Golden Pompano Trachinotus Ovatus Research Articles

Establishment a cell line of splenic fibroblasts from golden pompano and its application in heavy metal toxicology and pathogen infection

A cell line derived from golden pompano Trachinotus ovatus splenic fibroblasts (TOSF) was established, its application in toxicology and virus susceptibility was demonstrated in this study. The TOSF cells grew fastest with the L-15 medium containing 10% fetal bovine serum concentration at 28 °C. The chromosomal number of normal TOSF cells was 2N = 48. TOSF cells showed high sensitivity to grouper iridovirus (SGIV) and nervous necrosis virus (NNV). Cadmium and copper had toxic effects on TOSF cells, which could cause an oxidative stress response in TOSF cells and activate the antioxidant system to regulate the reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GSH) level in the cells. Cadmium and copper had an impact on the replication of SGIV and NNV in the TOSF cells, and copper could limit the proliferation of Aeromonas hydrophila in TOSF cells. Generally, the TOSF cell line can apply for heavy metal toxicity mechanisms study and environment monitoring, as well as the pathogen infection mechanism research.

Functional characterization of NOD1 from golden pompano Trachinotus ovatus

Fish rely on innate immune system for immunity, and nucleotide-binding oligomerization domain-like receptors (NLRs) are a vital group of receptor for recognition. In the present study, NOD1 gene was cloned and characterized from golden pompano Trachinotus ovatus, a commercially important aquaculture fish species. The ORF of T. ovatus NOD1 was 2820 bp long, encoding 939 amino acid residues with a highly conserved domains containing CARD-NACHT-LRRs. Phylogenetic analysis revealed that the T. ovatus NOD1 clustered with those of fish and separated from those of birds and mammals. T. ovatus NOD1 has wide tissue distribution with the highest expression in gills. Bacterial challenges (Streptococcus agalactiae and Vibrio alginolyticus) significantly up-regulated the expression of NOD1 with different response time. The results of T. ovatus NOD1 ligand recognition and signaling pathway analysis revealed that T. ovatus NOD1 could recognize iE-DAP at the concentration of ≧ 100 ng/mL and able to activate NF-κB signaling pathway. This study confirmed that NOD1 play a crucial role in the innate immunity of T. ovatus. The findings of this study improve our understanding on the immune function of NOD1 in teleost, especially T. ovatus.

Genome-wide characterization, phylogenetic and expression analysis of Galectin gene family in Golden pompano Trachinotus ovatus.

Galectins (Gals) are a type of S-type lectin that are widespread and evolutionarily conserved among metazoans, and can act as pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs). In this study, 10 Gals (ToGals) were identified in the Golden pompano (Trachinotus ovatus), and their conserved domains, motifs, and collinearity relationships were analyzed. The expression of ToGals was regulated following infection to Cryptocaryon irritans and Streptococcus agalactiae, indicating that ToGals participate in immune responses against microbial pathogens. Further analysis was conducted on one important member, Galectin-3, subcellular localization showing that ToGal-3like protein is expressed both in the nucleus and cytoplasm. Recombinant protein obtained through prokaryotic expression showed that rToGal-3like can agglutinate red blood cells of rabbit, carp and golden pompano and also agglutinate and kill Staphylococcus aureus, Bacillus subtilis, Vibrio vulnificus, S. agalactiae, Pseudomonas aeruginosa, and Aeromonas hydrophila. This study lays the foundation for further research on the immune roles of Gals in teleosts.

Bactericidal permeability-increasing protein/LPS-binding protein (BPI/LBP) enhances resistance of golden pompano Trachinotus ovatus against bacterial infection

