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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]

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.

The fishing management authorities are in need of some biometric throughput and analysis with a view to the administration and protection of fishery stocks. The inputs regarding the lengths and weights of fish species have frequently been taken into account in order to divulge biological information. In the present research, length-weight relationships were extrapolated for discarded eight flatfishes off Gallipoli Peninsula (Northern Aegean Sea, Türkiye). From January 2017 to December 2017, a total of 142 individuals of eight species (Arnoglossus imperialis, Arnoglossus laterna, Arnoglossus rueppelii, Arnoglossus thori, Symphurus nigrescens, Microchirus ocellatus, Microchirus varieagatus, Monochirus hispidus) belonging to three families (Bothidae, Cynoglossidae, Soleidae) were collected from commercial fishermen's catches. The length-weight relationships' slopes (b) varied from 2.64 to 3.41. Every length-weight relationships was statistically significant (P < 0.0001). This paper embodies preliminary data on the LWRs of discarded eight flatfishes for the Gallipoli Peninsula (Northern Aegean Sea, Türkiye). Hence, data on the discarded fish species is of importance when keeping in view sustainable ecosystem-based fisheries management and, in the continuation of the long-dated investigations of the length-weight relationships of the fish species in question. This must be performed on an ongoing basis so as to monitor the current state of fish stocks. The stakeholders could utilize the results of the present research in the coming times. [ABSTRACT FROM AUTHOR]

The Ocellated tonguesole Cynoglossus quadriocellatus n. sp. is described from off Exmouth Gulf and Dampier Archipelago, Western Australia, eastern Indian Ocean, based on specimens collected at depths of 1-48 metres. The new species is characterised within the Cynoglossus ogilbyi species group by the snout bluntly rounded; head length 19-28% of SL, snout length 4-8% of SL; eyes not contiguous; nostrils 2; rostral hook not extending to below eye; lateral lines on eyed side three, on blind side one; mid-lateral line scales 73-88; scales between dorsal and mid-lateral lines 11-14; scales on both eyed and blind sides ctenoid; dorsal-fin rays 96-112; anal-fin rays 88-101; caudal-fin rays 10; vertebrae 8 + 40-44; two ocelli on tail. A key to the species of the Cynoglossus ogilbyi species-group is presented, and variation within the group is discussed. Other species in the group include C. broadhursti Waite 1905, C. maccullochi Norman 1926, C. ogilbyi Norman 1926, C. macrophthalmus Norman 1926, C. maculipinnis Rendahl 1921. Cynoglossus maccullochi and C. ogilbyi are recorded from Western Australia for the first time. [ABSTRACT FROM AUTHOR]

This study examines the diversity and abundance of fish species at Ibaka beach landing site. Samples were purchased from fish mammies twice monthly. The sampling covered twelve months (June 2019 - May 2020). A total of 2427 fishes were sampled. Twenty eight (28) species representing 14 families and 7 orders were identified. The families Carangidae and Clupeida had the highest representation with four (4) species each. While Cynoglossidae and Polynemidae had three (3) species each. The remaining families; Mugilidae, Pomadasyidae, Sciaeneidae, Tetradontidae had two (2) species each; while Aruidae, Bagridae, Dasyidae, Liejtanidae, Sphyraenidae, and Dasyaidae had one (1) species each. Ethmalosa fimbriata and Sardinella madarensis which belong to the family Cupeidae had the highest percentage composition (13.47%), followed by Illisha africana and Chrysicthys nigrodigitatus (6.18%) and Pseudontilithus typhus (4.53%) and Tetradon pustulatus (Ephipion gullifer) was the least with 0.20%. [ABSTRACT FROM AUTHOR]

At present, the function and profile of long noncoding RNAs (IncRNAs) in half-smooth tongue soles Cynoglossus semilaevis remain poorly understood. Lherefore, we identified IncRNAs in the species using large-scale deep sequencing approaches. A total of 96 726 222 clean reads and 2497 IncRNAs were obtained from the compound samples. In total, 1 694 known IncRNAs and 803 novel IncRNAs were identified. Most of the novel IncRNAs distributed mainly in a range of 200–3 000 nt and contained 2–6 exons. Six novel IncRNAs were selected for expression analysis by quantitative reverse transcription-polymerase chain reaction, of which lnc_770 and lnc_150 were expressed mainly in the ovary. Lhis study provides a valuable resource for IncRNA studies of half-smooth tongue sole and improves our understanding of the function of non-coding RNA in fish. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome of Cynoglossus roulei was determined in this study. The 16,565-bp-long genome is made of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and two noncoding regions. We detected the rearrangement of tRNA-Gln and control region in C. roulei. Additionally, tRNA-Gln gene was inverted from the L-strand position to the H-strand position. Phylogenetic analysis showed that C. roulei is most closely related to C. semilaevis.

