Effect of nitrite exposure on the antioxidant enzymes and glutathione system in the liver of bighead carp, Aristichthys nobilis

Influence of High Temperature and Ammonia and Nitrite Accumulation on the Physiological, Structural, and Genetic Aspects of the Biology of Largemouth Bass (Micropterus salmoides)

Hyperthermia and nitrogenous pollutants like ammonia and nitrite are common risk factors that adversely affect fish health and pose significant threats to the aquaculture industry. However, the impacts of high temperatures on the accumulation of nitrogenous pollutants in the water of the aquaculture systems and their toxicity to farmed fish are not well understood. In this study, juvenile largemouth bass (Micropterus salmoides, LMB) were kept at 28 °C and 34 °C in a closed aquatic system to investigate the effects of higher temperatures on ammonia and nitrite accumulation. The fish were fed 2% of their body weight daily for a 14-day experiment. Ammonia levels gradually increased, peaking on day 7 at 34 °C and on day 9 at 28 °C, then decreased to near zero. Nitrite levels remained low initially and increased rapidly along with the reduction in ammonia levels at both temperatures. The 34 °C high temperature accelerated the accumulation of ammonia and its transformation into nitrite compared to 28 °C. Fish were sampled on day 1 (low ammonia and low nitrite, LALN), day 8 (high ammonia and low nitrite, HALN), and day 14 (low ammonia and high nitrite, LAHN) to explore toxic effects. Successive exposure to high levels of ammonia and nitrite caused oxidative stress in the liver and significant pathogenic changes in the liver and spleen, with more pronounced impacts observed at 34 °C. Significant changes in gene expression were detected in the liver and spleen of fish sampled at HALN and LAHN, compared to those at LALN, with upregulated genes primarily associated with extracellular matrix (ECM) and cytoskeleton organization. A second experiment was conducted at the same temperatures but without ammonia/nitrite accumulation. The results of this experiment confirmed the combined effects of hyperthermia and ammonia/nitrite toxicity on the expression of genes involved in ECM-receptor interaction and TGF-beta signaling. These findings are valuable for optimizing cultivation environments and promoting the health of farmed LMB.

Metabolomics-Based Analysis of Adaptive Mechanism of Eleutheronema tetradactylum to Low-Temperature Stress

Temperature is a critical environmental factor that influences the growth, development, metabolism, and overall physiological performance of fish. Eleutheronema tetradactylum is an economically significant fish species; however, its molecular mechanism's response to long-term cold stress is still unclear. In this study, we investigated the physiological responses of the liver in E. tetradactylum exposed to a constant temperature of 18 °C for durations of both 7 and 14 days, utilizing liquid chromatography-mass spectrometry (LC-MS), metabolomics, and conventional biochemical assays. The antioxidant status, liver histology, and metabolite profiles were examined at different time points. Our results revealed that, following sustained cold exposure, the activities of key antioxidant enzymes-superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)-initially increased and then decreased. Additionally, levels of malondialdehyde (MDA), a marker of oxidative damage, significantly elevated after 7 and 14 days of cold stress. Histopathological examination of liver tissues showed varying degrees of vacuolation and nuclear atrophy in hepatocytes, indicating oxidative damage. Metabolomic profiling identified 87 and 116 differentially expressed metabolites in the liver on days 7 and 14, respectively. Pathway enrichment analysis revealed significant alterations in pathways related to carbohydrate digestion and absorption, glutathione metabolism, and glycerolipid metabolism. These findings suggest that mechanisms regulating cell membrane fluidity, energy metabolism, autophagy, and antioxidant defense are crucial for the adaptation of E. tetradactylum to cold stress. Overall, this study provides valuable insights into the molecular and physiological adaptations of E. tetradactylum to low temperature, highlighting the activation of protective antioxidant responses and modifications of metabolic pathways in the liver.

Triflumezopyrim induced oxidative stress, DNA damage and apoptosis on Labeo rohita: Insights from Bioinformatics, Histopathological and Molecular approaches

Triflumezopyrim is a novel mesoionic pesticide used in Asian rice fields to control brown plant hopper, which can reach aquatic environments through drift during application or surface runoff. Thus, this study aimed to investigate the effect of chronic exposure of sub-lethal concentrations of triflumezopyrim (2.468 ppm, 1.480 ppm, and 0.740 ppm) on freshwater carp, Labeo rohita.This study encompassed a multi-pronged approach, including molecular docking studies to elucidate the interactions between triflumezopyrim and selected proteins, an assessment of 8-OHdG (8-hydroxy-2-deoxyguanosine) activity to gauge DNA damage, histopathological examinations to identify cellular alterations, and expression of genes involved in oxidative stress, DNA repair, and apoptosis in L. rohita. We observed dose-dependent responses in 8-OHdG activity and the expression of select genes, with higher concentrations of triflumezopyrim yielding more pronounced transcriptional alterations. Notably, histopathological examinations of liver and brain tissues vividly portrayed the impact of triflumezopyrim on L. rohita. These findings contribute to the assessment of biological toxicity and the environmental footprint left by chemical pollutants such as triflumezopyrim. The study emphasizes the crucial role of monitoring histopathological alterations, 8-OHdG activity and gene expression changes as potential biomarkers for assessing exposures to triflumezopyrim. This research provides valuable insights into the ecological implications of triflumezopyrim in aquatic ecosystems.

Structural characterization and hypoglycemic activity of a polysaccharide from Imperatae Rhizoma

In this study, high-temperature high-pressure ultrasound-assisted extraction method was used to extract polysaccharides from Imperatae Rhizoma (IRP). The yield of IRP was 14.79 ± 0.12 % under the optimal extraction conditions. IRP was purified by a DEAE-52 cellulose column and a Sephadex G-100 chromatography column to obtain two homogeneous fractions: IRP-0 and IRP-1. IRP-1 showed better inhibitory activity than IRP-0 in α-glucosidase inhibition assay. The chemical structure of IRP-1 was further characterized using molecular weight distribution, monosaccharide composition, infrared spectroscopy, methylation analysis, and nuclear magnetic resonance. The results indicated that IRP-1 (29.79 kDa) was a heteropolysaccharide composed of rhamnose, arabinose, galactose, glucose, xylose, mannose, and glucuronic acid, with a molar ratio of 2.48:11.76:20.08:50.92:10.25:2.08:2.12. The backbone of IRP-1 consisted of →6)-β-D-Glcp-(1→, →3,6)-α-D-Galp-(1→, →4)-β-L-Xylp-(1→, and →5)-Araf-(1→. The results of the in vitro hypoglycemic experiments showed that IRP-1 effectively improved glucose consumption and glycogen synthesis, pyruvate kinase (PK), and hexokinase (HK) activities in insulin-resistant HepG2 (IR-HepG2) cells. Additionally, IRP-1 significantly increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and the levels of glutathione (GSH), while reducing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), demonstrating its significant hypoglycemic activity. The findings provide a scientific foundation for the development and utilization of polysaccharides from Imperatae Rhizoma, suggesting their potential application in the treatment of diabetes.

Mitigation of the toxic effects of nitrite: Role and mechanism of isoleucine in mitigating mitochondrial DNA leakage-induced inflammation in grass carp (Ctenopharyngodon idella) under nitrite exposure

The physiological and growth processes of fish are closely associated with their surrounding environment. This study investigated the role and underlying mechanisms of isoleucine (Ile) in alleviating mitochondrial DNA (mtDNA) leakage-induced inflammation in grass carp under nitrite exposure. Grass carp were fed six experimental diets containing different Ile levels (0.00, 3.00, 6.00, 9.00, 12.00 and 15.00 g/kg) for 9 weeks, followed by a 96-hour nitrite exposure trial. Ile supplementation mitigated the deterioration of blood parameters including glutamic oxaloacetic transaminase (GOT), glutamic alanine transaminase (GPT), glucose, cortisol and lactate dehydrogenase (LDH) induced by nitrite exposure. Additionally, Ile enhanced its transport to the liver and mitochondria, as well as increased metabolism of Ile in mitochondria. Histological analyses revealed that Ile mitigated nitrite exposure-induced liver damage and mitochondrial cristae disruption. Furthermore, Ile preserved the mitochondrial cristae homeostasis by upregulating key proteins involved in mitochondrial structure maintenance, while inhibiting mtDNA leakage. Mechanistically, Ile attenuated mtDNA leakage-induced inflammation under nitrite exposure associated with the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-Stimulator of Interferon Genes (STING) and NOD-like receptor thermal protein domain associated protein 3 (NLRP3) pathways. These findings highlight the protective role of Ile in reducing inflammation triggered by environmental nitrite exposure, offering new insights into aquatic toxicology, and determined that Ile concentration of 11.13 g/kg diet could be optimal for mitigating nitrite-induced stress in grass carp, providing a theoretical basis for formulating anti- nitrite stress diets in aquaculture.

Interactions of a PFOS/sodium nitrite mixture in Chinese mitten crab (Eriocheir sinensis): Impacts on survival, growth, behavior, energy metabolism and hepatopancreas transcriptome

Perfluorooctanesulfonic acid (PFOS) and sodium nitrite may have complex adverse effects on aquatic animals. This study assessed the interactive effects of PFOS and sodium nitrite on Chinese mitten crab (Eriocheir sinensis). A 2 × 3 factorial experiment with 0, 0.1, and 5 mg/L PFOS and 0, 3.50 mg/L sodium nitrite evaluated impacts on growth, behavior, oxygen consumption, health, energy metabolism, and hepatopancreas transcriptome. PFOS <0.1 mg/L with 3.50 mg/L nitrite significantly decreased PFOS accumulation in the hepatopancreas and improved feeding rates and hepatopancreas structure (P < 0.05). Under 5 mg/L PFOS and nitrite, survival, weight gain, hepatosomatic index, and feeding rate significantly decreased (P < 0.05). PFOS (0.1 mg/L) with nitrite significantly prolonged righting response time and increased locomotion speed (P < 0.05). PFOS (5 mg/L) significantly decreased serum triglyceride and lactate levels, while PFOS and nitrite decreased glucose, triglyceride, and glycogen levels and increased lactate in hepatopancreas (P < 0.05). Transcriptomic analysis indicated that PFOS affects p53 signaling, cell cycle and neurotransmission pathways, with notable changes in cell proliferation genes (pcna, ccna, cdk1, cdk2, rbx1) primarily downregulated by PFOS. Overall, PFOS disrupts neurotransmitter regulation and causes hepatopancreatic damage, while nitrite can reduce the toxicity of PFOS by decreasing its hepatopancreas accumulation. However, high levels of PFOS combined with sodium nitrite exacerbate toxicity, emphasizing the need for comprehensive assessment of environmental pollutant interactions.

