibit oxidative stress and inflammation. The metagenomic analysis showed that L. plantarum supplementation could significantly decrease the relative abundance of Proteobacteria and increase the relative abundance of Firmicutes. Additionally, pathogenic bacteria (Aeromonadaceae, Aeromonas, and Enterobacterales) were inhibited and beneficial bacteria (Bacillales) were promoted. The metabolome analysis showed that acetic acid and propanoic acid were significantly elevated, and were associated with Kitasatospora, Seonamhaeicola, and Thauera. A correlation analysis demonstrated that the digestive enzymes, tight junction, oxidative stress, and inflammation effects were significantly associated with the increased acetic acid and propanoic acid levels. These results indicated that L. plantarum supplementation could improve intestinal microbial community structure and function, which could raise acetic acid and propanoic acid levels to protect intestinal health and improve growth performance in C. nasus larvae.

A High-Fat-Diet-Induced Microbiota Imbalance Correlates with Oxidative Stress and the Inflammatory Response in the Gut of Freshwater Drum (Aplodinotus grunniens).

Lipids are critical nutrients for aquatic animals, and excessive or insufficient lipid intake can lead to physiological disorders, which further affect fish growth and health. In aquatic animals, the gut microbiota has an important regulatory role in lipid metabolism. However, the effects of a high-fat diet on physical health and microbiota diversity in the gut of freshwater drum (Aplodinotus grunniens) are unclear. Therefore, in the present study, a control group (Con, 6%) and a high-fat diet group (HFD, 12%) were established for a 16-week feeding experiment in freshwater drum to explore the physiological changes in the gut and the potential regulatory mechanisms of bacteria. The results indicated that a high-fat diet inhibited antioxidant and immune capacity while increasing inflammation, apoptosis and autophagy in gut cells. Transcriptome analysis revealed significant enrichment in immune-related, apoptosis-related and disease-related pathways. Through 16S rRNA analysis, a total of 31 genus-level differentially abundant bacterial taxa were identified. In addition, a high-fat diet reduced gut microbial diversity and disrupted the ecological balance of the gut microbiota (Ace, Chao, Shannon and Simpson indices). Integrated analysis of the gut microbiota combined with physiological indicators and the transcriptome revealed that gut microbial disorders were associated with intestinal antioxidants, immune and inflammatory responses, cell apoptosis and autophagy. Specifically, genus-level bacterial taxa in Proteobacteria (Plesiomonas, Arenimonas, Erythrobacter and Aquabacteriumb) could serve as potential targets controlling the response to high-fat-diet stimulation.

Metagenomic Insight into the Effect of Probiotics on Nitrogen Cycle in the Coilia nasus Aquaculture Pond Water.

Recently, probiotics have been widely applied for the in situ remediation of aquatic water. Numerous studies have proved that probiotics can regulate water quality by improving the microbial community. Nitrogen cycling, induced by microorganisms, is a crucial process for maintaining the balance of the aquatic ecosystem. Nevertheless, the underlying mechanisms by which probiotics enhance water quality in aquatic systems remain poorly understood. To explore the water quality indicators and their correlation with nitrogen cycling-related functional genes, metagenomic analysis of element cycling was performed to identify nitrogen cycling-related functional genes in Coilia nasus aquatic water between the control group (C) and the groups supplemented with probiotics in feed (PF) or water (PW). The results showed that adding probiotics to the aquatic water could reduce the concentrations of ammonia nitrogen (NH4+-N), nitrite (NO2--N), and total nitrogen (TN) in the water. Community structure analysis revealed that the relative abundance of Verrucomicrobiota was increased from 30 d to 120 d (2.61% to 6.35%) in the PW group, while the relative abundance of Cyanobacteria was decreased from 30 d to 120 d (5.66% to 1.77%). We constructed a nitrogen cycling pathway diagram for C. nasus aquaculture ponds. The nitrogen cycle functional analysis showed that adding probiotics to the water could increase the relative abundance of the amoC_B and hao (Nitrification pathways) and the nirS and nosZ (Denitrification pathways). Correlation analysis revealed that NH4+-N was significantly negatively correlated with Limnohabitans, Sediminibacterium, and Algoriphagus, while NO2--N was significantly negatively correlated with Roseomonas and Rubrivivax. Our study demonstrated that adding probiotics to the water can promote nitrogen element conversion and migration, facilitate nitrogen cycling, benefit ecological environment protection, and remove nitrogen-containing compounds in aquaculture systems by altering the relative abundance of nitrogen cycling-related functional genes and microorganisms.

