Blunt Snout Bream Research Articles

Comparative expression analysis of let-7 microRNAs during ovary development in Megalobrama amblycephala.

As a critical regulator of gene expression, let-7 family miRNAs have been reported to be involved in multiple physiological processes. In this study, in order to elucidate the putative regulatory effect of let-7 miRNAs during fish gonadal development and to identify which member is crucial for this regulation, the expression of ten members including let-7a/b/c/d/e/f/g/h/i/j were quantified in ovary, pituitary, and brain tissues during the different ovarian developmental stages of blunt snout bream Megalobrama amblycephala. According to the data from analysis of expression patterns, let-7a showed the highest expression value in almost all the tested ovaries, pituitaries, and brains, with let-7b and let-7d moderately expressed, following by other let-7 miRNAs. In terms of the differential expression levels of ten let-7 miRNAs at each developmental stage, the results showed that let-7a/b/d/f/h expression gradually increased during the ovary development from stage I to V and dropped significantly at the phase VI in ovary tissues. However, the expression of let-7a/b/e/f in pituitary increased during the ovary development from stage I to IV and declined at stage V. Among all the let-7 miRNAs, let-7a/b/d had the highest expression and their expression patterns were consistent with the gonad development of M. amblycephala. Furthermore, the mostly predicted target genes of let-7 miRNAs are significantly enriched in signaling pathways closely related to gonadal development through KEGG enrichment analysis. These results indicate that let-7 miRNA members, especially let-7a/b/d, may play important roles in the regulation of ovary development in M. amblycephala through negatively regulating expression of their target genes.

Molecular and functional characterization of sirt4 and sirt6 in Megalobrama amblycephala under high glucose metabolism

We analyzed the sequences of sirt4 and sirt6 and their changes in expression after oral glucose administration in blunt snout bream (Megalobrama amblycephala). We cloned sirt4 and sirt6 and found that their full-length cDNA sequences were 1530 bp and 1723 bp, respectively; their amino acid sequences were 93% and 92% identical to Danio rerio. Megalobrama amblycephala were fed a high glucose solution (3 g/kg). Normally, sirt4 expression is higher in spleen, intestine, and gill (P < .05), and sirt6 expression is higher in intestine and gill (P < .05). After oral glucose administration, sirt4 and sirt6 expression increased in liver and gill, and sirt4 expression increased in intestine at 0.5 h (P < .05). In contrast, sirt4 in kidney and sirt6 in head kidney were downregulated at 1 h (P < .05). Expression of sirt4 was upregulated in brain, head kidney, spleen, muscle, and liver 2 h, 4 h, 4 h/24 h, 8 h, and 24 h, respectively (P < .05). Expression of sirt4 was downregulated in kidney at 8 h-48 h (P < .05). Expression of sirt6 was upregulated in intestine, liver, muscle, kidney, and spleen at 4 h/24 h, 8 h/24 h, 12 h, 12 h, and 24 h, respectively (P < .05). We report that sirt4 and sirt6 are highly conserved in evolution and exhibit tissue-specific expression profiles. We demonstrate that the expression of sirt4 and sirt6 are tissue-specific, and depend upon tissue-specific responses to glucose metabolism.

Novel insights into the immune regulatory effects of ferritins from blunt snout bream, Megalobrama amblycephala

Ferritins play vital roles in maintenance of iron homeostasis as iron storage proteins. Recently, the immune function of ferritins have attracted increasing attention, especially their roles in defense against pathogenic infections. However, the immune regulatory mechanism of fish ferritins are not well known. In the present study, comparative digital gene expression (DGE) profiling was performed to explore the regulatory effects of the Megalobrama amblycephala ferritins (MamFers) using MamFers overexpressed and control L8824 cells (Ctenopharyngodon idella hepatic cell line). Clean reads were aligned to the C. idella genome and differential expression analysis was conducted with representative differentially expressed genes pointed out. On that basis, further studies were performed to verify two pivotal regulated pathways in L8824 and EPC (Epithelioma Papulosum Cyprini cell line) cells, respectively. The results showed that NLRC5 (NOD-like Receptor Family CARD Domain Containing 5) mediated the regulation of MamFers on expression of MHC I (Major Histocompatibility Complex Class I) and its chaperone β2M (Beta-2-Microglobulin) in L8824 cells. Then, β2M further mediated the regulation of MamFers on hepcidin expression, indicating that MamFers regulated the expression of hepcidin via NLRC5/MHC I/β2M axis. In addition, MamFers regulated the adhesion of Aeromonas hydrophila to EPC cells by regulating the expression of two extracellular matrix proteins Intgβ1 (integrin β1) and FN (fibronectin). In a word, the present study provided novel insights into the immune regulatory functions of fish ferritins.