The complete mitochondrial genome was determined for the Robust tonguefish Cynoglossus robustus belonging to the family Cynoglossidae. The length of the complete mitochondrial genome is 16,720 bp, consisting of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. Rearrangements of the tRNAGln and a control region gene were found and tRNAGln is translocated from the light to the heavy strand. Phylogenetic analysis using mitochondrial genomes of 12 species showed that C. robustus formed a well-supported monophyletic group with other Cynoglossus species.

Abstract Lhx9 is a LIM-homeodomain protein related to gonad development and sex reversal. In this study, we cloned and characterized CS-Lhx9 in the gonads of the Chinese tongue sole (Cynoglossus semilaevis). The full-length cDNA of CS-Lhx9 was 3123 bp, including an ORF of 1149 bp encoding 383 amino acids which contains two LIM domains and a homeobox domain. CS-Lhx9 transcripts were primarily observed in the testis of male and neomale at 1 yah, but nearly undetectable in the ovary. During the development of gonad, CS-Lhx9 exhibited an increasing trend and appeared to reach its peak value of expression in testis at 1 yah. In situ hybridization was performed in male and neomale gonads at 210 dah and 1 yah. The results showed strong CS-Lhx9 signals in the spermatids and spermatozoa (germ cells). Methylation level of CS-Lhx9 promoter was higher in female and lower in male and neomale gonads, showing a negative correlation with CS-Lhx9 expression. Highlights • Lhx9 gene from Chinese tongue sole (Cynoglossus semilaevis) was cloned and characterized. • Their expression profiles in different tissues were examined. • The methylation profiles were analyzed. • The analogously potential role of CS-Lhx9 was first proved in Chinese tongue sole. [ABSTRACT FROM AUTHOR]

The Western Australian deep-water tonguesole Cynoglossus westraliensis n. sp. is described from off North West Cape, Western Australia, based on two specimens collected at a depth of 250 metres. The new species is characterised within the Cynoglossus carpenteri species group by the snout relatively long, bluntly rounded; head length 21-25% of SL, snout length 9.3-11.6% of SL (43.4-46.5% of HL); eyes not contiguous; corner of mouth nearer to posterior edge of opercle than to tip of snout; ocular side with 3 lateral lines, midlateral-line scales 111-115, scale rows between midlateral and dorsolateral lines 20, blind side without lateral lines; ctenoid scales on ocular side, cycloid scales on blind side; dorsal-fin-rays 120-126; anal-fin rays 105-106; caudal-fin rays 8; gill chamber and peritoneum black. A key to the species of the Cynoglossus carpenteri species-group is presented. [ABSTRACT FROM AUTHOR]

This study provides a comprehensive description of chondrocranial development before, during and after larval metamorphosis in the tongue sole Cynoglossus semilaevis, a commercially valuable flatfish in China. Samples were collected at regular intervals ranging from 1 to 23 days post hatching (dph). Based on observations of cleared and double‐stained specimens and images from sections stained with safranin O–fast green, major morphological events during early development were described. No cartilaginous structure was visible at hatching. From 2 dph onwards, cartilaginous structures such as the trabecular bar and some elements of the mandibular, hyoid and branchial arches appeared. At this time also, cartilaginous structures of the neurocranium started to form. Hypertrophic chondrocytes could be observed in many splanchnocranium elements at 5 dph. The start of ossification was indicated by alizarin red stain visible at 14 dph. At 17 dph, most of the cartilaginous skeleton was ossified. Soon after, the right eye started to migrate and pass through a slit beneath the dorsal‐fin base and above the skull. Metamorphosis was complete at 20 dph, at which time the dorsal‐fin base cartilage extended onto the anterior region of the head. Meanwhile, extremities of the hyoid and branchial arch elements remained cartilaginous. At 23 dph, endochondral ossification of the splanchnocranium was nearly complete. Unlike previous observations of other Pleuronectiformes, our study indicates that endochondral ossification of C. semilaevis skull cartilage occurs before metamorphosis. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome was determined for the Cynoglossus interruptus belonging to the family Cynoglossidae. The length of the complete mitochondrial genome is 17,262 bp, consisting of 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and a control region. The gene rearrangement related to tRNAGln and a control region gene were found, forming the gene order of CR-Ile-Gln-Met. Phylogenetic analysis using mitochondrial genomes of 12 species showed that C. interruptus formed a well-supported monophyletic group with other Cynoglossus species.