Antimicrobial peptides are crucial components of innate immunity against microbial invasions. As a kind of antimicrobial peptides, bactericidal permeability-increasing protein (BPI)/lipopolysaccharide-binding protein (LBP) play vital roles in defending the host against gram-negative bacteria. In the current study, a novel BPI/LBP from Trachinotus ovatus (TroBPI/LBP) was characterized. The full length of TroBPI/LBP cDNA sequence is 1434 bp, which contained 477 amino acids. Multiple amino acid alignments of TroBPI/LBP shows 34.07%–84.49% identity with other fish BPI/LBP. Similar to other BPI/LBP, TroBPI/LBP also possesses an N-terminal signal peptide, a BPI/LBP/CETP N-terminal domain, and a BPI/LBP/CETP C-terminal domain. In vitro, the recombinant protein of TroBPI/LBP showed effective bacterial depression activity and binding activity to gram-negative bacteria. In vivo, TroBPI/LBP was constitutively expressed in tested tissues, and the highest expression level was in liver. Following Vibrio alginolyticus stimulation, the mRNA expression of TroBPI/LBP was significantly upregulated in immune-related tissues, and peaked at 12 h post-infection, which confirmed that TroBPI/LBP was highly sensitive to V. alginolyticus stimuli. Furthermore, functional analyses showed that the overexpression of TroBPI/LBP could enhance the ability of fish to against V. alginolyticus infection, and the knockdown of TroBPI/LBP significantly diminished bacterial clearance capacity post-infection. Therefore, these results suggest that TroBPI/LBP may play an important role in host defense against bacterial infection.

Effect of replacement of fishmeal by soybean products with attractants supplementation on the growth performance, feed utilization, body composition, plasma physiological responses and hepatic antioxidant abilities of juvenile golden pompano Trachinotus ovatus

A feeding experiment was carried out to develop a practical diet with low fishmeal for juvenile golden pompano (Trachinotus ovatus) by substituting fishmeal protein with soybean products mixture. Six isocaloric (17.6 KJ g−1) diets were designed by replacing 0 (FM100), 5 (FM95), 10 (FM90), 15 (FM85), 20 (FM80), and 25% (FM75) of the fishmeal with soybean products mixture (SPM) (soybean meal and soybean protein concentrate). The experiment diets were supplemented with 1.5%, 3%, 4.5%, 6% and 7.5% squid paste as attractants or palatability enhancer. The experimental fish (6.9 g) were cultured in sea cages (1.0 m × 1.0 m × 1.5 m) with 25 fish in each cage. Fish were fed the corresponding experimental diets to satiation twice daily for 8 weeks. At the end of the feeding experiment, no differences were found in the final weight and weight gain (WG) of fish fed FM100, FM85, FM80, and FM75 diets (P > 0.05). The WG was significantly (P < 0.05) better in the fish-fed FM95 diet compared to FM100 and FM75 diets. FCR in diet FM95 and FM90 was significantly (P < 0.05) than that of FM80 and FM75, but these values were not significantly different from those in other treatments. Although the condition factor value in diets FM90, FM85, and FM80 was significantly (P < 0.05) higher than that of FM100, these values were not significantly different from the rest of the other groups. There was no statistical difference in SGR, FR, VSI, and survival rates among different dietary treatments. The plasma AST activity was significantly lower in fish fed FM90 diet compared to fish fed with control, FM85, FM80, and FM75 (P < 0.05). There was no significant difference in plasma AST among all dietary treatments except FM95 and FM90. In contrast, the plasma AKP activity showed the opposite trend. Compared with the control, the fish-fed FM80 and FM75 diets had significantly decreased plasma cholesterol, triglyceride total protein, albumin, and globulin level (P < 0.05) while significantly increasing plasma COR levels (P < 0.05). There was no significant difference in ALT, Urea and glucose values among all treatments. No statistical difference was observed among the FM100, FM80, and FM75 treatments for those of plasma LYZ activity, C3, and C4 levels. The hepatic T-AOC and SOD activities were significantly increased in fish fed the FM90 diet (P < 0.05) compared to those in fish fed with FM100 diet. According to the current experiment, it can be concluded that SPM supplemented with SP could partially substitute fishmeal (25%) for juvenile golden pompano without any adverse symptoms.

Effects of dietary chitosan on the growth, health status and disease resistance of golden pompano (Trachinotus ovatus)

The effects of dietary chitosan (0, 2, 4, 6, 8 and 10 g/kg) on the growth, health condition and disease resistance of golden pompano Trachinotus ovatus were evaluated. Dietary chitosan significantly enhanced weight gain, with the highest observed in fish fed the 6 g/kg chitosan diet. This chitosan level significantly promoted gut health by increasing villus length, lipase and protease activities and intestinal barrier-related genes expression. Meanwhile, dietary 6 g/kg chitosan improved the inflammatory response and anti-oxidative capacity of fish by regulating the expression of genes involved in NF-κB pathway and Nrf2 pathway, respectively. Furthermore, after challenge with Vibrio harveyi for 2 weeks, the survival rate increased significantly when dietary chitosan level was 6 g/kg. Overall, our results indicate that 6 g/kg chitosan is the optimal dose for enhancing growth, health and disease resistance of fish, but excessive chitosan (10 g/kg) weakens its beneficial effects.