Gene expression patterns indicate that a high-fat-high-carbohydrate diet causes mitochondrial dysfunction in fish.

Expensive and unsustainable fishmeal is increasingly being replaced with cheaper lipids and carbohydrates as sources of energy in aquaculture. Although it is known that the excess of lipids and carbohydrates has negative effects on nutrient utilization, growth, metabolic homeostasis, and health of fish, our current understanding of mechanisms behind these effects is limited. To improve the understanding of diet-induced metabolic disorders (both in fish and other vertebrates), we conducted an eight-week high-fat-high-carbohydrate diet feeding trial on blunt snout bream (Megalobrama amblycephala), and studied gene expression changes (transcriptome and qPCR) in the liver. Disproportionately large numbers of differentially expressed genes were associated with mitochondrial metabolism, neurodegenerative diseases (Alzheimer's, Huntington's, and Parkinson's), and functional categories indicative of liver dysfunction. A high-fat-high-carbohydrate diet may have caused mitochondrial dysfunction, and possibly downregulated the mitochondrial biogenesis in the liver. While the relationship between diet and neurodegenerative disorders is well-established in mammals, this is the first report of this connection in fish. We propose that fishes should be further explored as a potentially promising model to study the mechanisms of diet-associated neurodegenerative disorders in humans.

Molecular Characterization of Peroxisome Proliferator-Activated Receptor-Gamma Coactivator-1α (PGC1α) and Its Role in Mitochondrial Biogenesis in Blunt Snout Bream (Megalobrama amblycephala).

PGC1α is a transcriptional coactivator that plays key roles in mitochondrial biogenesis, so exploring its molecular characterization contributes to the understanding of mitochondrial function in cultured fish. In the present study, a full-length cDNA coding PGC1α was cloned from the liver of blunt snout bream (Megalobrama amblycephala) which covered 3741 bp with an open reading frame of 2646 bp encoding 881 amino acids. Sequence alignment and phylogenetic analysis revealed high conservation with other fish species, as well as other higher vertebrates. Comparison of the derived amino acid sequences indicates that, as with other fish, there is a proline at position 176 (RIRP) compared to a Thr in the mammalian sequences (RIRT). To investigate PGC1α function, three in vitro tests were carried out using primary hepatocytes of blunt snout bream. The effect of AMPK activity on the expression of PGC1α was determined by the culture of the hepatocytes with an activator (Metformin) or inhibitor (Compound C) of AMPK. Neither AMPK activation nor inhibition altered PGC1α expression. Knockdown of PGC1α expression in hepatocytes using small interfering RNA (si-RNA) was used to determine the role of PGC1α in mitochondrial biogenesis. No significant differences in the expression of NRF1 and TFAM, and mtDNA copy number were found between control and si-RNA groups. Also, hepatocytes were cultured with oleic acid, and the findings showed the significant reduction of mtDNA copy number in oleic acid group compared to control. Moreover, oleic acid down-regulated the expression of NRF1 and TFAM genes, while PGC1α expression remained unchanged. Our findings support the proposal that PGC1α may not play a role in mitochondrial biogenesis in blunt snout bream hepatocytes.

Complete Genome Sequence of Highly Virulent Aeromonas hydrophila Strain D4, Isolated from a Diseased Blunt-Snout Bream in China.

Aeromonas hydrophila is the causative agent of motile aeromonad septicemia. Here, we present the complete genome sequence of highly virulent A. hydrophila strain D4, which was isolated from a diseased blunt-snout bream in China. It comprises one circular chromosome and four previously unreported plasmids with a total length of 5,275,132 bp.

The effects of crowding stress on the growth, physiological response, and gene expression of the Nrf2-Keap1 signaling pathway in blunt snout bream (Megalobrama amblycephala) reared under in-pond raceway conditions