Abstract Marine populations are generally well connected through larval exchange, and juvenile and adult migration. Genetic differentiation and/or local adaptation among populations are sometimes observed at small spatial scales. The marbled flounder (Pseudopleuronectes yokohamae) is a commercially important coastal species in Tokyo Bay, Central Japan, exhibiting different spawning phenology at a small scale. Using 30 highly polymorphic microsatellite loci, including the 16 new microsatellite loci developed in the present study, we estimated the genetic structure and demographic connectivity of specimens collected along Tokyo Bay in 2012–2013 and 2015–2016. F -statistics indicated a genetic differentiation between adult populations collected within and outside Tokyo Bay during both collection periods, but almost no difference was detected between the populations from the inner and outer parts of Tokyo Bay. Assignment tests directly estimated demographic connectivity between the inner and outer bays via larval dispersal and juvenile and adult migration. The average movement distance of marbled flounder was 13.1–29.6 km, with a maximum distance of 42.8–54.0 km. This movement distance contributed to the strong demographic connectivity between the inner and outer bays. Meanwhile, an indirect method using the isolation by distance (IBD) theory underestimated the average movement distance (5.0–7.8 km) because the isolated setting of Tokyo Bay resulted in a higher IBD slope. Based on the results of F -statistics and assignment tests, we suggest that a multilayered management by local and regional organizations may benefit the fishery in Tokyo Bay. Highlights • We estimate the population connectivity of marbled flounder around Tokyo Bay. • F -statistics and assignment tests showed connections among populations of Tokyo Bay. • Assignment tests showed an average movement distance of marbled flounder of 13–30 km. • An indirect method using isolation by distance underestimated the movement distance. [ABSTRACT FROM AUTHOR]

Leptin (Lep) is a key factor for the regulation of food intake and energy homeostasis in mammals. To date, a number of studies have provided evidence for the existence of multiple leptin genes in teleosts, but not much information is available in fish regarding the regulation of leptin genes by sex steriods. As a first step, two leptin genes ( lepa and lepb ) and a leptin receptor ( lepr ) gene were cloned from the half-smooth tongue sole ( Cynoglossus semilaevis ), a representative species of the order Pleuronectiformes. The full-length cDNAs of tongue sole lepa and lepb were 1265 bp and 1157 bp in length, encoding for proteins of 160 aa and 158 aa, respectively. The three-dimensional structures modeling of tongue sole LepA and LepB showed strong conservation of tertiary structure with other vertebrates. The full-length cDNA of tongue sole lepr was 4576 bp, encoding a protein of 1133 aa which contained all functionally important domains conserved among vertebrate LepRs. Tissue distribution analysis showed that tongue sole lepa mRNA was highly detectable in the ovary and brain, while lepb mRNA was ubiquitously expressed in various tissues. Notably, the tongue sole lepr mRNA was most abundant in the ovary. Using a primary hepatocyte culture system, we evaluated the effects of sex steroids on lep / lepr gene expression. Both 17β-estradiol (E2) and testosterone (T) inhibited hepatic lepa and lepr mRNAs without affecting lepb mRNA levels. In addition, T also suppressed growth hormone receptor 1 ( ghr1 ), ghr2 , and insulin-like growth factor 2 ( igf-2 ) mRNA levels, and stimulated expression of igf-1 gene. On the other hand, none of these four genes were altered by E2. To the best of our knowledge, this is the first description of a direct and differential regulation of lep/lepr gene expression by sex steroids at the hepatocyte level of a flatfish, supporting that individual leptin peptide may possess different biological roles in teleosts. [ABSTRACT FROM AUTHOR]

