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The phagosome-lysosome (PL) signaling pathway plays an important role in the immune system of fish. However, the molecular mechanism underlying PL signaling in fish against Vibrio vulnificus infection remains still unclear. In this study, the half-smooth tongue sole (Cynoglossus semilaevis) infected with V. vulnificus strain ST-6 was used as an experiment model, the immunohistochemical features were evaluated, and spatiotemporal expression analysis of genes and proteins related to PL pathway was verified, respectively. The results showed that the positive staining was observed in the various tissues such as liver, intestine, kidney, spleen, and gills of the infected fish. The differential expressions of PL-related proteins were screened and identified by iTRAQ analysis, and their gene expressions were determined by qRT-PCR detection. The spatiotemporal expression patters were confirmed and most of PL-related genes tended to be downregulated during the early infection at 12 and 36 h post-infection (hpi). Moreover, the protein-protein interaction (PPI) analysis was described for PL pathway. This is the first report on the PL response of C. semilaevis to V. vulnificus infection, which will provide a scientific reference for further elucidating the molecular mechanism of the phagosome-lysosome in marine fish. [ABSTRACT FROM AUTHOR]

Vibrio spp. are major pathogens responsible for mortality and disease in various marine aquaculture organisms. Effective disease control and genetic breeding strategies rely heavily on understanding host vibriosis resistance mechanisms. The Chinese tongue sole (Cynoglossus semilaevis) is economically vital but suffers from substantial mortalities due to vibriosis. Through continuous selective breeding, we have successfully obtained vibriosis-resistant families of this species. In this study, we conducted RNA-seq analysis on three organs, including liver, spleen and intestine from selected resistant and susceptible tongue soles. Additionally, we integrated these data with our previously published RNA-seq datasets of skin and gill, enabling the construction of organ-specific transcriptional profiles and a comprehensive gene co-expression network elucidating the differences in vibriosis resistance. Furthermore, we identified 12 modules with organ-specific functional implications. Overall, our findings provide a valuable resource for investigating the molecular basis of vibriosis resistance in fish, offering insights into target genes and pathways essential for molecular selection and genetic manipulation to enhance vibriosis resistance in fish breeding programs. [ABSTRACT FROM AUTHOR]

DNA methylation is a key epigenetic mechanism orchestrating gene expression networks in many biological processes. Nonetheless, studying the role of specific gene methylation events in fish faces challenges. In this study, we validate the regulation of DNA methylation on empty spiracles homeobox 2 (emx2) expression with decitabine treatment in Chinese tongue sole testis cells. We used the emx2 gene as the target gene and developed a new DNA methylation editing system by fusing dnmt3a with catalytic dead Cas9 (dCas9) and demonstrated its ability for sequence-specific DNA methylation editing. Results revealed that utilizing dCas9-dnmt3a to target emx2 promoter region led to increased DNA methylation levels and decreased emx2 expression in Chinese tongue sole testis cells. More importantly, the DNA methylation editing significantly suppressed the expression of MYC proto-oncogene, bHLH transcription factor (myc), one target gene of emx2. Furthermore, we assessed the off-target effects of dCas9-dnmt3a and confirmed no significant impact on the predicted off-target gene expression. Taken together, we developed the first DNA methylation editing system in marine species and demonstrated its effective editing ability in Chinese tongue sole cells. This provides a new strategy for both epigenetic research and molecular breeding of marine species. [ABSTRACT FROM AUTHOR]

Estuaries are often observed as the boundary between the ocean and the river, separating coastal environments, rather than being seen as a continuum. Owing to insufficient research on demersal fish communities across nearshore marine to estuarine habitats, particularly in South Africa, this study employed a spatial seascape approach, with seasonal sampling of soft-bottom benthic habitats in two permanently open estuaries and the adjacent marine nearshore environment of Algoa Bay on the south coast of South Africa. A total of 790 fish representing 29 species were collected in the marine nearshore, and 6 414 fish (28 species) were caught in the estuarine zone. Two discrete demersal fish assemblages were identified as representing the marine nearshore and estuarine environments. The marine nearshore fish assemblages were dominated by marine species (e.g. Argyrosomus inodorus and Cynoglossus zanzibarensis) that were not recorded in the estuarine environment, whereas marine estuarine-opportunist species (e.g. Pomadasys olivaceus and Galeichthys feliceps) were more abundant in the marine nearshore than in the estuarine environment. The estuaries were dominated by benthic marine estuarine-dependent and marine and estuarine species (e.g. Rhabdosargus holubi, Solea turbynei, Heteromycteris capensis, Psammogobius knysnaensis and Glossogobius callidus). Differences observed in abundance and species richness along the estuarine to marine continuum were primarily related to the salinity gradient. These findings are significant as altered freshwater flows and consequent changes in salinity and productivity can have an impact on the nursery use of both estuaries and the marine nearshore by fish species. [ABSTRACT FROM AUTHOR]

Half-smooth tongue sole (Cynoglossus semilaevis) is regarded as a significant commercial marine fish species in China, and frequent outbreaks of vibriosis has led to substantial economic losses. In this study, we investigated the molecular mechanisms underlying the involvement of the extracellular matrix (ECM) signaling pathway in the skin immune response of C. semilaevis infected with Vibrio vulnificus. The results showed that most differentially expressed proteins (DEPs) were identified through iTRAQ proteome analysis, and ten ECM-related proteins were screened at 12 and 36 h post-infection (hpi). Notably, several DEPs associated with ECM including HSPG, FN, COCH, LAMB1, LAMC1, TSPN, COL6A1, AMBP, HX and ITGA6 were tested for their expression at the transcriptional level during V. vulnificus infection using qRT-PCR assay. The analysis of protein-protein interaction (PPI) showed that the integrin ITGA6 exhibited obvious interactions among ECM-related DEPs. Furthermore, the spatio-temporal expression of the Csitga6 gene was highest in the skin, gill, muscle, and spleen, but lower in the liver, kidney and intestine. To our knowledge, this is the first report on the involvement of ECM pathway in the skin immune response to V. vulnificus infection, and provides a reference for further study of the ECM mechanism in the mucosal immune response of marine fish. [ABSTRACT FROM AUTHOR]

Proteasome 26S Subunit, Non-ATPase 9 (psmd9) plays an important role in the balance of protamine and the stability of the nucleolar structure during spermatogenesis. In this study, we cloned the psmd9 of Cynoglossus semilaevis and analyzed its expression pattern. psmd9 was identified on the Z chromosome of C. semilaevis, which is considered an interesting candidate gene for spermatogenesis. qRT-PCR and FISH experiments showed that the psmd9 gene was significantly highly expressed in the testes. It is worth noting that the expression level of psmd9 in male fish testes is significantly higher than that in pseudomales. In order to further explore the role of psmd9 in spermatogenesis, a male testicular cell line was used as the experimental material. The results of the psmd9-RNAi and overexpression experiments showed that psmd9 had a synergistic effect with spermatogenesis-related genes dnd1, cfap69, dnah3 and dnajb13, but had an antagonistic effect with ccne2. Our findings offer a scientific foundation for comprehending the role of psmd9 in the spermatogenesis regulatory network of C. semilaevis. [ABSTRACT FROM AUTHOR]

Vibriosis, caused by Vibrio, seriously affects the health of fish, shellfish, and shrimps, causing large economic losses. Teleosts are represent the first bony vertebrates with both innate and adaptive immune responses against pathogens. Aquatic animals encounter hydraulic pressure and more pathogens, compared to terrestrial animals. The skin is the first line of defense in fish, constituting the skin-associated lymphoid tissue (SALT), which belongs to the main mucosa-associated lymphoid tissues (MALT). However, little is known about the function of immunity related proteins in fish. Therefore, this study used iTRAQ (isobaric tags for relative and absolute quantitation) to compare the skin proteome between the resistant and susceptible families of Cynoglossus semilaevis. The protein integrin beta-2, the alpha-enolase isoform X1, subunit B of V-type proton ATPase, eukaryotic translation initiation factor 6, and ubiquitin-like protein ISG15, were highly expressed in the resistant family. The 16S sequencing of the skin tissues of the resistant and susceptible families showed significant differences in the microbial communities of the two families. The protein-microbial interaction identified ten proteins associated with skin microbes, including immunoglobulin heavy chain gene (IGH), B-cell lymphoma/leukemia 10 (BCL10) and pre-B-cell leukemia transcription factor 1 isoform X2 (PBX2). This study highlights the interaction between skin proteins and the microbial compositions of C. semilaevis and provides new insights into understanding aquaculture breeding research. [ABSTRACT FROM AUTHOR]

A massive mortality event concerning farmed Chinese tongue soles occurred in Tianjin, China, and the causative agent remains unknown. Here, a novel Cynoglossus semilaevis papillomavirus (CsPaV) and parvovirus (CsPV) were simultaneously isolated and identified from diseased fish via electron microscopy, virus isolation, genome sequencing, experimental challenges, and fluorescence in situ hybridization (FISH). Electron microscopy showed large numbers of virus particles present in the tissues of diseased fish. Viruses that were isolated and propagated in flounder gill cells (FG) induced typical cytopathic effects (CPE). The cumulative mortality of fish given intraperitoneal injections reached 100% at 7 dpi. The complete genomes of CsPaV and CsPV comprised 5939 bp and 3663 bp, respectively, and the genomes shared no nucleotide sequence similarities with other viruses. Phylogenetic analysis based on the L1 and NS1 protein sequences revealed that CsPaV and CsPV were novel members of the Papillomaviridae and Parvoviridae families. The FISH results showed positive signals in the spleen tissues of infected fish, and both viruses could co-infect single cells. This study represents the first report where novel papillomavirus and parvovirus are identified in farmed marine cultured fish, and it provides a basis for further studies on the prevention and treatment of emerging viral diseases. [ABSTRACT FROM AUTHOR]