We evaluated the effects of high density stress on growth performance, antioxidant parameters, and Nrf2 pathway signaling molecules after different lengths of exposure (30, 60, or 90 days) of Megalobrama amblycephala to in-pond raceway aquaculture systems (IPRS). M. amblycephala (average initial weight 2.33 ± 0.15 g) were reared at two different initial densities (low density group [LD] had 534 fish/m3 and high density group [HD] had 1073 fish/m3) for 90 days. The growth performance was adversely influenced by the high stocking density. The HD group had elevated white blood cell counts, hemoglobin content, and hematocrit on days 60 and 90. The mRNA levels of NOX2 on days 60 and 90, Nrf2 on days 30, 60, and 90, Keap1 on day 30, Bach1 on days 30 and 60, SOD on day 30, and CAT on day 30 were significantly higher in the HD group than in the LD group. Similarly, higher trends were observed in the enzymatic activities of SOD on day 60, CAT on days 60 and 90, and GPx on day 60 in the HD group, compared to the LD group. Furthermore, HD bream showed an increased MDA content on days 60 and 90 compared to that of the LD group. This study demonstrates that high density-induced antioxidant defenses were involved in modifications to the enzymatic and transcriptional regulation of Nrf2-Keap1 signaling molecules and that M. amblycephala growth was reduced in a crowded IPRS.

Intelectin mediated phagocytosis and killing activity of macrophages in blunt snout bream (Megalobrama amblycephala)

Intelectin, a lectin discovered recently, has been identified in various vertebrate species, such as fish, amphibians, and mammals. In one of our previous studies, the efficient bacteria binding and agglutinating activity of the recombinant Megalobrama amblycephala intelectin protein (rMamINTL) and the enhanced immunopositive localization have been observed in the hepatic macrophage-like cells (kupffer cells) post Aeromonas hydrophila infection. Thus, the present study primarily focuses on the regulatory effects of rMamINTL on M. amblycephala macrophages. This study revealed a prominent LPS-binding activity of rMamINTL and a significantly increased phagocytosis of rMamINTL-treated A. hydrophila by M. amblycephala macrophages. However, the rMamINTL-treated M. amblycephala macrophages exhibited no evident regulatory effect on phagocytosis, whereas the enhanced killing activity of the rMamINTL-treated macrophages was observed, which may be attributed to the induced respiratory burst activity and the expression of inflammatory cytokines. In addition, the anti-proliferation effect of rMamINTL on two tumor cells was observed. However, its mechanism remains to be further studied. In short, these results show that MamINTL is a multifunctional immune protein with effective immunomodulatory activity.

Dietary betaine reduces liver lipid accumulation via improvement of bile acid and trimethylamine-N-oxide metabolism in blunt-snout bream.

Dietary betaine supplementation notably ameliorated fatty liver disease caused by high dietary carbohydrate. We hypothesised that the mechanism behind this is the alteration of bile acid and trimethylamine-N-oxide (TMAO) metabolism. We further explored this mechanism by supplementing betaine (1%) to the diet of a farmed fish Megalobrama amblycephala. Four diet groups were designed: control (CD, 27.11% carbohydrates), high-carbohydrate (HCD, 36.75% carbohydrates), long-term betaine (HCB, 35.64% carbohydrates; 16 weeks) and short-term betaine (HC4B; 12 weeks HCD + 4 weeks HCB) diets. We analysed the histology of the liver (hematoxylin and eosin staining), the metabolites related to TMAO in plasma (high-performance liquid chromatography-tandem mass spectrometry), the expression of the relative gene in the liver and gut microbiota (qPCR), and the composition of gut microbiota (terminal restriction fragment length polymorphism). HCD elevated lipid accumulation in the liver and decreased the gene expression of bile acid transport, trimethylamine (TMA) formation and the diversity of gut microbiota compared to CD. HCB reversed these patterns, and elevated the gene expression of bile acid receptors and decreased the total cholesterol and TMAO concentration (all compared to HCD). HCD and HCB both increased the gene expression of bile acid synthesis (all p < 0.05). In conclusion, we hypothesise that HCB decreased liver lipid accumulation caused by a high-carbohydrate diet through improvement of the gut microbial community (the diversity of gut microbiota), TMA formation (the expression of associated microbial genes and bacterial taxa), TMAO metabolism (the formation of TMAO) and bile acid metabolism (the gene expression of the synthesis and transport of bile acids and their receptors). HC4B produced intermediate effects of those between HCD and HCB.