Ultrastructural, Antioxidant, and Metabolic Responses of Male Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus) to Acute Hypoxia Stress.

Tilapia tolerate hypoxia; thus, they are an excellent model for the study of hypoxic adaptation. In this study, we determined the effect of acute hypoxia stress on the antioxidant capacity, metabolism, and gill/liver ultrastructure of male genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Fish were kept under control (dissolved oxygen (DO): 6.5 mg/L) or hypoxic (DO: 1.0 mg/L) conditions for 72 h. After 2 h of hypoxia stress, antioxidant enzyme activities in the heart and gills decreased, while the malondialdehyde (MDA) content increased. In contrast, in the liver, antioxidant enzyme activities increased, and the MDA content decreased. From 4 to 24 h of hypoxia stress, the antioxidant enzyme activity increased in the heart but not in the liver and gills. Cytochrome oxidase activity was increased in the heart after 4 to 8 h of hypoxia stress, while that in the gills decreased during the later stages of hypoxia stress. Hypoxia stress resulted in increased Na+-K+-ATP activity in the heart, as well as hepatic vacuolization and gill lamella elongation. Under hypoxic conditions, male GIFT exhibit dynamic and complementary regulation of antioxidant systems and metabolism in the liver, gills, and heart, with coordinated responses to mitigate hypoxia-induced damage.

Comparative Blood Transcriptome Analysis of Semi-Natural and Controlled Environment Populations of Yangtze Finless Porpoise.

The Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) living in different environments display significant differences in behavior and physiology. To compare and analyze gene expression differences between an ex situ population and a controlled environment population of the Yangtze finless porpoise, we sequenced the transcriptome of blood tissues living in a semi-natural reserve and an artificial facility, respectively. We identified 6860 differentially expressed genes (DEGs), of which 6603 were up-regulated and 257 were down-regulated in the controlled environment vs ex situ comparison. GO and KEGG enrichment analysis showed that the up-regulated genes in the controlled environment population were significantly associated with glucose metabolism, amino acid metabolism, and the nervous system, while those up-regulated in the ex situ population were significantly associated with energy supply and biosynthesis. Further analysis showed that metabolic and hearing-related genes were significantly affected by changes in the environment, and key metabolic genes such as HK, PFK, IDH, and GLS and key hearing-related genes such as OTOA, OTOF, SLC38A1, and GABBR2 were identified. These results suggest that the controlled environment population may have enhanced glucose metabolic ability via activation of glycolysis/gluconeogenesis, the TCA cycle, and inositol phosphate metabolism, while the ex situ population may meet higher energy requirements via enhancement of the amino acid metabolism of the liver and muscle and oxidative phosphorylation. Additionally, the acoustic behavior and auditory-related genes of Yangtze finless porpoise may show responsive changes and differential expression under different environment conditions, and thus the auditory sensitivity may also show corresponding adaptive characteristics. This study provides a new perspective for further exploration of the responsive changes of the two populations to various environments and provides a theoretical reference for further improvements in conservation practices for the Yangtze finless porpoise.

Transcriptomic analysis of hydrogen peroxide-induced liver dysfunction in Cyprinus carpio: Insights into protein synthesis and metabolism.