Effect of dietary carbohydrate on glycometabolism of juvenile golden pompano (Trachinotus ovatus) related to growth performance, hepatic histopathology, transcriptome profiles and identification of differentially expressed genes

A hepatic transcriptome was produced through the technology of RNA sequencing and short-read assembly in golden pompano Trachinotus ovatus fed with three experimental diets respectively containing low carbohydrate diet (LCD), intermediate carbohydrate diet (MCD), and high carbohydrate diet (HCD). In total, 57,217 unigenes were acquired in the current study, with average length 1182.24 bp. 21,920, 22,514 and 24,680 unigenes were acquired from LCD, MCD and HCD groups, respectively. There were 1513 differential expressed genes in LCD and MCD groups, with 676 up- and 837 down-regulated genes in LCD group; 2369 genes were differentially expressed between HCD vs MCD, containing 1397 up and 972 down-regulated genes in HCD group. 1686 differential expressed genes were observed in the comparison of HCD and LCD, containing 1044 up- and 642 down-regulated genes in HCD group. Some differential expressed genes, such as hexokinase-1-like isoform X3, pancreatic alpha-amylase-like, hexokinase-1-like isoform X1, ADP-dependent glucokinase isoform X2, fructose-bisphosphate aldolase A-like, and acetyl-CoA carboxylase isoform X8, were related to carbohydrate metabolism, indicating these genes in the golden pompano were in response to dietary carbohydrate. In this study, long-chain-fatty-acid-CoA ligase 5 was up-regulated in comparison of HCD_vs_MCD and HCD_vs_LCD, which indicated that FACL5 may be sensitive to high dietary carbohydrate. This result coincides with the pathological changes of hepatocyte morphology in the present study. The results of transcriptome analysis in this study were confirmed by RT-PCR in 14 randomly selected unigenes. This study may provide novel data and theoretical support on hepatic transcriptome information of the golden pompano, which is a vital resource for studies of bioinformatics in golden pompano. Besides, the present study identifies some pivotal genes related to dietary carbohydrate and lipid deposition, which will accumulate data on carbohydrate and/or lipid metabolism in marine fish species to support related research.

Corn-starch based formulated diet has growth and feed utilization efficiency advantages over trash fish diet for juvenile golden pompano Trachinotus ovatus

Until now, trash fish/low valued fish continues to be widely used in marine cage culture of pompano and many other carnivorous species in China and other Asian countries. This study is the first attempt to compare the performance of juvenile golden pompano Trachinotus ovatus fed trash fish or starch-based formulated diets. Three isonitrogenous (41 %) and isolipidic (11 %) diets containing 16, 22 or 28 % corn starch were prepared. Juvenile pompano (mean initial weight: 28.0 ± 0.3 g) were fed either formulated diets or trash fish on a equivalent dry-matter basis for 8 weeks. The survival rates were significantly higher in fish fed starch diets than fish fed trash fish (P < 0.05). Specific growth rate (SGR) of fish fed the 22 % and 28 % starch diets was significantly higher than fish fed 16 % starch diet and trash fish. Feed intake (FI) of fish fed trash fish was significantly higher than those fed formulated diets; however, feed efficiency (FE) and protein efficiency ratio (PER) of fish fed the formulated diets were higher than those fed trash fish, with the 22 % starch dietary group having a significantly higher FE value than fish fed trash fish. The whole-body energy retention (ER) of fish fed the diet containing 22 % starch had the highest ER, significantly higher than those fed 16 % starch and trash fish. The moisture in whole-body tissues of fish fed trash fish was significantly higher than the formulated dietary groups. On the other hand, whole-body protein and lipid contents of fish fed the 22 % starch diet was significantly higher than the other dietary treatments. The whole-body lipid level of fish fed trash fish was significantly lower than the other dietary groups. The body condition indices were significantly higher for fish fed formulated diets compared to those fed trash fish. The viscerosomatic index (VSI) was decreased with increasing dietary starch levels. Hexokinase (HK) activity significantly increased with increasing dietary starch levels, whereas pyruvate kinase (PK) activity had an opposite trend. The liver and muscle glycogen contents were generally increased with increasing dietary starch levels. In addition, the intestinal microbial communities of fish fed the formulated diets and trash fish was distinctly different. The results shown that formulated diet had advantages in performance and feed utilization efficiency over trash fish. Corn starch can be used as a suitable dietary carbohydrate. Evaluated on growth and FE, the optimal dietary corn starch level for T. ovatus is 22–24 % of diet.

