Rock Bream Oplegnathus Fasciatus Research Articles

Environmental enrichment improves behaviors rather than the growth and physiology of rock bream Oplegnathus fasciatus.

Environmental enrichment has the potential to improve the welfare and post-release survival of hatchery fish stocked for conservation purposes. However, the effectiveness of environmental enrichment is partly dependent on the fish species, life stage, and specific enrichment structure used. To enhance the effectiveness of environmental enrichment, it is crucial to focus on characteristic differences in enrichment structures, such as type and level. This study investigated how differences in enrichment type and level affected physiological and behavioral aspects of the welfare of pre-release juvenile rock bream Oplegnathus fasciatus by evaluating growth performance, basal and stressed cortisol levels, antioxidant enzyme activities, and exploratory behaviors regarding anxiety and flexibility. Fish were reared for 4 weeks in different enrichment treatments: barren, low-level cover structure, high-level cover structure, low-level interference structure (LI), and high-level interference structure (HI). The results revealed that fish reared with the LI treatment showed less anxiety and greater flexibility with respect to exploratory behaviors, without oxidative damage being detected. Despite exhibiting less anxiety as well, fish reared in the HI treatment had oxidative damage, indicated by lower superoxide dismutase activity, compared to those in the barren treatment. In addition, none of these enrichment structures enhanced growth performance or mitigate chronic and acute stress responses. Overall, the low-level interference structure may be more favorable in promoting the behavioral welfare of the fish. Application of this type and level of enrichment may increase the survival of the hatchery fish after release, which is critical to stocking success.

Characterization of Early Gonadal Differentiation and Induction of Sex Reversal in the Rock Bream Oplegnathus fasciatus.

Rock bream (Oplegnathus fasciatus) is a typical fish that has a unique multiple sex chromosome system (♀X1X1X2X2/♂X1X2Y). We examined the early gonadal development in rock bream via continuous histological observations of the gonads at 40-120days post hatching (dph). The fish was identified as a typical gonochorist, and female gonads were found to differentiate earlier than male gonads. The ovarian cavity of the female was initially observed at 80 dph, whereas the efferent duct of the male was not observed until 100 dph. Immunofluorescence with the vasa-antibody revealed that germ cells were predominantly distributed around the ovarian cavity in females and on the edge of the gonad in males during the early stages of sex differentiation. Sex reversal was induced via the oral administration of letrozole (LTZ), 17α-methyltestosterone (MT), and 17β-estradiol (E2), respectively, during the labile period of gonadal development. LTZ and MT induced 100% masculinization of genotype-females, whereas E2 induced only 50-60% feminization of genotype-males. Such findings suggest that the fish retained high sexual plasticity despite the existence of the neo-Y chromosome. MT and E2 had negative effect on fish growth, whereas LTZ did not exert such side effect. LTZ and MT could accelerate gonadal development in sex-reversed genotype-males, whereas E2 inhibited gonadal development in genotype-females of rock bream. These findings provide a basis for further research on the mechanisms of sex determination and differentiation in fishes with X1X2Y sex chromosome system and provide a sex reversal protocol for rock bream.

Proteome profile of spleen in rock bream (Oplegnathus fasciatus) naturally infected with rock bream iridovirus (RBIV).