Kidney transcriptome analysis reveals the molecular responses to salinity adaptation in largemouth bass (Micropterus salmoides)

Recently, against the background of increasing land salinization and global warming, many studies have examined the mechanisms of freshwater fish adaptation to elevated salinity. However, the mechanisms underlying salinity tolerance in the kidney of Micropterus salmoides, a popular saline aquaculture species, remain poorly understood. We used RNA-seq to explore the differentially expressed genes (DEGs) in the kidney of M. salmoides at 0 ‰, 5 ‰, and 10 ‰ salinity for 24 d and 48 d. These DEGs mainly affected metabolism-related pathways, such as secondary metabolite biosynthesis, arachidonic acid metabolism, etc., and immunity-related pathways, such as IL-17 signaling and ECM-receptor interaction. Trend analysis on days 24 and 48 showed that, as salinity increased, the up-regulated genes were notably enriched in the cytochrome P450 xenobiotic metabolic pathway, and down-regulated genes substantially linked to cell cycle, phagosome, etc. More importantly, we identified a total of 22 genes enriched in the cytochrome P450 xenobiotic metabolic pathway, including seven UDP-glucuronosyltransferase genes (UGTs) and five glutathione S-transferase genes (GSTs). We speculated that M. salmoides kidneys removed toxic substances produced due to salinity stress and mitigated oxidative damage by up-regulating UGTs and GSTs, hence maintaining normal physiological function. In addition, genes such as Cystatin A1, significantly up-regulated with increasing salinity stress and duration, favoured the recovery of kidney injury. This research delved into the molecular processes involved in the adaptability of M. salmoides to high salinity stress and provided valuable information for the future breeding of salinity-tolerant strains.

Effects of Eucalyptus Essential Oil on Growth, Immunological Indicators, Disease Resistance, Intestinal Morphology and Gut Microbiota in Trachinotus ovatus

Essential oils serve as potential additives that can enhance immune respons and disease resistance and regulate the gut microbiota of fish. Here, this research aims to identify the impacts of eucalyptus essential oil (EEO) on growth, liver antioxidative and immune parameters, resistance to Streptococcus iniae, intestinal morphology and gut microbiota in Trachinotus ovatus. All fish (initial weight: 26.87 ± 0.30 g) were randomly allocated to 12 floating cages (2.0 × 2.0 × 2.0 m3) with each cage containing 100 fish and fed for 30 days. Four diets were manufactured with the supplementation of varying levels of EEO (control and 5.0, 10.0, and 15.0 mL/kg) and were named CG, EEO1, EEO2 and EEO3, respectively. The results showed that EEO1 and EEO2 diets significantly increased WGR, thickness of the intestinal muscle layer, and the ratio of villus height to crypt depth (V/C), while decreasing the intestinal crypt depth of T. ovatus (p < 0.05). Significantly increased activities of SOD and CAT and significantly reduced MDA levels were present in the EEO1 and/or EEO2 groups (p < 0.05). Moreover, the mRNA levels of nrf2, HO-1, GSH-Px, SOD, C4 and GR genes were significantly upregulated and the expression of keap1 and HSP70 genes were significantly downregulated within the EEO1 and EEO2 groups (p < 0.05). After challenge with S. iniae B240703 for 24 h, the bacterial load for five organs in the EEO2 group was less than that in the CG group (p < 0.05). In addition, the fish fed EEO1 and/or EEO2 diets had significantly lower abundances of pathogenic bacteria (Proteobacteria, Planctomycetota, Burkholderia-Caballeronia-Paraburkholderia, Pseudomonas and Blastopirellula) and a higher beneficial bacteria proportion (Firmicutes) than those fed the CG diets (p < 0.05). In conclusion, a moderate dietary m EO level (5.0~10.0 mL/kg) improved the growth and gut morphology, promoted liver immune response, enhanced resistance to S. iniae and modulated the gut microbiota of T. ovatus.

Transcriptomic and physiological analyses reveal the toxic effects of inorganic filters (nZnO and nTiO2) on scleractinian coral Galaxea fascicularis

The effects of sunscreen on scleractinian corals have garnered widespread attention; however, the toxic effects and mechanisms remain unclear. This study investigated the toxicological effects of two common inorganic filters used in sunscreens, nano zinc oxide and titanium dioxide (nZnO and nTiO₂), on the reef-building coral Galaxea fascicularis, focusing on the phenotypic, physiological, and transcriptomic responses. The results showed that after exposure to 0.8 mg/L of nZnO and 30 mg/L of nTiO₂ for 48 h, all coral polyps exhibited retraction. Zn and Ti ions were detected in coral tissues at concentrations of 67.18 and 24.87 μg/g, respectively, indicating the accumulation of nZnO and nTiO2 in coral tissues. The zooxanthellae density, Fv/Fm, and chlorophyll-a content decreased significantly. The activity of antioxidant enzymes showed an increasing trend. Meanwhile, glutamine synthetase and glutamate dehydrogenase activities exhibited a decreasing trend. The health status of corals was impacted as a result of nZnO and nTiO2 stress. Transcriptomic analysis showed that the toxicity mechanisms of nZnO and nTiO2 differed in corals. Following exposure to nZnO, differentially expressed genes (DEGs) in corals were mainly enriched in signaling pathways related to immune response. The genes related to innate immunity, such as MASP1, MUC5AC, TLRs, and C2, were significantly upregulated, indicating that nZnO exposure induces an innate immune response in corals. Meanwhile, following nTiO2 exposure, the upregulated DEGs were mainly enriched in signaling pathways related to transporter activity. In contrast, the downregulated DEGs were mainly enriched in energy metabolism pathways, indicating that nTiO2 disrupted the energy supply of corals, thereby leading to an increased demand for nutrient transport. This study reveals the toxic effects of nZnO and nTiO2, and their mechanisms of action on scleractinian corals, providing a reference for further assessing the toxicity of sunscreen on corals.

Sustained swimming and improvements in anti-oxidative stress responses in matrinxa (Brycon amazonicus) exposed to environmental nitrite

Nitrite is usual in water of intensive rearing systems. Considering its oxidative harmful potential, it was selected to challenge matrinxa Brycon amazonicus reared in sustained swimming (SS) (with flowing water adjusted to speed at 1.0 BL seg-1 (long-duration aerobic metabolic characteristic) and evaluate any beneficial effect of such rearing system to enhance the fish potential to cope with this oxidant stressor in fish farmings. Some parameters of oxidative stress, intermediary metabolism and hematometry were measured in matrinxa adapted to SS and exposed to the highest environmental nitrite concentration allowed by law. The experiments were performed in two steps. At first, fish were adapted to exercise under SS for 90 days. Subsequently, adapted fish were exposed to environmental nitrite (1.0 mg L-1) for 24 h in order to evaluate their physiological responses. The results were compared with fish let in the same environment but from motionless water. Glycogen, glucose, pyruvate, lactate, free amino acids and ammonia were quantified in liver, plasma and muscle. Lipid peroxidation (LPO), glutathione peroxidase (GPx) and catalase (CAT) were assayed in liver and white muscle. Hematometry data were obtained using standard procedures. Sustained swimming practice enhance the hematological capacity of fish, improving oxidative metabolic responses; changing the ability to mobilize carbohydrates for energy purposes; facilitating the energy-dependent detoxification process; and minimizing the mobilization of amino acids for this purpose. In conclusion, the potential of matrinxa adapted to SS to cope with oxidative stress caused by environmental nitrite was enhanced.

Combined transcriptome and metabolome analysis reveals the mechanism of high nitrite tolerance in freshwater mussel Anodonta woodiana

Nitrite contamination and stress on aquatic organisms are increasingly emphasized in freshwater ecosystems. Freshwater bivalves exhibit high tolerance to nitrite; however, the underlying mechanism is unknown. Accordingly, this study investigated the tolerance mechanism of the globally occurring freshwater bivalve Anodonta woodiana. A. woodiana were exposed to nominal concentrations of 0, 250, 500, 1000, 2000, and 4000 mg/L nitrite for 96 h to calculate the 96-h median lethal concentration (96-h LC50). A combined transcriptome and metabolome analysis of the hemolymph (the most vital component of the bivalve immune system) was performed after exposing A. woodiana to 300 mg/L nitrite (approximately half the 96-h LC50) for 96 h. The 96-h LC50 of nitrite in A. woodiana was 618.7 mg/L. Transcriptome analysis identified 5600 differentially expressed genes (DEGs) primarily related to ribosomes, lysosomes, DNA replication, and nucleotide excision repair. Metabolome analysis identified 216 differentially expressed metabolites (DEMs) primarily involved in biosynthesis of amino acids, 2-oxocarboxylic acid metabolism, protein digestion and absorption, aminoacyl-tRNA biosynthesis, nucleotide metabolism, ABC transporters, and valine, leucine and isoleucine degradation. Combined transcriptome and metabolome analysis revealed that DEGs and DEMs were primarily associated with nucleotide (purine and pyrimidine) and amino acid metabolism (including aminoacyl-tRNA biosynthesis, cysteine and methionine metabolism, arginine and proline metabolism, and valine, leucine and isoleucine degradation) as well as the immune system (necroptosis and glutathione metabolism). This study is the first to describe the high tolerance of A. woodiana to nitrite and elucidate the molecular mechanisms underlying high nitrite tolerance in mussels.

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.

Changes in chemical components and hepatoprotective effect of red Panax notoginseng processed by aspartic acid impregnation treatment

BACKGROUND

Red Panax notoginseng (RPN) is one of the major processed products of P. notoginseng (PN), with more effective biological activities. However, the traditional processing method of RPN has some disadvantages, such as low conversion rate of ginsenosides and long processing time.

