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The investigation of fish bioenergetics primarily relies on using an energy budget equation to examine how the allocation of energy and nutrients in their diet impacts their growth rate and reproductive capabilities. By accurately forecasting the distribution of feeding intake energy towards growth, fecal excretion, and metabolism within the overall energetic framework of a fish, and considering diverse physiological factors or ecological influences that affect each aspect of this energetic balance sheet, scientific discoveries derived from these studies can provide valuable insights for making informed decisions regarding optimal dietary choices to enhance fish well-being. Additionally, it aids in refining rearing management strategies leading to improved feed utilization efficiencies, ultimately resulting in more sustainable aquaculture practices aimed at minimizing environmental pollution caused by excessive feeding activities. Temperature affects various physiological processes and growth potential, thereby, influencing feed requirements and utilization efficiency, which ultimately determine the allocation of feeding intake energy among growth, fecal, excretory, and metabolic energies. Extensive studies have been conducted to explore how temperature influences fish growth rates along with their overall energy budgets. The effects of temperature on the growth and energy budgets in triploid turbot, Scophthalmus maximus, were investigated in this study by establishing a series of five temperature gradients (13 ℃, 16 ℃, 19 ℃, 22 ℃, and 25 ℃). Measurements of the growth and energy budget allocations were conducted on large-sized triploid turbot juveniles with mean body weight of (120.24±17.20) g at the aforementioned temperatures for 49 d. The results indicate that under conditions of salinity 28.6, pH 7.8, dissolved oxygen content above 7.8 mg/L, light intensity of 300 lx, and a light period of 16 L∶8 D ratio; the feeding rates (FR) and weight gain rates (WG) of triploid juveniles initially increased with increasing temperature before declining, with the peak FR of (1.02±0.06)% and (0.95±0.04)% observed at 19 ℃ and 22 ℃, respectively, whereas the highest WG was recorded at 19 ℃ (62.17±3.10)% (P < 0.05). The relationship between specific growth rate (SGR) or feed conversion efficiency (FCE) and temperature, calculated based on different parameters including wet weight (SGRw and FCEw), dry weight (SGRd and FCEd), protein content (SGRp and FCEp), and energy content (SGRe and FCEe), was observed to follow a quadratic regression equation. The highest recorded temperature for the SGR values was observed at 19 ℃. At 25 ℃, the group exhibited significantly reduced levels of SGRs compared to that of other experimental groups, except for the data recorded at 13 ℃ (P < 0.05), where 13 ℃ and 25 ℃ showed relatively low SGR values. Additionally, no significant differences were observed in SGR values between 16 ℃ and 22 ℃. The maximum FCE values were also attained at 19 ℃ (P < 0.05). In contrast, the FCE values recorded at 13 ℃ and 25 ℃ exhibited considerable reductions when compared to those obtained from other experimental groups (P < 0.05). Regression analysis revealed that the optimal temperatures for SGRw, SGRd, SGRp, and SGRe were determined as 18.4 ℃, 18.7 ℃, 18.9 ℃, and 18.5 ℃, respectively, whereas the temperatures for achieving maximum FCEw, FCEd, FCEp, and FCEe were 18.1 ℃, 18.6 ℃, 18.9 ℃, and 18.2 ℃, respectively. Additionally, the rates of nitrogenous excretion and fecal production exhibited an initial decrease followed by an increase with increasing temperature, reaching their highest levels at 25 ℃. Dry matter, protein, and energy apparent digestibility coefficients at 25 ℃ were significantly lower than those observed at other temperatures. The feeding intake energy and growth energy proportion demonstrated an inverted "U" shape with increasing temperature, reaching its highest value at 19 ℃. The allocation of energy in triploid juveniles was primarily dominated by growth and metabolism energies, whereas the proportion of metabolism energy to feeding intake energy displayed a "U" shape trend with increasing temperature. The proportion of growth energy to feeding intake energy ranged from 17.86% to 34.58%, whereas the proportion of fecal energy varied from 4.12% to 5.57%. Furthermore, the proportion of excretion energy to feeding intake energy ranged from 6.61% to 9.19%, and metabolism energy accounted for 54.69% to 67.38% of feeding intake energy. The energy budget equation of triploid turbot juvenile at 19 ℃ was 100.00 C (feeding intake energy) = 34.58 G (growth energy) +4.12 F (fecal energy) +6.61 U (excretion energy) +54.69 R (metabolism energy) or 100.00 A (assimilated energy) = 38.74 G+61.26 R. The triploid turbot juveniles exhibited an energy allocation pattern characterized by high growth efficiency and low metabolic consumption. Consequently, the optimal rearing temperature for triploid turbot juveniles with an average weight of 120 g ranged from 18.1–18.9 ℃. These findings offer valuable insights into optimizing aquaculture conditions, improving feed efficiency, and controlling water environment pollution in the context of triploid turbot farming.

Turbot (Scophthalmus maximus) is one of the most economically important fish in the northern coastal areas of China. Recently, low salinity stress is an important factor influencing the development of the turbot industry. Lately, the industry has faced challenges posed by low salinity stress, a key factor influencing turbot development. Salinity fluctuations represent a crucial environmental stressor in aquaculture, impacting osmotic pressure and inducing abnormal energy metabolism. Our preliminary research had identified that low salinity stress contributes to lipid metabolism disorders in turbot. This study aims to investigate the impact of varying lipid concentration levels on the lipid metabolism disorders induced by low salinity stress. To achieve this, feeding experiments were conducted with different lipid concentration levels under low salinity stress conditions, determining the optimal lipid requirement for turbot to cope with reduced salinity. Three salinity gradients (10, 20, and 30) were employed, with four lipid concentration gradients (8%, 12%, 16%, and 20%) for each salinity group. The results revealed that at a lipid concentration of 16%, no significant difference in the growth performance of juvenile turbot was observed between the salinities of 20 and 30. However, the growth performance under a salinity of 10 was lower than that under salinities of 20 and 30. Notably, under a salinity of 10, the growth performance of juvenile turbot increased with higher lipid concentrations, reaching its peak at 20%, surpassing values under the salinities of 20 and 30. Regarding the expression of genes related to lipid metabolism, under the salinities of 10 and 20, the expression levels of genes related to lipid synthesis, lxrα, cyp7a1, and srebp-1, showed a trend of first increasing and then decreasing with increasing lipid concentration, particularly under the salinity of 10. The expression level of the 12% lipid group was higher than that of other groups and the expression level of the 20% lipid group was significantly lower than that of other groups (P < 0.05). In addition, under a salinity of 10, the expression levels of acc and fas also showed a similar situation. They were both suppressed in the 20% lipid group, and the expression levels were higher in the 12% lipid group. The expression level of the gene apoa-IV related to lipid absorption in the 20% lipid group under a salinity of 10 was markedly higher than that in other groups under the same salinity conditions (P < 0.05) and it showed a change with salt under the condition of 20% lipid concentration. The increasing and decreasing trends were contrary to the trends in other lipid groups. The aforementioned results show that after low-salt stress affects lipid metabolism, feeds with different lipid concentrations can alleviate the adverse effects of the stress from the perspectives of lipid synthesis and lipid absorption, and this mitigation effect is more reflected at the level of lipid absorption, thereby improving growth performance under low salt stress. The results reveal the adaptability of fish to low salt from the perspective of salinity affecting lipid metabolism, enrich the concentration of fish stress physiology, and provide theoretical and technical support for the breeding of low-salt tolerant turbot varieties.

Water temperature is one of the most important ecological environmental factors affecting fish survival and growth. When the water temperature is higher than the optimal temperature for fish survival, fish homeostasis may be disrupted. The heart plays a crucial role in maintaining vertebrate homeostasis. In this study, TMT and LC-MS/MS were performed to analyze differentially expressed protein (DEP) profiles in the hearts of turbot under high-temperature stress to explore the key proteins and metabolic pathways related to the high-temperature tolerance traits of turbot. Ninety turbot (mean weight 23.01±3.63 g, mean length 10.34±0.76 cm) were used in experiments. Three temperature points for heat stress experiments were designed: control=(14.0±0.5)℃, HT1=(20.0±0.5)℃, and HT2=(28.0±0.5)℃. Three parallel groups were established for each temperature group, with 10 turbots placed in each group. Fold Change≥1.2 or < 0.83, P < 0.05 was used as a criterion to screen for DEPs in turbot. Through mass spectrometry analysis of heart tissues from turbot, 85, 731 spectra were identified, with 35, 434 peptides, of which 31, 704 were unique, and 4, 765 proteins were identified. The HT1/control group in the heart of turbot had a total of 87 differentially expressed proteins, including 77 upregulated and 10 down-regulated proteins; the HT2/control group in the heart of turbot had 171 DEPs, including 149 upregulated and 22 down-regulated proteins; the HT2/HT1 group in the heart of turbot had a total of 188 DEPs, including 130 upregulated and 58 downregulated proteins. Through bioinformatics analysis, the DEPs between the 28℃ group and the 14℃ group, as well as the 28℃ group and the 20℃ group, were mainly enriched in KEGG pathways related to fatty acid metabolism, inflammation, and immune defense. Multiple proteins in the heat shock protein family (HSP90B, HSP70, etc.) were significantly upregulated in the 28℃ group compared to the 14℃ group. The protein interaction network revealed that HSP90B exhibited the highest correlation. A new discovery is that the expression levels of fibrinogen-related proteins (FGA, FGB, and FGG) increased, and their role in the thermal response requires further research. These results indicate that extremely high temperatures may cause fatty acid metabolic disorders in turbot, leading to inflammatory reactions. The upregulation of heat shock protein family proteins may have a positive effect on alleviating stress symptoms under heat stress. This study identified DEPs, such as HSP90B, HSPA5, and HYOU1, which were significantly upregulated under heat stress, as candidate proteins for high-temperature tolerance breeding in turbot and provided a theoretical basis for further elucidating the molecular mechanism of heat stress in turbot.