Influence of dietary fermented Folium mori on growing performance, lipometabolism and disease resistance of golden pompano Trachinotus ovatus

Folium mori, as a plant unconventional feedstuff, are comparatively available due to cost-effectiveness, whereas their usage as aquafeed in pure form is restricted owing to the great fibre and antinutritional factors (ANFs) levels. Thereof, several methods of processing are introduced to remove antinutrient factors from the plant products, leading to improvement of bioactivity and digestibility. The assay was completed to evaluate the method of fermentation and the role of dietary fermented Folium mori (FFM) in golden pompano. Each of 5 diets with FFM at contents of 0.0%, 2.0%, 4.0%, 6.0% and 8.0% (D0.0, D2.0, D4.0, D6.0 and D8.0) was fed to the fishes with original body weight of 9.02g in triplicate sea cages for 56 days. The outcomes revealed that FFM in D4.0 and D6.0 elevated the growing performance of the fishes and the growing performance of D4.0 was remarkably improved in contrast to D0.0 and D2.0(P < 0.05). Whole body lipidic levels were obviously elevated when the diet FFM contents were below 8.0% (P < 0.05), whereas the contents of muscular moisture were generally reduced. In addition, FFM significantly increased serum high density lipoprotein (HDL) and remarkably reduced overall triglyceride (TG) in D2.0 to D6.0(P < 0.05). Moreover, FFM remarkably elevated the activities of lipase of stomach and hepatopancreas in contrast to D0.0 (P < 0.05) as well as intestinal tryptic enzyme in the entire FFM groups (P < 0.05). Eventually, FFM remarkably ameliorated disease-resistant characters of golden pompano to Vibrio harveyi in D4.0 and D6.0 (P < 0.05) and the RPS in D4.0 was optimal. To sum up, the present research displayed favorable role of FFM in growing performance, digestion, lipometabolism and disease-resistant characters, and the recommendation as to the supplementation content of diet FFM in compound feed of juvenile golden pompano is 4.0% as per the experiment status herein.

Nuclear Factor-κB Plays a Positive Role in TNFα Expression in Golden Pompano, Trachinotus ovatus (Linnaeus 1758)

Tumour necrosis factor-α (TNFα) is a multifarious mediator of lymphoid tissue growth and antimicrobial defence mechanisms, and it acts as a pro-inflammatory regulator. The function of TNFα in parasite infection and the underlying mechanism through which nuclear factor-κB (NF-κB) regulates TNFα remain largely unclear in teleosts. In the present study, TNFα (ToTNFα) from golden pompano (Trachinotus ovatus) was identified, and its sequence features and expression levels were determined. The genomic DNA sequence is composed of 1,130 bp, consists of four exons and three introns, and encodes 341 amino acid polypeptides. The putative protein sequence shares 34.7%–61.9% identity with fish TNFα and possesses a TNF family signature and two conserved cysteine residues. Moreover, the expressions of ToNF-κB and ToTNFα are constitutively expressed in all examined tissues, with higher levels observed in the immune relevant tissues. Both ToNF-κB and ToTNFα transcription was increased in the local infection sites (skin and gill) and system immune tissues (liver, spleen and head kidney) after Cryptocaryon irritans stimulation. In addition, to investigate whether ToNF-κB is a regulator of ToTNFα, promoter analysis was performed. The region from -970 to +79 bp is known as the core promoter by different truncated mutants of ToTNFα. Subsequently, the activity of the ToTNFα-p2 promoter was dramatically reduced after targeted mutation of the M6-binding site. Additionally, an electrophoretic mobile shift assay (EMSA) verified that ToNF-κB interacted with the M6-binding site in the ToTNFα promoter region to control the expression of ToTNFα. In conclusion, the present study provides the positive regulation of TNFα transcription by NF-κB and contributes to a better understanding of the transcriptional mechanism of TNFα in fish.