RESULTS

In this work, we developed a green, safe, and efficient approach for RPN processing by aspartic acid impregnation pretreatment. Our results showed that the optimized temperature, steaming time, and concentration of aspartic acid were 120 °C, 1 h, and 3% respectively. The original ginsenosides in PN treated by aspartic acid (Asp-PN) were completely converted to rare saponins at 120 °C within just 1 h. The concentration of the rare ginsenosides in Asp-PN was two times higher than that in untreated RPN. In addition, we examined the protective effect of RPN and Asp-PN on acetaminophen-induced liver injury in a mouse model. The results showed that Asp-PN has significantly more potent hepatoprotective action than the RPN. The hepatoprotection of Asp-PN in acetaminophen-induced hepatotoxicity may be due to its anti-oxidative stress, anti-apoptotic, and anti-inflammatory activities.

CONCLUSION

These results indicated that aspartic acid impregnation pretreatment may provide an effective method to shorten the steaming time, improve the conversion rate of ginsenosides, and enhance hepatoprotective activity of RPN. © 2024 Society of Chemical Industry.

Exploring the novel benefits of leucine: Protecting nitrite-induced liver damage in sub-adult grass carp (Ctenopharyngodon idella) through regulating mitochondria quality control

Leucine is an essential amino acid for fish. The ability of leucine to resist stress in fish has not been reported. Nitrite is a common pollutant in the aquatic environment. Therefore, we investigated the effects of dietary leucine on growth performance and nitrite-induced liver damage, mitochondrial dysfunction, autophagy, and apoptosis for sub-adult grass carp. A total of 450 grass carp (615.91 ± 1.15 g) were selected and randomly placed into 18 net cages. The leucine contents of the six diets were 2.91, 5.90, 8.92, 11.91, 14.93, and 17.92 g/kg, respectively. After a 9-week feeding trial, the nitrite exposure experiment was set up for 96 h. These results indicated that dietary leucine significantly promoted FW, WG, PWG, and SGR of sub-adult grass carp (P < 0.05). Appropriate levels of dietary leucine (11.91-17.92 g/kg) decreased the activities of serum parameters (glucose, cortisol, and methemoglobin contents, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and lactate dehydrogenase), the contents of reactive oxygen species (ROS), nitric oxide (NO) and peroxynitrite (ONOO-). In addition, appropriate levels of dietary leucine (11.91-17.92 g/kg) increased the mRNA levels of mitochondrial biogenesis genes (PGC-1α, Nrf1/2, TFAM), fusion-related genes (Opa1, Mfn1/2) (P < 0.05), and decreased the mRNA levels of caspase 3, caspase 8, caspase 9, fission-related gene (Drp1), mitophagy-related genes (Pink1, Parkin) and autophagy-related genes (Beclin1, Ulk1, Atg5, Atg7, Atg12) (P < 0.05). Appropriate levels of dietary leucine (8.92-17.92 g/kg) also increased the protein levels of AMP-activated protein kinase (AMPK), prostacyclin (p62) and decreased the protein levels of protein light chain 3 (LC3), E3 ubiquitin ligase (Parkin), and Cytochrome c (Cytc). Appropriate levels of leucine (8.92-17.92 g/kg) could promote growth performance and alleviate nitrite-induced mitochondrial dysfunction, autophagy, apoptosis for sub-adult grass carp. Based on quadratic regression analysis of PWG and serum GPT activity, dietary leucine requirements of sub-adult grass carp were recommended to be 12.47 g/kg diet and 12.55 g/kg diet, respectively.

Integrated histological, physiological, and transcriptome analysis reveals the post-exposure recovery mechanism of nitrite in Litopenaeus vannamei

Nitrite is one of the most common toxic pollutants in intensive aquaculture and is harmful to aquatic animals. Recovery mechanisms post exposure to nitrite in shrimp have rarely been investigated. This study focuses on the effect of nitrite exposure and post-exposure recovery on the histological and physiological aspects of Litopenaeus vannamei and utilizes transcriptome sequencing to analyze the molecular mechanisms of adaptation to nitrite exposure. The results showed that histopathological damage to the hepatopancreas and gills caused by short-term nitrite exposure resolved with recovery. The total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) of shrimp were significantly reduced during nitrite exposure and returned to the control level after recovery, malondialdehyde (MDA) levels were opposite to them. Restoration of the antioxidant system after exposure mitigated oxidative damage. Nitrite exposure results in reduced activity of the immuno-enzymes acid phosphatase (ACP) and alkaline phosphatase (AKP), which can be recovered to the control level. L. vannamei can adapt to nitrite exposure by regulating Na+/K+-ATPase (NKA) activity. Transcriptome analysis revealed that activation of glutathione metabolism and peroxisomal pathways facilitated the mitigation of oxidative damage in L. vannamei during the recovery period. Excessive oxidative damage activates the apoptosis and p53 pathways. Additionally, Sestrin2 and STEAP4 may have a positive effect on recovery in shrimp. These results provide evidence for the damage caused by nitrite exposure and the recovery ability of L. vannamei. This study can complement the knowledge of the mechanisms of adaptation and recovery of shrimp under nitrite exposure.

Aquatic assessment of the chelating ability of Silica-stabilized magnetite nanocomposite to lead nitrate toxicity with emphasis to their impact on hepatorenal, oxidative stress, genotoxicity, histopathological, and bioaccumulation parameters in Oreochromis niloticus and Clarias gariepinus

BACKGROUND

In recent years, anthropogenic activities have released heavy metals and polluted the aquatic environment. This study investigated the ability of the silica-stabilized magnetite (Si-M) nanocomposite materials to dispose of lead nitrate (Pb(NO3)2) toxicity in Nile tilapia and African catfish.

RESULTS

Preliminary toxicity tests were conducted and determined the median lethal concentration (LC50) of lead nitrate (Pb(NO3)2) to Nile tilapia and African catfish to be 5 mg/l. The sublethal concentration, equivalent to 1/20 of the 96-hour LC50 Pb(NO3)2, was selected for our experiment. Fish of each species were divided into four duplicated groups. The first group served as the control negative group, while the second group (Pb group) was exposed to 0.25 mg/l Pb(NO3)2 (1/20 of the 96-hour LC50). The third group (Si-MNPs) was exposed to silica-stabilized magnetite nanoparticles at a concentration of 1 mg/l, and the fourth group (Pb + Si-MNPs) was exposed simultaneously to Pb(NO3)2 and Si-MNPs at the same concentrations as the second and third groups. Throughout the experimental period, no mortalities or abnormal clinical observations were recorded in any of the treated groups, except for melanosis and abnormal nervous behavior observed in some fish in the Pb group. After three weeks of sublethal exposure, we analyzed hepatorenal indices, oxidative stress parameters, and genotoxicity. Values of alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), urea, and creatinine were significantly higher in the Pb-intoxicated groups compared to the control and Pb + Si-MNPs groups in both fish species. Oxidative stress parameters showed a significant decrease in reduced glutathione (GSH) concentration, along with a significant increase in malondialdehyde (MDA) and protein carbonyl content (PCC) concentrations, as well as DNA fragmentation percentage in the Pb group. However, these values were nearly restored to control levels in the Pb + Si-MNPs groups. High lead accumulation was observed in the liver and gills of the Pb group, with the least accumulation in the muscles of tilapia and catfish in the Pb + Si-MNPs group. Histopathological analysis of tissue samples from Pb-exposed groups of tilapia and catfish revealed brain vacuolation, gill fusion, hyperplasia, and marked hepatocellular and renal necrosis, contrasting with Pb + Si-MNP group, which appeared to have an apparently normal tissue structure.

CONCLUSIONS

Our results demonstrate that Si-MNPs are safe and effective aqueous additives in reducing the toxic effects of Pb (NO3)2 on fish tissue through the lead-chelating ability of Si-MNPs in water before being absorbed by fish.

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.

Effects of Dietary Fish Meal Replaced by Fish Steak Meal on Growth Performance, Antioxidant Capacity, Intestinal Health and Microflora, Inflammatory Response, and Protein Metabolism of Large Yellow Croaker Larimichthys crocea

Although fish steak meal (FSM) is a potentially available protein source, its efficiency as a fish meal (FM) substitute remains unclear to date. To this end, this study was carried out to determine the effects of dietary FM replaced by FSM on growth performance, antioxidant capacity, intestinal health and microflora, inflammatory response, and protein metabolism of large yellow croaker. Five isolipidic and isonitrogenous diets were formulated by substituting FM with FSM at levels of 0% (FSM0, control diet), 25% (FSM25), 50% (FSM50), 75% (FSM75), and 100% (FSM100), and were fed to juvenile large yellow croaker for 8 weeks. Compared with the control diet, the replacement of 25% dietary FM with FSM did not markedly alter the weight gain (WG) and specific growth rate (SGR). When the FM substitution level was over 25%, WG and SGR markedly reduced. The intestinal structure observation found that the FSM75 and FSM100 diets markedly decreased villus height, villus width, and muscle thickness of the anterior intestine. The FSM75 and FSM100 diets significantly decreased enzyme activities of amylase (AMS), lipase (LPS), trypsin, catalase (CAT), and total superoxide dismutase (T-SOD) and the total antioxidant capacity (T-AOC), and increased the malondialdehyde (MDA) content in the liver of large yellow croaker. The mRNA expression levels of intestinal barrier and inflammatory response-related genes suggested that the FSM50, FSM75, and FSM100 diets significantly decreased the mRNA abundances of intestinal barrier-related genes and anti-inflammatory response-related genes, and increased the mRNA abundances of proinflammatory gene il-6 in the anterior intestine. The compositions of intestinal microflora displayed that the FSM50, FSM75, and FSM100 diets decreased relative abundances of Firmicutes phylum and increased relative abundances of Proteobacteria phylum. In addition, the results of protein expression levels showed that the phosphorylation level of mammalian target of rapamycin (mTOR) and 4E-binding protein 1 (4E-BP1) in FSM75 and FSM100 groups were markedly reduced. In conclusion, FSM can replace up to 25% dietary FM without compromising the growth performance, intestinal health, and protein metabolism of the large yellow croaker.