Hydrogen peroxide (H2O2), a prevalent reactive oxygen species (ROS) found in natural aquatic environments, has garnered significant attention for its potential toxicity in fish. However, the molecular mechanisms underlying this toxicity are not yet comprehensively understood. This study aimed to assess H2O2-induced liver dysfunction in common carp (Cyprinus carpio) and elucidate the underlying molecular mechanisms via biochemical and transcriptomic analyses. Common carp were divided into normal control (NC) and H2O2-treated groups (1 mM H2O2), the latter of which was exposed to H2O2 for 1 h per day over a period of 14 days. Serum biochemical analyses indicated that exposure to H2O2 resulted in moderate liver damage, characterized by elevated alanine aminotransferase (ALT) activity and lowered albumin (Alb) level. Concurrently, H2O2 exposure induced oxidative stress and modified the hepatic metabolic enzyme levels. Transcriptome analysis highlighted that 1358 and 1188 genes were significantly downregulated and upregulated, respectively, in the H2O2-treated group. These differentially expressed genes (DEGs) were significantly enriched in protein synthesis and a variety of metabolic functions such as peptide biosynthetic processes, protein transport, ribonucleoprotein complex biogenesis, oxoacid metabolic processes, and tricarboxylic acid metabolic processes. Dysregulation of protein synthesis is principally associated with the downregulation of three specific pathways: ribosome biogenesis, protein export, and protein processing in the endoplasmic reticulum (ER). Furthermore, metabolic abnormalities were primarily characterized by inhibition of the citrate cycle (TCA) and fatty acid biosynthesis. Significantly, anomalies in both protein synthesis and metabolic function may be linked to aberrant regulation of the insulin signaling pathway. These findings offer innovative insights into the mechanisms underlying H2O2 toxicity in aquatic animals, contributing to the assessment of ecological risks.

Effect of environmental level of methomyl on hatching, morphology, immunity and development related genes expression in zebrafish (Danio rerio) embryo.

The extensive use of carbamate pesticides has led to a range of environmental and health problems, such as surface and groundwater contamination, and endocrine disorders in organisms. In this study, we focused on examining the effects of toxic exposure to the carbamate pesticide methomyl on the hatching, morphology, immunity and developmental gene expression levels in zebrafish embryos. Four concentrations of methomyl (0, 2, 20, and 200 µg/L) were administered to zebrafish embryos for a period of 96 h. The study found that exposure to methomyl accelerated the hatching process of zebrafish embryos, with the strongest effect recorded at the concentration of 2 µg/L. Methomyl exposure also trigged significantly reductions in heart rate and caused abnormalities in larvae morphology, and it also stimulated the synthesis and release of several inflammatory factors such as IL-1ß, IL-6, TNF-α and INF-α, lowered the IgM contents, ultimately enhancing inflammatory response and interfering with immune function. All of these showed the significant effects on exposure time, concentration and their interaction (Time × Concentration). Furthermore, the body length of zebrafish exposed to methomyl for 96 h was significantly shorter, particularly at higher concentrations (200 µg/L). Methomyl also affected the expression levels of genes associated with development (down-regulated igf1, bmp2b, vasa, dazl and piwi genes), demonstrating strong developmental toxicity and disruption of the endocrine system, with the most observed at the concentration of 200 µg/L and 96 h exposure to methomyl. The results of this study provide valuable reference information on the potential damage of methomyl concentrations in the environment on fish embryo development, while also supplementing present research on the immunotoxicity of methomyl.

Microcystin-LR-induced autophagy via miR-282-5p/PIK3R1 pathway in Eriocheir sinensis hepatopancreas.