Commencing with sperm–egg fusion, the early stages of metazoan development include the cleavage and formation of blastula and gastrula. These early embryonic events play a crucial role in ontogeny and are accompanied by a dramatic remodeling of the gene network, particularly encompassing the maternal-to-zygotic transition. Nonetheless, the gene expression dynamics governing early embryogenesis remain unclear in most metazoan lineages. We conducted transcriptomic profiling on two types of gametes (oocytes and sperms) and early embryos (ranging from the four-cell to the gastrula stage) of an economically valuable flatfish–the Chinese tongue sole Cynoglossus semilaevis (Pleuronectiformes: Cynoglossidae). Comparative transcriptome analysis revealed that large-scale zygotic genome activation (ZGA) occurs in the blastula stage, aligning with previous findings in zebrafish. Through the comparison of the most abundant transcripts identified in each sample and the functional analysis of co-expression modules, we unveiled distinct functional enrichments across different gametes/developmental stages: actin- and immune-related functions in sperms; mitosis, transcription inhibition, and mitochondrial function in oocytes and in pre-ZGA embryos (four- to 1000-cell stage); and organ development in post-ZGA embryos (blastula and gastrula). These results provide insights into the intricate transcriptional regulation of early embryonic development in Cynoglossidae fish and expand our knowledge of developmental constraints in vertebrates. [ABSTRACT FROM AUTHOR]

Accurate and precise estimates of survey abundance indices are essential inputs for stock assessment models and are important for the successful conservation and management of fisheries stocks. Since abundance indices can be standardized in various different ways, from conventional design-based approaches to model-based approaches, it is essential to compare the efficiency of those approaches and quantify the consequences for stock assessments. In this study, we focus on an important commercial stock of witch flounder (Glyptocephalus cynoglossus) in NAFO 3N+3O divisions. We first compare the survey indices standardized by design-based and model-based approaches, and find that a model-based estimator provides more precise estimates of survey indices than design-based approach for this stock. We then apply a widely used age-structured statistical catch-at-length (ACL) assessment model to the standardized catch-at-length survey indices from both approaches to estimate the age-based population dynamics for this stock. We conclude that the ACL model fit to model-based indices performed better than the same model fit to design-based indices. [ABSTRACT FROM AUTHOR]

Simple Summary: The sex chromosome, especially specific in one sex, is considered to determine the sexual size dimorphism (SSD), a dimorphic sexual difference in the body size. For Cynoglossus semilaevis, a flatfish unique in China, the important role of female-specific chromosome W in its female-biased SSD was previously implied. Furthermore, a W chromosome-specific gene zbed1 was identified to potentially regulate female-biased SSD in C. semilaevis. However, the chromosome's location, family members, and detailed network information are still unknown. At present, the genome-wide identification of ZBED family members and dPCR experiment both confirm that three copies of the zbed1 gene are located in chromosome W, with no zbed1 gene in chromosome Z. Phylogenetic analysis for ZBED family revealed an existence of ZBED9 in the fish. Nine members were uncovered from C. semilaevis, clustering into three kinds, ZBED1, ZBED4 and ZBEDX, which is less than the eleven kinds of ZBED members in mammals. For the chromosome-W-specific zbed1, qPCR verified its predominant expression in the female brain and pituitary tissues. The dual luciferase activity test showed that transcription factor c/ebpα could significantly enhance the transcriptional activity of zbed1 promoter, which is opposite to its effect on the male determinant factor dmrt1. In addition, after zbed1 interfered in the brain cells, piwil1, esr2 and wnt7b were up-regulated, while cell-cycle-related genes (tbp, cdk2, cdk4, cdk6, ccng1 and ccndx) were down-regulated. It is suggested that the cell proliferation function of zbed1 may be realized by regulating esr2, piwil1, cell cycle and the Wnt pathway. The sex chromosome, especially specific in one sex, generally determines sexual size dimorphism (SSD), a phenomenon with dimorphic sexual difference in the body size. For Cynoglossus semilaevis, a flatfish in China, although the importance of chromosome W and its specific gene zbed1 in female-biased SSD have been suggested, its family members and regulation information are still unknown. At present, three zbed1 copies gene were identified on chromosome W, with no gametologs. Phylogenetic analysis for the ZBED family revealed an existence of ZBED9 in the fish. Nine members were uncovered from C. semilaevis, clustering into three kinds, ZBED1, ZBED4 and ZBEDX, which is less than the eleven kinds of ZBED members in mammals. The predominant expression of zbed1 in the female brain and pituitary tissues was further verified by qPCR. Transcription factor c/ebpα could significantly enhance the transcriptional activity of zbed1 promoter, which is opposite to its effect on the male determinant factor-dmrt1. When zbed1 was interfered with, piwil1, esr2 and wnt7b were up-regulated, while cell-cycle-related genes, including cdk4 and ccng1, were down-regulated. Thus, zbed1 is involved in cell proliferation by regulating esr2, piwil1, cell cycle and the Wnt pathway. Further research on their interactions would be helpful to understand fish SSD. [ABSTRACT FROM AUTHOR]

Copyright of Food Research & Development is the property of Food Research & Development 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.)

Simple Summary: There is sex dimorphism in Cynoglossus semilaevis. And the female C. semilaevis has reversed to the pseudomale, hindering the development of the industry. The growth state of pseudomale is similar to male C. semilaevis. However, the pseudomales only produce Z-sperm, with W-sperm specifically disappearing. As transcriptome technology has developed, we have begun to investigate the function of E3 ubiquitin ligase in the ubiquitination pathway during spermatogenesis. In this study, we have cloned and described the C. semilaevis Z-linked E3 ubiquitin ligase rnf34. Its effect might begin in the early development of gonads, which is mainly localized in germ cells. These data indicate its role in gametogenesis, which will provide new genetic resources for the mechanism of abnormal spermatogenesis in fish pseudomale as well as exploratory control techniques. The high proportion of males in C. semilaevis hinders their industrial development. The genetic ZW individual can become a pseudomale by sex reversal. And the pseudomale can produce Z-sperm (with epigenetic information to cause sex reversal) while W-sperm is absent, which leads to an even higher male proportion in offspring. Recently, with the development of transcriptomic technologies, research on spermatogenesis in C. semilaevis has been focused on the ubiquitination pathway. In this study, we analyzed the function of the ubiquitin ligase rnf34 gene on the Z chromosome. A qPCR experiment showed that its expression level in the gonad was the highest among different tissues. In the ovary, the expression gradually increased with development from 40 days post-hatching (dph) to 1.5 years post-hatching (yph). In the testis, rnf34 showed increased expression from 40 dph to 6 months post-hatching (mpf) and stabilized up until 1.5 ypf. In situ hybridization showed that the mRNA of rnf34 was mainly distributed in the germ cells of the testis and the ovary. In vivo siRNA-mediated knockdown of the rnf34 gene in male fish affected the expression of a series of genes related to sex differentiation and spermatogenesis. These results provide genetic data on the molecular mechanisms of gonadal development and spermatogenesis in C. semilaevis. [ABSTRACT FROM AUTHOR]

Simple Summary: Temperature is a pervasive environmental factor that plays a crucial role in the lives of aquatic organisms. However, the mechanisms governing the response to temperature remain unclear in teleost fish. In this research, the marine benthic fish Chinese tongue sole (Cynoglossus semilaevis), which is economically significant in northern China, is used as a model to analyze this issue. The brains of female and male C. semilaevis were examined via transcriptomics technology to investigate their response to temperature. Our findings revealed the existence of specific genes and pathways involved in cortisol synthesis and secretion, neuroactive ligand–receptor interactions, TGF-beta signaling pathway, and JAK/STAT signaling pathway. The genes identified includes the HSP family, tshr, c-fos, c-jun, cxcr4, camk2b, and igf2. Our study provides some evidence that C. semilaevis responds to temperature, highlighting a potential path for further investigation. As a common influencing factor in the environment, temperature greatly influences the fish that live in the water all their life. The essential economic fish Chinese tongue sole (Cynoglossus semilaevis), a benthic fish, will experience both physiological and behavioral changes due to increases in temperature. The brain, as the central hub of fish and a crucial regulatory organ, is particularly sensitive to temperature changes and will be affected. However, previous research has mainly concentrated on the impact of temperature on the gonads of C. semilaevis. Instead, our study examines the brain using transcriptomics to investigate specific genes and pathways that can quickly respond to temperature changes. The fish were subjected to various periods of heat stress (1 h, 2 h, 3 h, and 5 h) before extracting the brain for transcriptome analysis. After conducting transcriptomic analyses, we identified distinct genes and pathways in males and females. The pathways were mainly related to cortisol synthesis and secretion, neuroactive ligand–receptor interactions, TGF beta signaling pathway, and JAK/STAT signaling pathway, while the genes included the HSP family, tshr, c-fos, c-jun, cxcr4, camk2b, and igf2. Our study offers valuable insights into the regulation mechanisms of the brain's response to temperature stress. [ABSTRACT FROM AUTHOR]

The assembly of W and Y chromosomes poses significant challenges in vertebrate genome sequencing and assembly. Here, we successfully assembled the W chromosome of Verasper variegatus with a length of 20.48 Mb by combining population and PacBio HiFi sequencing data. It was identified as a young sex chromosome and showed signs of expansion in repetitive sequences. The major component of the expansion was Ty3/Gypsy. The ancestral Osteichthyes karyotype consists of 24 protochromosomes. The sex chromosomes in four Pleuronectiformes species derived from a pair of homologous protochromosomes resulting from a whole-genome duplication event in teleost fish, yet with different sex-determination systems. V. variegatus and Cynoglossus semilaevis adhere to the ZZ/ZW system, while Hippoglossus stenolepis and H. hippoglossus follow the XX/XY system. Interestingly, V. variegatus and H. hippoglossus derived from one protochromosome, while C. semilaevis and H. stenolepis derived from another protochromosome. Our study provides valuable insights into the evolution of sex chromosomes in flatfish and sheds light on the important role of whole-genome duplication in shaping the evolution of sex chromosomes. [ABSTRACT FROM AUTHOR]