Changes in the total viable count (TVC), total volatile base nitrogen (TVB-N) content, thiobarbituric acid (TBA) value, K value, water distribution, microstructure and protein degradation of whole, gutted and filleted turbot were determined during ice storage, and the taste profiles were collected using an electronic tongue. Meanwhile, the volatile substances were detected by gas chromatography-ion mobility spectrometry (GC-IMS). The results showed that the filleted fish had higher values of TVC, TVB-N and TBA than the whole and gutted fish during ice storage, with a TVC value of 7.05 (lg (CFU/g)) being recorded after 12 days, exceeding that at the end of storage. In addition, the content of salt-soluble protein in the fillet decreased to the lowest level of 1.57% on day 19, which was accompanied by a greater degree of muscle fiber breakage and increased space between muscle fibers. Compared with the whole fish, the gutted fish had higher TVC and TVB-N values of 6.58 (lg (CFU/g)) and 16.72 mg/100 g on day 19, respectively. The percentages of free water in the whole and gutted fish at the end of storage were 0.21% and 0.28%, respectively, which were significantly lower than that of the fillet (P < 0.05), indicating better maintenance of muscle tissue structure in the whole and gutted fish. Finally, orthogonal partial least squares-discriminant analysis (OPLS-DA) and clustered heatmap analysis based on the measured GC-IMS fingerprints distinguished the whole, gutted and filleted fish at different storage times. In conclusion, the rate of quality deterioration of the fillet was the fastest, followed by the gutted fish, and the quality of the whole fish deteriorated at the slowest rate under ice storage conditions. The results of this study can provide a reference for developing an alternative to traditional live circulation of turbot.

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Cystatin is a protease inhibitor that also regulates genes expression linked to inflammation and plays a role in defense and regulation. Methods and results: Cystatin 10 (Smcys10) was cloned from Scophthalmus maximus and encodes a 145 amino acid polypeptide. The results of qRT-PCR showed that Smcys10 exhibited tissue-specific expression patterns, and its expression was significantly higher in the skin than in other tissues. The expression level of Smcys10 was significantly different in the skin, gill, head kidney, spleen and macrophages after Vibrio anguillarum infection, indicating that Smcys10 may play an important role in resistance to V. anguillarum infection. The recombinant Smcys10 protein showed binding and agglutinating activity in a Ca2+-dependent manner against bacteria. rSmcys10 treatment upregulated the expression of IL-10, TNF-α and TGF-β in macrophages of turbot and hindered the release of lactate dehydrogenase (LDH) from macrophages after V. anguillarum infection, which confirmed that rSmcys10 reduced the damage to macrophages by V. anguillarum. The NF-κB pathway was suppressed by Smcys10, as demonstrated by dual-luciferase analysis. Conclusions: These results indicated that Smcys10 is involved in the host antibacterial immune response. [ABSTRACT FROM AUTHOR]

In China, a novel pathogen within the genus Circovirus has been identified as a causative agent of the ‘novel acute hemorrhage syndrome’ (NAHS) in aquacultured populations of turbot (Scophthalmus maximus L.). Histopathological examination using light microscopy revealed extensive necrosis within the cardiac, splenic, and renal tissues of the afflicted fish. Utilizing transmission electron microscopy (TEM), we detected the presence of circovirus particles within the cytoplasm of these cells, with the virions consistently exhibiting a spherical morphology of 20–40 nm in diameter. TEM inspections confirmed the predominance of these virions in the heart, spleen, and kidney. Subsequent molecular characterization through polymerase chain reaction (PCR) analysis corroborated the TEM findings, with positive signals in the aforementioned tissues, in stark contrast to the lack of detection in gill, fin, liver, and intestinal tissues. The TEM observations, supported by PCR electrophoresis data, strongly suggest that the spleen and kidney are the primary targets of the viral infection. Further characterization using biophysical, biochemical assays, and genomic sequencing confirmed the viral classification within the genus Circovirus, resulting in the nomenclature of turbot circovirus (TurCV). The current research endeavors to shed light on the pathogenesis of this pathogen, offering insights into the infection mechanisms of TurCV in this novel piscine host, thereby contributing to the broader understanding of its impact on turbot health and aquaculture.

To evaluate the effects of probiotics following the administration of different antibiotics on turbot Scophthalmus maximus, a 35-day culture experiment with dietary feeding with antibiotics and probiotics was conducted. Groups E and F received enrofloxacin and florfenicol for 15 days respectively, followed by supplementation of probiotics B. coagulans for 20 days. Fish growth, immunity, antibiotic resistance genes (ARGs), and intestinal microflora were investigated. Significant growth was observed, and the expression of IL-8 and TNF-α was significantly upregulated in most of examined organs in both groups, indicating B. coagulans supplementation improves the growth performance. The four analyzed ARGs were downregulated with B. coagulans supplementation though they were upregulated with antibiotic administration. The administration of florfenicol decreased Vibrio abundance but increased the abundance of potentially pathogenic bacteria such as Clostridia, Turicibacter, and Erysipelotrichia, and the administration of enrofloxacin increased the abundance of Clostridia. Notably, B. coagulans supplementation decreased the abundance of opportunistic pathogens such as Clostridia, Turicibacter, Erysipelotrichales, and Lachnospiraceae, indicating B. coagulans may help restore homeostasis of intestinal microflora. Overall, the present study results revealed the probiotic B. coagulans yields a beneficial effect on juvenile turbot and provides a novel therapeutic approach to reduce negative effects caused by antibiotics in fish. [ABSTRACT FROM AUTHOR]

Antibiotics are widely used in aquaculture to treat the bacterial diseases. However, the improper use of antibiotics could lead to environmental pollution and development of resistance. As a safe and eco-friendly alternative, antimicrobial peptides (AMPs) are commonly explored as therapeutic agents. In this study, a mutant strain of Tetraselmis subcordiformis containing AMP NZ2114 was developed and used as an oral drug delivery system to reduce the use of antibiotics in turbot (Scophthalmus maximus) aquaculture. The gut, kidney, and liver immune-related genes and their effects on gut digestion and bacterial communities in turbot fed with NZ2114 were evaluated in an 11-day feeding experiment. The results showed that compared with the group fed with wild-type T. subcordiformis, the group fed with T. subcordiformis transformants containing NZ2114 was revealed with decreased levels of both pro-inflammatory factors (TNF-α and IL-1β), inhibitory effect on Staphylococcus aureus, Vibrio parahaemolyticus, and Vibrio splendidus demonstrated by the in vitro simulation experiments, and increased richness and diversity of the gut microbiota of turbot. In conclusion, our study provided a novel, beneficial, and low-cost method for controlling bacteria in turbot culture through the oral drug delivery systems. [ABSTRACT FROM AUTHOR]

In this article, the effect of active coatings of flaxseed gum (FG) and sodium alginate (SA) containing carvacrol (CA) on the quality of turbot (Scophthalmus maximus) after storage at 4 °C for 18 days was evaluated. The experimental results showed that FG/SA-CA could effectively inhibit the growth of microorganisms. At the same time, FG/SA-CA reduced the value of odorous-related compounds including thiobarbituric acid reactive substances (TBARS), total volatile base nitrogen (TVB-N), and K values. The FG/SA-CA significantly delayed the oxidation of myofibrillar protein (MP) through controlling the development of carbonyl groups and maintaining a high content of sulfhydryl groups. Thus, FG/SA-CA inhibits the growth of spoilage microorganisms, maintains the structure of the protein, and extends the refrigerated shelf life of turbot. [ABSTRACT FROM AUTHOR]

Clostridium autoethanogenum protein (CAP) is an emerging protein source with several key advantages and it has investigated on juvenile turbot (9.13 g). However, it was indicated that fish growth stage is a decisive factor for CAP performance and the influence of CAP on turbot intestine health has not been reported. Thus, it is worth investigating the effects of CAP on turbot extensively. In the present study, a 67-day feeding experiment was conducted to evaluate the effects of CAP on turbot in the grow-out phase from growth performance, intestine and liver health. Six hundred and thirty turbot with an initial body weight of about 150 g were randomly divided into 6 groups, which were fed with fishmeal-based control diet or diet with CAP to replace 15%, 30%, 45%, 60% and 75% of fishmeal protein in control diet, respectively. From growth and feed utilization, the substitution level of CAP should not exceed 30%, which was less than previous reported on juvenile turbot. The palatability of the feed was linearly reduced. Although CAP did not induce enteritis, it decreased the intestine villi height in middle intestine and villi density in distal intestine. Except for decreasing the size of hepatocytes by CAP at 45% or higher substitution levels, no other abnormality observed in liver histology. However, dietary CAP reduced the triglyceride and cholesterol levels in the plasma at 30% or higher levels and linearly down-regulated genes related to lipogenesis in liver. The genes related lipid transportation and oxidation were up-regulated by CAP at the substitution levels of 15–60%. The present work confirmed the safety of CAP in fish feed and suggested more work should be conducted before it widely used in aquafeed.