Effects of crowding stress on gene expression of antioxidant enzymes and Nrf2-Keap1 signaling pathway in different tissues of blunt snout bream ( Megalobrama amblycephala ) for in-pond raceway aquaculture systems

Effects of crowding stress on gene expression of antioxidant enzymes and Nrf2-Keap1 signaling pathway in different tissues of blunt snout bream ( <i>Megalobrama amblycephala</i> ) for in-pond raceway aquaculture systems

Genetic parameter estimates for intermuscular bone in blunt snout bream (Megalobrama amblycephala) based on a microsatellite-based pedigree

Most of the freshwater aquaculture fish species in the world, especially cyprinid fishes, contain intermuscular bones (IBs). IBs are often small and sharp, and they consequently limit how the fish can be processed, cause injury or trauma if lodged in consumers' throat or mouth and therefore affect the appeal of the fish to many consumers. In order to assess the possibility of decreasing IBs counts through selective breeding, this study evaluated the heritability of the number of IBs in blunt snout bream (Megalobrama amblycephala), which is one major aquaculture species in China. A total of 758 offsprings from 69 parents were genotyped at nine polymorphic microsatellite loci, and then 672 offspring from 213 full-sib families (33 female and 25 male breeders) were used for genetic parameter estimates. IBs were carefully teased from different poached sections of the flesh and counted. Heritability was estimated using an animal model. The results showed that IB number ranged between 84 and 146 per individual in the test population, with an average of 118 IBs. Coefficient of variation in IB number (CV) in ventral sections (13.63%) was substantially higher in comparison to dorsal sections (6.60%). The genetic correlation of IB number between the two sections was significantly positive and high (0.93) (P < .01), however, the phenotypic correlation was significantly positive but low (0.26) (P < .01). The differences among the families showed that the variation in the ventral section accounted for most of the total variation in IB number within the species, which indicated that IBs may have develop by different processes in dorsal and ventral sections. The heritability of the IBs number in M. amblycephala was low (0.098) for the dorsal section, but medium (0.236–0.410) for other sections. This study provides the first reported estimates for the heritability of the number of IBs in fish species and the finding of significant additive genetic variation for IB number indicate that it should be feasible to decrease the number of IBs through selective breeding.

Essential amino acids supplementation to practical diets affects growth, feed utilization and glucose metabolism‐related signalling molecules of blunt snout bream ( Megalobrama amblycephala )

Six diets were formulated to investigate the success of fish meal (FM) replacement by plant proteins; diet 1 reflected a commercial feed (8% FM), diet 3 contained 4% FM, and diet 5 was devoid of FM. Whereas, diet 2, diet 4, and diet 6 reflected diet 1, diet 3, diet 5, respectively, and supplemented with essential amino acid (EAA). At the end of 8-week trial, there was no significant difference in survival rate. Significantly higher final weight, weight gain rate, and specific growth rate were recorded in the group fed diet 2 compared with the other treatments (except diet 4) (p < 0.05). Feed conversion ratio of fish fed diet 2 was significantly lower than those fed diets 1, 3, and 5 (p < 0.05). The lowest feed intake and highest protein efficiency rate were found in fish fed diet 2 (p < 0.05). There was no significant difference in whole body compositions between treatments. Plasma aspartate transaminases, alanine aminotransferase, and glucose were significantly affected by dietary treatments (p < 0.05), while plasma protein and albumin contents were not influenced by the treatments. The relative expression of target of rapamycin (TOR) and phosphatidylinositol 3-kinase, regulatory subunit 1 (alpha) (PIK3R1) in fish fed diet 3 (4% FM) were significantly down-regulated compared with those fed diet 6 for TOR and diets 4 and 6 for PIK3R1 (p < 0.05). Insulin receptor substrate 1 (IRS-1) and janus kinase 3 (JAK3) expressions were fluctuated, with the higher levels in fish fed diets 4 and 6. In conclusion, the findings of this study indicate that plant protein mixture supplemented with EAA could be used to substitute FM in practical diet for Megalobrama amblycephala.

High-fat diet induces aberrant hepatic lipid secretion in blunt snout bream by activating endoplasmic reticulum stress-associated IRE1/XBP1 pathway

This study was conducted to understand the effect of high-fat diet challenge on lipid transport and endoplasmic reticulum stress in blunt snout bream. Ninety fish (average weight: 41.84 ± 0.07 g) were randomly fed a control diet (6% fat) or a high-fat diet (11% fat) for 9 weeks. The growth performance and feed utilization efficiency were evaluated at the end of the trial. The liver samples of both groups were harvested for molecular analysis and histological evaluation. Compared to the Control group, the high-fat diet group showed no effects on either growth performance or energy intake in blunt snout bream. However, high-fat diet resulted in a massive accumulation of lipid and pathological structural alternations, and disrupted expression of lipid transport-related genes and endoplasmic reticulum stress in the liver of the fish. In vitro, after exposure of the isolated primary hepatocytes from blunt snout bream to oleic acid, the cells showed increased intracellular TG accumulation, decreased VLDL secretion, which was attributed to altered expression levels of lipid transport-related genes through the activated IRE1/XBP1 signaling. The oleic acid-induced detrimental effects were alleviated by co-incubating the cells with an IER1 inhibitor, 4μ8c. In conclusion, high-fat diet could lead to aberrant lipid secretion by activating the ER stress-associated IRE1/XBP1 pathway. Inhibiting the activity of IRE1 represents a promising target to rescue the side-effects of high-fat diet on the liver function of blunt snout bream.