The scale morphology of pleuronectiforms in the Gulf of Oman remains insufficiently known. This study used light microscopy and morphological analysis to examine scale variation across the flank of four Tonguefishes species; Cynoglossus arel, C. bilineatus, C. lingua, and C. puncticeps. Scales were extracted from six flank regions, three on the eyed and blind sides, respectively. The most differentiated species was C. arel, which showed significant differences in four size variables in five regions. In Cynoglossus arel and C. lingua, the scales of the eyed side were ctenoid, and those scales from the blind side were cycloid; C. puncticeps have ctenoid scales on both flank sides and C. bilineatus has cycloid scales on both sides. All species' scales on the blind side have fewer ctenial spines (except in C. bilineatus). This study indicated that scale morphology demonstrated considerable variation among the flank regions of the examined species. As a result, the scales from the head and the trunk regions of the eyed side and the scales from the head region of the blind side have a good power of species separation in this family. [ABSTRACT FROM AUTHOR]

The fatty acid accumulation in fish tissues are closely related to fish sex, yet the sex differences in fish fatty acids have not been fully known. This experiment investigated the sex differences in fatty acid composition of Chinese tongue sole (Cynoglossus semilaevis), which have typical sexual dimorphism and reversal. Three sexes, namely females, males and pseudomales, were involved in this study. Five batches of fish samples were collected from different fish farms in Shandong Province, China. These fish were identified to be at the gonadal development stage of III–IV. The disparity of fatty acid between sexes (female vs male and pseudomale vs. male) was evaluated by the distance coefficient (Dsex) and multi-variate similarity of percentages analysis (SIMPER). The highest Dsex values between females and males were found in gonad, followed by liver and eye. The fatty acids that differed between females and males were mainly DHA, 16:1n-7, 18:1n-9, and 18:0. The sex difference in DHA and 18:1n-9 contributed significantly to the overall sex difference in fatty acid of brain, eye, and gonad, whereas that in 16:1n-7 contributed significantly in heart, gill, liver, and muscle. The sex difference in 18:0 contributed significantly to the overall sex difference in fatty acid of heart, gill, gut, and skin. The sex differences in fatty acid between pseudomales and males were generally insignificant. In conclusion, at this gonadal development stage (III–IV), the sex differences in fatty acid between female and male Chinese tongue sole have emerged, mainly in the gonad. The testes had higher DHA levels but lower levels of 16:1n-7 and 18:1n-9 than ovaries. In addition, for pseudomales, the phenotypic sex more substantially determined the fatty acid composition than the genetic sex. [ABSTRACT FROM AUTHOR]

Phosphorylation is a post-translational modification that contributes to versatile protein functions in spermatogenesis, and the variations they generate usually results in abnormal spermatogenesis or sperm dysfunction. The sex-reversal phenomenon exists in Chinese tongue sole under certain conditions such that individuals with a ZW genotype can acquire a male phenotype and are thus called pseudomales. Pseudomale tongue sole can reach sexual maturity but produce only Z-type sperm, and the Z sperm carries paternal epigenetic information. Whether phosphorylation plays a role in the sperm abnormality of pseudomales is unknown. In this study, a phosphoproteomic analysis was performed to compare protein phosphorylation profiles between pseudomale and male testes. Altogether, we identified 14,253 phosphopeptides matching with 4843 proteins, with 1329 differentially phosphorylated peptides corresponding to 1045 differentially phosphorylated proteins (DPPs). Phosphorylation at 781 sites was upregulated and at 548 sites was downregulated. Four motifs were identified among differentially phosphorylated peptides, which were "SP", "SD", "RxxS", and "TP". Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggested that the cell cycle and DNA/RNA processing were significantly enriched with the genes encoding DPPs. To analyze DPP function in depth, a protein-protein interaction network was constructed, and Ran-binding protein 2 was found to play a central role in spermatogenesis by regulating several processes such as the cell cycle, eukaryotic translation, ubiquitination, and minichromosome maintenance. In kinase-associated network analyses, two "mitogen-activated protein kinase (Mapk)-centered" clusters were identified that may account for abnormal spermatogenesis in pseudomales. One cluster was centered on Mapk6, which predominantly regulated the cell cycle by interacting with several cyclin-dependent kinases, and the other was centered on the "testis-expressed kinase 1-like (Tesk1l)/Pim1l-Mapk4l- testis-expressed 14 (Tex14)" kinase cascade, which might contribute to spermatogenesis by regulating β-catenin. Taken together, these data suggested the new candidates involved in pseudomale sperm abnormalities and provided clues to discover the phosphorylated regulatory mechanism underlying tongue sole spermatogenesis. [ABSTRACT FROM AUTHOR]

Introduction: Vibriosis causes enormous economic losses of marine fish. The present study investigated the intestinal microbial response to acute infection of half-smooth tongue sole with different-dose Vibrio alginolyticus within 72 h by metagenomic sequencing. Methods: The inoculation amount of V. alginolyticus for the control, low-dose, moderate-dose, and high-dose groups were 0, 8.5 × 101, 8.5 × 104, and 8.5 × 107 cells/g respectively, the infected fish were farmed in an automatic seawater circulation system under a relatively stable temperature, dissolved oxygen and photoperiod, and 3 ~ 6 intestinal samples per group with high-quality DNA assay were used for metagenomics analysis. Results: The acute infections with V. alginolyticus at high, medium, and low doses caused the change of different-type leukocytes at 24 h, whereas the joint action of monocytes and neutrophils to cope with the pathogen infection only occurred in the high-dose group at 72 h. The metagenomic results suggest that a high-dose V. alginolyticus infection can significantly alter the intestinal microbiota, decrease the microbial α-diversity, and increase the bacteria from Vibrio and Shewanella, including various potential pathogens at 24 h. High-abundance species of potential pathogens such as V. harveyii, V. parahaemolyticus, V. cholerae, V. vulnificus, and V. scophthalmi exhibited significant positive correlations with V. alginolyticus. The function analysis revealed that the high-dose inflection group could increase the genes closely related to pathogen infection, involved in cell motility, cell wall/membrane/envelope biogenesis, material transport and metabolism, and the pathways of quorum sensing, biofilm formation, flagellar assembly, bacterial chemotaxis, virulence factors and antibiotic resistances mainly from Vibrios within 72 h. Discussion: It indicates that the half-smooth tongue sole is highly likely to be a secondary infection with intestinal potential pathogens, especially species from Vibrio and that the disease could become even more complicated because of the accumulation and transfer of antibiotic-resistance genes in intestinal bacteria during the process of V. alginolyticus intensified infection. [ABSTRACT FROM AUTHOR]

Length-weight relationships (LWRs) and Fulton's condition factor were estimated for two flatfishes, Cynoglossus lingua Hamilton, and Cynoglossus cynoglossus (Hamilton), from the Cox's Bazar coast of Bangladesh. Sampling was done from September to November 2022 from the landing center of Bangladesh Fisheries Development Corporation. In this study, the maximum total length of C. cynoglossus (34.0 cm) is a new record for this species. The length-weight relationships for these two species were highly significant (P < 0.001) with adjusted r2 values of 0.918 and 0.927 for C. lingua and C. cynoglossus, respectively. The calculated growth coefficient (b) for C. lingua and C. cynoglossus was 2.873 and 3.359, respectively. The estimated Fulton's condition factor (Kn) was 0.42 ± 0.05 for C. lingua and 0.72 ± 0.11 for C. cynoglossus. No information about the population parameters of C. lingua from the Bay of Bengal has been reported previously in any scientific database. The maximum Kn value of C. lingua was observed in the 13.0–15.9 cm length class while that of C. cynoglossus was found in the 31.0–33.9 cm length class. Our estimated LWR and Fulton's condition factor values for these two flatfishes can be useful for management and conservation. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agricultural Science & Technology (1008-0864) is the property of Journal of Agricultural Science & Technology 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.)