In this study, Lysinibacillus macroides G117 was isolated from vinegar residue, and the probiotic activity of its postbiotics was determined in Artemia salina and Scophthalmus maximus. First, the functional genome of L. macroides G117 was analysed. The total length of the genome was 4,728,501 bp, composed of one ring chromosome and two ring plasmids. Two gene clusters, β-lactone and type III polyketide synthases (T3PKS), well-known for anti-toxic, anti-inflammatory, antioxidant, anticancer activities, were predicted through the antiSMASH database. In addition, probiotic genes for antioxidants, stress resistance, and anaerobic respiration were identified using the KEGG database. These results suggest that L. macroides G117 could be used as a probiotic in aquaculture. To further assess the probiotic properties of L. macroides G117, postbiotics were cultured and collected. Based on the survival rate of pesticide-stimulated A. salina, the optimum culture condition of L. macroides G117 was analysed. The optimal culture conditions were 1 % sucrose, 1.5 % yeast extract, 0.1 % MgSO4·7H2O, 30 °C, pH 7.8, bottled fluid volume 100 mL, shaking speed 180 rpm, inoculation quantity 0.5 %, and fermentation for 48 h, with a 15 % increase in survival rate of A. salina with the addition of optimised postbiotics. Untargeted metabolomic analysis revealed significant differences between the non-optimised and optimised postbiotics, mainly in amino acid and carbohydrate metabolites. Notably, postbiotics significantly increased the antioxidant enzymes in A. salina (catalase (CAT) and total superoxide dismutase (T-SOD)) and S. maximus (T-SOD) and decreased malondialdehyde (MDA) content. In addition, the activities of anaerobic respiratory-related enzymes (lactate dehydrogenase (LDH) and pyruvate kinase (PK)) were significantly increased, whereas those of aerobic respiratory-related enzymes (malate dehydrogenase (MDH)) were significantly decreased in S. maximus. These results suggest that L. macroides G117 postbiotics could improve the antioxidant and anti-stress abilities of the two types of organisms.

Peroxisome proliferator–activated receptor β (pparβ) is a key gene–regulating lipid metabolism pathway, but its function in turbot remains unclear. In this study, the CDS of pparβ was cloned from kidney for the first time. The CDS sequence length was 1533 bp encoding 510 amino acids. Structural analysis showed that the pparβ protein contained a C4 zinc finger and HOLI domain, suggesting that the pparβ gene of turbot has high homology with the PPAR gene of other species. The high expression patterns of pparβ, acox, and cpt-1 at high temperatures, as shown through qPCR, indicated that high temperatures activated the transcriptional activity of pparβ and increased the activity of the acox and cpt-1 genes. The expression of acox and cpt-1 was significantly inhibited when pparβ was downregulated using RNAi technology and inhibitor treatments, suggesting that pparβ positively regulated acox and cpt-1 expression at high temperatures and, thus, modulates lipid catabolism activity. These results demonstrate that pparβ is involved in the regulation of lipid metabolism at high temperatures and expand a new perspective for studying the regulation of lipid metabolism in stress environments of teleost. [ABSTRACT FROM AUTHOR]

Turbot Scophthalmus maximus is an important mariculture fish species with high economic value. However, the bacterial diseases caused by Vibrio anguillarum infection bring huge economic losses to the turbot aquaculture industry. To understand the immune response of the turbot against V. anguillarum infection and to explore novel immune-related genes, the transcriptome analysis of turbot spleen and gills were conducted after V. anguillarum infection. Differentially expressed genes (DEGs) were identified in spleen and gill of the turbot amounted to 17 261 and 16 436, respectively. A large number of immune-related DEGs were enriched in cytokine-cytokine receptor interaction signaling pathway, and the others by the kyoto encyclopedia of genes and genomes (KEGG) enrichment. The gene ontology (GO) classification analysis revealed that V. anguillarum infection had the greatest effect on biological processes and cellular components. Twelve immune-related DEGs were identified in the spleen (cstl.1, egfl6, lamb21, v2rx4, calcr, and gpr78a) and gills (ghra, sh3gl2a, cst12, inhbaa, cxcl8, and il-1b) by heat map. The protein-protein interaction (PPI) networks were constructed to analyze the immune mechanism. The results demonstrate that the maturation and antigen processing of major histocompatibility complex (MHC) class II molecule, and calcitonin- or adrenomedullin-regulated physiological activity were important events in the immunity of turbot against V. anguillarum infection. In the gills, the protein interactions in TGF-β signaling pathway, production of inflammatory factors, and endocytosis regulation were most significant. Our research laid a foundation for discovering novel immune-related genes and enriching the knowledge of immune mechanisms of turbot against V. anguillarum infection. [ABSTRACT FROM AUTHOR]

Aim of study: Studies on the dietary needs of turbot fish (Scophthalmus maximus Linnaeus, 1758) have largely focused on the juvenile stage; however, there are not many on the larger (300–500 g) species. The purpose of this experiment was to determine the ideal dietary levels of protein, fat, and carbohydrate for large turbot. Area of study: Demre, Antalya, Türkiye. Material and methods: A three-component mixture design model was created to adjust the quantities of dietary protein between 45.6% and 63.4%, carbohydrates between 4.9% and 30.5%, and fat between 5.6% and 17.7%. The components of the model were fish meal (FM), fish oil (FO), and wheat flour (W). Fish initially weighing 301.6±0.1 g on average were fed 14 different diets for 10 weeks. The ideal dietary macronutrient levels were estimated by examining the prediction profiler at the highest desirability based on the variables that were selected to maximize final weight, daily growth coefficient, protein efficiency ratio, nitrogen and energy retentions, and minimize feed conversion ratio, nitrogen and carbon losses. Main results: The optimal diet formulation yielded the highest desirability of 0.87 for all selected responses and resulted in dietary inclusion levels of FM, W and FO as 63.6%, 20.8%, and 9.4%, respectively. The proposed optimal nutrient concentrations for large turbot (growing from 300 to 500 g) are 54% protein, approximately 17% lipid, and 15.8% carbohydrate on dry matter basis. Research highlights: The mixture design successfully allowed us to estimate the optimum levels of dietary protein, lipid and carbohydrate for large turbot.

This study describes the transcriptome profiles of turbot (Scophthalmus maximus) embryos exposed to various light spectra, helping to better understand the importance of light spectrum on the development of fish embryo. When exposed to red, orange, green or blue light, up-regulated genes were significantly enriched into lipid, carbohydrate metabolism, indicating enhanced energy consumption compared with full-spectrum light. Molecular functions related to signal transduction, such as supramolecular polymers/complexes/fibers, protein dimerization, were down-regulated in red, orange, and blue groups, while calcium ion binding was up-regulated under green light, indicating that turbot embryo might be more sensitive to green light. The transcription regulator activity and DNA binding transcription factor activity related to retina and nervous system development were down-regulated in orange, green and blue groups, suggesting full light spectrum could be more conducive to the development of nervous system. Moreover, orange light could be advantageous for enhancing the antioxidant capacity, while green light caused abnormal expression of some development related genes. The non-visual photoreceptors with vertebrate ancient opsin and exorhodopsin expression in hypothalamus, hindbrain and pineal area played mainly photosensitive roles. This study provides new insights into the molecular mechanisms underlying photosensitive-phototransduction-physiological-development process in fish embryos and further confirmed the feasibility of utilizing orange light and full spectrum light to establish optimized developmental light spectrum environment in turbot embryo incubation systems.

The mass production of triploid turbot Scophthalmus maximus is expected to enhance the economic benefits of aquaculture due to its sterility, growth, and survival advantages. Among the methods for inducing triploidy in teleost, pressure shock has been considered a more consistent and reliable approach. In this study, the optimal parameters for inducing triploidy in turbot through hydrostatic pressure shock were investigated in a series of trials, including the intensity (55–75 MPa), timing (3.5–8.5 min after fertilization, maf) and duration (4–12 min). The ploidy level was determined by flow cytometry analysis. Under a water temperature of 14.5 ± 0.5 °C, treatment optima for pressure shock were determined to be 4.5–5.5 maf with 60 MPa for 6 min, resulting in 100% triploidy rate. A comparison of induction efficiency between pressure shock using this combination and cold shock initiated at 6.5 maf in −2 °C sea water for 25 min was carried out using eggs from three females. The higher hatching rates and triploidy rates, and lower abnormality rates were investigated with pressure shock treatment compared with cold shock treatment. The optimized parameters were successfully applied to three large batches of eggs (∼ 250, 300 and 330 mL) for mass production of triploid turbot. The total length and body weight of triploids were significantly lower than those of diploid counterparts at 2 months after hatching (mah), however, they exhibited a significant increase at 8 and 11 mah, respectively, and maintained this higher level thereafter. Additionally, the survival rates remained similar from 2 to 12 mah. The results of this preliminary study indicate that pressure shock rather than cold shock is more beneficial for the commercial production of triploid turbot under farming conditions.