Spermatid perinuclear RNA-binding protein (Strbp) is a kind of double-stranded (ds) RNA specific binding protein that plays important roles in mammalian spermatogenesis. In this study, we have isolated and characterized the strbp gene of Chinese tongue sole, Cynoglossus semilaevis , termed as CS-strbp . The CS-strbp genomic sequence contained fifteen exons and fourteen introns. Its cDNA was 2655 bp in length, encoding a 666-amino-acid protein with two conserved ds binding motifs. Using quantitative PCR, we found that CS-strbp mRNA exhibited sex-biased and tissue-specific distribution, predominantly expressed in the fertile male testis, though the expression levels varied throughout different developmental stages. Comparison of methylation profile in different sexual genotypes demonstrated the low methylation level of CS-strbp promoter in male and pseudo-male, which is consistent with the high expression levels in those genotypes. In situ hybridization revealed that CS-strbp mRNA mainly localized in male germ cells, especially in spermatids and spermatozoa. Given these findings, we postulate that CS-strbp might function in spermatogenesis of Chinese tongue sole. [ABSTRACT FROM AUTHOR]

Gonadotropin-inhibitory hormone (GnIH), a novel hypothalamic neuropeptide, serves as a key player in the regulation of reproduction across vertebrates, acting on the brain and pituitary to modulate reproductive physiology and behavior. However, little information is available in teleosts regarding the intracellular signal transduction pathway in response to GnIH. To this end, we first cloned the gene of LPXRFa (the piscine ortholog of GnIH) receptor in the half-smooth tongue sole ( Cynoglossus semilaevis ), a representative species of the order Pleuronectiformes. The full-length cDNA of LPXRFa receptor was 2201 bp in size with an open reading frame (ORF) of 1365 bp that encoded 454 amino acids. Tissue distribution showed that LPXRFa receptor transcripts could be detected at high levels in the brain, to a lesser extent in the pituitary, and at low levels in the ovary and other peripheral tissues. In vitro functional analysis revealed that putative tongue sole LPXRFa-1 and LPXRFa-2 peptides significantly stimulated serum responsive element-dependent luciferase (SRE-luc) activity in COS-7 cells transfected with the novel receptor, and these stimulatory effects were evidently reduced by two inhibitors of the PLC/PKC pathway. In addition, neither LPXRFa-1 nor LPXRFa-2 altered the cAMP-responsive element (CRE)-luc activity, but only LPXRFa-2 could markedly decrease forskolin-induced CRE-luc activity in COS-7 cells expressing its cognate receptor. Taken together, our results encompass the first study reporting the existence of LPXRFa receptor in the order Pleuronectiformes and provide novel evidence of differential activation of signaling pathways by LPXRFa peptides in fish. [ABSTRACT FROM AUTHOR]

Background: Salinity is an important abiotic stress that influences the physiological and metabolic activity, reproduction, growth and development of marine fish. It has been suggested that half-smooth tongue sole (Cynoglossus semilaevis), a euryhaline fish species, uses a large amount of energy to maintain osmotic pressure balance when exposed to fluctuations in salinity. To delineate the molecular response of C. semilaevis to different levels of salinity, we performed RNA-seq analysis of the liver to identify the genes and molecular and biological processes involved in responding to salinity changes. Results: The present study yielded 330.4 million clean reads, of which 83.9% were successfully mapped to the reference genome of C. semilaevis. One hundred twenty-eight differentially expressed genes (DEGs), including 43 up-regulated genes and 85 down-regulated genes, were identified. These DEGs were highly represented in metabolic pathways, steroid biosynthesis, terpenoid backbone biosynthesis, butanoate metabolism, glycerolipid metabolism and the 2-oxocarboxylic acid metabolism pathway. In addition, genes involved in metabolism, osmoregulation and ion transport, signal transduction, immune response and stress response, and cytoskeleton remodeling were affected during acclimation to low salinity. Genes acat2, fdps, hmgcr, hmgcs1, mvk, pmvk, ebp, lss, dhcr7, and dhcr24 were up-regulated and abat, ddc, acy1 were down-regulated in metabolic pathways. Genes aqp10 and slc6a6 were down-regulated in osmoregulation and ion transport. Genes abat, fdps, hmgcs1, mvk, pmvk and dhcr7 were first reported to be associated with salinity adaptation in teleosts. Conclusions: Our results revealed that metabolic pathways, especially lipid metabolism were important for salinity adaptation. The candidate genes identified from this study provide a basis for further studies to investigate the molecular mechanism of salinity adaptation and transcriptional plasticity in marine fish. [ABSTRACT FROM AUTHOR]