The Chinese tongue sole (Cynoglossus semilaevis) is a traditional, precious fish in China. Due to the large growth difference between males and females, the investigation of their sex determination and differentiation mechanisms receives a great deal of attention. Forkhead Box O (FoxO) plays versatile roles in the regulation of sex differentiation and reproduction. Our recent transcriptomic analysis has shown that foxo genes may participate in the male differentiation and spermatogenesis of Chinese tongue sole. In this study, six Csfoxo members (Csfoxo1a, Csfoxo3a, Csfoxo3b, Csfoxo4, Csfoxo6-like, and Csfoxo1a-like) were identified. Phylogenetic analysis indicated that these six members were clustered into four groups corresponding to their denomination. The expression patterns of the gonads at different developmental stages were further analyzed. All members showed high levels of expression in the early stages (before 6 months post-hatching), and this expression was male-biased. In addition, promoter analysis found that the addition of C/EBPα and c-Jun transcription factors enhanced the transcriptional activities of Csfoxo1a, Csfoxo3a, Csfoxo3b, and Csfoxo4. The siRNA-mediated knockdown of the Csfoxo1a, Csfoxo3a, and Csfoxo3b genes in the testicular cell line of Chinese tongue sole affected the expression of genes related to sex differentiation and spermatogenesis. These results have broadened the understanding of foxo's function and provide valuable data for studying the male differentiation of tongue sole. [ABSTRACT FROM AUTHOR]

LPXRFa, also known as gonadotropin-inhibitory hormone (GnIH), and kisspeptin (Kiss) are two major hypothalamic peptides that modulate the reproductive axis of vertebrates, including teleosts. However, little information is available regarding the actions of nutritional status on the regulation of these two neuroendocrine systems in fish. Herein, we assessed the effects of starvation and refeeding on the expression of lpxrfa, kiss2 and their receptors (lpxrfa-r and kiss2r respectively) at the brain-pituitary level of half-smooth tongue sole (Cynoglossus semilaevis). Food deprivation for 4 weeks induced a rise in brain lpxrfa as well as brain and pituitary lpxrfa-r mRNA levels, and refeeding restored brain lpxrfa and lpxrfa-r expression back to normal. However, pituitary lpxrfa-r mRNA levels still remained high after 1 week of refeeding. Neither lpxrfa nor kiss2 transcripts in the pituitary were altered by fasting, but their mRNA levels increased significantly after 1 week of refeeding, and declined back to the control levels after 2 weeks of refeeding. None of brain kiss2 and kiss2r along with pituitary kiss2r transcripts were modified by the nutritional status. In summary, our results revealed an interaction between energy status and the elements of LPXRFa and Kiss systems in the brain-pituitary axis of half-smooth tongue sole. Food deprivation and refeeding differentially regulated the two systems, which provided additional evidence for the involvement of the LPXRFa and Kiss systems in the regulation of reproduction by energy balance in nonmammalian species. [ABSTRACT FROM AUTHOR]

Fish sex determination can be affected by environmental temperature. This process relies on temperature-sensitive proteins such as heat shock proteins (HSPs). Our previous work found that heat shock cognate proteins (HSCs) may participate in high-temperature associated sex reversal of Chinese tongue sole (Cynoglossus semilaevis). However, the role of hsc genes in responding to high temperature and affecting sex determination/differentiation remains unclear. Here, by using C. semilaevis as model, we identified hsc70 and hsc70-like. hsc70 was abundant in the gonads with a testicular-higher expression at all gonadal development stages except for 6 months post fertilization (mpf). Intriguingly, hsc70-like showed higher expression in testes from 6 mpf on. Both long-term heat treatment during the temperature-sensitive sex-determining period and short-term heat stress at the end of this period caused different expression of hsc70/hsc70-like between sexes. The dual-luciferase assay results also suggested that these genes can respond to high temperature rapidly in vitro. Heat treatment of C. semilaevis testis cells overexpressed with hsc70/hsc70-like could affect the expression of sex-related genes sox9a and cyp19a1a. Our results indicated that hsc70 and hsc70-like were key regulators linking external high-temperature signals with sex differentiation in vivo and provide a new idea for understanding the mechanism by which high temperature affects sex determination/differentiation in teleosts. [ABSTRACT FROM AUTHOR]

The experiment was to study the optimum proportion and time of compound feed for three kinds of probiotics. In the experiment, the feed of Cynoglossus semilaevis was used as substrate, the total inoculum amount was 3%, and the fermentation treatment of Saccharomyces cerevisiae, Bacillus subtilis and Lactobacillus plantarum was carried out at 35 ℃, while the control group was not inoculated with any inoculum. A total of 300 healthy Cynoglossus semilaevis with an average body weight of (80.27±0.19) g were randomly divided into two groups, with three replicates in each group and 50 Cynoglossus semilaevis in each replicate. The control group was fed with complex diet, and the experimental group was fed with complex diet supplemented with 10% fermented feed (fermented feed under the optimal conditions obtained in the optimization experiment). The experiment lasted for 56 d. The results showed that after fermentation, the number of live bacteria in each group of fermented food increased by about 100 000 times. The mixed fermentation effect of three strains was significantly better than that of control group (P<0.05). The fermentation effect was the best when the ratio of Saccharomyces cerevisiae∶ Bacillus subtilis∶ Lactobacillus plantarum was 1∶ 3∶ 2 for 5 d. Compared with control group, the body weight gain and specific growth rate of Cynoglossus semilaevis in test group were significantly higher (P<0.05). The experiment indicates that the fermentation effect of Saccharomyces cerevisiae∶ Bacillus subtilis∶ Lactobacillus plantarum at a ratio of 1∶3∶2 for 5 d is better at 35 ℃, and the fermentation feed can promote the growth and improve the feed utilization rate of Cynoglossus semilaevis. [ABSTRACT FROM AUTHOR]

Simple Summary: Chinese tongue sole (Cynoglossus semilaevis) is an important aquatic fish in northeast Asia that displays sexual growth morphism, with females being 2–4 times larger than males. Tongue sole has a ZZ/ZW sex determination system, and the genotypic female (ZW) can be sex-reversed into phenotypic males, namely, pseudomales. Pseudomales show similar growth to male fish and are disadvantageous in aquaculture. Moreover, pseudomale fish can produce sperm but only Z-type sperm, and its epigenetic information makes its ZW offspring prone to become pseudomale. Thus, screening the key genes for W absence would provide clues for producing high female ratio or all female fry, benefiting the tongue sole industry. In this study, we compared the transcriptomic profiles of pseudomale and male sperm and found that the FoxO signalling pathway, especially the foxo3a and foxo6-like genes, may play important roles in spermatogenesis. In addition, we identified an ~1 M bp area on the Z chromosome enriched with eight DEGs. The study has provided valuable data for screening candidate genes involved in pseudomale sperm abnormity, and their functional study in the future would shed light on sex control in the tongue sole industry. Chinese tongue sole (Cynoglossus semilaevis) has a ZZ/ZW sex determination system, but the genotypic female (ZW) can be sex-reversed into phenotypic males, namely, pseudomales. Pseudomale fish can produce only Z-type sperm but not W sperm. However, the molecular mechanism is unclear. To screen the key genes involved in pseudomale sperm abnormalities, we analysed the transcriptomic profiles of pseudomale and male sperm. In comparison to male sperm, 592 differentially expressed genes (DEGs) were identified in pseudomale sperm, including 499 upregulated and 93 downregulated genes. KEGG analysis indicated that the FoxO signalling pathway, especially the foxo3a and foxo6-like genes, may play an important role in spermatogenesis. The DEGs were mainly distributed on sex chromosomes, with 158 downregulated genes on the Z chromosome and 41 upregulated genes on the W chromosome. A specific area (14–15 M) on the Z chromosome was identified, which enriched eight DEGs inside the ~1 M region. In addition, there were five gene alleles on the sex chromosomes, which showed the opposite transcription pattern (upregulated for the W allele, downregulated for the Z allele). This study has provided valuable data for screening candidate genes involved in the pseudomale sperm abnormality. [ABSTRACT FROM AUTHOR]

The complement component 5a/complement component 5 receptor 1 (C5a/C5aR1) pathway plays a crucial role in the onset and development of inflammation, but relevant studies in fish are lacking. In this study, we successfully characterized the relationship between half-smooth tongue sole (Cynoglossus semilaevis) C5aR1 (CsC5aR1) and bacterial inflammation. First, we showed that the overexpression of CsC5aR1 significantly increased bacterial pathological damage in the liver and intestine, whereas inhibition attenuated the damage. The in vitro experiments suggested that CsC5aR1 was able to positively regulate the phagocytic activity and respiratory burst of tongue sole macrophages. In terms of both transcriptional and translational levels, overexpression/inhibition of CsC5aR1 was followed by a highly consistent up-regulation/decrease of its downstream canonical inflammatory factor interleukin-6 (CsIL-6). Furthermore, we stimulated macrophages by lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and found a broad-spectrum response to bacterial infections by the C5a/C5aR1 complement pathway together with the downstream inflammatory factor CsIL-6. Subsequently, we directly elucidated that CsIL-6 is an indicator of C5a/C5aR1-mediated inflammation at different infection concentrations, different infectious bacteria (Vibrio anguillarum and Mycobacterium marinum), and different detection levels. These results might provide a new inflammation bio-marker for early warning of bacteria-induced hyperinflammation leading to fish mortality and a promising target for the treatment of bacterial inflammation in teleost. • By directly manipulating CsC5aR1, it was demonstrated that its overactivation could lead to bacterial inflammatory damage. • The IL-6 gene in C. semilaevis was functionally characterized for the first time. • CsC5aR1 and CsIL-6 were widely involved in bacterial inflammation triggered by Gram-positive/negative bacteria. • CsIL-6 could serve as an indicator of bacterial inflammation. [ABSTRACT FROM AUTHOR]

Simple Summary: Chinese tongue sole (Cynoglossus semilaevis) typically displays female-biased sexual size dimorphism (SSD), but its epigenetic regulatory mechanisms are poorly understood, especially the role of circRNAs. To explore the function of circRNAs in Chinese tongue sole SSD, we firstly identified differentially expressed circular RNAs (DE circRNAs) in female, male, and pseudo-male C. semilaevis. Secondly, the ceRNA network containing DE circRNAs, miRNAs, and mRNAs in the three genders was constructed. Among the ceRNA network, several circRNAs such as novel_circ_004374 and novel_circ_014597 may regulate hipk2 expression by sponging miR-130-x. It is also worth exploring whether or how novel_circ_008696 regulates setd2 by binding to novel-m0387-3p. The present study provided the cirRNA and its ceRNA network that potentially regulate C. semileavis female-biased SSD for the first time. Sexual size dimorphism (SSD), which is the sexual differences in body size, has been widely reported in various species including fishes. For Chinese tongue sole (Cynoglossus semilaevis), a flatfish exhibiting typically female-biased SSD, little is known for its epigenetic regulation mechanism, especially the role of circRNAs. Here, we identified the differently expressed abundances of circRNAs in females, males, and pseudo-males to explore the potential functions of circRNAs in Chinese tongue sole SSD. In total, 14,745 novel circRNAs were screened, among which 1461 DE circRNAs were identified from the brain, gonad, liver, and muscle in female, male, and pseudo-male individuals. The ceRNA network was subsequently constructed, including 10 circRNAs, 26 mRNAs, and 11 miRNAs. These DE mRNAs were mainly related to the mRNA surveillance pathway, metabolic pathways, and cellular senescence. Importantly, the ceRNA network has revealed that several circRNAs such as novel_circ_004374 and novel_circ_014597 may regulate homeodomain interacting protein kinase 2 (hipk2) expression by sponging miR-130-x. It is also worth exploring whether or how novel_circ_008696 regulates SET Domain Containing 2, histone lysine methyltransferase (setd2), which in turn affects the epigenetic patterns of different sexual individuals. The present study not only enriches the knowledge on the potential roles of circRNA in the physiological process, but also provides new clues for the explanation of fish SSD. In future studies, the precise function and involvement of circRNAs in female-biased SSD will require more efforts. [ABSTRACT FROM AUTHOR]