Long non-coding RNAs (lncRNAs) play crucial roles in a variety of biological processes, including stress response. However, the number, characteristics and stress-related expression of lncRNAs in turbot are still largely unknown. In this study, a total of 12,999 lncRNAs were identified at the genome-wide level of turbot for the first time using 24 RNA-seq datasets. Sequence characteristic analyses of transcripts showed that lncRNA transcripts were shorter in average length, lower in average GC content and in average expression level as compared to the coding genes. Expression pattern analyses of lncRNAs in 12 distinct tissues showed that lncRNAs, especially lincRNA, exhibited stronger tissue-specific expression than coding genes. Moreover, 612, 1351, 1060, 875, 420 and 1689 differentially expressed (DE) lncRNAs under Vibrio anguillarum, Enteromyxum scophthalmi, and Megalocytivirus infection and heat, oxygen, and salinity stress conditions were identified, respectively. Among them, 151 and 62 lncRNAs showed differential expression under various abiotic and biotic stresses, respectively, and 11 lncRNAs differentially expressed under both abiotic and biotic stresses were selected as comprehensive stress-responsive lncRNA candidates. Furthermore, expression pattern analysis and qPCR validation both verified the comprehensive stress-responsive functions of these 11 lncRNAs. In addition, 497 significantly co-expressed target genes (correlation coefficient (R) > 0.7 and q-value < 0.05) for these 11 comprehensive stress-responsive lncRNA candidates were identified. Finally, GO and KEGG enrichment analyses indicated that these target genes were enriched mainly in molecular function, such as cytokine activity and active transmembrane transporter activity, in biological processes, such as response to stimulus and immune response, and in pathways, such as protein families: signaling and cellular processes, transporters and metabolism. These findings not only provide valuable reference resources for further research on the molecular basis and function of lncRNAs in turbot but also help to accelerate the progress of molecularly selective breeding of stress-resistant turbot strains or varieties. [ABSTRACT FROM AUTHOR]

Pheromones play a vital role in regulating fish behavior, including reproduction, aggregation, hazard recognition and food location. To gain a better understanding of chemical communication in fish produced by density changes, this study analyzed the metabolites released by turbot (Scophthalmus maximus) under different stocking densities. The experiment was conducted at low (LD: 3.01 kg/m2), medium (MD: 6.62 kg/m2) and high (HD: 10.84 kg/m2) densities for 15 days. High-throughput non-targeted metabolomics (LC-MS/MS) was used to identify variations in metabolites released into the aquatic environment by turbot at different densities. Results showed that 29 and 47 metabolites were significantly upregulated in the MD and HD groups, respectively, compared with the LD group. Among them, hexadecanedioic acid, xanthine, phenethylamine, proline and styrene were significantly upregulated in the MD vs. LD, HD vs. MD and HD vs. LD. The VIP diagram of OPLS-DA alignment showed that phenethylamine was the most important metabolite shared by MD vs. LD, HD vs. MD and HD vs. LD. Key gene changes in the GH/IGF-1 signaling pathway, HPI axis of turbot were studied using qRT-PCR for density treatment. The results demonstrated that the expression of GH, GHR and IGF-1 was significantly lower, while the expression of CRH and ACTH was higher in the HD group. Additionally, plasma levels of cortisol, glucose, triglycerides and T3 were also highest in the HD group compared with the LD and MD groups. Phenylethylamine concentration was positively correlated with the HPI axis and negatively correlated with the GH/IGF-1 signaling pathway. To investigate the impact of phenethylamine accumulation on turbot, an acute treatment experiment with phenethylamine was set up. Its concentration in the aquatic environment was set at 0 (CON), 10−7 (LP) and 10−5 (HP) mol/L via exogenous addition, and turbot were exposed to these environments for 2 days. There was a high degree of concordance between the GH/IGF-1 signaling pathway (GH, GHR, IGF-1), HPI axis (CRH, ACTH) and plasma physiological changes (cortisol, glucose, triglycerides, T3) in the phenethylamine-treated group and the density-treated group. Therefore, accumulation of phenethylamine with increasing stocking density may be a potential cause of density stress. Phenylethylamine has a dose-dependent and trace effect as a pheromone. [ABSTRACT FROM AUTHOR]

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A turbot (Scophthalmus maximus) cell line named SMSP was obtained from the spleen. The origin of the cells was identified by morphology, chromosome number and COI gene. The optimal basic medium, serum concentration and growth temperature of the cells were detected. SMSP cell line is mainly composed of fibroblast-like cells. Most of the SMSP cells contained 44 chromosomes, and the sequence of COI gene confirmed that the cells were originated from turbot. The optimal culture conditions were 24 °C, DMEM + 10% FBS. The cell line had high transfection efficiency for siRNA and plasmid. After stimulation with lipopolysaccharide (LPS) or poly (I:C), the expressions of immune-related genes such as TNF-β, IL-12s, IL-10 and IL-1β were up-regulated significantly in the early stage (P<0.05). This study will provide a model for exploring immune mechanism of turbot against pathogen in vitro. [ABSTRACT FROM AUTHOR]

Fish blood tends to coagulate due to its specialized characteristics. In general, the detection of blood physiological indices using anticoagulants reflects normal physiological status. However, the selection and application of anticoagulants have no uniform standards because of the specificity and diversity of fish species. In the present study, the effects of three different anticoagulants (sodium heparin, K2EDTA, and sodium citrate) were investigated on coagulation, blood cell type, hematological parameters (white blood cells, red blood cells, hematocrit, and hemoglobin), and plasma cortisol and glucose contents in turbot during acute hypoxic stress. The choice of anticoagulants may result in significant differences in turbot blood physiology and chemistry. To supply technological support in turbot hematological research and best-practice aquaculture, this study compared the effects of three common anticoagulants between normal dissolved oxygen and acute hypoxic states. The recirculating aquaculture system is the main culture model for turbot; water temperature and dissolved oxygen levels are important environmental factors, especially in high-density industrial systems. Sufficient oxygen is key to maintaining normal metabolism in turbot. Experimental procedures were designed for control and treatment groups, each group had three parallels, and 54 turbots were studied in all. In the control group, 200 mg/L MS-222 was used to anesthetize a specimen before collecting 5 mL of blood from the caudal vein; the blood was transferred through a needle and vacuum tubes containing three different anticoagulants, then the vacuum tubes were stored for evaluation after 6 h and 12 h. In the treatment group, nitrogen gas was used to rapidly reduce the concentration of dissolved oxygen in the container to (1.2±0.3) mg/L (measured with a dissolved oxygen meter), after which the same procedure of anesthesia and blood collection was conducted. For blood cell type and morphology studies, the Giemsa staining method was used to make blood smears. The original solution of Giemsa was diluted before use. The slide was sterilized before a drop of blood was placed on one side of the slide; one edge of a cover glass was placed in contact with the drop of blood and pushed to the opposite side of the slide at a constant velocity; the slide was then fixed with methanol for 10~15 min and stained for 15~30 min. The smears were washed and dried after staining. Finally, the stained smears were observed under a Leica microscope to determine blood cell morphology, and images were taken. Blood samples were divided into two parts for detecting physiological and biochemical indices: one was centrifuged at 3500 r/min for 10 min, and the supernatant was stored at –80℃ for the detection of plasma glucose and cortisol content using commercial kits. The residual blood samples were stored in a refrigerator at 4℃ for the detection of physiological indices using an automatic blood cell analyzer. The anticoagulant effect of K2EDTA was most effective under a normal dissolved oxygen state, and the anticoagulant effect of K2EDTA and heparin sodium were most effective after 6 h and 12 h of exposure to acute hypoxia stress, respectively. In addition to coagulation, blood cell morphology showed that binucleate cells occurred through sodium heparin, eosinophils, and basophils through sodium citrate and basophils through K2EDTA in the control. Three nucleus abnormality types were identified in the smears: micronucleus cells, binucleate cells, and erythroplastids. Binucleate cells were found using sodium heparin in the control group. In addition, binucleate cells were observed under three different anticoagulants in the treatment group, and micronucleus cells and erythroplastids were observed in the treatment group. The hematological index showed that the number of white blood cells was significantly increased by treatment with three anticoagulants during acute hypoxic stress (P < 0.05), and the number of red blood cells and hemoglobin content was significantly increased by treatment with K2EDTA and sodium heparin (P < 0.05). However, they were significantly reduced after treatment with sodium citrate. In addition, the plasma glucose and cortisol content were significantly increased when subjected to acute hypoxic stress, but the content of sodium heparin was significantly lower than that of both sodium citrate and K2EDTA. In summary, K2EDTA showed less blood coagulation than other anticoagulants, sodium heparin caused binucleate cells and decreased plasma glucose and cortisol, and sodium citrate affected the number of red blood cells and hemoglobin content. K2EDTA is the more promising anticoagulant compared to sodium heparin and sodium citrate for blood analysis of turbot and promotes the precision of turbot hematological studies under acute hypoxic conditions.

Manganese superoxide dismutase (MnSOD) and catalase (CAT) could eliminate reactive oxygen species (ROS) and maintain the reduction-oxidation balance in cells. This study aimed to investigate their functions in turbot (Scophthalmus maximus) response to the Vibro anguillarum challenge. SmMnSOD, the full-length liver cDNA of MnSOD from S. maximus, was cloned by fast amplification of cDNA ends (RACE). Sequencing of nucleotides indicated that the SmMnSOD cDNA was 1267 base pairs with a 684-base-pair open reading frame, encoding a 228 amino acid protein with 28 amino acid residues. The SmMnSOD sequence contains MnSOD signatures (DVWEHAYY) and probable N-glycosylation sites (NVT, NHT, and NLS). The deduced sequence of SmMnSOD revealed sequence homology between 85.3% and 92.9% with those of other species. A phylogenetic study found that SmMnSOD clustered with other fish MnSOD, indicating that SmMnSOD was a member of the MnSOD family. The SmMnSOD transcript was discovered by qRT-PCR in the gill, stomach, head-kidney, muscle, liver, intestine, and heart of S. maximus, with the highest expression in the liver. Upon intervention by V. anguillarum, the liver and head kidney transcript levels of SmMnSOD were up-regulated at 12 and 48 h, whereas the temporal expression profiles of the CAT transcript increased at 6 and 24 h. As the pathogenic bacterial stress processing was prolonged to 72 h, the liver and head kidney transcript levels of SmMnSOD and CAT decreased gradually. Thus, SmMnSOD was triggered and may be related to S. maximus' immunological responses against V. anguillarum. [ABSTRACT FROM AUTHOR]

