Large Yellow Croaker Larimichthys Crocea Research Articles

Genome-wide association analysis on host resistance against the rotten body disease in a naturally infected population of large yellow croaker Larimichthys crocea

Large yellow croaker (Larimichthys crocea) is one of the most important marine fish in China, representing the highest yield of fish species in marine net cage aquaculture. In recent years, the rotten body disease caused by scuticociliate was the main perniciousness for the fish fry, and led considerable economic losses. To date, no treatments had proven to be effective to the disease, so it was urgent to carry out the researches on disease-resistance breeding of this fish. Based on genome resequence for a natural population, a genome-wide association study (GWAS) to identify those loci associated with the rotten body disease resistance was performed in this work. A total of 3000 fish from 6 sub-populations were collected, and 270 phenotypic extremes were selected for genotyping. Two analysis models were employed to verify the accuracy and reliability of GWAS results. 2,019,067 SNPs were remained, and 14 SNPs were finally identified to be correlated with disease resistance, explaining phenotypic variance ranging from 5.4% to 9.2%. Within these regions, 5 candidate genes, NF-κB1, UBXN1, PTX3, DAB2IP and CYR61, which were involved in NF-κB signaling pathway, suggested the importance of NF-κB signaling pathway in the disease resistance. These results showed the complex polygenic architecture in large yellow croaker resistance against parasite scuticociliate. It also provided valuable foundation for future marker-assisted selection breeding of large yellow croaker against scuticociliate.

RIP3 Associates with RIP1, TRIF, MAVS, and Also IRF3/7 in Host Innate Immune Signaling in Large Yellow Croaker Larimichthys crocea.

Receptor-interacting protein 3 (RIP3) has been demonstrated to be a key regulator not only in cell death pathways including apoptosis and necroptosis but also in inflammation and host immune responses. In this study, a RIP3 ortholog named Lc-RIP3 is identified in large yellow croaker (Larimichthys crocea). The open reading frame (ORF) of Lc-RIP3 is 1524 bp long and encodes a protein of 507 amino acids (aa). The deduced Lc-RIP3 protein has an N-terminal kinase domain and a C-terminal RHIM domain, and the genome organization of Lc-RIP3 is conserved in teleosts with 12 exons and 11 introns but is different from that in mammals, which comprises 10 exons and 9 introns. Confocal microscopy revealed that Lc-RIP3 is a cytosolic protein. The expression analysis at the mRNA level indicated that Lc-RIP3 is ubiquitously distributed in various tissues/organs, and could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation in vivo. Notably, Lc-RIP3 could induce NF-κB but not IRF3 activation. In addition, Lc-RIP3 co-expression with Lc-TRIF, Lc-MAVS, or Lc-IRF3 significantly abolishes the activation of NF-κB but enhances the induction of IRF3 activity. Moreover, NF-κB activity could be up-regulated when Lc-RIP3 is co-expressed with Lc-RIP1 or Lc-IRF7. These results collectively indicate that Lc-RIP3 acts as an important regulator in host innate immune signaling in teleosts.

Proteome analysis and thermal-tolerant protein marker screening in the skin mucus of large yellow croaker Larimichthys crocea

Fish skin mucus serves as the first line of defense against pathogens and external stressors. To screen thermal-tolerant protein marker in the skin mucus of large yellow croaker Larimichthys crocea, this study conducted proteome analysis on skin mucus between thermal-tolerant and thermal-sensitive groups of large yellow croaker. A total of 396 differentially expressed proteins (DEPs) were identified, among which 215 proteins were upregulated and 181 proteins were downregulated. Ten selected random DEPs were validated using a parallel reaction monitoring (PRM) assay, and the results showed that the proteome analysis results were reliable (r = 0.805, P < 0.01). The bioinformatics analysis indicated that the proteins with significant changes were involved in immune defense, energy metabolism and heat shock, in which lily-type lectin, plasma protease C1 inhibitor, thrombospondin-1, calreticulin, pyruvate kinase and heat shock protein 70 played important roles in the course of adaption to high temperature and can be used as candidate thermal-tolerant protein markers in large yellow croaker. The results of this study provide a reference for constructing a noninvasive detection technology for assisting in the breeding of thermal-tolerant strains of large yellow croaker in the future.