The half-smooth tongue sole ( Cynoglossus semilaevis Günther) is a major cultivated marine fish species of high economic value. However, splenic and renal granulomas disease is a major disease of C. semilaevis and results in high mortality; its first outbreak was reported in 2009, and the pathogen responsible was believed to be associated with an unidentified virus. In this study, we investigated the prevalence of this disease in three fish farms located in different cities; we isolated homogeneous colonies from affected fish from each farm. Healthy half-smooth tongue sole were subjected to bacterial challenge tests by intraperitoneal injection of 0.5 × 10 7  cfu/fish of the isolates from each farm. The accumulative mortality rate was >80% within 30 days post infection. Diseased sole displayed symptoms similar to those seen in naturally infected fish. These strains were all identified as Mycobacterium marinum based on bacterial morphology, analytical profile index identification and 16S rDNA sequencing. The results of this study suggest that M. marinum is the causal agent of splenic and renal granulomas disease in half-smooth tongue sole; therefore, more attention should be paid to the occurrence of this bacterium in the flat fish aquaculture industry in China. [ABSTRACT FROM AUTHOR]

R-spondin 1 ( Rspo1 ) is a potential female-determining gene in mammals that could regulate the Wnt/ β- catenin signaling pathway. The deletion of Rspo1 causes sex reversal in females. To investigate sexual determination and differentiation, we cloned and analyzed the Rspo1 gene in Cynoglossus semilaevis . Phylogenetic and gene structure analyses revealed that Rspo1 gene exhibited high sequence conservation and contained an N-terminal signal peptide, two furin-like cysteine-rich domains (FU1 and FU2), a thrombospondin type 1 repeat, and a C-terminal region enriched with basic charged amino acids. qRT-PCR revealed that Rspo1 expressed sexual dimorphism in gonad, with higher expression levels in the ovary than in the testis, thus, suggesting the involvement of Rspo1 in gonad differentiation. In situ hybridization results demonstrated that Rspo1 was expressed in premature germ cells, including spermatogonia and spermatocytes in the testis and stage II and stage III oocytes in the ovary. The methylation levels in two CpG sites of Rspo1 promoter significantly differed among females, males, and pseudomales. After 30 days of exposure to high temperature, the expression of Rspo1 significantly decreased in female individuals, some of which were prone to males. However, no difference of Rspo1 gene expression was observed between the control group and high-temperature group in males. These preliminary findings suggested that Rspo1 played a crucial role in sex determination and development. This study laid the groundwork for further sex control breeding techniques in C. semilaevis . [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effects of dietary DHA/EPA ratio on lipid accumulation in farmed fish, with an 80-day feeding trial on tongue sole Cynoglossus semilaevis , a typical marine flatfish. Six experimental diets differing basically in DHA/EPA ratio, i.e., 0.61, 1.02, 1.46, 1.91, 2.32, and 2.75, were randomly assigned to 18 tanks of juvenile tongue sole. Fish were reared in a flow-through seawater system and fed to apparent satiation twice daily. Compared to very low (0.61) or high (2.32 and 2.75) dietary DHA/EPA levels, moderate dietary DHA/EPA ratios of 1.02 and 1.46 induced higher lipid accumulation in fish flesh and whole fish. Although also inducing increased liver lipid accumulation, the moderate dietary DHA/EPA ratios did not compromise the fish health in terms of growth performances and hematological parameters. The fatty acid profile of fish tissues reflected closely those of the diets, but DHA had more efficient deposition in fish flesh than EPA. Excess EPA or DHA in diets down-regulated the mRNA expression of lipogenic genes in fish tissues, and DHA seemed to be more efficient than EPA in up-regulating gene expression of β-oxidation-related proteins. Both esterification and hydrolyzation of triglycerides in fish tissues seemed to be more active in groups with intermediate DHA/EPA ratios (1.02 and 1.46). The present study provided a new way to modulate the nutritive quality of farmed fish, as well as to make better use of precious LC-PUFA resources. [ABSTRACT FROM AUTHOR]