High-quality eggs are essential for the sustainability of commercial aquaculture production. Melatonin is a potent candidate for regulating the growth and maturation of oocytes. Therefore, research on the effect of melatonin on marine fish oocytes in vitro has been conducted. The present study successfully established a culture system of turbot (Scophthalmus maximus) oocytes in vitro and investigated the effect of melatonin on oocyte meiotic maturation, antioxidant capacity, and the expression of apoptosis-related genes. The cultures showed that turbot Scophthalmus maximus late-vitellogenic denuded oocytes, with diameters of 0.5–0.7 mm, had a low spontaneous maturation rate and exhibited a sensitive response to 17α, 20β-dihydroxyprogesterone (DHP) treatment in vitro. Melatonin increased by four times the rate of oocyte germinal vesicle breakdown (GVBD) in a concentration- and time-dependent manner. The mRNA of melatonin receptor 1 (mtnr1) was significantly upregulated in the oocyte and follicle after treatment with melatonin (4.3 × 10−9 M) for 24 h in vitro, whereas melatonin receptor 2 (mtnr2) and melatonin receptor 3 (mtnr3) remained unchanged. In addition, melatonin significantly increased the activities of catalase, glutathione peroxidase, and superoxide dismutase, as well as the levels of glutathione, while decreasing the levels of malondialdehyde and reactive oxygen species (ROS) levels in turbot oocytes and follicles cultures in vitro. p53, caspase3, and bax mRNAs were significantly downregulated in oocytes and follicles, whereas bcl2 mRNAs were significantly upregulated. In conclusion, the use of turbot late-vitellogenesis oocytes (0.5–0.7 mm) is suitable for establishing a culture system in vitro. Melatonin promotes oocyte meiotic maturation and antioxidative capacity and inhibits apoptosis via the p53-bax-bcl2 and caspase-dependent pathways, which have important potential to improve the maturation and quality of oocytes. [ABSTRACT FROM AUTHOR]

In this study, the exopolysaccharide (EPS) from Lactiplantibacillus plantarum (HMX2) was isolated from Chinese Northeast Sauerkraut. Its effects on juvenile turbot were investigated by adding different concentrations of HMX2-EPS (C: 0 mg/kg, H1: 100 mg/kg, H2: 500 mg/kg) to the feed. Compared with the control group, HMX2-EPS significantly improved the growth performance of juvenile turbot. The activities of antioxidant enzymes, digestive enzymes, and immune-related enzymes were significantly increased. HMX2-EPS could also increase the secretion of inflammatory factors and enhance the immune response of turbot by regulating the IFN signal transduction pathway and exhibit stronger survival rates after the A. hydrophila challenge. Moreover, HMX2-EPS could improve the diversity of intestinal microbiota in juvenile fish, increase the abundance of potential probiotics, and reduce the abundance of pathogenic bacteria. The function of gut microbes in metabolism and the immune system could also be improved. All results showed better effects with high concentrations of HMX2-EPS. These results indicated that HMX2-EPS supplementation in the diet could promote growth, improve antioxidant activity, digestive capacity, and immunity capacity, and actively regulate the intestinal microbiota of juvenile turbot. In conclusion, this study might provide basic technical and scientific support for the application of L. plantarum in aquatic feed. [ABSTRACT FROM AUTHOR]

Fish reproduction is closely related to the regulation of the brain and liver, making it essential to identify the factors that control this process. The turbot (Scophthalmus maximus) is an economically significant species that has been successfully breeding through industrial aquaculture. Investigation of factors into the involvement of gonadal development is crucial for artificial breeding. In this study, a new insulin-like growth factor 3 igf3 gene was cloned and characterized. Additionally, all three types of turbot IGFs contain a distinct IGF domain, with IGF3 and IGF2 being grouped with other teleosts, demonstrating a closely related genetic relationship. The expression analysis showed that igf3 mRNA is predominantly expressed in the gonad and brain (specifically in the pituitary and hypothalamus), suggesting its effects at multiple levels in the brain–pituitary–gonadal axis. Furthermore, the mRNA levels of igfs during gonadal development were examined. In the gonad and liver of female turbots, the expression levels of igfs mRNA significantly increased from stage II to VI during the process of oogenesis, including maturation and degeneration. In the testis and liver of male turbots, igf3 mRNA maintained high expression levels during the proliferation of spermatogonia at stages II and III. In addition, the highest levels of igf1 and igf2 were observed at the beginning of spermatogenesis and during sperm production at stages V and VI. All the results suggest that the IGFs were closely related to the gonadal development in turbot and improve a better understanding of the IGF system in the regulation of gonadal development in teleost. [ABSTRACT FROM AUTHOR]

Simple Summary: There have been reports on alternate feeding between diets based on different lipid sources, but how the intestinal microbiota of fish responds to alternate feeding strategies and its relevant roles in the host's health have not been reported. The present study provides novel results in this area. The main objective of the study was to assess how the intestinal microbiota of fish responds to alternate feeding between diets based on different lipid sources. Foremost, the juvenile turbot accepted alternate feeding between diets based on different lipid sources with no negative effects on survival or growth performance. Additionally, novel results were observed regarding the different bacterial compositions, microbial co-occurrence networks, and functional predictions among the different alternating feeding strategies. The results of this study indicate that a more comprehensive evaluation should be conducted from the perspective of intestinal microorganisms when a new feeding strategy is applied in aquaculture practices. These results will contribute to the nutritional regulation of aquatic animals from the perspective of microorganisms. A nine-week feeding trial was conducted to investigate changes in the intestinal microbiota of turbot in response to alternate feeding between terrestrially sourced oil (TSO)- and fish oil (FO)-based diets. The following three feeding strategies were designed: (1) continuous feeding with the FO-based diet (FO group); (2) weekly alternate feeding between soybean oil (SO)- and FO-based diets (SO/FO group); and (3) weekly alternate feeding between beef tallow (BT)- and FO-based diets (BT/FO group). An intestinal bacterial community analysis showed that alternate feeding reshaped the intestinal microbial composition. Higher species richness and diversity of the intestinal microbiota were observed in the alternate-feeding groups. A PCoA analysis showed that the samples clustered separately according to the feeding strategy, and among the three groups, the SO/FO group clustered relatively closer to the BT/FO group. The alternate feeding significantly decreased the abundance of Mycoplasma and selectively enriched specific microorganisms, including short-chain fatty acid (SCFA)-producing bacteria, digestive bacteria (Corynebacterium and Sphingomonas), and several potential pathogens (Desulfovibrio and Mycobacterium). Alternate feeding may maintain the intestinal microbiota balance by improving the connectivity of the ecological network and increasing the competitive interactions within the ecological network. The alternate feeding significantly upregulated the KEGG pathways of fatty acid and lipid metabolism, glycan biosynthesis, and amino acid metabolism in the intestinal microbiota. Meanwhile, the upregulation of the KEGG pathway of lipopolysaccharide biosynthesis indicates a potential risk for intestinal health. In conclusion, short-term alternate feeding between dietary lipid sources reshapes the intestinal microecology of the juvenile turbot, possibly resulting in both positive and negative effects. [ABSTRACT FROM AUTHOR]

Acidic digestion is an important digestive process of marine fish. In fish stomach, two enzymes are involved in the secretion of hydrochloric acid (HCl) and proteomic digestion: H+/K+-ATPase and pepsinogen. However, the starting of digestive function in fish is still unclear. To reveal the details of acidic digestion of turbot Scophthalmus maximus in early development, a 40 day of turbot larvae culture was conducted. The H+/K+-ATPase gene from the turbot S. maximus (smH+/K+-ATPase) was identified and characterized. Based on our previous discription on pepsinogen of turbot S. maximus, we combined pepsinogen and H+/K+-ATPase and analyzed the mechanism of acidic digestion in turbot. Results show that the spatial and temporal expression profiles of H+/K+-ATPase agreed with pepsinogen A and C in turbot, indicating a synergetic action between H+/K+-ATPase and pepsinogen during the acidic digestion process. In addition, the turbot juveniles showed a faster growth after the expressions of H+/K+-ATPase gene and pepsinogen gene, demonstrating that pepsin had a higher digestive efficiency, for which a compound diet should be provided to the fish from Day 22 onward. This study provided a reference for biology research and aquaculture of turbot and other marine fishes. [ABSTRACT FROM AUTHOR]

Heat shock proteins 70 (HSP70s) are known to play essential roles in organisms' response mechanisms to various environmental stresses. However, no systematic identification and functional analysis has been conducted for HSP70s in the turbot (Scophthalmus maximus), a commercially important worldwide flatfish. Herein, 16 HSP70 genes unevenly distributed on nine chromosomes were identified in the turbot at the genome-wide level. Analyses of gene structure, motif composition, and phylogenetic relationships provided valuable data on the HSP70s regarding their evolution, classification, and functional diversity. Expression profiles of the HSP70 genes under five different stresses were investigated by examining multiple RNA-seq datasets. Results showed that 10, 6, 8, 10, and 9 HSP70 genes showed significantly up- or downregulated expression after heat-induced, salinity-induced, and Enteromyxum scophthalmi, Vibrio anguillarum, and Megalocytivirus infection-induced stress, respectively. Among them, hsp70 (hspa1a), hspa1b, and hspa5 showed significant responses to each kind of induced stress, and qPCR analyses further validated their involvement in comprehensive anti-stress, indicating their involvement in organisms' anti-stress mechanisms. These findings not only provide new insights into the biological function of HSP70s in turbot adapting to various environmental stresses, but also contribute to the development of molecular-based selective breeding programs for the production of stress-resistant turbot strains in the aquaculture industry. [ABSTRACT FROM AUTHOR]