A Mitochondrial Nanoguard Modulates Redox Homeostasis and Bioenergy Metabolism in Diabetic Peripheral Neuropathy

As a major late complication of diabetes, diabetic peripheral neuropathy (DPN) is the primary reason for amputation. Nevertheless, there are no wonder drugs available. Regulating dysfunctional mitochondria is a key therapeutic target for DPN. Resveratrol (RSV) is widely proven to guard mitochondria, yet the unsatisfactory bioavailability restricts its clinical application. Tetrahedral framework nucleic acids (tFNAs) are promising carriers due to their excellent cell entrance efficiency, biological safety, and structure editability. Here, RSV was intercalated into tFNAs to form the tFNAs-RSV complexes. tFNAs-RSV achieved enhanced stability, bioavailability, and biocompatibility compared with tFNAs and RSV alone. With its treatment, reactive oxygen species (ROS) production was minimized and reductases were activated in an in vitro model of DPN. Besides, respiratory function and adenosine triphosphate (ATP) production were enhanced. tFNAs-RSV also exhibited favorable therapeutic effects on sensory dysfunction, neurovascular deterioration, demyelination, and neuroapoptosis in DPN mice. Metabolomics analysis revealed that redox regulation and energy metabolism were two principal mechanisms that were impacted during the process. Comprehensive inspections indicated that tFNAs-RSV inhibited nitrosation and oxidation and activated reductase and respiratory chain. In sum, tFNAs-RSV served as a mitochondrial nanoguard (mito-guard), representing a viable drilling target for clinical drug development of DPN.

Comparative Transcriptomic Analysis of Largemouth Bass (Micropterus salmoides) Livers Reveals Response Mechanisms to High Temperatures

High temperatures are considered one of the most significant limitations to subtropical fishery production. Largemouth bass (Micropterus salmoides) is an economically important freshwater species grown in subtropical areas, which are extremely sensitive to heat stress (HS). However, comprehensive transcriptomic data for the livers of largemouth bass in response to HS are still lacking. In this study, a comparative transcriptomic analysis was performed to investigate the gene expression profiles of the livers of largemouth bass under HS treatment. As a result, 6114 significantly differentially expressed genes (DEGs), which included 2645 up-regulated and 3469 down-regulated genes, were identified in response to HS. Bioinformatics analyses demonstrated that the 'ECM-receptor interaction' pathway was one of the most dramatically changed pathways in response to HS, and eight DEGs assigned to this pathway were taken as hub genes. Furthermore, the expression of these eight hub genes was determined by quantitative reverse transcription PCR, and all of them showed a significant change at the transcriptional level, suggesting a crucial role of the 'ECM-receptor interaction' pathway in the response of largemouth bass to HS. These findings may improve our understanding of the molecular mechanisms underlying the response of largemouth bass to HS.

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.

Fatty acid metabolism and antioxidant capacity in Gymnocypris przewalskii (Kessler, 1876) response to thermal stress

The Qinghai-Tibet Plateau is undergoing a wet-warming transition, which could affect the survival of the native fish. However, the tolerance and physiological response to thermal stress is rarely studied in Gymnocypris przewalskii, a rare native fish in the Tibetan plateau. In this study, first, we detected the thermal tolerance of five groups of six-month G. przewalskii which acclimated at 8, 12, 16, 20, and 24 °C for two weeks, respectively, by critical thermal methodology. Then, through heat challenge, we detected the metabolites, key enzyme activities, and gene expressions involved in metabolism and antioxidant in the hepatopancreas when the temperatures increased from 16 °C to 18, 20, 22, 24, 26, and 28 °C for 12 h, respectively. The results showed that although the fish are sensitive to high temperatures, the quick acclimation at mild high temperatures could significantly improve the tolerance to acute high-temperature stress in juvenile G. przewalskii. During the heat challenge study, blood glucose significantly increased at heat stress (P < 0.05). At the same time, total cholesterol (TC), triglyceride (TG), and free fatty acid (FFA) significantly decreased when the temperature rose continuously to 20 °C. Metabolic enzyme activities of carnitine palmityl transferase I (CPT-Ⅰ), acetyl-CoA carboxylase (ACC), and fatty acid synthase (FAS) significantly decreased at 20 °C (P < 0.05). Superoxide dismutase (SOD) and antioxidant capacity (T-AOC) significantly increased at 20 °C (P < 0.05). The relative transcript levels of genes involved in antioxidant and glycolysis/gluconeogenesis were markedly higher than the control at 20-26 °C (P < 0.05). The genes involved in fatty acid biosynthesis or metabolism showed different expression patterns under heat stress. Heat shock protein 70 (Hsp70) and Hsp90 were significantly higher than the control at 18 °C and 26 °C, respectively. These results confirmed the prediction that G. przewalskii is sensitive to high temperatures, so conservation efforts should pay more attention to the warming damage.

Glutathione reductase, a biomarker of pollutant and stress in Pacific abalone

Abalone are frequently exposed to several environmental factors including heavy metal toxicity, thermal stress, H2O2-stress, starvation, viral and bacterial infection that can induce oxidative stress. Glutathione reductase is a vital enzyme in the antioxidant defense system that catalyzes the reduction of oxidized glutathione to reduced glutathione. The present study aimed to identify and localize glutathione reductase in Pacific abalone (Hdh-GR) and assess its potential role in stress physiology, heavy metal toxicity, immune response, gonadal development, and metamorphosis. The mRNA expression of Hdh-GR was upregulated in response to thermal stress, starvation, H2O2-stress, and cadmium-exposed toxicity. The induced mRNA expression was also quantified in immune-challenged abalone. Moreover, the Hdh-GR expression was significantly higher during metamorphosis. The Hdh-GR mRNA expression showed an inverse relationship with ROS production in heat stressed Pacific abalone. These results suggest that Hdh-GR has central role in the stress physiology, immune response, gonadal development, and metamorphosis of Pacific abalone.

Apoptotic Changes, Oxidative Stress and Immunomodulatory Effects in the Liver of Japanese Seabass (Lateolabrax japonicus) Induced by Ammonia-Nitrogen Stress during Keep-Live Transport

This study investigated the effects of NH₃-N on antioxidant responses, histoarchitecture, and immunity of Japanese seabass (Lateolabrax japonicus) during keep-live transport. The findings suggest that NH₃-N stress transport alters the transcription of P53, Caspase 9, Bcl2, Caspase 3 and Bax genes, demonstrating that NH₃-N stress can trigger the apoptotic pathway of P53-Bax-Bcl2 and Caspase and induce apoptosis. NH₃-N stress transport also evoked transcriptional upregulation of inflammatory cytokines (tumor necrosis factor α (TNF-α), Toll-like receptor 3 (TLR-3), nuclear factor kappa β (NF-κB), interleukin 6 (IL-6) and interleukin 1β (IL-1β)) and increased complement C3, C4, lysozyme (LZM) and immunoglobulin (IgM) levels, activating the innate immunological system during keep-live transport. In addition, NH₃-N stress transport altered changes in the levels of superoxide dismutase (SOD), catalase (CAT), glutathione-related enzymes, and heat shock proteins 70 and 90 in the liver, indicating that the antioxidant system and Hsp protected the cells from NH₃-N-induced oxidative stress. When excess ROS were not removed, they caused the body to respond with immunological and inflammatory responses, as well as apoptosis and tissue damage. This helps towards understanding the effect of NH₃-N levels on sea bass during keep-live transport.

Glutathione S-transferase gene diversity and their regulation by Nrf2 in Chinese mitten crab (Eriocheir sinensis) during nitrite stress

Eriocheir sinensis is one of the most important economic aquatic products in China. However, nitrite pollution has become a serious threat to the healthy culture of E. sinensis. Glutathione S-transferase (GST) is an important phase II detoxification enzyme, which plays a leading role in the cellular detoxification of exogenous substances. In this study, we obtained 15 GST genes (designated as EsGST1-15) from E. sinensis, and their expression and regulation in E. sinensis under nitrite stress were studied. EsGST1-15 belonged to different GST subclasses. EsGST1, EsGST2, EsGST3, EsGST4, and EsGST5 belonged to Delta-class GSTs; EsGST6 and EsGST7 are Theta-class GSTs; EsGST8 is a mGST-3-class GST; EsGST9 belonged to mGST-1-class GSTs; EsGST10 and EsGST11 belonged to Sigma-class GSTs; EsGST12, EsGST13, and EsGST14 are Mu-class GSTs; EsGST15 is a Kappa-class GST. Tissue distribution experiments showed that EsGSTs were widely distributed in all detected tissues. The expression level of EsGST1-15 was significantly increased in the hepatopancreas under nitrite stress, indicating that EsGSTs were involved in the detoxification of E. sinensis under nitrite stress. Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a transcription factor that can activate the expression of detoxification enzyme. We detected the expression of EsGST1-15 after interfering with EsNrf2 in the hepatopancreas of E. sinensis with or without nitrite stress. Results showed that EsGST1-15 were all regulated by EsNrf2 with or without nitrite stress. Our study provides new information about the diversity, expression, and regulation of GSTs in E. sinensis under nitrite stress.