Effects of Antarctic Krill Euphausia superba Meal Inclusion on Growth, Body Color, and Composition of Large Yellow Croaker Larimichthys crocea

AbstractThe effects of Antarctic krill Euphausia superba meal inclusion in the diet of Large Yellow Croaker Larimichthys crocea were studied. Inclusion levels were 0.000, 4.125, 8.250, and 12.375% (control, KM4.125, KM8.250, and KM12.375, respectively), and groups of large‐sized fish (average body weight = 190.6 g) received these diets for 99 d. No significant differences were found in body length, body weight, and specific growth rate compared with the control group, but the KM4.125 and KM8.250 groups had significantly increased condition factors and hepatosomatic indices. The KM8.250 fish showed a significant increase in redness values in the dorsal skin, while the KM12.375 fish presented significantly higher yellowness in the ventral skin and tail fin. Addition of krill meal exerted no significant effect on whole‐body proximate composition. The KM8.250 group showed significantly higher lipid content and lower ash content, which differed from those of the KM12.375 group. Most of the amino acids in muscle and liver tissues remained unchanged compared to those in the control. The KM4.125 group showed significantly higher muscle proline, serine, and total functional amino acids, while the total amino acid content in KM12.375 fish significantly decreased. The results indicated that dietary inclusion of fish meal with up to 8.25% krill meal does not result in adverse effects on growth and body composition of large‐sized Large Yellow Croaker; however, addition of krill meal could improve skin coloration in these fish.

In silico and gene expression analysis of the acute inflammatory response of gilthead seabream (Sparus aurata) after subcutaneous administration of carrageenin

Inflammation is one of the main causes of loss of homeostasis at both the systemic and molecular levels. The aim of this study was to investigate in silico the conservation of inflammation-related proteins in the gilthead seabream (Sparus aurata L.). Open reading frames of the selected genes were used as input in the STRING database for protein–protein interaction network analysis, comparing them with other teleost protein sequences. Proteins of the large yellow croaker (Larimichthys crocea L.) presented the highest percentages of identity with the gilthead seabream protein sequence. The gene expression profile of these proteins was then studied in gilthead seabream specimens subcutaneously injected with carrageenin (1%) or phosphate-buffered saline (control) by analyzing skin samples from the injected zone 12 and 24 h after injection. Gene expression analysis indicated that the mechanisms necessary to terminate the inflammatory response to carrageenin and recover skin homeostasis were activated between 12 and 24 h after injection (at the tested dose). The gene analysis performed in this study could contribute to the identification of the main mechanisms of acute inflammatory response and validate the use of carrageenin as an inflammation model to elucidate these mechanisms in fish.

Transcriptome analysis revealed multiple immune processes and energy metabolism pathways involved in the defense response of the large yellow croaker Larimichthys crocea against Pseudomonas plecoglossicida

The large yellow croaker (Larimichthys crocea) aquaculture industry is suffering substantial financial losses caused by visceral white nodules disease resulting from Pseudomonas plecoglossicida infection. However, how L. crocea responds to P. plecoglossicida infection remains largely unknown. Here, we characterized the changes in the mRNA profile in the spleen of L. crocea upon P. plecoglossicida infection and explored the related defensive strategies. Sample clustering analysis and qRT-PCR indicated that P. plecoglossicida induced profound and reproducible transcriptome remodeling in the L. crocea spleen. Many innate immune-related genes, such as IL-17 signaling molecules, chemokines and chemokine receptors, complement components, TLR5 signaling molecules, and antimicrobial peptide hepcidins (Hamps), were upregulated by P. plecoglossicida and may play important roles in the L. crocea defense against P. plecoglossicida. The antibacterial activity of Hamp2–5 against P. plecoglossicida was further confirmed by using synthetic mature peptide of Hamp2–5. Additionally, significant enrichment of “Glycolysis/Gluconeogenesis”, “Citrate cycle” and “Oxidative phosphorylation” pathways and a significant upregulation of all 6 rate-limiting enzyme genes (HK1, PFK, PKM, CS, IDH2, DLST) in the Glycolysis and Citrate cycle pathways in P. plecoglossicida-infected fish suggested that ATP synthesis may be accelerated to ensure energy supply in response to pathogenic infection. Altogether, our results not only identified the key immune-related genes and immune pathways that participated in the defense response of L. crocea against P. plecoglossicida, but also revealed a novel defensive strategy involving ATP synthesis in this species.