In the present study, the effect of Clostridium butyricum H129 on the growth performance and intestinal health of Scophthalmus maximus was investigated in an indoor circulating aquaculture system during an 8-week trial period. Three hundred sixty healthy turbots were randomly divided into four groups fed with C. butyricum H129 at different concentrations (0, 106, 107, and 108 CFU/g), respectively. In terms of terminal body weight, weight gain rate and specific growth rate of turbot, the CB2 (107 CFU/g) group performed best. The amylase enzyme activity of the intestine was significantly increased in CB2 groups (p

Turbot (Scophthalmus maximus) is an important commercial fish in China that can be infected by a series of bacterial pathogens, leading to great economic losses. In this study we focused on the epidemiology of turbot bacterial diseases in the major farming areas in China for three years. A total of 155 cases with 446 diseased turbots were investigated, and dominant bacterial pathogens were isolated from 137 cases (344 turbots). Thus, bacteria are the major threat to farming turbot in China. Edwardsiella piscicida was the major pathogen, which isolated as the dominant colony in 62 cases (40.00%) with 151 turbots (33.85%). Aeromonas salmonicida was isolated in 57 cases (36.77%) with 116 turbots (26.01%). Vibrio anguillarum was isolated in nine cases (5.81%), and Streptococcus parauberis in five cases (3.23%). Photobacterium damselae and Mycobacterium marinum were also isolated from one or two diseased fish. Other Vibrio spp. were isolated in 15 cases (9.68%). Two species of pathogen were isolated in 13 cases, and three species (E. piscicida, A. salmonicida, and S. parauberis) in one case. In 19 cases, no bacteria were isolated. Based on the annual disease analysis, we found that the E. piscicida infection proportion of total cases was greatly decreased, which may be caused by the attenuated vaccine inoculated in 2018. The antibiotic resistance of E. piscicida strains isolated in Weifang city was also determined. We found that the resistance to ceftriaxone, doxycycline, and SMZ/TMP were significantly increased from October 2016 to June 2018, and all the E. piscicida isolates exhibited resistance to SMZ/TMP in June 2018. These results indicated that E. piscicida is the major threat to turbot farming in China, and the attenuated E. piscicida vaccine exhibits effective protection. The usage of antibiotics may induce resistance quickly. Thus, development of vaccines is an important work for sustainable development of turbot farming in the future.

LncRNA plays key role in several biological processes, including transcriptional regulation, post transcriptional control and epigenetic regulation. However, research on the functional roles of lncRNAs in teleost species remains limited. Here, we discovered a lncRNA (BCO1-AS) with a critical role in antibacterial responses. Briefly, the full length of BCO1-AS was 2005 bp. Subsequently, BCO1-AS was distributed throughout the nucleus, where it may either trans - or cis -regulate the nearby genes. In addition, BCO1-AS was widely expressed in all the examined tissues with the highest expression level in intestine, while the lowest expression level was detected in muscle. Moreover, following Vibrio anguillarum challenge, BCO1-AS was significantly down-regulated in intestine, and up-regulated in gill and skin. In CHIRP experiment, BCO1-AS could effectively enrich RNA and might interact with several immune-related genes. Furthermore, we found that LPS could induce the expression of BCO1-AS. Finally, BCO1-AS could positively regulate caspase-1 at the mRNA and protein level. The BCO1-AS was speculated to inhibit the synthesis of inflammatory components. In summary, these results showed the roles of BCO1-AS in the regulation of inflammatory in turbot, which provided valuable information for further understanding the immune regulation network of lncRNA in teleost fish. [ABSTRACT FROM AUTHOR]

• Discovered and identified a new type of aquaculture virus turbot circovirus (TurCV);. • The entire genome of TurCV was sequenced and its intracellular colonization morphology was identified. • TurCV mainly infects spleen and kidney in turbot. In China, a novel pathogen within the genus Circovirus has been identified as a causative agent of the 'novel acute hemorrhage syndrome' (NAHS) in aquacultured populations of turbot (Scophthalmus maximus L.). Histopathological examination using light microscopy revealed extensive necrosis within the cardiac, splenic, and renal tissues of the afflicted fish. Utilizing transmission electron microscopy (TEM), we detected the presence of circovirus particles within the cytoplasm of these cells, with the virions consistently exhibiting a spherical morphology of 20–40 nm in diameter. TEM inspections confirmed the predominance of these virions in the heart, spleen, and kidney. Subsequent molecular characterization through polymerase chain reaction (PCR) analysis corroborated the TEM findings, with positive signals in the aforementioned tissues, in stark contrast to the lack of detection in gill, fin, liver, and intestinal tissues. The TEM observations, supported by PCR electrophoresis data, strongly suggest that the spleen and kidney are the primary targets of the viral infection. Further characterization using biophysical, biochemical assays, and genomic sequencing confirmed the viral classification within the genus Circovirus , resulting in the nomenclature of turbot circovirus (TurCV). The current research endeavors to shed light on the pathogenesis of this pathogen, offering insights into the infection mechanisms of TurCV in this novel piscine host, thereby contributing to the broader understanding of its impact on turbot health and aquaculture. [ABSTRACT FROM AUTHOR]

Long non-coding RNAs (lncRNAs) play crucial roles in a variety of biological processes, including stress response. However, the number, characteristics and stress-related expression of lncRNAs in turbot are still largely unknown. In this study, a total of 12,999 lncRNAs were identified at the genome-wide level of turbot for the first time using 24 RNA-seq datasets. Sequence characteristic analyses of transcripts showed that lncRNA transcripts were shorter in average length, lower in average GC content and in average expression level as compared to the coding genes. Expression pattern analyses of lncRNAs in 12 distinct tissues showed that lncRNAs, especially lincRNA, exhibited stronger tissue-specific expression than coding genes. Moreover, 612, 1351, 1060, 875, 420 and 1689 differentially expressed (DE) lncRNAs under Vibrio anguillarum, Enteromyxum scophthalmi, and Megalocytivirus infection and heat, oxygen, and salinity stress conditions were identified, respectively. Among them, 151 and 62 lncRNAs showed differential expression under various abiotic and biotic stresses, respectively, and 11 lncRNAs differentially expressed under both abiotic and biotic stresses were selected as comprehensive stress-responsive lncRNA candidates. Furthermore, expression pattern analysis and qPCR validation both verified the comprehensive stress-responsive functions of these 11 lncRNAs. In addition, 497 significantly co-expressed target genes (correlation coefficient (R) > 0.7 and q-value < 0.05) for these 11 comprehensive stress-responsive lncRNA candidates were identified. Finally, GO and KEGG enrichment analyses indicated that these target genes were enriched mainly in molecular function, such as cytokine activity and active transmembrane transporter activity, in biological processes, such as response to stimulus and immune response, and in pathways, such as protein families: signaling and cellular processes, transporters and metabolism. These findings not only provide valuable reference resources for further research on the molecular basis and function of lncRNAs in turbot but also help to accelerate the progress of molecularly selective breeding of stress-resistant turbot strains or varieties.

Pheromones play a vital role in regulating fish behavior, including reproduction, aggregation, hazard recognition and food location. To gain a better understanding of chemical communication in fish produced by density changes, this study analyzed the metabolites released by turbot (Scophthalmus maximus) under different stocking densities. The experiment was conducted at low (LD: 3.01 kg/m2), medium (MD: 6.62 kg/m2) and high (HD: 10.84 kg/m2) densities for 15 days. High-throughput non-targeted metabolomics (LC-MS/MS) was used to identify variations in metabolites released into the aquatic environment by turbot at different densities. Results showed that 29 and 47 metabolites were significantly upregulated in the MD and HD groups, respectively, compared with the LD group. Among them, hexadecanedioic acid, xanthine, phenethylamine, proline and styrene were significantly upregulated in the MD vs. LD, HD vs. MD and HD vs. LD. The VIP diagram of OPLS-DA alignment showed that phenethylamine was the most important metabolite shared by MD vs. LD, HD vs. MD and HD vs. LD. Key gene changes in the GH/IGF-1 signaling pathway, HPI axis of turbot were studied using qRT-PCR for density treatment. The results demonstrated that the expression of GH, GHR and IGF-1 was significantly lower, while the expression of CRH and ACTH was higher in the HD group. Additionally, plasma levels of cortisol, glucose, triglycerides and T3 were also highest in the HD group compared with the LD and MD groups. Phenylethylamine concentration was positively correlated with the HPI axis and negatively correlated with the GH/IGF-1 signaling pathway. To investigate the impact of phenethylamine accumulation on turbot, an acute treatment experiment with phenethylamine was set up. Its concentration in the aquatic environment was set at 0 (CON), 10−7 (LP) and 10−5 (HP) mol/L via exogenous addition, and turbot were exposed to these environments for 2 days. There was a high degree of concordance between the GH/IGF-1 signaling pathway (GH, GHR, IGF-1), HPI axis (CRH, ACTH) and plasma physiological changes (cortisol, glucose, triglycerides, T3) in the phenethylamine-treated group and the density-treated group. Therefore, accumulation of phenethylamine with increasing stocking density may be a potential cause of density stress. Phenylethylamine has a dose-dependent and trace effect as a pheromone.