Simple Summary: In fish, it is obvious that the asynchronous development of the gonads and sexual dimorphism limit the development of aquaculture, so the research into sex-differentiation and gonadal growth is very important. Due to the sexual reversal phenomenon (genetic females becoming phenotypic males), the Chinese tongue sole (Cynoglossus semilaevis) is a great model for investigating sex-differentiation. Herein, we report one gene involved in sex-differentiation and gonadal growth of the Chinese Tongue Sole. The gene cyp26b1 (cytochrome P450 family 26 subfamily b member 1) is a metabolizing Retinoic Acid (RA) enzyme. Since it regulates RA to control sex determination and differentiation, cyp26b1 is considered a critical part of mammals' ovary-antagonizing and testis-determining downstream passageway of Sry (sex-determining region Y) and Sox9 (sry-box transcription factor 9). In fish, the related research is reported only on the Japanese flounder (Paralichthys olivaceus) and zebrafish (Danio rerio). In the current investigation, the identification and expression pattern of the cyp26b1 gene in the Chinese tongue sole suggested that cyp26b1 might impact sex-differentiation and gonadal development. As an RA-metabolizing enzyme, cyp26b1 has a substantial impact on RA-signaling pathways. The cyp26b1 gene from the Chinese tongue sole was cloned and identified in this investigation. The cyp26b1 ORF was 1536 bp in length and encoded a 512 amino acid protein. A quantitative real-time PCR (qPCR) indicated that the cyp26b1 expression is no significant sexual dimorphism in the gonads at the 80 days post-hatching (dph) stages. After 4 months post-hatching (mph), the expression of cyp26b1 showed sexual dimorphism and lower level of expression in the ovaries than in the testes. An in situ hybridization demonstrated that cyp26b1 mRNA was primarily located in the testis. Interestingly, the cyp26b1 mRNA probe was also detected in the ovaries. These results suggested that cyp26b1 participates in the sex-differentiation and gonadal development of the Chinese tongue sole. [ABSTRACT FROM AUTHOR]

Simple Summary: Sexual dimorphism is a phenomenon commonly existing in animals. Chinese tongue sole Cynoglossus semilaevis is an economical marine fish with obvious female-biased size dimorphism. So, it is important to explore the molecular mechanism beyond gonadal development for sex control in aquaculture industry. RNA-binding protein Ewing Sarcoma protein-like (ewsr1) gene is important for mouse gonadal development and reproduction, however there are limited studies on this gene in teleost. In this study, two ewsr1 genes were cloned and characterized from C. semilaevis. The ewsr1-w gene, located in W chromosomes, showed female-biased expression during C. semilaevis gonadal development. In addition, knock-down effect and transcriptional regulation of Cs-ewsr1-w further suggested its essential role in ovarian development. This study broadened our understanding on ewsr1 function in teleost, and provided genetic resources for the further development of sex control breeding techniques in C. semilaevis aquaculture. Ewsr1 encodes a protein that acts as a multifunctional molecule in a variety of cellular processes. The full-length of Cs-ewsr1-w and Cs-ewsr1-z were cloned in Chinese tongue sole (Cynoglossus semilaevis). The open reading frame (ORF) of Cs-ewsr1-w was 1,767 bp that encoded 589 amino acids, while Cs-ewsr1-z was 1,794 bp that encoded 598 amino acids. Real-time PCR assays showed that Cs-ewsr1-w exhibited significant female-biased expression and could be hardly detected in male. It has the most abundant expression in ovaries among eight healthy tissues. Its expression in ovary increased gradually from 90 d to 3 y with C. semilaevis ovarian development and reached the peak at 3 y. After Cs-ewsr1-w knockdown with siRNA interference, several genes related to gonadal development including foxl2, sox9b and pou5f1 were down-regulated in ovarian cell line, suggesting the possible participation of Cs-ewsr1-w in C. semilaevis ovarian development. The dual-luciferase reporter assay revealed that the -733/-154 bp Cs-ewsr1-w promoter fragment exhibited strong transcription activity human embryonic kidney (HEK) 293T cell line. The mutation of a MAF BZIP Transcription Factor K (Mafk) binding site located in this fragment suggested that transcription factor Mafk might play an important role in Cs-ewsr1-w basal transcription. Our results will provide clues on the gene expression level, transcriptional regulation and knock-down effect of ewsr1 gene during ovarian development in teleost. [ABSTRACT FROM AUTHOR]

Background: Infectious diseases have caused huge economic loss and food security issues in fish aquaculture. Current management and breeding strategies heavily rely on the knowledge of regulative mechanisms underlying disease resistance. Though the intestinal microbial community was linked with disease infection, there is little knowledge about the roles of intestinal microbes in fish disease resistance. Cynoglossus semilaevis is an economically important and widely cultivated flatfish species in China. However, it suffers from outbreaks of vibriosis, which results in huge mortalities and economic loss. Results: Here, we used C. semilaevis as a research model to investigate the host-microbiome interactions in regulating vibriosis resistance. The resistance to vibriosis was reflected in intestinal microbiome on both taxonomic and functional levels. Such differences also influenced the host gene expressions in the resistant family. Moreover, the intestinal microbiome might control the host immunological homeostasis and inflammation to enhance vibriosis resistance through the microbe-intestine-immunity axis. For example, Phaeobacter regulated its hdhA gene and host cyp27a1 gene up-expressed in bile acid biosynthesis pathways, but regulated its trxA gene and host akt gene down-expressed in proinflammatory cytokines biosynthesis pathways, to reduce inflammation and resist disease infection in the resistant family. Furthermore, the combination of intestinal microbes and host genes as biomarkers could accurately differentiate resistant family from susceptible family. Conclusion: Our study uncovered the regulatory patterns of the microbe-intestine-immunity axis that may contribute to vibriosis resistance in C. semilaevis. These findings could facilitate the disease control and selective breeding of superior germplasm with high disease resistance in fish aquaculture. 8F1qVDdq8rkntrj1jj62Gc Video Abstract [ABSTRACT FROM AUTHOR]

Exosomes are a class of extracellular vesicles with diameters ranging from ~50 to 150 nm. Incorporating diverse biological substances and being present extensively in biofluids, exosomes are involved in intracellular communication in various physiological and pathological processes and emerging as promising biomarkers for the prognosis and diagnosis of many diseases. Accumulating evidence shows that exosomes also play important roles in the inflammatory and immune responses to bacterial infection. However, the study of exosomes in teleost fish remains scarce. In the present study, we focused on the exosomal microRNAs (miRNAs) in the plasma of Chinese tongue sole (Cynoglossus semilaevis) in response to Vibrio harveyi infection. After bacterial challenge, the plasma was sampled at both the early (6 and 16 h) and late stages. (48, 72, and 96 h) of infection, followed by exosome isolation and exosomal miRNA sequencing. Results showed that the expression profile of 85 exosomal miRNAs was significantly different among the control, early-, and late-infection groups. The predictive genes targeted by exosomal miRNAs were extensively involved in various inflammatory and immune processes by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, suggesting that a series of processes were regulated by exosomal miRNAs in the plasma, including the pathogen invasion and recognition and the activation and regulation of signaling pathways related to cytokine production. Moreover, the spleen was found to be a preference for exosome enrichment and the underlying mechanism of interleukin-6 production regulated by ZC3H12A, ARID5A, and exosomal ssa-miR-146a-5p were probably present in Chinese tongue sole. Additionally, the enhanced levels of ssa-miR-146a-5p and nbrmiR- 731 in plasma exosomes and the spleen of the infection groups were identified, indicating their application as biomarkers in favor of the prognosis and diagnosis of V. harveyi infection in Chinese tongue sole. Therefore, the collective results in the present study indicated the pleiotropic roles of exosomal miRNAs in the regulation of inflammatory and immune responses and their potential utilization as biomarkers in teleost fish. [ABSTRACT FROM AUTHOR]