Rock bream iridovirus (RBIV) is one of the most dangerous pathogens that causes the highest mortality in the aquaculture of rock bream (Oplegnathus fasciatus). Even though RBIV infection leads to huge economic loss, proteome studies on RBIV-infected rock bream have not been conducted to provide information about the differential protein expression pattern by the host protection system. The purpose of this study was to investigate the protein expression patterns in spleens of rock bream olive after infection by RBIV or mixed infection by RBIV and bacteria. Depending on the infection intensity and sampling time point, fish were divided into five groups: uninfected healthy fish at week 0 as the control (0C), heavily infected fish at week 0 (0H), heavily mixed RBIV and bacterial infected fish at week 0 (0MH), uninfected healthy fish at week 3 (3C), and lightly infected fish at week 3 (3L). Proteins were extracted from the spleens of infected rock bream. We used 2-DE analysis with LC-MS/MS to investigate proteome changes in infected rock bream. The results of the LC-MS/MS analyses showed different protein expression profiles after infection. Proteins related to oxygen transport and energy generation, such as hemoglobin, beta-globin, and ATP synthase, were mostly expressed in the infected spleen. Whereas proteins involved in structure and cell movement, such as tubulin, myosin, actin binding proteins, and intermediate filament proteins, were down-regulated in the infected spleens. The protein expression profiles between infection by RBIV and mixed infection by RBIV and bacteria showed similar patterns. Our results indicated that infection by RBIV or mixed infection by RBIV and bacteria triggered energy generation and oxygen-transport, but cell migration and constructional changes in the spleen were extremely decreased.

Spectral sensitivity and photoresponse in the rock bream Oplegnathus fasciatus and their relationships with the absorption maximum of the photoreceptor.

The spectral characteristics of visual pigments are a major determinant in eliciting a response to light. To study the absorption maximum of the photoreceptors and their sensitivity to light in fish, rod outer segments (ROS) and cone cells were purified from the rock bream Oplegnathus fasciatus adapted to the dark. Ultraviolet/visible spectroscopic analyses of the ROS in the dark and its difference spectra indicated an absorption maximum of the visual pigment at ~ 500nm, and each eye of 1-year-old rock bream contained at least 1.2nmol of rhodopsin-like visual pigments. Microspectrophotometric analysis of the cone cell outer segments led to identification of three visual pigments with individual absorption maxima at 425, 520, and 585nm. Monochromatic light-emitting diode (LED) modules with different wavelengths (violet 405nm, blue 465nm, cyan 505nm, green 530nm, amber 590nm, and red 655nm) were constructed to examine the spectral sensitivity and photoresponse in association with the absorption maximum of the photoreceptor. Analysis of chromophore decay upon illumination with each LED at low (27μmol/m2/s) and high (343μmol/m2/s) intensities showed the highest sensitivity of the photoreceptor upon illumination with the 505-nm cyan LED, followed by LEDs with wavelengths of 530nm > 465nm > 405nm > 590nm > 655nm. Photoresponse analysis of the fish using a video tracking system, in the dark and upon illumination, also showed faster movement of fish with illumination with the cyan LED followed by in the order of green ≈ blue > violet > amber > red. These results indicated that a light with a wavelength closer to the absorption maximum of rhodopsin was more effective in eliciting a response to the light.

Effect of feed deprivation on compensatory growth in juvenile rock bream Oplegnathus fasciatus

A feed-deprivation study was conducted for 9 weeks with four feeding regimes, estimating compensatory growth and proximate composition of rock bream Oplegnathus fasciatus (56.0 ± 0.9 g). Feeding regimes included continuous feeding (control), feed-deprivation for 1 week (S1) in week 3, for 2 weeks (S2, weeks 2–3), and for 3 weeks (S3, weeks 1–3). Following 3 weeks, fish were on a continuous feeding regime for the remaining period. Complete compensation was achieved in S1 and S2 after resuming feeding for 3 weeks and 6 weeks. Although specific growth rate, feeding rate and feed efficiency in S3 were higher than in the control during the feeding resumption period, S3 fish did not catch up the body weight of control fish by the end of the experiment. At the end of the feed-deprivation period, the ratio of lipid to lean body mass and the levels of protein, lipid, and energy in S1, S2 and S3 were lower than those in the control. After feeding resumption for 6 weeks, protein and lipid contents in S3 were significantly (P < 0.05) lower than those in the control. Rock bream with single-phase feed-deprivation for 1–2 weeks could exhibit full compensatory growth after feeding resumption for 3–6 weeks under our experimental conditions.