Effects of acute low temperature stress on the hormones and gene expression of glucocorticoid receptor of large yellow croaker Larimichthys crocea.

The neuroendocrine system of fish responds to low temperature via regulating hormones. To explore the adaptability of Larimichthys crocea to low temperature, the levels of the plasma cortisol, thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), total cholesterol (TC), and glucose were determined after exposure to low temperature and during subsequent rewarming. Furthermore, the mRNA expression of the glucocorticoid receptor (GR) gene was analyzed under the stress. We found that the levels of the plasma cortisol, TSH, T3, glucose, and TC increased under the low temperature stress, suggesting that elevated hormones may be conducive to promoting the mobilization of the glucose and lipid in L. crocea exposed to low temperature. During the rewarming period, the plasma cortisol level decreased, whereas the T3 level was still significantly higher than that in the control group. Notably, the plasma T4 level was unaffected by the temperature changes. Furthermore, the sequence alignment and phylogenetic tree analysis revealed that the GR protein of L. crocea had high homology and a similar protein structure with those from other teleosts. Under the low temperature stress, the GR mRNA expression increased in the brain and head kidney, whereas it basically returned to the control level following rewarming. These findings revealed the changes of the hormones and the potential function of the GR gene in L. crocea following exposure to low temperature, providing some insights into breeding low temperature-resistant varieties of L. crocea.

Oxidative stress induced by nanoplastics in the liver of juvenile large yellow croaker Larimichthys crocea

There are many toxicological studies on microplastics, but little is known about the effect of nanoplastics (NPs). Here, we evaluated the oxidative stress responses induced by NPs (10, 104 and 106 particles/l) in juvenile Larimichthys crocea during 14-d NPs exposure followed by a 7-d recovery. After exposure, the activities of antioxidant enzymes (SOD, CAT, GPx) and MDA levels increased in the liver of fish at the highest NPs concentration. SOD and CAT activities remained elevated above the baseline after recovery under high-concentration NPs but returned to the baseline in two other NP treatments. Although lipid peroxidation in liver was reversible, juvenile fish in NPs treatments exhibited a lower survival rate than the control during both exposure and recovery. Furthermore, IBR value and PCA analysis showed the potential adverse effects of NPs. Considering that NPs can reduce the survival of fish juveniles, impacts of NPs on fishery productivity should be considered.

Dietary polystyrene nanoplastics exposure alters liver lipid metabolism and muscle nutritional quality in carnivorous marine fish large yellow croaker (Larimichthys crocea)

Nanoplastics (NPs) cause various adverse effects on marine fish. However, effects of dietary NPs exposure on liver lipid metabolism and muscle nutritional quality of carnivorous marine fish are not fully understood. In this study, a 21-day feeding test was conducted to simulate the food chain transfer of polystyrene nanoplastics (PS NPs) and then evaluate effects of different dietary PS NPs levels on the survival, growth performance, liver lipid metabolism, and muscle nutritional quality of large yellow croaker Larimichthys crocea. Results indicated that the survival and growth of large yellow croaker decreased with the increase of PS NPs levels. Moreover, PS NPs induced excessive liver lipid accumulation by down-regulating the expression of lipolysis-related genes and inhibiting the AMPK-PPARα signaling pathway. In vitro, PS NPs could be accumulated in hepatocytes, reduce cell viability, and disrupt lipid metabolism of hepatocytes. Also, we found for the first time that PS NPs altered fatty acid composition and texture of fish muscle by enhancing oxidative stress and disrupting lipid metabolism. Overall, this study indicated that PS NPs induced liver lipid deposition by inhibiting lipolysis, and demonstrated that PS NPs altered the nutritional quality of fish, which might cause potential health effects for human consumers.