Identification of Nrf2/Keap1 pathway and its transcriptional regulation of antioxidant genes after exposure to microcystins in freshwater mussel Cristaria plicata

Microcystins (MC) are one of the most abundant and widely distributed cyanotoxins in aquatic systems. MC inhibits the functions of protein phosphatase 1 and 2A (PP1/2A), which can seriously affect ecosystem integrity. The NF-E2-related nuclear factor 2 (Nrf2)/Kelch-like epichlorohydrin-related protein-1 (Keap1) signaling pathway protects against oxidative damage by activating phase II detoxification/antioxidant enzymes. Our previous study revealed that MC upregulates the expression and enhances the activities of the antioxidant enzymes by stimulating the CpNrf2 signaling pathway. In the current study, to further clarify the regulatory role of Keap1 in response to MC-induced oxidative stress in shellfish, we cloned the full-length cDNA of Keap1a and Keap1b from Cristaria plicata (designated CpKeap1a and CpKeap1b), which are 2952 and 3710 bp peptides, respectively. The amino acid sequence of CpKeap1a and CpKeap1b contained Tram-track and Bric-a-brac (BTB), Intervening region (IVR), and Double glycine repeat (DGR) domain. Additionally, CpKeap1a contained two cysteine residues analogous to Cys-273 and -288 in zebrafish, but CpKeap1b did not. Moreover, CpKeap1a and -1b formed a homodimer and heterodimer, respectively, and also formed a heterodimer with CpNrf2. In the hepatopancreas, the expression levels of CpKeap1a and -1b were the highest, but MC treatment down-regulated the expression of these proteins. Moreover, the transcription of antioxidant enzymes with antioxidant response element (ARE-driven enzymes), including CpMnSOD, CpCu/ZnSOD, CpTRX, CpPrx, CpSe-GPx, and Cpsigma-GST was upregulated by CpNrf2 in the hepatopancreas. Compared with the MC-induced group, CpKeap1a-siRNA1117 injection significantly increased the transcription of mRNAs for ARE-driven enzymes and Nrf2. CpKeap1a-siRNA1117 also enhanced the activities of antioxidation enzymes. These findings demonstrated that Keap1a negatively regulated the expression of Nrf2 protein and MC-induced oxidative stress response in C. plicata. Therefore, we speculated that CpKeap1a promoted CpNrf2 by recognizing and binding MC. These events then protected molluscs from MC-induced oxidative damage.

The effects of sustained and diel-cycling hypoxia on high-latitude fish Phoxinus lagowskii

High-latitude fish are subjected to sustained and diel-cycling hypoxia. Oxygen deficiency could pose a serious threat to fish, but little information is available regarding the response mechanisms employed by high-latitude fish to sustained and diel-cycling hypoxia. In this study, a combination of transcriptomics and metabolomics were used to examine the molecular response mechanisms actioned by sustained and diel-cycling hypoxia in the high-latitude fish, Phoxinus lagowskii. P. lagowskii was divided into normoxic control (6.0-7.0 mg/L dissolved oxygen), sustained (1.5 mg/L dissolved oxygen), and diel-cycling hypoxic treatment (6.0-7.0 mg/L between 07:00-21:00, and 3.0-4.0 mg/L between 21:00-07:00) tanks for 28 days. Differentially expressed genes (DEGs) and significantly different metabolites (DMs) related to digestive proteases, lipid metabolism, estrogen signaling pathway, steroid hormone biosynthesis, glutathione metabolism, and tryptophan metabolism were identified from comparative metabolomic and transcriptomic data expression profiles within the liver. The current study found that P. lagowskii had significantly different responses between sustained and diel-cycling hypoxia. P. lagowskii faced with sustained hypoxia may enhance their tolerance capacity through phospholipid and glutathione metabolism. Our data provide new insights into the high latitude fish coping with changes in hypoxia and warrants further investigation into these potentially important genes and metabolites.

Environmental concentrations of benzophenone-3 disturbed lipid metabolism in the liver of clown anemonefish (Amphiprion ocellaris)

Benzophenone-3 (BP-3) often used as a UV filter in various products and an endocrine disruptor. In this work, we exposed the clown anemonefish to 10 μg/L and 50 μg/L BP-3 for 7 and 14 days. Liver histological, biochemical analysis, and transcriptome sequencing were used to explore the mechanism of the lipid metabolism disorder in the liver of three-month-old clown anemonefish treated with BP-3. The histological and biochemical analysis showed that BP-3 induces morphological changes and lipid droplet accumulation, and the lipid content, lipase, and antioxidant enzyme activity were abnormal. After treatment with 10 μg/L and 50 μg/L BP-3 for 7 days, the transcriptome analysis further demonstrated that the KEGG analysis revealed that the differentially expressed genes (DEGs) were mainly associated with fat digestion and absorption, PPAR signaling pathway, circadian rhythm, and mineral absorption pathways; After 10 μg/L and 50 μg/L of BP-3 exposure for 14 days, the KEGG analysis were mainly associated with circadian rhythm, circadian rhythm-fly, protein processing in the endoplasmic reticulum, and beta-alanine metabolism pathways. Several key genes were involved in the process of liver lipid metabolism, including CD36, APoA-Ⅰ, FABP, LPL, ACS, and PEPCK. The qRT-PCR validation results showed that eight genes (CYP8B1, FABP1, LPL, MGAT, PEPCK, PER1, PSMB4, PSME2) were significantly down-regulated, and the other two genes (Fbxl3, RXR) were significantly up-regulated after 7 days of BP-3 exposure. Similarly, eleven genes (AMPK, ARNTL, Bmal1, CASP3, CYC, CYP2J, CYP2U1, GSK3A, PEPCK, RAC1, RORA) were significantly up-regulated, and the other four genes (NR1D1, PER1, PTGDS, HLF) were significantly down-regulated after 14 days of BP-3 exposure. In conclusion, our results elucidate the physiological and molecular responses to BP-3 exposure in the liver lipid metabolism of clown anemonefish, and these findings reveal that the regulation of lipid metabolism is disturbed when clown anemonefish is exposed to UV filters.

Depletion of chop suppresses procedural apoptosis and enhances innate immunity in loach Misgurnus anguillicaudatus under ammonia nitrogen stress

Ammonia nitrogen is highly toxic to fish, and it can easily cause fish poisoning or even high mortality. So far, many studies have been conducted on the damages to fish under ammonia nitrogen stress. However, there are few studies of ammonia tolerance improvement in fish. In this study, the effects of ammonia nitrogen exposure on apoptosis, endoplasmic reticulum (ER) stress, and immune cells in loach Misgurnus anguillicaudatus were investigated. Loaches (60 d post fertilization) were exposed to different concentrations of NH4Cl, and their survival rates were examined every 6 h. The results showed that high-concentration and long-time NH4Cl exposure (20 mM + 18 h; 15 mM + 36 h) induced apoptosis and gill tissue damages, finally causing a decline in survival. chop plays an important role in ER stress-induced apoptosis, and thus we constructed a model of chop-depleted loach by using CRISPR/Cas9 technology to investigate its response to ammonia nitrogen stress. The results showed that ammonia nitrogen stress down-regulated the expressions of apoptosis-related genes in chop+/- loach gills, while wildtype (WT) exhibited an opposite gene expression regulation pattern, suggesting that the depletion of chop suppressed apoptosis level. In addition, chop+/- loach showed a larger number of immunity-related cells and higher survival rate than WT under the NH4Cl exposure, indicating that the inhibition of chop function strengthened the innate immune barrier in general, thus increasing survival. Our findings provide the theoretical basis for developing high ammonia nitrogen-tolerant germplasm with aquaculture potential.

Screening of new Paenibacillus polymyxa S3 and its disease resistance of grass carp (Ctenopharyngodon idellus)

A new strain of Paenibacillus polymyxa S3 with antagonistic effects on 11 major fish pathogens (especially Aeromonas hydrophila), but had no toxicity to grass carp, was screened from the sediment of fishponds. In vivo colonization studies showed that strain S3 could be colonized and distributed in the gill and abdomen of the grass carp. Bioassay results showed that the weight growth rate of grass carp in the strain S3 oral group (16.01%) and strain S3 immersion group (16.44%) was significantly higher than those of the control group (8.61%). At the same time, the activities of ACP, AKP, CAT and GSH-Px in the serum of grass carp in oral and immersion groups were significantly higher than those of the control group. In addition, the treatment with strain S3 could significantly upregulate the expression of the antioxidant-related genes and immune-related genes Keap1, Nrf2, C3, LZM, IgM, TLR-4 and MyD-88 in grass carp tissues. The challenge test showed that strain S3 treatment significantly increased the survival rate of grass carp infected with Aeromonas hydrophila. Whole genome sequencing analysis showed that strain S3 had 16 active metabolite gene clusters, indicating that it had abundant gene resources, which provided important support for its development for fish microecological preparations. In summary, a new strain of Paenibacillus polymyxa S3 with antibacterial activity against a variety of fish pathogens was screened in this study and its probiotic function was evaluated, proving its potential value in fisheries.

Effect of dietary phenylalanine on growth performance and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) in low fishmeal diets

This study aimed to investigate the effects of phenylalanine on the growth, digestive capacity, antioxidant capability, and intestinal health of triploid rainbow trout (Oncorhynchus mykiss) fed a low fish meal diet (15%). Five isonitrogenous and isoenergetic diets with different dietary phenylalanine levels (1.82, 2.03, 2.29, 2.64, and 3.01%) were fed to triplicate groups of 20 fish (initial mean body weight of 36.76 ± 3.13 g). The weight gain rate and specific growth rate were significantly lower (p < 0.05) in the 3.01% group. The trypsin activity in the 2.03% group was significantly higher than that in the control group (p < 0.05). Amylase activity peaked in the 2.64% treatment group. Serum superoxide dismutase, catalase, and lysozyme had the highest values in the 2.03% treatment group. Liver superoxide dismutase and catalase reached their maximum values in the 2.03% treatment group, and lysozyme had the highest value in the 2.29% treatment group. Malondialdehyde levels in both the liver and serum were at their lowest in the 2.29% treatment group. Interleukin factors IL-1β and IL-6 both reached a minimum in the 2.03% group and were significantly lower than in the control group, while IL-10 reached a maximum in the 2.03% group (p < 0.05). The tight junction protein-related genes occludin, claudin-1, and ZO-1 all attained their highest levels in the 2.03% treatment group and were significantly higher compared to the control group (p < 0.05). The intestinal villi length and muscle layer thickness were also improved in the 2.03% group (p < 0.05). In conclusion, dietary phenylalanine effectively improved the growth, digestion, absorption capacity, antioxidant capacity, and intestinal health of O. mykiss. Using a quadratic curve model analysis based on WGR, the dietary phenylalanine requirement of triploid O. mykiss fed a low fish meal diet (15%) was 2.13%.