Molecular Characterization, Tissue Distribution Profile, and Nutritional Regulation of acsl Gene Family in Golden Pompano (Trachinotus ovatus).

Long chain acyl-coA synthase (acsl) family genes activate the conversion of long chain fatty acids into acyl-coA to regulate fatty acid metabolism. However, the evolutionary characteristics, tissue expression and nutritional regulation of the acsl gene family are poorly understood in fish. The present study investigated the molecular characterization, tissue expression and nutritional regulation of the acsl gene family in golden pompano (Trachinotus ovatus). The results showed that the coding regions of acsl1, acsl3, acsl4, acsl5 and acsl6 cDNA were 2091 bp, 2142 bp, 2136 bp, 1977 bp and 2007 bp, encoding 697, 714, 712, 659 and 669 amino acids, respectively. Five acsl isoforms divided into two branches, namely, acsl1, acsl5 and acsl6, as well as acsl3 and acsl4. The tissue expression distribution of acsl genes showed that acsl1 and acsl3 are widely expressed in the detected tissues, while acsl4, acsl5 and acsl6 are mainly expressed in the brain. Compared to the fish fed with lard oil diets, the fish fed with soybean oil exhibited high muscular C18 PUFA contents and acsl1 and acsl3 mRNA levels, as well as low muscular SFA contents and acsl4 mRNA levels. High muscular n-3 LC-PUFA contents, and acsl3, acsl4 and acsl6 mRNA levels were observed in the fish fed with fish oil diets compared with those of fish fed with lard oil or soybean oil diets. High n-3 LC-PUFA levels and DHA contents, as well as the acsl3, acsl4 and acsl6 mRNA levels were exhibited in the muscle of fish fed diets with high dietary n-3 LC-PUFA levels. Additionally, the muscular acsl3, acsl4 and acsl6 mRNA expression levels, n-3 LC-PUFA and DHA levels were significantly up-regulated by the increase of dietary DHA proportions. Collectively, the positive relationship among dietary fatty acids, muscular fatty acids and acsl mRNA, indicated that T. ovatus Acsl1 and Acsl3 are beneficial for the C18 PUFA enrichment, and Acsl3, Acsl4 and Acsl6 are for n-3 LC-PUFA and DHA enrichment. The acquisition of fish Acsl potential function in the present study will play the foundation for ameliorating the fatty acids nutrition in farmed fish products.

Responses of two marine fish to organically complexed Zn: Insights from microbial community and liver transcriptomics

The diversity and adjustability of metal-organic complex enhance the function of metals and promote the burgeoning fields of chemical biology. In the present study, we chose two marine fish to explore the effects of a dihydromyricetin (DMY)-Zn(II) complex on the intestinal microbiome composition and liver biological function using high-throughput sequencing technology. Two economic fish species commonly found in Southern China (golden pompano Trachinotus ovatus and pearl gentian grouper ♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus) were exposed to dietary DMY-Zn complex for 4-week. Our study found that DMY-Zn performed a vital function on the improved anti-oxidative ability of both fish species. The Zn complex improved the stability of microbial community structure of the golden pompano by enhancing the α-diversity, but its impacts on the composition and diversity of intestine microorganisms of grouper were insignificant. BugBase results showed that the intestine microbiota following DMY-Zn exposure contained a lower abundance of potentially pathogenic bacteria and higher abundance of aerobic bacteria. Intestine health and utilization of carbohydrates were improved in the golden pompano, and unclassified bacteria were significantly enriched in the grouper. Liver transcriptome indicated that DMY-Zn affected the oxidative phosphorylation process (OXPHOS). Specifically, the OXPHOS process (map00190) was activated by promoting the glucose uptake (map04251, map04010) in golden pompano and lipid metabolism (map00071, map00140, map00062 and map00564) in grouper. Such difference in the responses of intestine microbiome and liver metabolism may be possibly explained by their different Zn basal requirements. Our study demonstrated that different fish species may have different responses to dietary DMY-Zn complex. The results provided a reference for the application of new additives in aquatic animal feed, and new insights into the roles of metal-organic complex in their biological impacts on fish.