With the intensifying climate warming, blue-green algae blooms have become more frequent and severe, releasing environmental hazards such as microcystin that pose potential threats to human and animal health. Autophagy has been shown to play a crucial role in regulating immune responses induced by environmental hazards, enabling cells to adapt to stress and protect against damage. Although microcystin-LR (MC-LR) has been identified to affect autophagy in mammalian, its impact on aquatic animals has been poorly studied. To investigate the toxicological effects of MC-LR in aquatic ecosystems, we constructed a microRNA profile of acute MC-LR stress in the hepatopancreas of the Chinese mitten crab. Interestingly, we found the MC-LR exposure activated autophagy in the hepatopancreas based on the following evidence. Specifically, mRNA expression level of ATG7, Beclin1 and Gabarap was significantly up-regulated, autophagy regulatory pathways were significantly enriched, and numerous autolysosomes and autophagosomes were observed. Additionally, we found that miR-282-5p and its target gene PIK3R1 played important regulatory roles in autophagy by in vivo and in vitro experiments. Overexpression of miR-282-5p mimicked MC-LR-induced autophagy by inhibiting PIK3R1 expression, while miR-282-5p silencing inhibited autophagy by promoting PIK3R1 expression. Altogether, our findings suggest that MC-LR increases miR-282-5p, which then targets inhibition of PIK3R1 to stimulate autophagy. This study focused on the stress response regulatory mechanisms of juvenile crabs to toxic pollutants in water, offering a potential target for alleviating the toxicity of MC-LR. These findings lay a foundation for reducing the toxicity of MC-LR and environmental hazards in organisms.

Tea Tree Oil Improves Energy Metabolism, Non-Specific Immunity, and Microbiota Diversity via the Intestine-Hepatopancreas Axis in Macrobrachium rosenbergii under Low Fish Meal Diet Administration.

Tea tree oil (TTO) is an essential plant oil with diverse antibacterial and antioxidant properties; however, whether the role played by TTO in low fish meal (LF) diets induced the observed effects in the farmed crustaceans remains unclear. Therefore, this study used Macrobrachium rosenbergii as the model crustacean, and an 8-week feeding experiment with NF (normal fish meal), LF (soybean meal replacing 40% fish meal), and LFT (LF with 200 mg/kg TTO) diets was conducted to evaluate the positive effects of TTO under the LF diet. Compared to the NF diet, the LF diet reduced hemolymph antioxidant capacity and non-specific immunity, and induced hepatopancreas apoptosis and damage. However, in comparison with LF, LTF significantly ameliorated morphological impairment in the hepatopancreas, improved hepatopancreas energy metabolism by upregulating the Bcl-2/Bax and Akt/mTOR pathways, and enhanced antioxidant and non-specific immune capacity by activating the NF-κB/NO pathway. In addition, LFT repaired intestinal barrier injury and the imbalance of intestinal microbiota induced by the LF diet. Moreover, the Pearson correlation revealed the variations of the above indicators, which were related to the abundance changes of Klebsiella, Clostridium sensu stricto 12, Thermobifida, Bifidobacterium, and Alistipes, indicating that these microbes might serve as prospective targets for the intestine-hepatopancreas axis to affect hepatopancreas apoptosis, metabolism, and non-specific immunity. In summary, 200 mg/kg TTO supplementation mediated gut microbiota and positively improved energy metabolism and non-specific immunity, thereby alleviating hepatopancreas dysplasia and damage induced by the LF diet in M. rosenbergii.

The Gill-Associated Bacterial Community Is More Affected by Exogenous Chlorella pyrenoidosa Addition than the Bacterial Communities of Water and Fish Gut in GIFT Tilapia (Oreochromis niloticus) Aquaculture System.

Microalgae has been widely used in aquaculture to improve both the water environment and fish growth; however, the current understanding of the effects of microalgae addition on the key players involved in regulating the water environment and fish health, such as microorganisms, remains limited. Here, a 50-day mesocosm experiment was set up to simulate the culture of Genetic Improvement of Farmed Tilapia (GIFT, Oreochromis niloticus) with an average weight of 14.18 ± 0.93 g and an average length of 82.77 ± 2.80 mm. Different amounts of Chlorella pyrenoidosa were added into these artificial systems to investigate dynamics of bacterial communities in aquaculture water, fish gill, and gut using amplicon-based high-throughput sequencing technology. Our results showed that Chlorella pyrenoidosa addition increased diversity and network complexity of gill-associated bacterial communities rather than those of the water and gut. Furthermore, more biomarkers in the gill-associated bacterial communities were detected in response to Chlorella pyrenoidosa addition than the water and fish gut samples. These findings highlighted the high sensitivity of gill-associated bacterial communities in response to the Chlorella pyrenoidosa addition, implying Chlorella pyrenoidosa addition could play important roles in regulating the fish mucosal immunity by altering the gill-associated microbiota.