Dietary ferulic acid supplementation improved cottonseed meal-based diet utilization by enhancing intestinal physical barrier function and liver antioxidant capacity in grass carp (Ctenopharyngodon Idellus)

The present study explored the effects of ferulic acid (FA) supplementation in cottonseed meal (CSM)-based diets on grass carp growth performance, feed utilization, liver antioxidation status, and intestinal physical barrier function. Here, four experimental diets supplemented with FA at graded levels (0, 50, 100 and 200 mg/kg) and CSM as the main protein source (384.6 g/kg feed) for an 8-week feeding trial. Our results indicated that 200 mg/kg FA supplementation in a CSM-based diet significantly improved growth performance [including final body weight (FBW), weight gain rate, and specific growth rate] and feed utilization [including feed conversion ratio and protein efficiency ratio] in grass carp (p &lt; 0.05). The results of polynomial regression analysis based on FBW recommended that the optimal dose for FA supplementation was 204 mg/kg. Compared with that no FA supplementation, 200 mg/kg FA supplementation significantly reduced liver malondialdehyde levels and increased glutathione reductase activities (p &lt; 0.05) and 100 mg/kg FA supplementation significantly increased liver total superoxide dismutase activities and reduced blood alanine transaminase levels (p &lt; 0.05). Compared with the control group, 100 mg/kg FA supplementation also led to significantly increased mRNA expression of zo-1, zo-2, occludin, claudin-b, claudin-3, claudin-7a, and claudin-12, encoding intestinal tight junction proteins (p &lt; 0.05). Notably, FA supplementation could reduce lipid deposition by regulating bile acid (BA) secretion. In this study, 100 and 200 mg/kg FA supplementation significantly increased blood and liver total BA levels, respectively (p &lt; 0.05); 100 mg/kg FA also significantly activated mRNA expressions of fxr and cyp7a1 (p &lt; 0.05). Furthermore, the whole-body composition results presented that FA treatment relieved lipid deposition, particularly 50 and 200 mg/kg FA supplementation (p &lt; 0.05). Moreover, triglyceride and total cholesterol levels were significantly lower and high-density lipoprotein levels were significantly higher with 200 mg/kg FA supplementation than with no FA supplementation (p &lt; 0.05). Taken together, the results indicated that FA may be a beneficial feed additive to boost fish growth performance and increase CSM utilization.

Protective Effect of Selenium on the Oxidative Damage of Kidney Cells Induced by Sodium Nitrite in Grass Carp (Ctenopharyngodon idellus)

The present study was conducted to investigate the protective effects of selenium on the oxidative damage of kidney cells (CIK) caused by nitrite exposure in grass carp (Ctenopharyngodon idella). Cells were pre-incubated by Na₂SeO₃ (10 μmol/L) for 12 h and then exposed to NaNO₂ (25 mg/L) for 24 h, the cell viability, apoptosis, gene expression, and antioxidant enzyme activity were assayed. The results show that nitrite reduced cell viability and induced apoptosis, and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) as well as the sod, cat, and gpx genes reduced (p < 0.05), while the intracellular calcium ion concentration increased (p < 0.05). Interestingly, selenium treatment significantly alleviated the nitrite induced changes in cell growth, apoptosis, and calcium influx. The cell viability after low-concentration selenium treatment is higher than that of normal cells (p < 0.05). CIK cells were pre-incubated with Na₂SeO₃ and then exposed to NaNO₂, the antioxidant indicators could be maintained at normal levels. And compared with nitrite exposure, intracellular calcium ion concentration and apoptotic rate of selenium-incubated still decreased. The expressions of Nrf2 and Keap1 genes increased significantly in CIK cells treated with sodium selenite for 12 h, and the same trend as the enzyme activities of this group. The results show that the supplement of selenium can enhance the cell's resistance to sodium nitrite exposure to a certain extent, by alleviating the antioxidant imbalance, high apoptosis rate, and intracellular calcium ion disturbance caused by nitrite exposure. And the Nrf2-Keap1 pathway may play an important role in the process.

Analysis of Acute Nitrite Exposure on Physiological Stress Response, Oxidative Stress, Gill Tissue Morphology and Immune Response of Large Yellow Croaker (Larimichthys crocea)

Nitrite is a common pollutant in aquaculture water, and nitrite toxicity that negatively affects aquatic species is common in aquaculture systems when the water quality is low. Therefore, the present research aimed to evaluate the effect of acute nitrite exposure on the hematological parameters, antioxidant enzymes, immune response, and gill morphology of large yellow croaker (Larimichthys crocea). The fish were randomly separated and exposed to four (i.e., 0, 29.36, 58.73, and 88.09 mg/L) nitrite concentrations for 48 h. The fish blood and gills were collected at 0, 12, 24, 36, and 48 h of nitrite exposure for further analysis. In hematological parameters, the results showed that the levels of hemoglobin, triglyceride, and total cholesterol in blood significantly decreased (p < 0.05) in all nitrite-treated samples after 12 h, while the contents of methemoglobin in blood significantly increased (p < 0.05) in these treatments. After 48 h of nitrite exposure, the levels of cortisol in serum showed a 94.5%, 132.1%, and 165.6% increase in fish exposed to 29.36, 58.73, and 88.09 mg/L nitrite, respectively. The nitrite (i.e., 29.36, 58.73, and 88.09 mg/L) exposure significantly increased (p < 0.05) the levels of antioxidant enzymes (i.e., catalase and glutathione) in the gill and serum after 12 h of exposure compared with the control. The lysozyme levels in serum decreased in the nitrite (i.e., 29.36, 58.73, and 88.09 mg/L) exposure samples. It was found that immunoglobulin levels in the 29.36, 58.73, and 88.09 mg/L nitrite-treated samples (i.e., 1.86, 1.58, and 0.74 μg/mL, respectively) were lower than that of the control (2.56 μg/mL). In addition, the surface of the gill lamellae displayed deformation and contraction after 48 h of nitrite, especially in the fish exposed to 88.09 mg/L nitrite. These results indicate that the nitrite exposure induced the oxidative stress, affected the immune response, and changed the gill morphology, leading to nitrite poisoning in large yellow croaker.

Acute Nitrite Exposure Induces Dysfunction and Oxidative Damage in Grass Carp Isolated Hemocytes

To evaluate the effects of nitrite on the oxidative damage of blood cells of Grass Carp Ctenopharyngodon idella, the isolated hemocytes were exposed to nitrite (0, 1, 10, or 100 mg/L) for up to 24 h. Hemoglobin (Hb) and methemoglobin (MetHb) concentrations, reactive oxygen species (ROS) and malondialdehyde (MDA) levels, mitochondrial membrane potential (∆Ψm), and antioxidant enzyme activity were assayed to assess hematological parameters and the antioxidant defense mechanism. Results showed a remarkable decrease in Hb concentration with increasing nitrite concentration after a 24-h exposure, while the MetHb concentration increased significantly in nitrite exposure groups. The levels of ROS, ∆Ψm, and MDA increased to varying degrees with increases in nitrite exposure concentration and time. The total antioxidant capacity, catalase (CAT) activity, glutathione peroxidase (GPx) activity, and glutathione content showed a trend of rising initially and then decreasing with prolonged exposure time. Superoxide dismutase (SOD) activity was higher in the 1-mg/L nitrite exposure group and lower in the 100-mg/L group than in the control. The relative messenger RNA expression ratios of cat, sod1, and gpx were up-regulated significantly in the 1- and 10-mg/L groups and then declined in the 100-mg/L group. Therefore, it can be concluded that nitrite exposure activates the antioxidant defense mechanism of Grass Carp hemocytes and that the balance of oxidant-antioxidant homeostasis will be undermined by higher nitrite doses or longer exposure periods.

The intestinal histopathology, innate immune response and antioxidant capacity of blunt snout bream (Megalobrama amblycephala) in response to Aeromonas hydrophila

The present study was performed to determine the effects of Aeromonas hydrophila infection on intestinal -histopathology, innate immune response and changes in antioxidant capacity of blunt snout bream (Megalobrama amblycephala). A series of histopathological changes, innate immune enzyme activities, antioxidant enzyme activities, and the corresponding mRNA relative genes expressions in intestines were measured at 0, 1, 2, and 3 weeks post-treatment of Aeromonas hydrophila (1✕10⁷ CFU mL^-1) infection. The results showed that Aeromonas hydrophila induced changes in intestinal morphology, including the decreased muscularis thickness, the proliferated goblet cells, and the atrophied intestine villi height. Moreover, the innate immune enzymes activities in serum such as acid phosphatase, alkaline phosphatase, lysozyme activities and immunoglobulin M were significantly reduced after infection at 1week, 2week and 3week. The contents of complement 3 and complement 4 were significantly decreased after infection as well. In addition, the antioxidant enzymes activities, including superoxide dismutase, catalase and glutathione peroxidase in the experimental groups were significantly decreased compared with the control group, whereas the content of malondialdehyde was significantly increased after infection at 1week, 2week and 3week. Furthermore, the mRNA relative expressions of the inflammatory cytokines such as tumor necrosis factor-α, interleukins-1β, interferon-γ, and interleukins-6 were significantly increased after infection with Aeromonas hydrophila. The TJ-related gene expressions in the intestine of zonula occluden-1, occludin, occludin-1, occludin-2 were significantly reduced throughout the infection period. The mRNA relative expressions of signal transducers and activators of transcription 4 and janus kinase-3 in the intestine were significantly ascended compared with the non-infected group. Overall, the results elucidated that the intestine tissue injury and innate immune response reduction, as well as antioxidant capacity attenuation were occurred against Aeromonas hydrophila infection of the blunt snout bream.

Effects of Nitrite Exposure on the Hematological Properties, Antioxidant and Stress Responses of Juvenile Hybrid Groupers, Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀

Nitrite concentrations can reach high levels in indoor aquaculture systems, thus it is vital to determine the nitrite tolerance of aquaculture fish species. Here, juvenile hybrid groupers (Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀, Family: Serranidae) were exposed to waterborne nitrite at 0, 10, 20, 40, and 80 mg NO₂⁻/L for 2 weeks. Nitrite exposure caused significant reductions in hematocrit and hemoglobin levels, significant increases in plasma calcium and plasma ALP levels, but had no significant effects on magnesium and total protein levels. Of the antioxidant responses investigated, SOD activity increased significantly in the liver and gills, but GST activity and GSH levels were significantly inhibited by nitrite exposure. Stress indicators, such as plasma cortisol and HSP 70 levels, were significantly stimulated by nitrite exposure. In brief, nitrite exposure over 20 mg NO₂⁻/L had toxic effects and affected the hematological properties, antioxidant responses, and stress indicators of juvenile hybrid groupers.