METABOLIC RATES (SMR, RMR, AMR, AND MMR) OF Oplegnathus fasciatus ON DIFFERENT TEMPERATURE AND SALINITY SETTINGS

The metabolic rate of aquatic animals is closely related to oxygen concentration and influenced by internal and external factors. Despite its high value as marine fish species in South Korea, information on rock bream Oplegnathus fasciatus metabolism is scarcely available. This study observed the standard metabolic rate (SMR), routine metabolic rate (RMR), and active metabolic rate (AMR) of rock bream Oplegnathus fasciatus subjected to different temperature settings. Another observation was performed to find out the maximum metabolic rate (MMR) on rock bream subjected to different salinity settings. Fish (TL: 26.86 ± 0.29 cm and BW: 469.40 ± 38.21 g for SMR, RMR, and AMR measurement; TL: 26.7 ± 0.4 cm and BW: 451.0 ± 44.4 g for MMR measurement) were observed using respirometer (dimension = 30 cm × 20 cm × 20 cm; volume: 10.4 L) inside a recirculation systems. SMR, RMR, and AMR were measured at 15°C, 20°C, and 25°C. Meanwhile, MMR was measured at 15, 25, and 35 psu. The results showed that SMR, RMR, and AMR increased linearly by increasing the temperatures (SMR: 58.7 ± 3.2, 102.7 ± 4.3, and 157.1 ± 4.1 mg O2/kg/h at 15°C, 20°C, and 25°C, respectively; RMR: 66.0 ± 8.6, 112.6 ± 10.2, and 175.2 ± 21.3 mg O2/kg/h at 15°C, 20°C, and 25°C, respectively; AMR: 73.4 ± 7.4, 122.0 ± 6.3, and 196.7 ± 15.4 mg O2/kg/h at 15°C, 20°C, and 25°C, respectively), whilst MMR decreased by lowering salinity (48.5 ± 5.2, 61.1 ± 5.5, and 89.3 ± 14.7 mg O2/kg/hour at salinity of 15, 25, and 35 psu, respectively).

Expression Analysis of Interferon-Stimulated Gene 15 in the Rock Bream Oplegnathus fasciatus against Rock Bream Iridovirus (RSIV) Challenge.

ABSTRACTInterferon-stimulated gene 15 (ISG15) is known to interfere with viral replication and infection by limiting the viral infection of cells. Interferon-stimulated gene 15 (ISG15) interferes with viral replication and infectivity by limiting viral infection in cells. It also plays an important role in the immune response. In this study, tissue-specific expression of ISG15 in healthy rock bream samples and spatial and temporal expression analysis of rock bream ISG15 (RbISG15) were performed following rock bream iridovirus (RSIV) infection. RbISG15 expression was significantly higher in the eye, gill, intestine, kidney, liver, muscle, spleen, and stomach, but low in the brain. There were particularly high levels of expression in the liver and muscle. RbISG15 expression was also examined in several tissues and at various times following RSIV infection. ISG15 expression increased within 3 h in the whole body and decreased at 24 h after infection. In addition, temporal expression of several tissues following RSIV infection showed a similar pattern in the muscle, kidney, and spleen, increasing at 3 h and decreasing at 72 h. These results suggest that ISG15 plays an important role in the immune response of rock bream. Overall, this study characterizes the response of RbISG15 following RSIV infection.

Molecular, structural, and functional comparison of N lobe and C lobe of the transferrin from rock bream, Oplegnathus fasciatus, with respect to its immune response