Beneficial contribution of the microalga Odontella aurita to the growth, immune response, antioxidant capacity, and hepatic health of juvenile golden pompano (Trachinotus ovatus)

Under specific culture conditions, the marine diatom Odontella aurita can accumulate chrysolaminarin, which has antioxidant and anti-inflammatory functions, to improve immunity and regulating lipid metabolism. The current study investigated the use of chrysolaminarin-rich O. aurita as an immunostimulant in the diet of juvenile golden pompano Trachinotus ovatus. Three experimental diets containing 0%, 1% and 5% O. aurita were used to feed T. ovatus for 6-week. The results indicated that diet supplementation with O. aurita powder boosted the growth of T. ovatus by decreasing the feed conversion ratio, increasing the activities of lipase and pepsin in the intestine, and improving intestinal villi structure. Supplementation with 5% O. aurita promoted its antioxidant capacity by stimulating the Nrf2-ARE signal pathway and enhancing the total antioxidant capacity and activities of catalase, superoxide dismutase, and glutathione peroxidase. It also exerted hepatoprotective effects by inhibiting lipid deposition and downregulating the expression of proinflammatory cytokines and apoptosis-related genes, as well as improving the nonspecific immune response by increasing the expression levels of c-type lysozyme and complement 4. Therefore, a diet supplemented with 5% O. aurita is recommended to enhance the growth, antioxidant ability, and immunity of T. ovatus.

Molecular characterization and expression analysis of acyl-CoA synthetase 6 in golden pompano Trachinotus ovatus reveal its function in DHA enrichment

Acyl-CoA synthetase 6 (Acsl6) involves the enrichment of docosahexaenoic acid (DHA) and lipid synthesis in mammals, while its molecular function is still unknown in teleost. To explore the potential function of teleost Acsl6, this study investigated the molecular characterization and expression analysis of the acsl6 gene in the marine fish golden pompano (Trachinotus ovatus). The acsl6 cDNA cloned has a coding region (2169 bp) encoding 722 amino acids, which possesses a typical structure of Acsl including the gate domain and linker motif. The highest acsl6 mRNA expression was detected in the brain, followed in eyes, muscle, intestine, liver, and other tissues. Comparing to the fish fed with lard oil or soybean oil diets, the fish fed with fish oil exhibited high muscular DHA contents, and acsl6 mRNA levels (p < 0.05). Additionally, feeding T. ovatus three experimental diets containing different n-3 LC-PUFA levels (5.25%, 10.05%, and 14.05%) showed that the muscular DHA and n-3 LC-PUFA contents, as well as the acsl6 mRNA levels, matched the dietary n-3 LC-PUFA levels. The transcript level of acsl6 and contents of DHA in the muscle was significantly affected by dietary DHA/EPA ratios, and high DHA/EPA ratios increased the muscular DHA contents and acsl6 gene expression (p < 0.05). Moreover, the over-expression of acsl6 promoted the DHA contents of hepatocytes and enterocytes, suggesting that T. ovatus Acsl6 plays an active role in the deposition of DHA content. Collectively, the positive relationship among dietary DHA, muscular acsl6 mRNA and DHA levels, as well as the increase of cellular DHA contents by over-expression of acsl6, indicated that Acsl6 is beneficial to the DHA enrichment in T. ovatus. The acquisition of fish Acsl6 potential function in the present study will play the foundation for ameliorating the DHA contents in farmed fish products.