Molecular characterization and role in virus infection of Beclin-1 in large yellow croaker (Larimichthys crocea)

Beclin-1, the ortholog of yeast autophagy-related gene 6 (Atg6), has a central role in autophagy, which has been linked to diverse biological processes including immunity, development, tumor suppression, and lifespan extension. However, understanding of function of fish Beclin-1 is limited now. In this study, the complete Beclin-1 cDNA of large yellow croaker Larimichthys crocea (LcBeclin-1) was cloned, whose open reading frame (ORF) is 1344 bp long and encodes a protein of 447 amino acids (aa). The deduced LcBeclin-1 possesses a typical Bcl-2 homology domain 3(BH3) and an APG6 domain that contains a central coiled-coil domain (CCD, residues 174 to 231) and a C-terminal evolutionarily conserved domain (ECD, residues 241 to 334). LcBeclin-1 shared a high amino acid identity of 81.66–98.66% with reported Beclin-1 molecules from other vertebrate species. LcBeclin-1 gene was constitutively expressed in all tissues tested, with the highest levels in heart. LcBeclin-1 transcripts were also detected in primary head kidney granulocytes (PKGs), primary head kidney macrophages (PKMs), primary head kidney leukocytes (PKLs), and large yellow croaker head kidney cell line (LYCK), and were significantly upregulated by poly (I:C) in PKMs and LYCK cells. Subcellular localization showed that LcBeclin-1 was evenly distributed in the cytoplasm and nucleus of LYCK cells. Overexpression of LcBeclin-1 significantly increased the replication of SVCV, as evidenced by increased severity of the cytopathic effects, enhanced viral titre, and upregulated transcriptional levels of viral genes. Further studies showed that LcBeclin-1 induced the occurrence of autophagy in LYCK cells. Additionally, LcBeclin-1 also decreased the expression levels of large yellow croaker interferons (IFNs; IFNc, IFNd, and IFNh), interferon regulatory factor 3 (IRF3) and IRF7, IFN-stimulated genes (ISGs; Mx, PKR, and Viperin) in LYCK cells. All these data suggest that LcBeclin-1 promoted the viral replication possibly by inducing autophagy or negatively modulating IFN response, which will help us to further understand the function of fish Beclin-1.

Alterations in fatty acid composition and volatile compounds in muscle of large yellow croaker Larimichthys crocea fed different dietary lipid sources

A 12-week feeding trial was performed to evaluate the impacts of different dietary lipid sources on the fatty acid composition and volatile compounds in muscle of large yellow croaker Larimichthys crocea (initial body weight: 36.87 ± 0.32 g). The 6.5 % of fish oil, soybean oil, palm oil, vegetable oil blend (soybean oil: palm oil = 1:1), rapeseed oil and linseed oil were added respectively to formulate six isonitrogenous (46 % crude protein) and isolipidic (13 % crude lipid) experimental diets, which were named as FO, SO, PO, BO, RO and LO respectively. Results showed that dietary vegetable oils significantly reduced the contents of arachidonic acid (ARA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in muscle. While the highest levels of linoleic acid (LA), palmitic acid (PA), oleic acid (OA) and linolenic acid (ALA) were found in fillet of fish fed SO, PO, RO and LO respectively. Among the 39 identified volatile compounds in fillet, 23 were significantly affected by replacement of dietary fish oil with vegetable oils. Fish fillets in different treatments were mostly characterized by distinct volatiles and odours. Principal component analysis and Pearson’s correlation analysis indicated that some volatiles had strong positive correlations with main fatty acids in muscle, for example, (E)-2-pentenal, 1-penten-3-ol, etc. In conclusion, replacement of dietary fish oil by vegetable oils changed the volatile compounds in muscle of large yellow croaker, which could be ascribed to the modifications of muscle fatty acids induced by dietary vegetable oils.