The iron-withholding strategy of innate immunity is an effective antimicrobial defense mechanism that combats microbial infection by depriving microorganisms of Fe3+, which is important for their growth and propagation. Transferrins (Tfs) are a group of iron-binding proteins that exert their antimicrobial function through Fe3+ sequestration. The current study describes both structural and functional characteristics of a transferrin ortholog from rock bream Oplegnathus fasciatus (RbTf). The RbTf cDNA possesses an open reading frame (ORF) of 2079 bp encoding 693 amino acids. It has a molecular mass of approximately 74 kDa and an isoelectric point of 5.4. In silico analysis revealed that RbTf has two conserved domains: N-terminal domain and C-terminal domain. Pairwise homology analysis and phylogenetic analysis revealed that RbTf shared the highest identity (82.6%) with Dicentrarchus labrax Tf. According to the genomic analysis, RbTf possesses 17 exons and 16 introns, similar to the other orthologs. Here, we cloned the N terminal and C terminal domains of RbTf to evaluate their distinct functional features. Results obtained through the CAS (chrome azurol S) assay confirmed the iron-binding ability of the RbTf, and it was further determined that the iron-binding ability of rRbTfN was higher than that of rRbTfC. The antimicrobial functions of the rRbTfN and the rRbTfC were confirmed via the iron-dependent bacterial growth inhibition assay. Tissue distribution profiling revealed a ubiquitous expression with intense expression in the liver. Temporal assessment revealed that RbTf increased after stimulation of LPS, Edwardsiella tarda, and Streptococcus iniae post injection (p.i.). These findings demonstrated that RbTf is an important antimicrobial protein that can combat bacterial pathogens.

A proto-type galectin-2 from rock bream (Oplegnathus fasciatus): Molecular, genomic, and expression analysis, and recognition of microbial pathogens by recombinant protein

A β-galactoside binding lectin, designated as galectin-2, was identified and characterized from rock bream Oplegnathus fasciatus (OfGal-2). The cDNA of OfGal-2 comprised of 692 bp with a coding sequence of 396 bp, encoding a putative polypeptide of 131 amino acids. Gene structure analysis of OfGal-2 revealed a four exon-three intron organization. A single carbohydrate-binding domain containing all seven important residues for carbohydrate binding was located in the third exon, which formed a carbohydrate-binding pocket. Homology screening and sequence analysis demonstrated that OfGal-2 is an evolutionarily conserved proto-type galectin. OfGal-2 transcripts were detected in several healthy fish tissues, with the highest level observed in the intestine, followed by the liver. The expression of OfGal-2 was elevated upon the injection of various mitogenic stimulants and pathogens in a time-dependent manner. Upregulated expression in the liver after tissue injury suggested its role as a damage-associated molecular pattern. Recombinant OfGal-2 protein had hemagglutinating potential and possessed affinity towards lactose and galactose. Moreover, the recombinant protein agglutinated and bound potential pathogenic bacteria and a ciliate. The results of this study indicate that the galectin-2 from rock bream has a potential role in immunity, particularly in the recognition of invading pathogens.

EFFECTS OF DIFFERENT SALINITY LEVELS ON PHYSIOLOGICAL AND HEMATOLOGICAL RESPONSE OF ROCK BREAM Oplegnathus fasciatus

Rock bream Oplegnathus fasciatus is one of economically important marine fish species in East Asia. However, lack of information about the salinity tolerance of rock bream related to its physiological response made this issue were needed to be studied. The present study was conducted to determine the effects of different salinity levels on physiological and hematological response of rock bream in order to obtain its salinity tolerance. Twelve rock breams (total length: 26.9 ± 0.6 cm, body weight: 477.3 ± 61.9 g) were used for experiments. Four experimental groups with three replications were conducted to measure the effects of salinity (5, 15, 25, and 35 practical salinity unit (psu)) on physiological and hematological response of rock bream. Fish were stocked into the chamber inside the closed recirculation system. At the end of each experiment, blood samples were collected. The study revealed that lower salinity exposure had tendency to decrease the physical and chemical properties of blood in rock bream. The value of Na+, Cl-, Ca, Mg, and osmolality showed tendency to decrease with lowering salinity, while cortisol and glucose showed tendency to increase from 35 psu to low salinity environment, indicating the enhancement of fish stress and resulted in fish mortality at 5 psu. The lowest cortisol value was 76.3 ng/mL in 25 psu, and the highest value was 188.8 ng/mL in 5 psu. Meanwhile, the lowest glucose value was 35.3 mg/dL and the highest value was 166.7 mg/dL (P<0.05). Results indicate that rock bream could tolerate lower salinity up to 15 psu.