Genetic Effects on the Gut Microbiota Assemblages of Hybrid Fish From Parents With Different Feeding Habits.

Gut microbiota play critical roles in host nutrition and metabolism. However, little is known about the genetic effects on the gut microbiota assemblages because a suitable model for investigation is lacking. In the present study, we established the reciprocal hybrid fish lineages derived from the parents with different feeding habits, namely, herbivorous blunt snout bream (Megalobrama amblycephala, BSB, 2n = 48) and carnivorous topmouth culter (Culter alburnus, TC, 2n = 48). We investigated the genetic effects on gut microbiota assemblages by using 16S rRNA gene sequencing. The results showed that the gut characteristics (structure, relative gut length, relative gut mass, and Zihler’s index) differed between the two types of hybrids and the two parents. In particular, a strong correlation between genotype and gut microbial assemblages indicated that host genetic (subgenome) significantly altered the gut microbial communities. In addition, the microbial structures (composition and abundance) in the two types of hybrids were more similar to those in BSB parent (P > 0.05) than to those in TC parent (P < 0.05), and the cellulase contents in the gut (produced by gut microbes) also showed the similar results. The results suggested that the host genomic interaction (mainly subgenome domination) had a sizeable effect on shaping the gut microbiota assemblages in reciprocal hybrid fish. This study enriches our understanding of the relationship between host genetic and gut microbiota assemblages, and provides insight into gut microbiota and metabonomics.

Effects of stocking density on the growth performance, digestive enzyme activities, antioxidant resistance, and intestinal microflora of blunt snout bream ( Megalobrama amblycephala ) juveniles

In this study, effects of stocking density on the growth performance and physiological responses of blunt snout bream, Megalobrama amblycephala juveniles were evaluated. The fish (average body weight, 25.76 ± 2.25 g) were randomly stocked at densities of 30F (30 fish/m³), 60F, 90F and 120F in 12 cages (1 m × 1 m × 1 m) in a concrete pond, with three cages for each density, for a period of 6 weeks. The higher stocking densities had a negative effect on individual growth performance. The results indicated that serum cortisol, triglyceride, alanine aminotransferase, aspartate transaminase, alkaline phosphatase and malondialdehyde activities; and Acinetobacter, Aeromonas, Pseudomonas and Vibrio numbers in the intestinal microflora increased significantly as the stocking density increased. In contrast, the viscerosomatic index, hepatosomatic index survival rate; serum glucose, total cholesterol, lipase, protease, glutathione peroxidase and superoxide dismutase activities; and Clostridium, Bacteroides, Lactococcus, Lactobacillus and Bacillus numbers in the intestinal microflora decreased significantly. The 90F and 120F groups showed obvious enlargement of the lamina propria and goblet cell damage, indicating that the gut showed inflammatory responses. The specific growth rate and weight gain rate increased significantly as the stocking density increased from 30 to 60 fish/m³, but decreased significantly when the stocking density was over 60 fish/m³.

Transcriptome profiling and histology changes in juvenile blunt snout bream (Megalobrama amblycephala) liver tissue in response to acute thermal stress

To understand the precise mechanism and the pathways activated by thermal stress in fish, we sampled livers from juvenile Megalobrama amblycephala exposed to control (25 °C) and test (35 °C) conditions, and performed short read (100 bp) next-generation RNA sequencing (RNA-seq). Using reads from different temperature, expression analysis identified a total of 440 differentially-expressed genes. These genes were related to oxidative stress, apoptosis, immune responses and so on. We used quantitative real-time reverse transcriptase PCR to assess the differential mRNA expression of selected genes that encode antioxidant enzymes and heat shock proteins in response to thermal stress. Fish exposed to thermal stress also showed liver damage associated with serum biochemical parameter changes. The set of genes identified showed regulatory modulation at different temperatures, and therefore could be further studied to determine how thermal stress damages M. amblycephala livers and the possible roles of reactive oxygen species in this process.