IntroductionDNA methylation was one of the most important modification in epigenetics and played an important role in immune response. Since the introduction of Scophthalmus maximus, the scale of breeding has continued to expand, during which diseases caused by various bacteria, viruses and parasites have become increasingly serious. Therefore, the inactivated vaccines have been widely researched and used in the field of aquatic products with its unique advantages. However, the immune mechanism that occurred in turbot after immunization with inactivated vaccine of Aeromonas salmonicida was not clear.MethodsIn this study, differentially methylated regions (DMRs) were screened by Whole Genome Bisulfite Sequencing (WGBS) and significantly differentially expressed genes (DEGs) were screened by Transcriptome sequencing. Double luciferase report assay and DNA pull-down assay were further verified the DNA methylation state of the gene promoter region affected genes transcriptional activity after immunization with inactivated vaccine of Aeromonas salmonicida.ResultsA total of 8149 differentially methylated regions (DMRs) were screened, in which there were many immune-related genes with altered DNA methylation status. Meanwhile, 386 significantly differentially expressed genes (DEGs) were identified, many of which were significantly enriched in Toll-like receptor signaling pathway, NOD-like receptor signaling pathway and C-type lectin receptor signaling pathway. Combined analysis of WGBS results and RNA-seq results, a total of 9 DMRs of negatively regulated genes are located in the promoter region, including 2 hypermethylated genes with lower expression and 7 hypomethylated genes with higher expression. Then, two immune-related genes C5a anaphylatoxin chemotactic receptor 1-like (C5ar1-Like) and Eosinophil peroxidase-like (EPX-Like), were screened to explore the regulation mechanism of DNA methylation modification on their expression level. Moreover, the DNA methylation state of the gene promoter region affected genes transcriptional activity by inhibiting the binding of transcription factors, which lead to changes in the expression level of the gene.DiscussionWe jointly analyzed WGBS and RNA-seq results and revealed the immune mechanism that occurred in turbot after immunized with inactivated vaccine of A. salmonicida from the perspective of DNA methylation.

In this research, Vibrio vulnificus formalin‐killed (FKCs) vaccine and ghost (VVGs) vaccine were successfully developed, and shown to prevent vibriosis of Scophthalmus maximus resulting from V. vulnificus. The antibody titre of FKCs and VVGs vaccine was 1: 28 and 1: 211. The RPS of FKCs and VVGs vaccine was 60% and 80%. In order to improve the understanding of vaccine protection mechanism, transcriptome data was used to analyse the immune response of S. maximus infected with V. vulnificus after vaccination with FKCs and VVGs vaccine. In the SmCon and SmIV groups, a series of innate immune‐related genes were upregulated (such as, TLR5, Tp12, AP‐1 and IL‐1β) or downregulated (such as, CASP6 and CASP8), which suggested that the immune protection mechanism induced by inactivated vaccine was similar to that of autoimmune response. In the SmIV and SmGho group, a number of innate and adaptive immune‐related genes (such as, STAT1, IFN‐γ and MHC Ia) were activated, in which the expression of these genes was higher in SmGho, and VVGs vaccine induced stronger innate and acquired immune responses. In conclusion, the results lay a foundation for further study on the molecular mechanisms of immune protection induced by VVGs vaccine and FKCs vaccine. [ABSTRACT FROM AUTHOR]

Three antioxidant properties (corresponding to the enzymes superoxide dismutase (SOD), catalase, and glutathione peroxidase) were measured in the livers of Scophthalmus maximus under different salinities/temperatures (5, 10, 20, 30, and 40‰/17, 20, 23, 25, and 28 °C). Split-plot (SP) analysis, additive main effects, and multiplicative interaction (AMMI) and genotype × environment interaction (GGE) biplots were used to analyze genotype × salinity/temperature interactions for antioxidant properties. The results of the SP analysis show that the activity of the three antioxidant properties was significantly (p < 0.01) affected by salinity/temperature, antioxidant, and salinity/temperature × antioxidant interaction. The results of the AMMI analysis for salinity reveal that the effect of genotype, salinity, and genotype × salinity interaction on antioxidant properties reached a significant level (p < 0.001); 92.1065%, 2.6256%, and 4.4360% of the total sum of squares for antioxidant property activity were attributable to the effects of genotype, salinity, and genotype × salinity interaction, respectively. The results of GGE biplot analysis for salinity reveal differences in the activity ranking of the three antioxidant properties under five salinities; this difference expands with an decrease or increase in salinity from 30‰ (optimum salinity). A salinity of 5‰ had the strongest ability to identify the three antioxidant properties. The five experimental salinities were divided into one region, and SOD activity was the highest in this region. In a comprehensive analysis of stability and activity, SOD had the best activity and stability. The results of AMMI analysis for temperature reveal that genotype, temperature, and genotype × temperature interaction had significant effects on the antioxidant properties (p < 0.001); 82.4720%, 4.0666%, and 12.0968% of the total sum of squares for antioxidant property activity were attributable to the effects of genotype, temperature, and genotype × temperature interaction, respectively. The results of GGE biplot analysis for temperature reveal a large difference in the activity ranking of antioxidant properties between 17 °C and the other four temperatures, while only small differences in the activity rankings were detected among the other four temperatures. The difference in the activity ranking of antioxidant properties was greatest between the temperatures of 17 and 20 °C. A temperature of 17 °C showed the strongest ability to distinguish the three antioxidant properties. Additionally, the five test temperatures were grouped into one region, and comprehensive analysis of activity and stability showed that SOD had the best activity and stability. [ABSTRACT FROM AUTHOR]

The mitogen-activated protein kinase (MAPK) gene family performs crucial roles in cell division, migration, development, apoptosis, inflammatory response, and abiotic and biotic stress responses. However, very little information is available about the MAPKs in turbot (Scophthalmus maximus). In this study, 15 turbot MAPKs (SmMAPKs) were identified throughout the whole genome, and their basic chemical and physical properties and subcellular localization were illustrated. All SmMAPKs contained the serine/threonine protein kinases, catalytic domain (S_TKc, SMART00220). Phylogenetic analysis revealed that SmMAPKs were classified into three subfamilies, namely, c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38. Conserved motif and gene structure analysis revealed high levels of conservation within and between phylogenetic subfamilies. Expression patterns of MAPKs in distinct tissues and under diverse abiotic and biotic stresses were examined using the published available RNA-seq data sets. As a result, SmMAPKs showed obviously tissue-specific expression. Furthermore, 7 and 10 candidate stress-responsive MAPK genes were detected under abiotic and biotic stresses, respectively, among which five common MAPK genes, namely, SmMAPK4 (ERK4), SmMAPK6 (ERK3), SmMAPK11 (p38β), SmMAPK12b (p38γ), and SmMAPK15 (ERK7/8) showed extremely significant responses to both abiotic and biotic stresses, demonstrating their potential functions in comprehensive antistress. These results demonstrate that MAPKs might play vital roles in response to various abiotic and biotic stresses in turbot, which would contribute to making scientific preventive measures to environmental changes in the process of farming and promoting the development of selective breeding for comprehensive stress resistance in turbot.

High-quality eggs are essential for the sustainability of commercial aquaculture production. Melatonin is a potent candidate for regulating the growth and maturation of oocytes. Therefore, research on the effect of melatonin on marine fish oocytes in vitro has been conducted. The present study successfully established a culture system of turbot (Scophthalmus maximus) oocytes in vitro and investigated the effect of melatonin on oocyte meiotic maturation, antioxidant capacity, and the expression of apoptosis-related genes. The cultures showed that turbot Scophthalmus maximus late-vitellogenic denuded oocytes, with diameters of 0.5–0.7 mm, had a low spontaneous maturation rate and exhibited a sensitive response to 17α, 20β-dihydroxyprogesterone (DHP) treatment in vitro. Melatonin increased by four times the rate of oocyte germinal vesicle breakdown (GVBD) in a concentration- and time-dependent manner. The mRNA of melatonin receptor 1 (mtnr1) was significantly upregulated in the oocyte and follicle after treatment with melatonin (4.3 × 10−9 M) for 24 h in vitro, whereas melatonin receptor 2 (mtnr2) and melatonin receptor 3 (mtnr3) remained unchanged. In addition, melatonin significantly increased the activities of catalase, glutathione peroxidase, and superoxide dismutase, as well as the levels of glutathione, while decreasing the levels of malondialdehyde and reactive oxygen species (ROS) levels in turbot oocytes and follicles cultures in vitro. p53, caspase3, and bax mRNAs were significantly downregulated in oocytes and follicles, whereas bcl2 mRNAs were significantly upregulated. In conclusion, the use of turbot late-vitellogenesis oocytes (0.5–0.7 mm) is suitable for establishing a culture system in vitro. Melatonin promotes oocyte meiotic maturation and antioxidative capacity and inhibits apoptosis via the p53-bax-bcl2 and caspase-dependent pathways, which have important potential to improve the maturation and quality of oocytes.

In recent years, turbot (Scophthalmus maximus L.) ascites caused by Edwardsiella tarda has occurred frequently in China, causing serious economic losses. In this study, with E. tarda ET9 as the host bacteria, a lytic phage was isolated and named vB_EtaM_ET‐ABTNL‐9 (referred to as PETp9). The effect of using phage to prevent and control E. tarda infection in turbot was discussed. The results showed that the best preventive effect was achieved after 7 days of feeding phage with multiplicity of infection (MOI) = 10 in the phage‐feeding experiment; in the phage‐injection therapy, treatment was most effective when the phage with MOI = 10 was injected intraperitoneally immediately after the challenge; in the phage‐immersion therapy, the best therapeutic effect was obtained when the infected turbot were immersed in phage‐seawater mixture (MOI = 10) for 3 h. During the experimental period, the activities of non‐specific immune‐related enzymes in the blood of turbot were significantly increased in the untreated group, while that of the phage treated group showed a downward trend and gradually reached normal levels. It was also observed that a certain concentration of phages was present in both turbot cultured water and the intestinal tract during the experiment. Therefore, phage may be another effective control agent against E. tarda infection in turbot culture. [ABSTRACT FROM AUTHOR]

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Lysophosphatidylcholine (LPC) has been widely used as emulsifier in animal feeds to enhance the lipid utilization. However, the effects of LPC on fillet quality has rarely been known. The present study was the first time to investigate the response of fish muscle lipidomics to dietary LPC supplementation. Turbot muscle samples were collected after a 56-day feeding trial where the experimental diet contained 0 or 0.25% LPC. Targeted tandem mass spectrometry was used in the lipidomic analysis. A total of 62 individual lipids (58 up-regulated and 7 down-regulated by LPC) showed significant difference in concentration in response to dietary LPC. Most of these differentially abundant lipids were diacylglycerol, free fatty acid and cardiolipin, and they all were up-regulated by dietary LPC. However, LPC exerted only marginal effects on muscle fatty acid composition and lipid content. The effects of dietary LPC on fillet lipid composition cannot be neglected in fish product evaluation.