Maternal effector genes (MEGs) encode maternal RNA and protein, accumulating in the cytoplasm of oocytes. During oocyte development, MEGs participate in oocyte meiosis and promote oocyte development. And MEGs can also regulate maternal transcriptome stability and promote maternal–zygotic transition (MTZ) in early embryonic development. Long noncoding RNAs (lncRNAs), as new epigenetic regulators, can regulate gene expression at both the transcriptional and post-transcriptional levels through cis- or trans-regulation. The oogenesis-related gene org is a germ-cell-specific gene in fish, but the role of org in embryonic development and oogenesis has rarely been studied, and the knowledge of the lncRNA-mediated regulation of org is limited. In this study, we cloned and identified the org gene of Chinese tongue sole (Cynoglossus semilaevis), and we identified a lncRNA named lncRNA ORG-anti-sequence (ORG-AS), located at the reverse overlapping region of org. The results of qRT-PCR and FISH demonstrated that org was highly expressed during the early stages of embryonic development and oogenesis and was located in the cytoplasm of oocytes. ORG-AS was expressed at low levels in the ovary and colocalized with org in the cytoplasm of oocytes. In vitro experiments showed that overexpression of ORG-AS inhibited org expression. These results suggest that org, as a MEG in C. semilaevis, participates in the MTZ and the oogenesis. The lncRNA ORG-AS negatively regulates the gene expression of org through trans-regulation. These new findings broaden the function of MEGs in embryonic development and the oogenesis of bony fish and prove that lncRNAs are important molecular factors regulating org. [ABSTRACT FROM AUTHOR]

Spexin (SPX) is an evolutionarily conserved neuropeptide, which was first identified in human proteome by data mining. Two orthologs (SPX1 and SPX2) are present in some non-mammalian species, including teleosts. It has been demonstrated that SPX1 is involved in reproduction and food intake, whereas the functional role of SPX2 is still absent in any vertebrate. The aim of the current study was to evaluate the actions of intraperitoneal injection of endogenous SPX2 peptide on the expression levels of some key reproductive genes of the brain-pituitary axis in half-smooth tongue sole. Our data showed an inhibitory action of SPX2 on brain gnih, spx1, tac3 and pituitary gtha, lhb mRNA levels. However, SPX2 had no significant effect on brain gnihr, gnrh2, gnrh3, kiss2, kiss2r, spx2 expression or pituitary gh expression. On the other hand, SPX2 induced an increase in pituitary fshb expression. Taken together, our results provide initial evidence for the involvement of SPX2 in the regulation of reproduction in vertebrates, which is in accordance with previous studies on SPX1. [ABSTRACT FROM AUTHOR]

A systematic checklist of fish and shellfishes of the Poonthura estuary, Kerala, India is provided including notes on their conservation status. This checklist includes 66 finfish and five shellfish, belonging to 17 orders, 35 families, and 60 genera. Carangiformes is the richest order (11 species, eight genera, and three families), representing 15.4% of the total fish diversity. Carangidae, is the most diverse family with nine representatives, contributing to 12.6% of the total fish diversity. Following the IUCN Red List Categories, of the total 69 species (excluding both exotic and transplanted fish species), 59 belong to the 'Least Concern', while one species Pampus argenteus is listed as 'Vulnerable', four are 'Data Deficient' (Megalops cyprinoides, Arius maculatus, Cynoglossus semifasciatus, and Epinephelus tauvina) and five are 'Not Evaluated' (Nuchequula blochii, Channa pseudomarulius, Penaeus indicus, P. monodon, and Scylla serrata). Around 94% of the recorded fish fauna have commercial value and contribute to subsistence fisheries throughout the year. Taxonomy and diversity of fish fauna of least studied or isolated estuarine ecosystems should be updated with proper documentation of their conservation status, in order to design and implement pragmatic management and conservation programs. [ABSTRACT FROM AUTHOR]

Mammalian toll-like receptor 5 (TLR5) is crucial for recognizing bacterial flagellin and initiating the inflammatory signaling cascades via myeloid differentiation factor 88 (MyD88) signaling pathway, which plays vital roles in innate immune against pathogenic bacteria. Herein, we reported the signaling pathway and antibacterial property of tongue sole (Cynoglossus semilaevis) membrane forms of TLR5 (i.e. CsTLR5M1and CsTLR5M2). CsTLR5M1/M2 contain 936 and 885 amino acid residues respectively. CsTLR5M1 shares 86.7% overall sequence identities with CsTLR5M2. CsTLR5M1/M2 possess the same extracellular domain (ECD) and transmembrane domain (TMD), but the different toll-interleukin-1 receptor (TIR) domain. CsTLR5M1/M2 expression occurred constitutively in multiple tissues and regulated by bacterial stimulation. Recombinant CsTLR5M1/M2 (rCsTLR5M) could bind to flagellin and Gram-negative/positive bacteria, which could suppress bacterial growth. Stimulation of the CsTLR5M pathway by flagellin resulted in increased expression of MyD88-dependent signaling molecules and inflammatory cytokines. Blocking rCsTLR5M by antibody markedly reduced the phagocytosis and ROS production of peripheral blood leukocytes (PBLs), which in turn in vivo promoted the dissemination of bacteria. Overall, these observations add new insights into the signaling pathway and immune function of teleost TLR5M. • CsTLR5M1/M2 expression constitutively occurred in tissues and regulated by bacterial infection. • Recombinant CsTLR5M could bind to bacteria and suppress the bacterial growth. • Flagellin stimulated the expression of inflammatory cytokines via MyD88-dependent pathway. • In vitro blockade of CsTLR5M1/M2 suppressed the phagocytosis and ROS production of PBLs. • In vivo anti-rCsTLR5M antibody could significantly facilitate the bacterial dissemination. [ABSTRACT FROM AUTHOR]

Simple Summary: The eukaryotic elongation factor 1 alpha (eef1a) gene is vital for protein translation by delivering aminoacylated tRNAs to the A/P site of the ribosome via the GTP-dependent reaction. Here, the Chinese tongue sole (Cynoglossus semilaevis) eef1a1 gene was identified, and its potential role in gonadal high-temperature perception was assessed. The full-length sequence of eef1a1 cDNA was 1809 base pair (bp) encoding a putative protein of 461 amino acids. The expression levels of eef1a1 in the ovary were significantly higher than that in the testis from 6 mpf to 3 ypf. Under high-temperature induction during sex differentiation, eef1a1 was significantly down-regulated in males, while the difference was not detected in females. Furthermore, the rapid response of eef1a1 to environmental high temperature was assessed in vitro. Our findings suggest that C. semilaevis eef1a1 might be essential for the molecular response regulatory network of external temperature affecting internal sex differentiation. The eukaryotic translation elongation factor 1 alpha (eef1a) gene has a well-defined role in protein synthesis. However, its role in external temperature perception and internal sex differentiation and development is still unclear. In this study, eef1a1 was identified and functionally analyzed in Chinese tongue sole (Cynoglossus semilaevis). The eef1a1 cDNA, 1809 bp in length, had a 1386 bp open reading frame (ORF) that encoded a 461 amino acid polypeptide containing one EF-1_alpha domain. eef1a1 expression levels were investigated across different tissues and during gonadal development. In the gonad, eef1a1 showed a sexually dimorphic expression pattern with a statistically higher expression level in the ovary than in the testis from 6 months postfertilization to 3 years postfertilization. Under high temperature (28 °C) treatment during C. semilaevis sex differentiation (from 30 days postfertilization to 3 months postfertilization), eef1a1 was statistically down-regulated in males, while the difference was not detected in females. In addition, the dual-luciferase assay exhibited that eef1a1 can respond to high temperature rapidly. Based on these results, C. semilaevis eef1a1 might have a dual role in the perception of external temperature changes and sex differentiation regulation. [ABSTRACT FROM AUTHOR]

Steroidogenesis controls the conversion of cholesterol into steroid hormones through the complex cascade reaction of various enzymes, which play essential roles in sexual differentiation and gonadal development in vertebrates, including teleosts. Japanese flounder (Paralichthys olivaceus) and Chinese tongue sole (Cynoglossus semilaevis) are important marine cultured fishes in China and have remarkable sexual dimorphism with bigger females and sex reversal scenarios from female to neo-male. Several steroidogenic genes have been analyzed individually in the two species, but there is a lack of information on the coordinated interaction of steroidogenic gene regulation. Therefore, in this study, through genomic and transcriptomic analysis, 39 and 42 steroidogenic genes were systematically characterized in P. olivaceus and C. semilaevis genomes, respectively. Phylogenetic and synteny analysis suggested a teleost specific genome duplication origin for cyp19a1a/cyp19a1b, hsd17b12a/hsd17b12b, ara/arb and esr2a/esr2b but not for star/star2 and cyp17a1/cyp17a2. Comparative transcriptome analysis revealed conserved expression patterns for steroidogenic genes in P. olivaceus and C. smilaevis gonads; star/star2, cyp11a/cyp11c, cyp17a1/cyp17a2, cyp21a, hsd3b1, hsd11b and hsd20b were strongly expressed in testis, while cyp19a1a and hsd17b genes were highly expressed in ovaries. Only a few genes were differentially expressed between male and neo-male testis of both P. olivaceus and C. semilaevis, and even fewer genes were differentially regulated in the brains of both species. Network analysis indicated that cyp11c, cyp17a1 and hsd3b1 actively interacted with other steroidogenic genes in P. olivaceus and C. semilaevis, and may play a more sophisticated role in the steroid hormone biosynthesis cascade. The coordinated interaction of steroidogenic genes provided comprehensive insights into steroidogenic pathway regulation with a global biological impact, as well as sexual development in teleost species. [ABSTRACT FROM AUTHOR]