Nitrite Stress Induces Oxidative Stress and Leads to Muscle Quality Decreased in Wuchang Bream (Megalobrama amblycephala Yih) Juveniles

To determine the effects of nitrite exposure on muscle quality and physiological functions in Wuchang bream (Megalobrama amblycephala), we exposed M. amblycephala juveniles to acute nitrite (0, 1, 5, 10, 20 mg/L), and the muscle and blood samples were measured at 12, 24, 48, and 96 h. The results showed that when exposed to nitrite for 12 h, the concentrations of blood glucose, cortisol, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in the 20 mg/L experimental group had the maximum value. The activity of lactate dehydrogenase (LDH) increased significantly in a dose-dependently manner and peaked at 96 h in the 20 mg/L group. During 96 h of exposure to nitrite, the total antioxidant capacity (T-AOC) and catalase (CAT) activity in the liver of the 20 mg/L experimental group were significantly higher than those of the control group, while the concentration of muscle glycogen showed a downtrend. At 12 h and 96 h, the hardness of the four experimental groups were significantly higher than that of the control group. Our research shows that acute sodium nitrite exposure will not only cause oxidative stress and decreased muscle quality in M. amblycephala juveniles but also will be accompanied by changes in serum biochemical index, liver antioxidant capacity, muscle physiological characteristics, and muscle physical characteristics. Preliminary speculation may be that acute nitrite exposure may cause M. amblycephala juveniles to choose to reduce muscle quality and activate antioxidant systems.

Biomarkers of Exposure and Effect in Nile Tilapia (Oreochromis niloticus) Environmentally Exposed to Multiple Stressors in Egypt

Chemical pollution poses adverse effects on aquatic organisms, including altered gene expression. This study, therefore, investigated the hepatic expression of biomarkers of exposure and effect in Oreochromis niloticus inhabiting the drainage canal of a sugarbeet factory (an industrially polluted habitat) and the Nile River (a reference habitat). Compared to the Nile River, the drainage canal contained significantly elevated levels of heavy metals (Cd, Fe, Mn, Co, and Pb), nitrate, ammonia, nitrite, chemical oxygen demand, and biological oxygen demand. The liver of O. niloticus from the drainage canal accumulated significantly higher concentrations of the heavy metals. O. niloticus from the drainage canal had significantly higher hepatic expressions of genes related to oxidative stress (GSTa, GPx, and NRF2), metal toxicity (MT), endocrine disruption (Vtg), and hypoxia (HIF1a) and a significantly lower hepatic expression of the apoptosis-associated CAS gene. CYP1A (a detoxification biomarker) expression did not exhibit significant differences. These results provide insights into complex adaptive responses of O. niloticus to multiple chemicals and support the utilization of molecular biomarkers as warning signals for water pollution.

Heavy metal toxicity in Buriganga river alters the immunology of Nile tilapia (Oreochromis niloticus L)

The objective of the current study was to evaluate the biochemical and immunological responses of tilapia, Oreochromis niloticus due to heavy metals pollution. Histomorphological alterations in the liver and kidney suggested tissue damages due to this polluted water exposure. The brain acetylcholinesterase (AChE) as an indicator of neurotoxicity was significantly (P < 0.01) decreased after 10 days exposure of fish to heavy metal contained river water, while plasma glutamate oxalacetate transaminase and plasma glutamate pyruvate transaminase were significantly increased (P < 0.01). Moreover, superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase enzyme activities, as well as reduced glutathione and malondialdehyde levels were significantly increased in heavy metals contained river water treated fish compared to the control. Additionally, glucose level and blood serum Ca2+ concentrations were significantly (P < 0.01) decreased in fish exposed to heavy metal contained river water compared to the control. Hematological indices such as Hemoglobin, RBC, WBC, MCV etc. of polluted river water treated fish were significantly (P < 0.01) different in comparison to that of control fish. The cytokines i.e. IL-1β, IL-6, and TNF-α level were significantly (P < 0.01) increased in the fish exposed to heavy metals contained river water in comparison to that of control fish. The present findings explored the detrimental effects of heavy metal contained river water on fish at biochemical and immunological levels.

Updating the use of biochemical biomarkers in fish for the evaluation of alterations produced by pharmaceutical products

The evaluation of toxic effects in stressful environmental conditions can be determined through the imbalance between exogenous factors (environmental contaminants) and enzymatic and non-enzymatic defenses in biological systems. The use of fish for the identification of alterations in biochemical biomarkers provides a comprehensive vision of the effects that pharmaceutical products cause in the aquatic ecosystem, as they are organisms with high sensitivity to contaminants, filtering capacity, and potential for environmental toxicology studies. A wide range of pharmaceuticals can stimulate or alter a variety of biochemical mechanisms, such as oxidative damage to membrane lipids, proteins, and changes in antioxidant enzymes. This review includes a summary of knowledge of the last 20 years, in the understanding of the different biochemical biomarkers generated by exposure to pharmaceuticals in fish, which include different categories of pharmaceutical products: NSAIDs, analgesics, antibiotics, anticonvulsants, antidepressants, hormones, lipid regulators and mixtures. This review serves as a tool in the design of studies for the evaluation of the effects of pharmaceutical products, taking into account the most useful biomarkers, type of matrix, enzyme alterations, all taking the pharmaceutical group of interest.

Genome-wide identification and expression profiling of glutathione S-transferase family under hypoxia stress in silver sillago (Sillago sihama)

Glutathione S-transferase (GST) is an important detoxification enzyme in organisms. GSTs play an important role in responding to environmental stresses. This study aimed to identify the GST gene superfamily in silver sillago (Sillago sihama) and analyze its expression pattern under hypoxia stress. A total of 17 GST genes were identified in silver sillago. Phylogenetic analysis showed that the GST gene family contained two subgroups (cytosolic and MAPEGs), and lacked three subgroups (i.e. Pi, Kappa, and MGST2). Phylogenetic and syntenic analysis revealed that GST genes were conserved in evolution. Eight SsGSTs were significantly differentially expressed under hypoxia stress in silver sillago by RNA-seq and qRT-PCR analysis. The expression levels of SsMGST3b, SsGSTO1, SsGSTT1b and SsGSTR2 genes were significantly up-regulated after 4 h of reoxygenation in the gill tissue. In the heart tissue, the expression of SsGSTR3 was significantly up-regulated after 1 h of hypoxia while the expression levels of SsGSTT1b and SsFLAP genes were significantly down-regulated after 4 h of hypoxia. In summary, this study provides for the first time a comprehensive analysis of the GST gene superfamily of silver sillago.

Effect of cell-permeable grouper Manganese Superoxide Dismutase on environmental stress in fish

Nitrite levels are generally high in high-density aquaculture. Nitrite is a potential stress-inducing factor and can cause oxidative stress because excessive reactive oxygen species (ROS) formation through nitrite induction cannot be scavenged by the endogenous antioxidant system, thus leading to cell damage or death. Manganese Superoxide Dismutase (MnSOD) is a highly efficient endogenous ROS scavenger that quenches mitochondrial ROS and protective against oxidative stress. To enhance the efficiency of MnSOD in removing ROS and reducing oxidative caused by nitrite, in this study, we cloned grouper MnSOD (gMnSOD) fused with a cell-penetrating peptide, TAT, to construct a TAT-gMnSOD fusion protein and assessed its potential to eliminate excess ROS induced by high nitrite concentrations and enhance the resistance of zebrafish to environmental stressors. Our results revealed that TAT-gMnSOD penetrated the grouper fin (GF-1) cells, scavenged nitrite-induced intracellular ROS, and enhanced cell viability on NaNO₂ treatment. Furthermore, pretreatment of zebrafish with TAT-gMnSOD fusion protein reduced the MDA content and increased the survival rate. In addition, the TAT-gMnSOD fusion protein reduced 2-phenoxyethanol toxicity and attenuated excessive anesthesia among zebrafish. In conlusion, our cell-permeable TAT-gMnSOD fusion protein effectively counters oxidative stress, prevents environmental stress-induced damage, and increases aquaculture benefits.

Physiological and transcriptional analysis of Chinese soft-shelled turtle (Pelodiscus sinensis) in response to acute nitrite stress

Nitrite is a harmful substance in aquaculture, and has a serious impact on the survival of the Chinese soft-shelled turtle, Pelodiscus sinensis. However, the cellular responses of P. sinensis to nitrite stress have not yet been investigated. The present study showed that nitrite led to a decrease in hemoglobin content and an increase in methemoglobin content in the blood, thus reducing the oxygen-carrying capacity of blood in P. sinensis. Nitrite also affects the antioxidant system of the liver and leads to lipid peroxidation. In addition, nitrite caused immune responses, including a decrease in lysozyme content and an increase in total complement activity, interleukin-6, and heme oxygenase concentrations in the serum. Additionally, the terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay showed that apoptosis occurred in liver cells. Finally, a comparative transcriptome analysis was conducted. A total of 573 differentially expressed genes and 15 significantly enriched KEGG pathways were identified. Among them, the glutathione S-transferase omega 1 (GSTO1) gene may relieve nitrite-induced oxidative damage in P. sinensis by participating in a variety of redox-related pathways, while the PPAR signaling pathway has been proposed to play an important regulatory role in lipid metabolism and immune responses. The present study comprehensively explored the cellular responses of P. sinensis to nitrite stress and provided guidance for future studies.