Dietary Effect of Probiotic Bacteria, Bacillus amyloliquefaciens-JFP2 on Growth and Innate Immune Response in Rock Bream Oplegnathus fasciatus, Challenged with Streptococcus iniae

The present study was conducted to evaluate the use of Bacillus amyloliquefaciens as a probiotic source in the diet of rock bream, Oplegnathus fasciatus. A total of 210 fingerlings (25.4 ± 0.13 g) were divided into two groups, three replicates each; control (C) and probiotic (P) group (35×3=105 fish per group). C group was fed a basal diet without probiotic while P group was fed with B. amyloliquefaciens spores at a concentration of 1.4 ×106 colony-forming units per gram (CFU/g) of feed. After 90 days, P group fish showed significant improvements in body weight (BW), weight gain (WG), specific growth rate (SGR) and food conversion ratio (FCR) when compared with C group fish. Also, in bi-weekly assessments, serum protein and glucose level showed a significant increase (p&lt;0.05) in probiotic fed fish compared with the control group. Similar increase in serum antioxidant and lysozyme activity was found in the probiotic fed fish group. However, there was a significant decrease in triglyceride and total cholesterol along with increased alanine aminotransferase (ALT) and aspartate amonotransferase (AST) levels in probiotic diet fed fish compared to the control. After seventy days the fish were challenged with Streptococcus iniae and mortality of the probiotic fed fish was significantly lower (p&lt;0.05) when compared with the control. These results demonstrate the benefit of incorporation of B. amyloliquefaciens as a feed supplement to improve the health status of Oplegnathus fasciatus challenged with Streptococcus iniae.

Dietary Effect of Probiotic Bacteria, Bacillus amyloliquefaciens-JFP2 on Growth and Innate Immune Response in Rock Bream Oplegnathus fasciatus, Challenged with Streptococcus iniae

The present study was conducted to evaluate the use of Bacillus amyloliquefaciens as a probiotic source in the diet of rock bream, Oplegnathus fasciatus. A total of 210 fingerlings (25.4 ± 0.13 g) were divided into two groups, three replicates each; control (C) and probiotic (P) group (35×3=105 fish per group). C group was fed a basal diet without probiotic while P group was fed with B. amyloliquefaciens spores at a concentration of 1.4 ×106 colony-forming units per gram (CFU/g) of feed. After 90 days, P group fish showed significant improvements in body weight (BW), weight gain (WG), specific growth rate (SGR) and food conversion ratio (FCR) when compared with C group fish. Also, in bi-weekly assessments, serum protein and glucose level showed a significant increase (p&lt;0.05) in probiotic fed fish compared with the control group. Similar increase in serum antioxidant and lysozyme activity was found in the probiotic fed fish group. However, there was a significant decrease in triglyceride and total cholesterol along with increased alanine aminotransferase (ALT) and aspartate amonotransferase (AST) levels in probiotic diet fed fish compared to the control. After seventy days the fish were challenged with Streptococcus iniae and mortality of the probiotic fed fish was significantly lower (p&lt;0.05) when compared with the control. These results demonstrate the benefit of incorporation of B. amyloliquefaciens as a feed supplement to improve the health status of Oplegnathus fasciatus challenged with Streptococcus iniae.

Development of PCR method for detecting Kudoa iwatai (Myxozoa: Multivalvulida) from rock bream Oplegnathus fasciatus.