Fish reproduction is closely related to the regulation of the brain and liver, making it essential to identify the factors that control this process. The turbot (Scophthalmus maximus) is an economically significant species that has been successfully breeding through industrial aquaculture. Investigation of factors into the involvement of gonadal development is crucial for artificial breeding. In this study, a new insulin-like growth factor 3 igf3 gene was cloned and characterized. Additionally, all three types of turbot IGFs contain a distinct IGF domain, with IGF3 and IGF2 being grouped with other teleosts, demonstrating a closely related genetic relationship. The expression analysis showed that igf3 mRNA is predominantly expressed in the gonad and brain (specifically in the pituitary and hypothalamus), suggesting its effects at multiple levels in the brain–pituitary–gonadal axis. Furthermore, the mRNA levels of igfs during gonadal development were examined. In the gonad and liver of female turbots, the expression levels of igfs mRNA significantly increased from stage II to VI during the process of oogenesis, including maturation and degeneration. In the testis and liver of male turbots, igf3 mRNA maintained high expression levels during the proliferation of spermatogonia at stages II and III. In addition, the highest levels of igf1 and igf2 were observed at the beginning of spermatogenesis and during sperm production at stages V and VI. All the results suggest that the IGFs were closely related to the gonadal development in turbot and improve a better understanding of the IGF system in the regulation of gonadal development in teleost.

In this study, the exopolysaccharide (EPS) from Lactiplantibacillus plantarum (HMX2) was isolated from Chinese Northeast Sauerkraut. Its effects on juvenile turbot were investigated by adding different concentrations of HMX2-EPS (C: 0 mg/kg, H1: 100 mg/kg, H2: 500 mg/kg) to the feed. Compared with the control group, HMX2-EPS significantly improved the growth performance of juvenile turbot. The activities of antioxidant enzymes, digestive enzymes, and immune-related enzymes were significantly increased. HMX2-EPS could also increase the secretion of inflammatory factors and enhance the immune response of turbot by regulating the IFN signal transduction pathway and exhibit stronger survival rates after the A. hydrophila challenge. Moreover, HMX2-EPS could improve the diversity of intestinal microbiota in juvenile fish, increase the abundance of potential probiotics, and reduce the abundance of pathogenic bacteria. The function of gut microbes in metabolism and the immune system could also be improved. All results showed better effects with high concentrations of HMX2-EPS. These results indicated that HMX2-EPS supplementation in the diet could promote growth, improve antioxidant activity, digestive capacity, and immunity capacity, and actively regulate the intestinal microbiota of juvenile turbot. In conclusion, this study might provide basic technical and scientific support for the application of L. plantarum in aquatic feed.

A nine-week feeding trial was conducted to investigate changes in the intestinal microbiota of turbot in response to alternate feeding between terrestrially sourced oil (TSO)- and fish oil (FO)-based diets. The following three feeding strategies were designed: (1) continuous feeding with the FO-based diet (FO group); (2) weekly alternate feeding between soybean oil (SO)- and FO-based diets (SO/FO group); and (3) weekly alternate feeding between beef tallow (BT)- and FO-based diets (BT/FO group). An intestinal bacterial community analysis showed that alternate feeding reshaped the intestinal microbial composition. Higher species richness and diversity of the intestinal microbiota were observed in the alternate-feeding groups. A PCoA analysis showed that the samples clustered separately according to the feeding strategy, and among the three groups, the SO/FO group clustered relatively closer to the BT/FO group. The alternate feeding significantly decreased the abundance of Mycoplasma and selectively enriched specific microorganisms, including short-chain fatty acid (SCFA)-producing bacteria, digestive bacteria (Corynebacterium and Sphingomonas), and several potential pathogens (Desulfovibrio and Mycobacterium). Alternate feeding may maintain the intestinal microbiota balance by improving the connectivity of the ecological network and increasing the competitive interactions within the ecological network. The alternate feeding significantly upregulated the KEGG pathways of fatty acid and lipid metabolism, glycan biosynthesis, and amino acid metabolism in the intestinal microbiota. Meanwhile, the upregulation of the KEGG pathway of lipopolysaccharide biosynthesis indicates a potential risk for intestinal health. In conclusion, short-term alternate feeding between dietary lipid sources reshapes the intestinal microecology of the juvenile turbot, possibly resulting in both positive and negative effects.

Heat shock proteins 70 (HSP70s) are known to play essential roles in organisms’ response mechanisms to various environmental stresses. However, no systematic identification and functional analysis has been conducted for HSP70s in the turbot (Scophthalmus maximus), a commercially important worldwide flatfish. Herein, 16 HSP70 genes unevenly distributed on nine chromosomes were identified in the turbot at the genome-wide level. Analyses of gene structure, motif composition, and phylogenetic relationships provided valuable data on the HSP70s regarding their evolution, classification, and functional diversity. Expression profiles of the HSP70 genes under five different stresses were investigated by examining multiple RNA-seq datasets. Results showed that 10, 6, 8, 10, and 9 HSP70 genes showed significantly up- or downregulated expression after heat-induced, salinity-induced, and Enteromyxum scophthalmi, Vibrio anguillarum, and Megalocytivirus infection-induced stress, respectively. Among them, hsp70 (hspa1a), hspa1b, and hspa5 showed significant responses to each kind of induced stress, and qPCR analyses further validated their involvement in comprehensive anti-stress, indicating their involvement in organisms’ anti-stress mechanisms. These findings not only provide new insights into the biological function of HSP70s in turbot adapting to various environmental stresses, but also contribute to the development of molecular-based selective breeding programs for the production of stress-resistant turbot strains in the aquaculture industry.

Peroxisome proliferator‐activated receptor alpha (PPARα), as a transcription factor, plays an important role in the regulation of lipid metabolism. To better understand the regulatory role of PPARα in lipid metabolism in turbot, we analyzed the sequence structure of PPARα and its stress response to a high temperature. We also investigated the regulation of genes related to lipid metabolism after the knockdown of PPARα. The CDS of PPARα was 1410 bp, encoding 469 amino acids. The relative molecular weight of the protein was 52.64 kDa, and the predicted pI was 5.63. The architecture of the PPARα gene exhibited a ZnF‐C4 domain and a HOLI domain. Phylogenetic analysis indicated that PPARα has been highly conserved during evolution. The qPCR results showed that the mRNA level of PPARα was significantly increased, and the expression of the lipid synthesis genes FASN and SCD was significantly downregulated under high‐temperature stress. PPARα interference and inhibition results showed that the expression levels of FASN and SCD were significantly increased. Our results suggest that high temperatures activate PPARα and inhibit lipid synthesis by downregulating the expression of FASN and SCD in order to reduce lipid deposition and maintain lipid metabolism disorder caused by high‐temperature stress. This is the first report of PPARα in turbot. It will help for studying the evolution of PPARα and provide a reliable reference for studying the regulation mechanism of lipid metabolism in fish under stress. [ABSTRACT FROM AUTHOR]

Successful viral infection and multiplication chiefly rely on virus subversion mechanisms against host anti-viral immune responses. In this study, in order to reveal the anti-viral immune-related pathways suppressed by megalocytivirus infection, transcriptome analysis was performed on the head-kidney of turbot (Scophthalmus maximus) infected with lethal dose of RBIV-C1 at 3, 6 and 9 days post challenge (dpc). The results showed that, compared to unchallenged groups, 190, 1220, and 3963 DEGs were detected in RBIV-C1 infected groups at 3, 6 and 9 dpc, respectively, of which, DEGs of complement components and pattern recognition proteins were up-regulated at 3 dpc and down-regulated at 6 and 9 dpc, DEGs of cytokines were up-regulated at 6 dpc and down-regulated at 9 dpc. Expression trend analysis revealed that DEGs of profiles 9 and 13 featured decreased expression patterns and were significantly enriched into 10 immune-related pathways, i.e., complement and coagulation cascades, cytokine-cytokine receptor interaction, chemokine signaling pathway, B/T cell receptor signaling pathway, antigen processing and presentation, and so on. Further co-expression network analysis (WGCNA) revealed positive correlated innate immune related pathways at 3 and 6 dpc, and negative correlated innate and adaptive immune related pathways at 9 dpc. This study revealed a set of anti-viral immune genes/pathways that would also be potential targets subverted by RBIV-C1 for immune evasion, which can serve as a valuable resource for future studies on the molecular mechanisms of anti-viral immune defense of turbot and immune escape of megalocytivirus. • Transcriptome analysis was performed on the head-kidney of turbot infected with RBIV-C1. • Innate immune related DEGs exhibited an earlier increasing and later decreasing expression trend. • Adaptive immune related DEGs exhibited a trend toward down-regulation. • Down-regulated immune pathways would be potential targets suppressed by virus for immune evasion. [ABSTRACT FROM AUTHOR]