Transcriptional Knock-down of mstn Encoding Myostatin Improves Muscle Quality of Nile Tilapia (Oreochromis niloticus).

Myostatin (encoded by mstn) negatively regulates skeletal muscle mass and affects lipid metabolism. To explore the regulatory effects of mstn on muscle development and lipid metabolism in Nile tilapia (Oreochromis niloticus), we used antisense RNA to transcriptionally knock-down mstn. At 180 days, the body weight and body length were significantly higher in the mstn-knock-down group than in the control group (p < 0.05). Additionally, fish with mstn-knock-down exhibited myofiber hyperplasia but not hypertrophy. Oil red O staining revealed a remarkable increase in the area of lipid droplets in muscle in the mstn-knockdown group (p < 0.05). Nutrient composition analyses of muscle tissue showed that the crude fat content was significantly increased in the mstn-knock-down group (p < 0.05). The contents of saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids were all significantly increased in the mstn-knock-down group (p < 0.05). Comparative transcriptome analyses revealed 2420 significant differentially expressed genes between the mstn-knock-down group and the control group. KEGG analysis indicates that disruptions to fatty acid degradation, glycerolipid metabolism, and the PPAR signaling pathway affect muscle development and lipid metabolism in mstn-knock-down Nile tilapia: acaa2, eci1, and lepr were remarkably up-regulated, and acadvl, lpl, foxo3, myod1, myog, and myf5 were significantly down-regulated (p < 0.05). These results show that knock-down of mstn results in abnormal lipid metabolism, acceleration of skeletal muscle development, and increased adipogenesis and weight gain in Nile tilapia.

Corrigendum: Gut microbes reveal Pseudomonas medicates ingestion preference via protein utilization and cellular homeostasis under feed domestication in freshwater drum, Aplodinotus grunniens.

[This corrects the article DOI: 10.3389/fmicb.2022.861705.].

Vitamin E Ameliorates Impaired Ovarian Development, Oxidative Stress, and Disrupted Lipid Metabolism in Oreochromis niloticus Fed with a Diet Containing Olive Oil Instead of Fish Oil.

Aquaculture feed containing olive oil (OO) instead of fish oil (FO) can cause oxidative stress and impair gonad development in fish. We determined the effect of dietary OO-induced oxidative stress on ovarian development, and explored whether vitamin E (VE) could mitigate negative effects. Female Nile tilapia (Oreochromis niloticus) were fed for 10 weeks with four diets: 5% OO + 70 mg/kg VE, 5% OO + 200 mg/kg VE, 5% FO + 70 mg/kg VE, or 5% FO + 200 mg/kg VE. Dietary OO reduced the specific growth rate and gonadosomatic index, inhibited superoxide dismutase and catalase, delayed ovarian development, decreased serum sex hormone levels, and reduced ovarian triglyceride and n-3 highly unsaturated fatty acid contents. The transcript levels of genes encoding sex hormone receptors (erα, fshr, lhr) and components of the lipid metabolism pathway (pparα, pparγ, hsl, accα, elovl6), the nrf2 signaling pathway (nrf2, keap1), and the nf-κb signaling pathway (nf-κb, tnfα, infγ, il1ß) differed between the 70VE/OO and 70VE/FO groups. Supplementation with 200 mg/kg VE mitigated the adverse effects of OO by improving antioxidant capacity and alleviating inflammation and abnormal lipid metabolism. This may be because VE is an antioxidant and it can regulate the nrf2-nf-κb signaling pathway.

Peroxisome Proliferator-Activated Receptor Signaling-Mediated 13-S-Hydroxyoctadecenoic Acid Is Involved in Lipid Metabolic Disorder and Oxidative Stress in the Liver of Freshwater Drum, Aplodinotus grunniens.