We developed a PCR assay targeting the 28S rDNA of Kudoa iwatai (Multivalvulida: Myxozoa) and investigated the prevalence of infection in rock bream Oplegnathus fasciatus, which is commercially an important aquaculture species in Korea, with this assay. Detection limit of the PCR assay was 2.5fg/μl with plasmid DNA and 8.6×103 spores/ml with purified spores, respectively. This PCR assay did not amplify DNA of other Kudoa species (Kudoa septempunctata, Kudoa lateolabracis, Kudoa thyrsites) tested. Sliced muscles of whole body from 318 rock bream (wild and cultured) were examined by this PCR assay and also with the naked eyes. All of the wild fish did not produce amplicons nor did harbor visible Kudoa cysts (0/70). Three of the cultured fish were PCR-positive and also harbored visible Kudoa cysts (3/248, 1.2%). The sequences of amplicons (574bp) were 100% identical with those of the K. iwatai already registered in Genbank. When the visceral organs of these three fish were examined, visible cysts were not found, but one stomach sample was found to be PCR-positive. There was no difference in the prevalence of infection estimated by PCR assay and the presence of visible Kudoa cysts in our samples. This is thought to be because the development of K. iwatai is already completed and only mature Kudoa cysts existed in our samples.

Establishment of rock bream Oplegnathus fasciatus embryo (RoBE-4) cells with cytolytic infection of red seabream iridovirus (RSIV)

Red seabream iridovirus (RSIV) is a member of genus Megalocytivirus in the family Iridoviridae. RSIV infection causes significant economic losses of marine-fishes in East Asian countries. Grunt fin (GF) cell line has been commonly used for culturing RSIV. However, it is not suitable for definite evaluation of infectivity titer of RSIV because cells infected with RSIV are not completely cytolysed. Thus, we established a new cell line, RoBE-4, from rock bream (Oplegnathus fasciatus) eyed-egg embryos in this study. Morphologically, RoBE-4 cells were fibroblastic-like. They have been stably grown over two-years with 60 passages using Leibovitz’s L-15 medium containing 10% (v/v) fetal bovine serum. RoBE-4 cells infected with RSIV exhibited cytopathic effects (CPE) with cell rounding. They were cytolysed completely after ≥2 weeks of culture. Numerous RSIV particles with icosahedral morphology of approximately 122nm in diameter were observed in cytoplasmic area of infected RoBE-4 cells. The RSIV-suceptibility and amount of extracellular RSIV released by RoBE-4 cells were 100-fold higher than those by GF cells. RSIV cultured with RoBE-4 cells was highly virulent to rock bream in infection experiments. Therefore, using RoBE-4 cells instead of GF cells will enable accurate and sensitive measurement of RSIV infectivity. In addition, RoBE-4 cells might be used to produce RSIV vaccine in the future with significant reduction in cost.

Antimicrobial response of galectin-1 from rock bream Oplegnathus fasciatus: Molecular, transcriptional, and biological characterization.

In this study, we describe the identification and characterization of a proto type galectin, galectin-1, from rock bream Oplegnathus fasciatus (OfGal-1). Galectins are evolutionarily conserved carbohydrate binding lectins that show a wide range of functions related to development and immune physiology. They have been identified as pattern recognition receptors of innate immune system that recognize a broad range of microbes. OfGal-1 cDNA comprised of 993 bp with an open reading frame of 408 bp that encodes 135 amino acids. A single carbohydrate recognition domain was present in the OfGal-1 amino acid sequence. The sequence comparison by multiple and pairwise alignments and the phylogenetic tree emphasized the strong evolutionary conservation of Gal-1. The typical β-sandwich structure was identified from the predicted tertiary structure. The constitutive expression of mRNA transcripts was detected in a wide range of tissues examined, with the highest expression in the heart. Immune challenges with live bacteria (Edwardsiella tarda and Streptococcus iniae), rock bream irido virus, and mitogens (lipopolysaccharide and poly I:C) modulated the expression of OfGal-1 mRNAs in the gills, head kidney, and liver. The recombinant OfGal-1 (rOfGal-1) strongly agglutinatinated the human erythrocytes, and this hemagglutination was inhibited by lactose and D-galactose. A wide range of bacteria (S. iniae, S. parauberis, Escherichia coli, Edwardsiella tarda, Vibrio anguillarum, Vibrio harveyi, and Vibrio tapetis) and a ciliate (Miamiensis avidus) were also effectively recognized by rOfGal-1. Significant antiviral activity against rock bream irido virus was also demonstrated by rOfGal-1. Collectively, results from the present study indicate that OfGal-1 can recognize a wide range of microbes and is a vital pattern recognition receptor in the innate immune system of rock bream.