Complete replacement of fish meal by plant protein ingredients with dietary essential amino acids supplementation for juvenile blunt snout bream ( Megalobrama amblycephala )

Complete replacement of fish meal by plant protein ingredients with dietary essential amino acids supplementation for juvenile blunt snout bream ( <i>Megalobrama amblycephala</i> )

Effects of the total fish meal replacement by soybean meal on growth parameters, serum biochemistry, and hepatic and intestinal histology of juvenile blunt snout bream (Megalobrama amblycephala)

ABSTRACTFish meal is the main protein source in fish diet, but due to its unsustainability, it has to be replaced with more sustainable protein sources, such as soybean meal (SBM), in fish feeds. As SBM often produces negative effects on fish growth and health, we conducted an eight-week trial of complete fish meal replacement with SBM in the diet of juvenile (48.2 ± 0.55 g) blunt snout bream (Megalobrama amblycephala), a herbivorous cyprinid fish native to the Yangtze basin (China). SBM-fed fish exhibited: a worsened growth performance; improved survival rate (P > 0.05); elevated serum triglycerides and total cholesterol but reduced low-density lipoprotein in plasma (P < 0.05); mild lipid droplet accumulation and swelling of the liver; elevated goblet cell counts and mild signs of enteritis in the intestines. With negligible effects on growth and mild effects on health, M. amblycephala appears to be comparatively tolerant of SBM, but total fish meal replacement is not recommended. Future studies should aim to identify the SBM tolerance threshold in long-term growth trials.

High-fat-diet-induced inflammation depresses the appetite of blunt snout bream (Megalobrama amblycephala) through the transcriptional regulation of leptin/mammalian target of rapamycin.

The aim of this article was to investigate the mechanism of appetite suppression induced by high-fat diets (HFD) in blunt snout bream (Megalobrama amblycephala). Fish (average initial weight 40·0 (sem 0·35) g) were fed diets with two fat levels (6 and 11 %) with four replicates. HFD feeding for 30 d could significantly increase the weight gain rate, but feeding for 60 d cannot. Food intake of M. amblycephala began to decline significantly in fish fed the HFD for 48 d. HFD feeding for 60 d significantly reduced the expression of neuropeptide Y and elevated the expression of cocaine- and amphetamine-regulated transcript (CART), actions both in favour of suppression of appetite. The activation of fatty acid sensing was partly responsible for the weakened appetite. In addition, inflammatory factors induced by the HFD may be involved in the regulation of appetite by increasing the secretion of leptin and then activating the mammalian target of rapamycin (mTOR). Lipopolysaccharide (LPS, 2·0 mg/kg of fish weight) was administered to induce inflammation, and sampling was performed after 3, 6, 9, 12, 18, 24 and 48 h of LPS injection. Within 6-24 h of LPS injection, the food intake and appetite of M. amblycephala decreased significantly, whereas the mRNA expression of leptin and mTOR increased significantly. Our results indicate that inflammatory cytokines may be the cause of appetite suppression in M. amblycephala fed a HFD.

Molecular characterization of p38 MAPK from blunt snout bream (Megalobrama amblycephala) and its expression after ammonia stress, and lipopolysaccharide and bacterial challenge

p38 mitogen-activated protein kinase (MAPK) is an important protein which plays a key role in regulating the innate immunity, so exploring its molecular characterization is helpful in understanding the resistance against microbial infections in cultured fish. Here, a full-length cDNA of p38 MAPK was cloned from liver of blunt snout bream (Megalobrama amblycephala) which covered 2419 bp with an open reading frame of 1086 bp encoding 361 amino acids. p38 MAPK contained the characteristic structures of Thr-Gly-Tyr (TGY) motif and substrate binding site Ala-Thr-Arg-Trp (ATRW), which are conserved in MAPK family. To investigate p38 MAPK functions, two in vivo experiments were carried out to examine its expression following ammonia exposure and bacterial challenge. Also, an in vitro experiment was conducted to assess the role of p38 MAPK in inflammation of primary hepatocytes induced by lipopolysaccharide (LPS). The results showed the ubiquitous expression of p38 MAPK in all the tested tissues with varying levels. p38 MAPK mRNA expression was significantly up-regulated by ammonia stress and Aeromonas hydrophila challenge, and altered in a time-dependent manner. Moreover, the results indicated that the inflammatory response induced by LPS in hepatocytes is p38 MAPK dependent as knockdown of p38 MAPK using siRNA technology depressed the expression of IL-1β and IL-6. The findings in this study showed that p38 MAPK has anti-stress property, and plays key role in protection against bacterial infection and inflammation in blunt snout bream.