The appropriate level of dietary lipids is essential for the nutrient requirements, rapid growth, and health maintenance of aquatic animals, while excessive dietary lipid intake will lead to lipid deposition and affect fish health. However, the symptoms of excessive lipid deposition in the liver of freshwater drums (Aplodinotus grunniens) remain unclear. In this study, a 4-month rearing experiment feeding with high-fat diets and a 6-week starvation stress experiment were conducted to evaluate the physiological alteration and underlying mechanism associated with lipid deposition in the liver of A. grunniens. From the results, high-fat-diet-induced lipid deposition was associated with increased condition factor (CF), viscerosomatic index (VSI), and hepatosomatic index (HSI). Meanwhile, lipid deposition led to physiological and metabolic disorders, inhibited antioxidant capacity, and exacerbated the burden of lipid metabolism. Lipid deposition promoted fatty acid synthesis but suppressed catabolism. Specifically, the transcriptome and metabolome showed significant enrichment of lipid metabolism and antioxidant pathways. In addition, the interaction analysis suggested that peroxisome proliferator-activated receptor (PPAR)-mediated 13-S-hydroxyoctadecenoic acid (13 (s)-HODE) could serve as the key target in regulating lipid metabolism and oxidative stress during lipid deposition in A. grunniens. Inversely, with a lipid intake restriction experiment, PPARs were confirmed to regulate lipid expenditure and physiological homeostasis in A. grunniens. These results uncover the molecular basis of and provide specific molecular targets for fatty liver control and prevention, which are of great importance for the sustainable development of A. grunniens.

Gap-free genome assembly of anadromous Coilia nasus.

The Chinese tapertail anchovy, Coilia nasus, is a socioeconomically important anadromous fish that migrates from near ocean waters to freshwater to spawn every spring. The analysis of genomic architecture and information of C. nasus were hindered by the previously released versions of reference genomes with gaps. Here, we report the assembly of a chromosome-level gap-free genome of C. nasus by incorporating high-coverage and accurate long-read sequence data with multiple assembly strategies. All 24 chromosomes were assembled without gaps, representing the highest completeness and assembly quality. We assembled the genome with a size of 851.67 Mb and used BUSCO to estimate the completeness of the assembly as 92.5%. Using a combination of de novo prediction, protein homology and RNA-seq annotation, 21,900 genes were functionally annotated, representing 99.68% of the total predicted protein-coding genes. The availability of gap-free reference genomes for C. nasus will provide the opportunity for understanding genome structure and function, and will also lay a solid foundation for further management and conservation of this important species.

Integrated transcriptome and miRNA sequencing analyses reveal that hypoxia stress induces immune and metabolic disorders in gill of genetically improved farmed tilapia (GIFT, Oreochromis niloticus).

The survival and growth of fish are significantly impacted by a hypoxic environment (low dissolved oxygen). In this study, we compared tissue structure, physiological changes, and mRNA/miRNA transcriptome, in gills of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) between the hypoxic group (DO: 0.55 mg/L, HG) and the control group (DO: 5 mg/L, CG). The results showed that the gill filaments in the hypoxic group showed curling, engorgement, and apoptotic cells increased, and that exposure for 96 h resulted in a reduction in the antioxidant capacity. We constructed and sequenced miRNA and mRNA libraries from gill tissues of GIFT at 96 h of hypoxia stress. Between the HG and CG, a total of 14 differentially expressed (DE) miRNAs and 1557 DE genes were obtained. GO and KEGG enrichment showed that DE genes were mainly enriched in immune and metabolic pathways such as natural killer cell mediated cytotoxicity, steroid biosynthesis, primary immunodeficiency, and synthesis and degradation of ketone bodies. Based on the results of mRNA sequencing and screening for miRNA-mRNA pairs, we selected and verified six DE miRNAs and their probable target genes. The sequencing results were consistent with the qRT-PCR validation results. The result showed that under hypoxia stress, the innate immune response was up-regulated, and the adaptive immune response was down-regulated in the gill of GIFT. The synthesis of cholesterol in gill cells is reduced, which is conducive to the absorption of solvent oxygen. These findings offer fresh information about the processes of fish adaptation to hypoxic stress.