Profiles of teleost DNA fragmentation factor alpha and beta from rock bream (Oplegnathus fasciatus): molecular characterization and genomic structure and gene expression in immune stress

Apoptosis serves to protect normal cells during the processes of development, aging, tissue homeostasis, immunity, and inflammation. Molecules such as caspases, the Bcl-2 family proteins, cytochrome c, APAF-1, and apoptotic endonucleases are concerned with and regulate different stages of apoptosis. DNA fragmentation factor (DFF) is a key final molecule in chromosomal DNA fragmentation during the last step of apoptosis, and is a heterodimeric complex consisting of alpha/inhibitor of caspase-activated DNase (DFFA/ICAD) and beta/caspase-activated DNase (DFFB/CAD) subunits. DFFB/CAD is normally combined with the inhibitor, DFFA/ICAD, in healthy cells. However, after cleavage of the DFF complex by effector caspases, DFFB/CAD acts as an apoptotic nuclease and induces DNA fragmentation in apoptotic cells. The study of DFF proteins is focused on the roles of the apoptotic pathway in mammals. However, gene expression and functions under immune stimulation are not well known in other species. In the present study, we first characterized teleost DFFA/ICAD and DFFB/CAD from rock bream at the molecular level and analyzed the transcriptional expression pattern under immune challenges, to understand their role in immunity. These putative proteins have shown conserved domains and interaction sites orthologous to those of other species. High mRNA expression of both genes was found in the gills and blood of tissues involved in the immune response. The increased expression of DFF genes upon bacterial and viral stimulation was confirmed by qPCR analysis. DFFA/ICAD and DFFB/CAD of rock bream may play a pivotal role in apoptosis and may be involved in host immunity against bacterial and viral infection.

The Molecular Profiling of a Teleostan Counterpart of Follistatin, Identified from Rock Bream Oplegnathus fasciatus which Reveals its Transcriptional Responses against Pathogenic Stress

The follistatin (FST) gene encodes a monomeric glycoprotein that plays a role in binding and inhibiting the functions of members of the transforming growth factor (TGF)-β superfamily. Thus, FST facilitates a wide variety of functions, ranging from muscle growth, to inflammation and immunity. In this study, we sought to characterize an FST counterpart, RbFST, which was identified from rock bream Oplegnathus fasciatus. The RbFST cDNA sequence (2,419 bp) contains a 933-bp open reading frame (ORF) that encodes a putative amino acid sequence for RbFST (35 kDa). The putative amino acid sequence contains a Kazal-type serine protease inhibitor domain (51-98 residues) and an EF-hand, calcium-binding domain (191-226 residues). Additionally, this sequence shares a high identity (98.7%) with the Siniperca chuatsi FST sequence, with which it also has the closest evolutionary relationship according to a phylogenetic study. Omnipresent distribution of RbFST transcripts were detected in the gill, liver, spleen, head kidney, kidney, skin, muscle, heart, brain, and intestine of healthy animals, with significantly higher expression levels in the heart, followed by the liver tissue. Under pathogenic stress caused by two bacterial pathogens, Streptococcus iniae and Edwardsiella tarda, RbFST transcription was found to be significantly up-regulated. Altogether, our findings suggest the putative role of RbFST in immune related responses against pathogenic infections, further prefig uring its significance in rock bream physiology.