MAVS splicing variants associated with TRAF3 and TRAF6 in NF-κB and IRF3 signaling pathway in large yellow croaker Larimichthys crocea

Mitochondrial antiviral signaling protein (MAVS) acts as an essential adaptor in host RIG-I-like receptors (RLRs) mediated antiviral signaling pathway. In the present study, two MAVS transcript variants, the typical form and a splicing variant, namely Lc-MAVS_tv1 and Lc-MAVS_tv2 were characterized in large yellow croaker (Larimichthys crocea). The putative Lc-MAVS_tv1 protein contains 512 aa, with an N-terminal CARD domain, a central proline-rich region, and a C-terminal transmembrane (TM) domain, whereas Lc-MAVS_tv2 contains 302 aa and lacks the C-terminal TM domain due to a premature stop in the 102 bp intron fragment insertion. Lc-MAVS_tv1 was identified as a mitochondrion localized protein whereas Lc-MAVS_tv2 exhibited an entire cytosolic distribution. Quantitative real-time PCR revealed that Lc-MAVS_tv1 mRNA was broadly expressed in examined organs/tissues and showed extremely higher level than that of Lc-MAVS_tv2, and both of them could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation in vivo. Interestingly, overexpression of Lc-MAVS_tv2 could induce the activation of NF-κB but not IRF3, and Lc-MAVS_tv2 co-transfected with Lc-MAVS_tv1 induced a significantly higher level of NF-κB and IRF3 promoter activity. In addition, Lc-MAVS_tv2 overexpression could enhance TRAF3 and TRAF6 mediated NF-κB activation, but suppress TRAF3 and TRAF6 mediated IRF3 activation, implying that the splicing variant Lc-MAVS_tv2 may function as an important regulator in MAVS mediated signaling pathway.

Acoustic Properties of the Otolith of the Large Yellow Croaker Larimichthys crocea (Perciformes: Sciaenidae).

The inner ears of fish contain three pairs of otoliths-lapilli, asterisci and sagittae-which play important roles in hearing and balance. However, acoustic properties and dynamic responses of fish otoliths are poorly understood. The large yellow croaker (Larimichthys crocea), like many species in the family Sciaenidae, is extremely sensitive to sound. The present study used L. crocea sagittae as the research subject and examined the variation in shear stress on sagittae under different acoustic stimuli. For the first time, the sound speed of the sagitta was measured using ultrasonic pulse-echo techniques, and the acoustic impedance and natural frequency of the sagitta were calculated. Larimichthys crocea adults (20-22 cm standard length, n = 10) had a sagitta density of 2781.5 ± 28.06 kg/m3, sound speed of 4828-6000 m/s and acoustic impedance range of 13.4-16.7 MPa·s/m, approximately 9-11 times that of seawater (1.48 MPa·s/m). The natural frequency of the sagitta was 76.4-95.5 kHz. The shape and structural details of sagittae were reconstructed by 3D scanner and the shear stress responses of sagittae under different acoustic stimulus were investigated based on a finite element model. The simulation results showed that the shear stress responses tended to increase and then decrease in the range of sciaenid hearing frequency from 200 to 1300 Hz, peaking at 800 Hz. The shear stress responses varied with the direction of acoustic stimulus and peaked when the incident direction was perpendicular to the inner surface of the otolith. These results provide important parameters that may be used to protect L. crocea from possible underwater noise damage, particularly during their spawning aggregations and over-wintering aggregations.

Effects of Dietary Wheat Gluten Meal on Growth, Intestinal Morphology, and Microbiome in Juvenile Large Yellow croaker Larimichthys crocea

Wheat gluten meal (WGM) was evaluated as a replacement for fish meal (FM) for juvenile Larimichthys crocea．FM was replaced by 0%, 25%, 50%, 75%, and 100% of WGM (WGM0, WGM25, WGM50, WGM75, and WGM100, respectively). In addition, all diets except the control group were supplemented with amino acids. Fish were fed twice daily for 56 days. There were no significant differences in survival and feed conversion ratio (FCR) among all treatments (P&gt;0.05). WGM25, WGM50, and WGM75 groups had significantly higher specific growth rate (SGR) and weight gain ratio (WGR) than those fed with WGM0 (P&lt;0.05). There were no significant differences in mucosal thickness (MT), lamina propria width (LW), mucosal fold height (MH), and goblet cell quantity of single hair (GC) for all the diets (P&gt;0.05). The indexes of Chao1, Shannon, Simpson, and Good coverage in fish fed with WGM0, WGM50, and WGM100 were not significantly affected (P&gt;0.05). Firmicutes (81.03~94.03%) were the dominant bacterial community in juvenile large yellow croaker. Compared with the WGM0 group, the abundance of Firmicutes increased significantly, and Proteobacteria decreased significantly in the WGM100 group (P&lt;0.05). These results suggested that WGM could replace 366.3 g kg-1 FM of the juvenile large yellow croaker diet.