Multi-omics reveals the regulatory mechanisms of zinc exposure on the intestine-liver axis of golden pompano Trachinotus ovatus

Metal zinc (Zn) has been the focus of many environmental toxicological studies, but there are limited studies on its potential dietary molecular toxicity and physiology. The present study was the first to use multi-omics-based approaches to explore the fish intestine-liver axis under dietary Zn exposure. Golden pompano Trachinotus ovatus were exposed to different dietary concentrations (78.4, 134.6, and 161.4 mg/kg as the control, low-dose Zn, and high-dose Zn groups, respectively) of Zn for 4-week. Low-dose Zn exposure significantly promoted the fish growth, whereas the high-dose Zn exposure reduced the fish growth. Co-analysis of 16S diversity, metagenome and transcriptome showed that the low-dose Zn enriched the intestinal microflora and changed the dominant microflora abundances (Proteobacteria, Fusobacteria, Firmicutes and Bacteroidetes), as well as activated the growth hormone metabolism in the liver. Meanwhile, the high-dose of Zn caused the intestinal microbiota dysbiosis, activated the Type VI secretion systems (T6SSs), and further triggered the oxidative stress response, immunity, and antiviral function of the liver. Multi-omics revealed the interference of long-term Zn dietary exposure on the intestine-liver axis. There was an apparent homeostasis of Zn accumulation in the fish tissues, but the window of dietary Zn nutritional requirements versus toxicity appeared to be narrow for the golden pompano. These results provided new insight into the adverse effects and regulatory mechanisms of dietary Zn requirements and toxicity in marine fish.

Increasing fish meal replacement level with feather meal in golden pompano Trachinotus ovatus diet through gamma‐ray irradiation

This study evaluated the potential to replace dietary fish meal with gamma-ray (γ)-irradiated feather meal and non γ-irradiated feather meal for golden pompano Trachinotus ovatus. The basal diet (R) contained 250 g/kg fish meal, and 20% and 40% of the fish meal were replaced by either γ-irradiated feather meal (IF20 and IF40) or non γ-irradiated feather meal (F20 and F40). Fish were fed the test diets in inshore net pens for eight weeks. The weight gain of fish fed diet R did not significantly differ from those fed diet IF20, but was higher than those fed diets F20, F40 and IF40. No significant differences were found in feed intake, feed conversion ratio, retention efficiencies of carbon and nitrogen, condition factor, hepatosomatic index and wastes of carbon and nitrogen between fish fed diet R and diets F20, F40, IF20 and IF40. This study reveals that γ-irradiated feather meal could replace more fish meal in golden pompano diet than that replaced by non γ-irradiated feather meal, and dietary fish meal content could be reduced to 200 g/kg by inclusion of 43 g/kg γ-irradiated feather meal as a fish meal substitute. Replacing dietary fish meal with either γ-irradiated feather meal or non γ-irradiated feather meal could shift carbon–nitrogen–phosphorus atomic stoichiometry in the coastal waters for golden pompano aquaculture.

Genome-wide association study reveals multiple novel SNPs and putative candidate genes associated with low oxygen tolerance in golden pompano Trachinotus ovatus (Linnaeus 1758)

Golden pompano (Trachinotus ovatus) is one of the most economically critical marine fishes in South China. Low oxygen stress, which is caused by a variety of factors, has resulted in substantial economic losses to the aquaculture of golden pompano. Genome-wide association study (GWAS) has been widely used to study the genetic basis of important economic traits in aquatic animals. In the present study, 100 individuals were used for genome-wide association study of hypoxia tolerance trait based on genome-wide resequencing technology to explore the SNPs and related candidate genes affecting hypoxia tolerance trait in golden pompano. Four significant SNPs were identified to be suggestively significantly associated with the hypoxia tolerance trait. In the 50 kb window surrounding the suggestive SNPs, 16 potential candidate genes affecting hypoxia tolerance trait were detected. Moreover, validation results of the screened significant loci in the large population were consistent with the results of the GWAS. Among these results, the survival times of individuals with different genotypes at SNP24101852 and SNP24194184 were significantly different (p < 0.01). These results have specific guiding significance for the genetic improvement and determining the molecular mechanism of hypoxia tolerance. These SNPs could be used as molecular markers to screen for hypoxia tolerance be used for further applications in the heritage breeding of golden pompano.