Alleviative effects of total flavones of Glycyrrhiza uralensis Fisch on oxidative stress and lipid metabolism disorder induced by high-fat diet in intestines of Tilapia (Oreochromis niloticus)

Total flavones of Glycyrrhiza uralensis Fisch (GTF) are main components of Glycyrrhiza uralensis Fisch, which have anti-oxidation and lipid-lowering effects. However, its protective effects on the intestinal tissue of tilapia (Oreochromis niloticus) are unknown. The aims of the study were to evaluate the protective effects of GTF on the intestinal tissue of tilapia after high-fat diet (HFD) feeding. Tilapia (initial weight 30 ± 1 g) received diets containing four doses of GTF (0.05, 0.1, 0.5, and 1.0 g/kg diet) for 90 days. The intestinal tissues were collected to determine biochemical parameter, gene expression and protein level. The results showed that the HFD reduced antioxidant indexes and increased the fat level, lipid oxidation products in the intestinal tissue relative to the control. Adding GTF to the HFD resulted in an increase of antioxidant indexes, fat level and lipid oxidation products decreased after 60, 90 days. In the HFD group, mRNA level of fatty acid transport protein 1 (FATP1) was increased at 60 day and then decreased at 90 day. The mRNA levels of fatty acid binding protein 1 (FABP1) and sterol regulatory element binding protein 1c (SREBP 1c) were significantly increased at 60 or 90 day after HFD feeding. The mRNA levels of acetate coenzyme A carboxylase (ACCA) peroxisome proliferator-activated receptor γ (PPAR-γ) and PPAR-α were decreased significantly at 30, 60 and/or 90 days after HFD feeding. Western blotting results also showed that nuclear factor (NF)-κβ C-Rel (NF-κβ C-Rel) and mitogen-activated protein kinase 8 (MAPK8) protein expression in intestinal tissue increased after consumption of the HFD. However, adding GTF to the HFD reversed the changes of genes related to fatty acid synthesis and metabolism, and the level of NF-κβ c-Rel and MAPK8 at different degrees. Overall, these results indicated that GTF promoted decomposition and metabolism of fatty acids in intestinal tissue, alleviated oxidative stress damage caused by the HFD, and had certain protective effects on the intestinal tissue of tilapia.

Which Is More Toxic? Evaluation of the Short-Term Toxic Effects of Chlorpyrifos and Cypermethrin on Selected Biomarkers in Common Carp (Cyprinus carpio, Linnaeus 1758)

The general aim of this study was to investigate the negative short-term effects of different concentrations of chlorpyrifos (CPF) and cypermethrin (CYP), based on the EU legislation (MAC-EQS) in common carp (Cyprinus carpio Linnaeus, 1758) under laboratory conditions and to compare their toxicity. The fish were exposed to the pesticides for 96 h and then different histological and biochemical biomarkers were investigated in the gills and liver, and bioaccumulation analyses were conducted. The chemical studies showed increased pesticide concentrations in the gills as the first site for pollutants compared to the liver at the 96th hour. In addition, the histological analyses showed severe alterations in the gills and liver after exposure to both tested pesticides. In the gills, we found mainly intense proliferative and, to a lesser extent, degenerative changes and alterations in the circulatory system, such as necrosis and vasodilation. In the liver, regressive and progressive lesions, as well as circulatory disturbances and inflammation, were observed. The regressive lesions showed a higher degree of expression compared to the other changes. Furthermore, we found altered enzymatic activities—catalase, glutathione reductase, and glutathione peroxidase—in the liver, compared to the control. Overall, both tested pesticides impacted the studied biomarkers in common carp, even at concentrations lower than those permitted by law. However, the results of the comparative analysis showed a relatively higher toxicity of CYP compared to CPF in the fish. Still, questions persist as to whether the observed changes are adaptive or entirely destructive. To avoid any danger or risk, these pesticides must be applied cautiously, especially near water bodies.

Delivery of selenium using chitosan nanoparticles: Synthesis, characterization, and antioxidant and growth effects in Nile tilapia (Orechromis niloticus)

This study aimed to elucidate the effects of selenium-loaded chitosan nanoparticles used as a dietary supplement on Nile tilapia (Oreochromis niloticus) antioxidant and growth responses. First, chitosan-based nanoparticles containing selenium (Se) were synthesized using the ionotropic gelation method and their physicochemical characteristics, controlled release profile, and antioxidant activity properties were investigated. Thereafter, the effects on glutathione peroxidase and antioxidant activities (by radical scavenging activity), growth, and whole-body composition of Nile tilapia were evaluated when they were fed with Se-loaded chitosan nanoparticles and compared with other selenium dietary supplements. Se-loaded chitosan nanoparticles showed high entrapment efficiency (87%), spherical shape, smooth surface, and broad size distribution. The controlled release of Se consisted of an initial burst followed by a gradual release over 48 h. Se-loaded nanoparticles presented significantly higher antioxidant activity compared to free Se. A 60-day feeding trial was conducted to compare the effects of supplementing different dietary Se sources, including selenomethionine (as organic source), sodium selenite (as inorganic source), and Se-loaded chitosan nanoparticles (Se-Nano and Se-Nano x1.5) on antioxidant and growth responses of Nile tilapia. A basal diet without Se supplementation was used as the control. The dietary supplementations with different Se sources (free and encapsulated selenium) lead to significant improvements in final weight and feed efficiency of Nile tilapia fingerlings. However, dietary treatments did not affect whole-body protein and lipid content. Diets containing Se-Nano and Se-Nano x1.5 were more effective than sodium selenite and selenomethionine in preventing oxidative stress and improving antioxidant activity in Nile tilapia. Overall, Se-loaded nanoparticles presented a great potential as an efficient source for delivering dietary Se to Nile tilapia, directly affecting the growth performance, feed efficiency, oxidative stress, and antioxidant activity of this species.

Molecular cloning and functional characterization of the hypoxia-inducible factor-1α in bighead carp (Aristichthys nobilis)

HIF-l is the earliest documented and most widely studied hypoxia-inducible factor (HIF) and plays a key role in the cell hypoxia signal transduction pathway. Particularly, the HIF-1α protein is sensitive to oxygen and plays a critical role in hypoxia regulation. This study is the first to report on the molecular cloning and characterization of HIF-1α in bighead carp (Aristichthys nobilis; anHIF-1α). The full-length cDNA of anHIF-1α was 2361 bp, and encodes an estimated 674 amino acids with a predicted molecular mass of 76.10 kDa and a theoretical isoelectric point of 7.72. Moreover, the conserved basic Helix-Loop-Helix domain along with two Per-ARNT-Sim domains (A/B), and C-TAD were identified in this protein. Interestingly, the tertiary structure of the anHIF-1α protein was found to be extremely similar to that of mice. Multiple comparison and phylogenetic tree results demonstrated that anHIF-1α was highly conserved. Under normoxic conditions, anHIF-1α mRNA transcripts could be detected in all tissues examined with the highest expression level in the heart. With gradually decreasing oxygen concentrations, anHIF-1α mRNA level was upregulated significantly in the gill, liver, kidney, spleen, intestine, brain, and muscle tissues (P < 0.05). Similarly, anHIF-1α was expressed in all examined bighead carp tissues, and the results suggested that the upregulation of anHIF-1α at the transcriptional level may be an important stress response adaptation to hypoxia in bighead carp. Finally, based on the tertiary structure comparative analyses between anHIF-1α with mouse HIF-1α, we think the physiological function, and protein structure of HIF-1α could be compared between fish and mammal in the future.

Effects of Nrf2-Keap1 signaling pathway on antioxidant defense system and oxidative damage in the clams Ruditapes philippinarum exposure to PAHs

NF-E2-related factor 2 (Nrf2) is a master regulator of antioxidant defense system which can maintain the oxidation balance in the cell. In our previous study, we first cloned the Nrf2 gene in clams and preliminarily explored the role of the Nrf2 at the transcription level. In this study, RNA interference (RNAi) technology was used to interfere with the expression of Nrf2 after being exposed to benzo(a)pyrene (BaP) for 5 days to verify the role of Nrf2 in the antioxidant defense system. Besides, we examined the mRNA expression and enzyme activities of antioxidases and the oxidative damage. The positive correlations between the Nrf2 with the mRNA expression and the enzyme activities of antioxidases indicated that Nrf2 was required for the induction of these antioxidant genes. Additionally, the mRNA expression and the enzyme activities of the glutathione peroxidase (GPx) in the Nrf2-dsRNA group were significantly higher than those in the control groups on the fifth day, indicating that the GPx is more sensitive to oxidative stress. Moreover, the oxidative damage in the RpNrf2-dsRNA group was markedly increased than control groups, indicating that Nrf2 transcriptional regulation may play an essential role in defending against oxidative damage. This study provides a foundation for further research on the mechanism of detoxification and antioxidation of polycyclic aromatic hydrocarbons (PAHs) in the clams at the transcription level and the protein level.

Effect of nitrite exposure on haematological status, oxidative stress, immune response and apoptosis in yellow catfish (Pelteobagrus fulvidraco)

Nitrite can cause fishes poisoning. This study evaluated the effects of nitrite exposure on haematological status, ion concentration, antioxidant enzyme activity, immune response, cytokine release and apoptosis in yellow catfish. In this study, yellow catfish were exposed to three levels of nitrite (0, 3.00 and 30.00 mg L^-1) for 96 h. The results showed that nitrite poisoning could lead to blood deterioration (red blood cell and hemoglobin reduced; white blood cell and methemoglobin elevated), ion imbalance (Na⁺ and Cl^- declined; K⁺ elevated), oxidative stress (total antioxidant capacity, superoxide dismutase, catalase and glutathione peroxidase activities declined; malondialdehyde accumulation), immunosuppression (lysozyme activity, 50% hemolytic complement, immunoglobulin M, respiratory burst and phagocytic index declined) and cytokines release (TNF, IL 1 and IL 8 elevated). In addition, nitrite poisoning could induce up-regulation of antioxidant enzymes (Cu/Zn-SOD, Mn-SOD, CAT and GPx), cytokines (TNF, IL 1 and IL 8) and apoptosis (P53, Bax, Cytochrome c, Caspase 3, Caspase 9, ERK and JNK) genes transcription. This study suggesting that the nitrite exposure triggers blood deterioration, disrupts the ionic homeostasis, induces oxidative stress, immunosuppression, inflammation and apoptosis in yellow catfish.