Simple Summary: Limited understanding of molecular mechanisms of immune response constrains marine fish farming. Analyzing the dynamic gene expression profile of fish in response to pathogen infection is gaining interest. We analyzed the expression changes of the Chinese tongue sole kidney after Vibrio harveyi infection with a series of transcriptome data. Notably, we observed rapid up-regulation of IL-17, TNF and TLR signaling pathways, indicating treatment measures should be taken in the early stage after infection. We also found a close connection between the immune system and neuroendocrine system, which may be the new strategy to improve immune function. Our research provides insights into disease prevention and treatment in fish farming. Pathogenic infection of fishes is an important constraining factor affecting marine aquaculture. Insufficient understanding of the molecular mechanisms has affected the diagnosis and corresponding treatment. Here, we reported the dynamic changes of gene expression patterns in the Chinese tongue sole kidney at 16 h, 48 h, 72 h and 96 h after Vibrio harveyi infection. In total, 366, 214, 115 and 238 differentially expressed genes were obtained from the 16 h−vs. −C, 48 h−vs. −C, 72 h−vs. −C and 96 h−vs. −C group comparisons, respectively. KEGG enrichment analysis revealed rapid up-regulation of several immune-related pathways, including IL-17, TNF and TLR signaling pathway. More importantly, time-series analyses of transcriptome showed that immune genes were specifically up-regulated in a short period of time and then decreased. The expression levels of chemokines increased after infection and reached a peak at 16 h. Specifically, Jak-STAT signaling pathway played a crucial role in the regulation during Vibrio harveyi infection. In the later stages of infection, genes in the neuroendocrine pathway, such as glucocorticoid-related genes, were activated in the kidney, indicating a close connection between the immune system and neuroendocrine system. Our dynamic transcriptome analyses provided profound insight into the gene expression profile and investigation of immunogenetic mechanisms of Chinese tongue sole. [ABSTRACT FROM AUTHOR]

Chinese tongue sole (Cynoglossus semilaevis) is an economically important marine fish species with a ZZ/ZW sex determination mechanism, which can be influenced by temperature. Alternative splicing (AS) is an important mechanism regulating the expression of genes related to sex determination and gonadal differentiation, but has rarely been reported in fish. In this study, to explore the molecular regulatory mechanisms of sex determination and gonadal differentiation, we combined isoform and RNA sequencing (Iso-Seq and RNA-Seq) to perform transcriptome profiling of male and female gonads in C. semilaevis. In total, 81 883 and 32 341 full-length transcripts were obtained in males and females, respectively. A total of 8 279 AS genes were identified, including 2 639 genes showing differential AS (DAS) between males and females. Many intersecting DAS genes and differentially expressed genes (DEGs) were enriched in the meiotic cell cycle pathway, and genes related to gonadal differentiation, such as esrrb and wt1a, were found to have sex-specific isoforms. Thus, this study revealed AS events in the gonadal transcriptomes of male and female C. semilaevis, described the characteristics of active transcription in the testes, and identified candidate genes for studying the regulatory mechanisms of AS during gonadal differentiation. [ABSTRACT FROM AUTHOR]

MicroRNAs are increasingly recognized for their pivotal role in the immune system, yet the specific regulatory functions of fish-derived microRNAs remain largely unexplored. In this research, we discovered a novel miRNA, Cse-miR-144, in the Chinese tongue sole (Cynoglossus semilaevis), characterized by a 73-base pair precursor and a 21-nucleotide mature sequence. Our findings revealed that the expression of Cse-miR-144 was notably inhibited by various Vibrio species. Utilizing bioinformatics and dual-luciferase assay techniques, we established that the pro-inflammatory cytokine gene CsMAPK6 is a direct target of Cse-miR-144. Subsequent in vitro and in vivo western blotting analyses confirmed that Cse-miR-144 can effectively reduce the protein levels of CsMAPK6 post-transcriptionally. Moreover, CsMAPK6 is known to be involved in the activation of the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB). Additional investigations using qPCR and ELISA demonstrated that suppression of Cse-miR-144 leads to an upsurge in the liver mRNA levels of various immune genes (including MYD88 , TRAF6 , NF -κB , TRAF2 , TRAF3 , and TNF), alongside a marked increase in the production and secretion of pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) in the bloodstream of C. semilaevis. These findings collectively underscore the potential of Cse-miR-144 as a key inhibitor of CsMAPK and its crucial role in modulating the immune and inflammatory responses in teleost fish. Compared to the siRNA, miRNA is a better tool in controlling the expression of target gene with a lower cost. • A novel Cse-miR-144 with potential regulatory impacts on the infection of Vibrio by targeting CsMAPK6 gene was analysis. • Cse-miR-144 has been shown effect on the production of pro-inflammatory cytokines in by downregulating CsMAPK6. • Cse-miR-144 are more efficient than siRNAs for expression control of CsMAPK6 gene and immune response modulation. [ABSTRACT FROM AUTHOR]

Annexin A2 (AnxA2), belonging to the annexin family, plays a crucial role in immune responses. In this study, the cDNA of the AnxA2 gene was identified in half-smooth tongue sole, Cynoglossus semilaevis. The transcript of AnxA2 gene in C. semilaevis (CsAnxA2) showed broad tissue distribution, with the highest expression level observed in the gut. CsAnxA2 expression was significantly up-regulated in the intestine, spleen, and kidney tissues following exposure to Shewanella algae. Immunohistochemical staining revealed that CsAnxA2 was predominantly expressed in epithelial cells and significantly elevated after S. algae challenge. Subcellular localization showed that CsAnxA2 was primarily localized in the cytoplasmic compartment. Moreover, proinflammatory cytokines (IL-6, IL-8 and IL-1β) exhibited significant upregulation after CsAnxA2 was overexpressed in vivo. One hundred and fifty-eight CsAnxA2-interacting proteins were captured in the intestinal tissue, showing the top two normalized abundance observed for actin beta (ACTB) and protein S100-A10 (p11). Fifty-four high abundance CsAnxA2-interacting proteins (HIPs) were primary enriched in ten pathways, with the top three significantly enriched pathways being Salmonella infection, glycolysis/gluconeogenesis, and peroxisome proliferator-activated receptor (PPAR) signaling pathway. These results provide valuable information for further investigation into the functional mechanism of AnxA2 in C. semilaevis. • The full length of CsAnxA2 is 1014 bp, encoding 337 amino acids. • CsAnxA2 exhibits the highest expression level in gut. • CsAnxA2 was up-regulated in gut, liver and spleen following S. algae infection. • Overexpression of CsAnxA2 promoted the expression of IL-6, IL-8 and IL-1β. • One hundred and fifty-eight CsAnxA2-interacting proteins were captured in gut. [ABSTRACT FROM AUTHOR]

For solving the global shortage of fish meal (FM) supplies from fisheries, the black soldier fly (Hermetia illucens) has become a new protein alternative in aquatic feeds. The present study investigated the effects of dietary inclusion of defatted H. illucens larvae meal (DBLM) on growth, serum biochemical parameters, digestive function, and muscle quality of tongue sole (Cynoglossus semilaevis). The feeding experiment consisted of five experimental diets: a control diet based on FM protein (H0) and four DBLM diets, substituting 25% (H25), 50% (H50), 75% (H75), and 100% (H100) of FM. C. semilaevis (initial weight 563.48 ± 22.81 g) were randomly allocated over five treatments in quadruplicate. After 65 days of feeding, the weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) were significantly higher in H0 and H25 groups with less feed conversion ratio (FCR) and feed intake (FI). The concentrations of serum ALT, TG, T-CHO, ALB, and GLO and their ratio (i.e., A/G) in the H25 group were also significantly higher than those in the other DBLM diet-feeding groups. The digestive enzyme activities first increased (from 25% to 75%) and then decreased (from 75%) with the increased level of DBLM in diets. Meanwhile, there were significant improvements in the thickness of the intestinal longitudinal muscle (LM), circular muscle (CM), columnar epithelium (CE), and lamina propria (LP) in H25 C. semilaevis compared to the control group (p < 0.05). The fish from the other DBLM diets groups presented significant reductions in the thicknesses of LM, CM, CE, and LP, as well as the length of microvilli (ML) in a dose-dependent manner (p < 0.05). However, the substitution of FM increased up to 50% would result in intestinal structural damage. Moreover, the proximate compositions, antioxidant and water holding capacity, and muscular structures of C. semilaevis fillets were all significantly affected after substituting 25% FM with DBLM (p < 0.05). Except for the dry matter, moisture, ash, crude fat, and protein contents were significantly higher in H25 C. semilaevis muscles. The SOD activity in the H0 group was significantly lower than that in the H25 group. The CAT activity in C. semilaevis muscles prominently reduced along with the increase in DBLM content in feeding diets (p < 0.05). The water holding capacity of C. semilaevis fillets was best in the H25 group. In summary, the optimum proportion of DBLM with FM for feeding C. semilaevis may be around 25%. [ABSTRACT FROM AUTHOR]