Dietary Sulfur Amino Acids Can Spare Taurine in Rock Bream Oplegnathus fasciatus

An 8 week feeding trial was conducted to evaluate whether methionine and cysteine would effectively spare taurine supplementation on growth performance in juvenile rock bream Oplegnathus fasciatus. Triplicate groups of 25 fish averaging 2.74 ± 0.04 g (mean ± SD) were fed one of the experimental diets. Five experimental diets including a fish meal based control diet were prepared by adding sulfur amino acid at fixed level of 1.0% and taurine at graded levels of 0%, 0.25%, 0.5% and 1.0% (S + Tau 0, S + Tau0.25, S + Tau0.5 and S + Tau1.0, respectively). After the feeding trial, growth performance of fish fed the S + Tau 0.25, S + Tau0.5 and S + Tau1.0 diets were significantly higher ( P < 0.05) than those of fish fed the Control diet. ANOVA test suggested that when sulfur amino acid were supplemented to the diets, the optimum taurine supplementation level could be 0.25% in the diet, and broken line analysis of weight gain indicated a level of 0.33%, for positive effects on growth and feed utilization. Fish whole-body protein content and taurine concentration steadily increased with the increase of dietary level in the presence of sulfur amino acid in the diets. On the other hand, whole-body lipid content significantly decreased with the incremental levels of dietary taurine. In conclusion, the results of the present study clearly indicated that dietary supplementation of methionine and cysteine at a level of 1% could spare 0.25 to 0.33% of taurine in juvenile O. fasciatus diets.

Molecular and transcriptional characterization of GTHs and mPRα during ovarian maturation in rock bream Oplegnathus fasciatus.

The membrane progestin receptor α (mPRα) plays an important role in the regulation of oocyte meiotic maturation in fish. However, the endocrine regulation of multiple spawning in fish with asynchronous ovarian development remains to be determined. We identified four genes (FSHβ, LHβ, CGα and mPRα) that are widely expressed in both the reproductive and non-reproductive tissues of rock bream Oplegnathus fasciatus and examined their expression during ovarian maturation. The level of FSHβ transcripts in the pituitary remained high during vitellogenic stages, when the plasma levels of estradiol-17β reached maximum levels and oocyte development was stimulated. LHβ expression in the pituitary and ovary reached maximum levels during oocyte maturation when the plasma levels of testosterone also reached a maximum. A significant correlation between mPRα transcript levels and the gonadosomatic index was observed during vitellogenesis and final maturation. Brain gonadotropin (FSHβ and LHβ) and mPRα were continuously expressed at different stages of ovarian development. The dynamic and diverse nature of gonadotropins and mPRα gene expression patterns suggests that these genes might jointly regulate ovarian development and maturation through the brain-pituitary-ovary axis in the rock bream endocrine system.

Molecular profile and expressional modulation of a Toll like receptor-1 homolog from rock bream (Oplegnathus fasciatus)

Toll-like receptors (TLRs) are well-described pattern recognition receptors that recognize different pathogen-associated molecular patterns (PAMPs) to activate innate immune responses. TLR1 forms a heterodimer with TLR2 that works to identify PAMPs including bacterial components. In the present study, we identified a TLR1 homolog from rock bream Oplegnathus fasciatus (RbTLR1) and characterized it at the genomic level. The complete coding sequence of RbTLR1 was 2406 bp in length and encoded an 802 amino acid protein possessing a calculated molecular mass of 90.7 kDa and typical TLR domain architecture. A single exon spanned the genomic length (2931 bp) of RbTLR1. Phylogenetic analysis showed a close evolutionary relationship between RbTLR1 and its fish orthologs. Using quantitative real time polymerase chain reaction, we detected RbTLR1 mRNA in all the tissues examined, suggesting its merely universal tissue expression. RbTLR1 was expressed strongly in the spleen, kidney, and liver. Following immune stimulation by bacterial pathogens and mitogens, RbTLR1 transcript levels were elevated at various time points post stimulation. Moreover, injection of a viral stimulant, polyinosinic:polycytidylic acid, and rock bream iridovirus altered the basal transcription of RbTLR1. Collectively, these data showed that RbTLR1 is transcriptionally regulated in response to bacterial and viral stimulation, suggesting its putative importance in host immune defense.