Transcriptional response of golden pompano Trachinotus ovatus larvae to cold and heat stress

In order to investigate the molecular response pattern of golden pompano Trachinotus ovatus larvae under cold and heat stress, transcriptome sequencing was performed in three temperature-treated groups (24 °C, low temperature, LT; 28 °C, moderate temperature, MT; and 32 °C, high temperature, HT) after one week of treatment. A total of 501,367,768 clean reads were obtained, with an average GC content of about 47 %. 94,144 unigenes were recovered, with an average length of 1045 bp. Gene ontology (GO) analysis and Kyoto encyclopedia of genes and genomes (KEGG) analysis showed that a large number of differentially expressed genes were related to metabolic processes, protein synthesis and nutrient digestion and absorption. The differentially expressed genes (DEGs) were most highly enriched into the pathways including protein digestion and absorption, fat digestion and absorption, starch and sucrose metabolism, vitamin digestion and absorption, glutathione metabolism. High temperature may inhibit the secretion of type II collagen by down-regulating the expression of Shh and Sox9a genes. The results of this study provide important support for understanding mechanism of the response to high temperature in Trachinotus ovatus and guiding relevant production practices.

The optimal dietary lipid level for golden pompano Trachinotus ovatus fed the diets with fish meal replaced by soy protein concentrate

A feeding trial was conducted to determine the optimal dietary lipid level for golden pompano Trachinotus ovatus and the effect of dietary lipid level on fish meal replacement with soy protein concentrate (SPC). Eight isonitrogenous diets were formulated to contain four lipid levels (65 g/kg, 85 g/kg, 105 g/kg and 125 g/kg) and two fish meal levels (280 g/kg and 140 g/kg) respectively. Fish (initial weight 25.2 ± 0.5 g) were fed the test diets in net pens for 7 weeks. At the same dietary fish meal level, weight gain and nitrogen retention efficiency (NRE) tended to increase, while feed intake, feed conversion ratio (FCR) and nitrogen waste tended to decrease, with elevating dietary lipid level from 65 g/kg to 105 g/kg. At the same dietary lipid level, no significant differences were found in weight gain, feed intake, FCR, NRE, condition factor, hepatosomatic index, proximate composition and nitrogen waste between fish fed the diets containing 280 g/kg and 140 g/kg fish meal. This study reveals that the optimal dietary lipid level for golden pompano should be 107 g/kg, and dietary fish meal level could be reduced to 140 g/kg by using SPC as a fish meal substitute. Elevating dietary lipid level could not significantly increase fish meal replacement level with SPC.

Effects of dietary leucine on glucose metabolism, lipogenesis and insulin pathway in juvenile golden pompano Trachinotus ovatus

The aim of the study was to evaluate the effects of dietary leucine on the insulin signaling pathway, glucose metabolism and lipogenesis in juvenile golden pompano T. ovatus. A total of 300 juvenile golden pompano (9.15 ± 0.04 g) were fed four isonitrogenous diets with graded levels of leucine (1.25 %, 2.77 %, 5.84 and 8.73 %) for 8 weeks. They were randomly distributed to 12 cages (1.0 m × 1.0 m × 1.5 m; three cages per treatment) at an equal stocking rate of 25 fish per cage. Results indicated that compared with 1.25 % (the control), 2.77 % dietary leucine upregulated the relative expressions of IRS-1, PI3K, AKT and TOR, while 8.73 % dietary leucine lowered the relative expression of IRS-1. Compared with 1.25 % (the control), 5.84 % and 8.73 % dietary leucine significantly upregulated the relative expression of S6K1. Compared with 1.25 % (the control), 2.77 % dietary leucine led to the increment of the expression levels of GK, PK, GS and GLUT2, and the plasma insulin level, while led to inhibition of PEPCK. Compared with 1.25 % (the control), 8.73 % dietary leucine significantly decreased the relative expressions of PK and GLUT2, and plasma insulin level, while increase the relative expressions of G6Pase and PEPCK, plasma glucose level. Compared with 1.25 % (the control), 2.77 % dietary leucine significantly upregulated the relative expression of G6PDH, FAS, ACC SREBP1, plasma triglyceride level. Furthermore, 8.73 % dietary leucine resulted in low plasma triglyceride content. Our results suggest that the PI3K/AKT/TOR insulin signaling pathway mediates chronic leucine supplementation induced hepatic glucose metabolism and lipogenesis in juvenile T. ovatus. Optimal level of leucine could activate insulin signaling pathway, thus enhance the glycolysis and fatty acid synthesis in juvenile T. ovatus, while dietary excess leucine resulted in hyperglyceria by reducing the insulin signaling pathway and improving gluconeogenesis.