IgT is a specific Ig isotype in teleosts, which plays extremely important roles in the mucosal immunity of fish. In the present study, the membrane-bound and secretory IgT of the half-smooth tongue sole (Cynoglossus semilaevis) were identified for the first time. The V-D-J-C structure of two forms of csIgT are translated by the same Cτ gene, and the secretory tail and transmembrane domain were encoded through alternative splicing at the 3′ end of the Cτ4. The CH regions of csIgT had high similarity with that of other flatfish (P. olivaceus and S. maximus). In healthy C. semilaevis , sIgT and mIgT were mainly expressed in mucus related tissues such as skin, intestine and gill. The transcript levels of sIgT and mIgT mRNA showed a significant induction in the immune-related tissues upon Vibrio Harveyi infection. A polyclonal rabbit anti-csIgT was successfully prepared using the csIgT heavy chain recombinant protein. Using this antibody, we detected the native IgT with the molecular mass at 220 kDa in skin total protein under non-reducing SDS-PAGE condition. Immunofluorescence analysis indicated that IgT+ B lymphocytes were intensively located in the skin, gill, intestine, and head kidney of C. semilaevis. These results suggest that IgT may participate in the immune response of C. semilaevis , which will facilitate the investigations of the immunoglobulins of marine fish. • The m IgT and sIgT genes of C. semilaevis were identified for the first time. • sIgT and mIgT were predominantly expressed in the mucosal related tissues. • After V. harveyi infection, the transcript levels of sIgT and mIgT mRNA were up-regulated. • Immunofluorescence showed the IgT+ B cells in skin, intestine, gill and head kidney. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism (SSD), characterized by the body size difference in different sexes, has been commonly announced in various species included mammals, birds, reptiles, and fishes. The endocrine factors in the gonads has been regarded to be involved in SSD. Two oocyte secreted factors-growth differentiation factor 9 (gdf9) and bone morphogenetic factor 15 (bmp15) has been shown to be differentially expressed in the gonad of Chinese tongue sole (Cynoglossus semilaevis), a typical marine fish demonstrating female-biased SSD. To figure out their possible roles in fish SSD, gdf9 and bmp15 of C. semilaevis were firstly cloned. The subsequently phylogenetic and structural analysis revealed that gdf9 and bmp15 were clustered with other fish species and both contained TGF-beta domain in the C-terminal. Furthermore, the temporal and spatial expression by qRT-PCR showed that gdf9 and bmp15 displayed the highest expression level in the female gonad. Moreover, the highest levels of gdf9 and bmp15 transcripts were both detected in the 1.5-year-old female gonad. The in situ hybridization and immunofluorescence experiments revealed that their mRNAs and proteins were both located in the oocyte. Based on the methylome data and bisulfite sequencing PCR, the lowest DNA methylation levels for gdf9 was observed in the female gonad, mainly distributed in the upstream and genebody regions. As for bmp15 gene, the methylation level of females in the genebody region, especially the exon 1, was higher than that of males and pseudomale, while the methylation level of females in the downstream was the lowest. Finally, knock-down of gdf9 siRNA in C. semilaevis ovarian cells resulted in the down-regulation of alk4 and tgfbr1 , and up-regulation of bmpr2 , smad8 , and bmp15. Taken together, the female-gonad-biased expression of gdf9 and bmp15 may be partly attributed to their upstream or genebody DNA methylation status. Gdf9 might be involved in reproduction and growth regulation of C. semilaevis by affecting Smad signaling pathway. Further exploration for these two ovarian factors would be helpful to better understand C. semilaevis SSD. • C. semilaevis gdf9 and bmp15 showed female-biased expression in the gonad, with mRNAs and proteins located in the oocyte. • The female-biased expression of gdf9 in the gonad may be partly attributed to its hypomethylation in the upstream region. • The gdf9 knock-down by siRNA resulted in down-regulation of alk4 and tgfbr1 , and up-regulation of bmpr2 , smad8 , and bmp15. [ABSTRACT FROM AUTHOR]

Phosphatidylinositol transfer protein (pitp) plays an important role in phospholipid transfer in animals. A pitp variant (pitpβ_w) in Chinese tongue sole was identified by transcriptomic analysis for its female-biased expression. The coding sequence of pitpβ_w was 816 bp, encoding a 371-amino-acid protein. pitpβ_w showed female-biased expression and was relatively high in brain, muscle, and ovary tissues. In different developmental stages of the ovary, pitpβ_w could be detected from 40 days until 3 years post hatching, and the highest expression was observed at 90 days. In situ hybridization revealed that pitpβ_w was predominantly localized in early-stage oocytes (I–III stages). After siRNA-mediated knockdown of pitpβ_w in an ovarian cell line, the expression of sox9a was reduced, while that of figla_tv1 and sox9b was significantly increased. Our findings suggest that pitpβ_w might be involved in female differentiation and early oogenesis. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the microplastic (MP) pollution in sediments, surface waters, and four fish species in the northern coast of the Persian Gulf. Sampling was conducted in seven important regions during December 2019. The abundance of MPs was respectively 190 ± 35.5 items/kg dry weight for sediments, 9.28 ± 2.1 items/km2 for surface waters, and 0.33 ± 0.05 items/individual for fish. There was no correlation between MP abundance in surface water, sediment, and fish samples. Except for Cynoglossus arel, abundance of isolated MPs did not show significant relationships with body weight, body length, and gastrointestinal tract weight (P > 0.05). MPs were ranged from 0.3 to 5 mm in size and were prevailed by fiber in shape; black, red, and blue in color; and polypropylene and polyethylene in polymer. This study may help in increasing our knowledge regarding MP pollution in marine water systems and biota. [ABSTRACT FROM AUTHOR]

Blind-side hypermelanosis has emerged as a major concern in commercial rearing environments of the flatfish aquaculture industry. To date, the underlying molecular mechanisms are not well understood. To fill this gap, in this study, whole transcriptomic sequencing and analyses were performed using normal skins and hypermelanic skins of the blind side of Chinese tongue sole (Cynoglossus semilaevis). Differentially expressed long non-coding RNAs (DElncRNAs), miRNAs (DEmiRNAs), and differentially expressed genes as well as their competing endogenous RNA (ceRNA) networks were identified. A total of 34 DElncRNAs, 226 DEmiRNAs, and 610 DEGs were identified. Finally, lncRNA–miRNA–mRNA regulatory networks (involving 29 DElncRNAs, 106 DEmiRNAs, and 162 DEGs) associated with blind-side hypermelanosis were constructed. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of 162 DEGs in ceRNA networks identified DEGs (e.g., oca2, mc1r, and ihhb) in pigmentation-related biological processes and DEGs (e.g., ca4, glul, and fut9) in nitrogen metabolism, glycosphingolipid biosynthesis, and folate biosynthesis pathways, as well as their corresponding DElncRNAs and DEmiRNAs to potentially play key regulatory roles in blind-side hypermelanosis. In conclusion, this is the first study on the ceRNA regulatory network associated with blind-side hypermelanosis in flatfish. These new findings expand the spectrum of non-coding regulatory mechanisms underpinning blind-side hypermelanosis, which facilitates the further exploration of molecular regulatory mechanisms of malpigmentation in flatfish. [ABSTRACT FROM AUTHOR]

Witch Flounder (Glyptocephalus cynoglossus) are a slow growing and late maturing deepwater flatfish. In the 1970s, the mean length of a 12-year-old female in the southern Gulf of St. Lawrence was only 41 cm, and the age at 50% maturity of females was 10 years. These lifehistory characteristics make the species particularly vulnerable to overexploitation. A fishery for Witch Flounder was developed in the Gulf of St. Lawrence (NAFO Divisions 4RST) in the 1950s. Annual landings averaged over 3,500 t in the 1960s and 1970s, declining to an average of 1,800 t in the 1980s. Landings declined further in the early 1990s to a low of 320 t in 1995. Landings then increased to an average of 850 t annually in 1998-2008 but declined again in 2009-2010. While the total allowable catch (TAC) remained at 1,000 t until 2011, landings in 2011 were 425 t. The TAC was reduced to 500 t in 2012, further reduced to 300 t in 2013 and then increased back to 500 t in 2017. Landings have closely matched the TAC for the period 2013-2016 and have been below the TAC since 2017. A research vessel (RV) survey index of commercial biomass (fish 30 cm or longer) was constructed for 4RST based on the August RV survey of the northern Gulf and the September RV survey of the southern Gulf. This index, available since 1987, declined sharply in the early 1990s, increased to an intermediate level in 1999 and 2000, but then declined again, fluctuating around 40% of the 1987-1990 for the period 2001-2010 and has shown an increasing trend since. A sentinel survey index of fish 30 cm or longer, based on the July sentinel survey of the northern Gulf and the August sentinel survey of the southern Gulf, is available for the period 2003 to 2019. This index declined after 2006, was at its lowest level in 2011 and has shown an increasing trend since. A Bayesian surplus production model indicates a 90% decline in commercial biomass between 1961 and 2011 and an increasing trend since. The limit reference point (LRP) for this stock is estimated to be 10,700 t of commercial sized fish (30 cm and longer) and the Upper Stock Reference (USR) is estimated to be 21,400 t of commercial sized fish. The estimate of the biomass of fish 30 cm and longer in 2021 is 17,770 t. Based on the uncertainties in the estimates of both the 2021 biomass, the LRP and the USR, the probability that the biomass is above the LRP in 2021 is 77%. Projections of the population model indicate that the biomass is expected to increase, with probabilities of 60% that the biomass will be above the USR in 2026 with no catches, 52% with annual catches of 500 t and 44% with annual catches of 1,000 t. [ABSTRACT FROM AUTHOR]

Fisheries and Oceans Canada conducts an annual multidisciplinary survey in the Estuary and northern Gulf of St. Lawrence. The objectives of this survey are varied; assess the biodiversity of species found near the bottom; estimate the abundance of groundfish and invertebrates; assess physical and biological (phytoplankton and zooplankton) oceanographic conditions; monitor the pelagic ecosystem; and collect samples for various research projects. In 2021, the survey was conducted between July 25 and August 26 on board the CCGS Teleost. The survey successfully carried out 149 trawl tows as well as 74 CTD water column casts, and 57 zooplankton samples. This report presents the results of the 149 tows. In total, 82 fish taxa and 214 invertebrate taxa were identified during the mission. Historical perspectives (catch rates, spatial distribution and length frequency) are presented for 25 taxa. These commercial fishery-independent data will be used in several stock assessments including cod (Gadus morhua), redfish (Sebastes spp.), Greenland halibut (Reinhardtius hippoglossoides), Atlantic halibut (Hippoglossus hippoglossus), witch flounder (Glyptocephalus cynoglossus) and northern shrimp (Pandalus borealis). A preliminary analysis of water temperature data collected in 2021 shows that conditions have warmed at 150 m and deeper, reaching new records since 1915 at 150, 200 and 300 m. The August cold intermediate layer (CIL) minimum temperature was much warmer in 2021 than in 2020, reaching the highest values of the modern CTD era. Surface waters temperatures were near normal in July-August. [ABSTRACT FROM AUTHOR]