CHANGES IN LIPID CONTENT WITH ROASTING TEMPERATURE OF LARGE YELLOW CROAKER (LARIMICHTHYS CROCEA) ROE

This study aims to clarify the changes with roasting temperature in the lipid content of ready-to-eat large yellow croaker (Larimichthys crocea) roe product. Almost all the lipid class/species showed the same trend with the increasing temperature. Except for some minor differences, the relative amounts of lipids decreased with temperature increase from 0°C (control group, raw roe) to 100°C; increased with further temperature increase to 120°C, at which the amount was maximum; and then decreased with further temperature increase to 180°C. Finally, 120°C was selected as the optimal processing temperature, which may result in a better appearance and a high lipid quality, indicating its potential application value. This study also enhances the understanding of lipid profile in fish roe and demonstrates the applicability of the lipidomic method in aquatic food production.

Antibacterial and antiparasitic activities analysis of a hepcidin-like antimicrobial peptide from Larimichthys crocea

As an economically important marine fish, the large yellow croaker Larimichthys crocea suffered from marine white spot disease caused by the ectoparasite Cryptocaryon irritans in recent years. This disease not only could result in physiological damage, but also lead to secondary bacterial invasion. Reports indicated some AMPs (antimicrobial peptides) were of antiparasitic activity to C. irritans. Hepcidin-like (Lc-HepL) was one of the significant differential expression genes excavated from the transcriptome following a challenge with C. irritans. In this study, we characterized this AMP’s bioactivity based on the levels of mRNA and protein. After challenged by C. irritans, qRT-PCR showed Lc-HepL was significantly upregulated in six tissues, including gill, muscle, liver, head kidney and spleen during theront infection, trophont falling off, and secondary bacterial invasion stages, which implicated a role Lc-HepL played in the immune defense against C. irritans and secondary bacterial infection. Recombinant Lc-HepL (rLc-HepL) was induced and purified successfully. rLc-HepL exhibited antibacterial activity to certain bacteria in a dose- and time-dependent manners. Anti-C. irritans activity was explored for the first time and found it could cause the theronts membrane rupture and contents leakage. These results provided the first evidence that Lc-HepL had strong antiparasitic activity against marine fish ectoparasites C. irritans theronts. Together, data indicated that Lc-HepL might be an important component in the innate immune system against C. irritans and has the potential to be employed in future drug development.

Growth and maturity heterogeneity of three croaker species in the East China Sea

Big head croaker (BC) Collichthys lucidus, Large yellow croaker (LC) Larimichthys crocea, and Yellow croaker (YC) Larimichthys polyactis are important ecological and commercial species along the coastal seas of China. Based on samples collected from seasonal bottom trawl surveys in the southern East China Sea from 2015 to 2018, we analyzed the growth and maturity characteristics of these three croaker species. Simple linear model, mixed-effects model and hierarchical methods were conducted in this study to evaluate the variations in growth and maturity among sexes, seasons and years for each species. Our results showed that, mixed-effects model performed better than simple linear models, while hierarchical methods could reveal variations in different life stages. Female LC and YC tended to gain more weight at the same length and matured earlier than the male for LC and YC. The individuals tended to gain more weight in spring and fall, while all croakers had larger weight at the same length and matured earlier from 2015 to 2017 compared to those in 2018. Results from the hierarchical model indicated that for all captured croakers, individuals with bigger sizes were mostly females, especially for LC. Big head croaker and LC tend to gain more weight in spring, while YC tends to gain less weight in winter. Mixed-effects models and hierarchical methods can be incorporated to provide more information about the heterogeneity of fish life history traits. These results will help provide more insights related to the growth and maturity of these three important species in the East China Sea. Also, the methodology applied in this study may be used on the life history research for species with multiple data sources.

Interactions of dietary vitamin C and proline on growth performance, anti-oxidative capacity and muscle quality of large yellow croaker Larimichthys crocea

A 60-day feeding trial was conducted to investigate the effect of dietary proline and vitamin C, and their interactions on growth performance, anti-oxidative capacity and muscle quality of large yellow croaker Larimichthys crocea (initial body weight: 150.83 ± 3.81 g). Four isonitrogenous and isolipidic diets from a 2 × 2 factorial design were formulated with two levels of vitamin C (50 mg/kg and 150 mg/kg) and two levels of proline (0 and 0.6%), respectively. The results showed that dietary supplementation of proline significantly improved the growth performance regardless of dietary vitamin C levels (p < .05). Significant interactions between dietary vitamin C and proline were found in muscle quality (p < .05). Liquid loss and water loss of muscle significantly decreased with dietary proline supplementation at lower level of dietary vitamin C, while the pH, hardness, and contents of alkaline-soluble hydroxyproline, total collagen and pyridinium crosslink of muscle significantly increased (p < .05). Dietary supplementations of vitamin C and proline significantly increased the activity of prolyl 4-hydroxylase in muscle (p < .05), even though no significant interaction between dietary vitamin C and proline was found (p > .05). Activity of matrix metalloproteinase 2 of muscle significantly increased with dietary vitamin C supplementation regardless of dietary proline level (p < .05). Significant interactions between dietary vitamin C and proline were found in anti-oxidative capacity of muscle (p < .05). Dietary supplementation of proline significantly increased the activities of glutathione peroxidase and copper/zinc superoxide dismutase in muscle at higher level of dietary vitamin C (p < .05). The present study indicated that dietary vitamin C and proline had synergistic effects on muscle quality and anti-oxidative capacity of large yellow croaker.

Nanoplastics impair the intestinal health of the juvenile large yellow croaker Larimichthys crocea

Microplastics (MPs) have become a severe concern in marine environment worldwide. Micro-polystyrene particles have been proved to accumulate in vivo and caused disorders of digestion, antioxidant system, immunity and intestinal microflora, but little is known about the effects of nano-polystyrene (nano-PS). In order to understand response mechanism of marine fish to nano-PS, the effects of nanoplastics on the intestinal health and growth performance of the juvenile Larimichthys crocea were investigated. After 14-d exposure, the reduced digestive enzyme activities indicated that nano-PS had a negative impact on the digestion and absorption of juvenile fish. Moreover, analysis of the intestinal microbiota showed that the proportion of the three-dominant bacterial phyla (Bacteroidetes, Proteobacteria and Firmicutes) in the gut changed significantly, accompanied by a significant increase of potentially pathogenic bacteria (Parabacteroides and Alistipes). In addition, lysozyme activity and specific growth rate (SGR) were significantly reduced, and total mortality of juvenile fish was significantly increased. Overall, nano-PS exposure was harmful for the health of juvenile fish, which might threaten their population in the long term.

Evidence of virus-responsive pathways in response to poly I: C challenge in a muscle cell line derived from large yellow croaker Larimichthys crocea

In this study, a new continuous muscle cell line, LYCMS (large yellow croaker muscle cell line), derived from the muscle tissue of larva of large yellow croaker (Larimichthys crocea) was developed with modified DMEM/F12 medium at 27 °C. The muscle cell line could be passaged at different ratios for different growth rates. Karyotype analysis showed that a large proportion of LYCMS cells had 48 chromosomes. The proliferation of LYCMS cell line could be affected by mammalian growth factors such as human basic fibroblast growth factor (b-FGF), epidermal growth factor (EGF), and hepatocyte growth factor (HGF). GFP expression experiments indicated that the LYCMS cell line could be used for exogenous genes’ expression. Different virus response-related genes tested in this study showed diverse change types in expression before and after (0–24 h) polycytidylic acid (poly I: C) challenge of LYCMS cells. This is the first study of virus response signaling pathways of large yellow croaker based on the muscle cell line. The results showed that compared with the in vivo experiments, the use of the LYCMS cell line for immune research is more convenient, efficient, and rapid. By using this model, we demonstrated that MDA5-IPS1-TRAF6-NFκB-cytokines, MDA5-IPS1-TRAF3-IRF3-interferon or TLR22-TRIF-IRF3-interferon, TLR8-MyD88-NFκB-cytokines, and TLR3-TRIF-IRF3-interferon pathways were able to response to poly I: C challenge in the muscle cell line of large yellow croaker.