Neutrophil extracellular traps (NETs) are a form of extracellular antimicrobial structure of neutrophils observed in higher and lower vertebrates, the latter including the teleost fish tongue sole Cynoglossus semilaevis . However, the antimicrobial mechanism of fish NETs is unknown. In the present study, we examined the potential contribution of histones and elastases to the antibacterial effect of tongue sole NETs. For this purpose, two histones (CsH2B and CsH4) and two elastases (CsEla1 and CsEla2) of tongue sole were investigated. The histones and elastases possess the conserved domain structures characteristic of that of histones H2B/H4 and trypsin-like serine protease, respectively. Recombinant CsH2B, CsH4, CsEla1, and CsEla2 bound a wide range of Gram-negative and Gram-positive bacteria, and some of the bound bacteria were inhibited in growth by the bound histones/elastases. CsH2B, CsH4, CsEla1, and CsEla2 were all localized in NETs induced by various stimuli including bacterial pathogen. Treatment of NETs with antibodies targeting CsH2B, CsH4, CsEla1, and CsEla2 significantly reduced the antimicrobial effect of NETs. These results indicate that histones and chymotrypsin-like elastases are fundamental components of teleost NETs that play important roles in the antimicrobial activity of NETs. [ABSTRACT FROM AUTHOR]

Calreticulin (CRT) is highly conserved chaperone located in the endoplasmic reticulum. It plays important roles in innate immunity. Although various immune-related functions of CRT have been reported in vertebrates and invertebrates, information on the potential functions of teleost CRT is very limited. In the present study, we characterized two calreticulin-related molecules from tongue sole ( Cynoglossus semilaevis ), calreticulin-like1 and calreticulin-like2 ( CsCRTL1 and CsCRTL2 ). CsCRTL1 and CsCRTL2 contain signature CRT motifs that are highly conserved in different species. CsCRTL1 and CsCRTL2 were expressed in liver, head kidney, brain, spleen, heart, muscle, skin, intestine and gills. The expression levels of CsCRTL1 and CsCRTL2 were highest in liver and spleen, respectively. After stimulation by Vibrio anguillarum and Streptococcus agalactiae , CsCRTL1 and CsCRTL2 were significantly up-regulated. The expression patterns depended on the tissue type, pathogen type, and infection time. The recombinant proteins rCsCRTL1and rCsCRTL2 bound to different pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and to different bacteria, such as Gram-negative bacteria V. anguillarum and Gram-positive bacteria Staphylococcus aureus . Moreover, rCsCRTL1and rCsCRTL2 significantly enhanced the killing of V. anguillarum by tongue sole macrophages. Our results indicate that CsCRTL1 and CsCRTL2 play important roles in antibacterial immunity of tongue sole. [ABSTRACT FROM AUTHOR]

Pod1 encodes a Class II bHLH transcription factor involved in the development of a number of tissues such as gonad, spleen, lungs and heart. However, to date, little is known about its function in teleosts. In this study, we cloned and characterized Pod1 gene from Cynoglossus semilaevis . This gene contains three exons and two introns, with the full-length cDNA of 918 nucleotides that encodes a 183 amino acid protein with a conserved bHLH domain. Realtime quantitative PCR revealed that Pod1 was predominantly expressed in the testes of C. semilaevis . In different stages of testes development, Pod1 expression was undetectable up to 120 days after hatching (dah), and then increased at 210 dah and 1 year after hatching (yah). Furthermore, in situ hybridization (ISH) analysis revealed that Pod1 was mainly localized in the germ cells of testes, but was not detected in ovarian cells; which suggested its possible functions in spermatogenesis of C. semilaevis . The methylation profile analysis of Pod1 genomic sequence in the gonads showed that the differences in their putative promoter regions of Pod1 among ovary, male and pseudo-male testes were not obvious. Thus, further research might be needed to evaluate whether Pod1 expression is regulated by epigenetic level. [ABSTRACT FROM AUTHOR]

Li, F.; Yao, L.; Sun, W.; Jiang, Y.; Li, Z., and Zhai, Y., 2017. Histopathological liver and testis alterations in male half-smooth tongue sole ( Cynoglossus semilaevis) exposed to endocrine disruptors. Endocrine-disrupting chemicals are a class of xenobiotics that may interfere with the function of the endocrine system. The adverse effects of these substances can be identified through pathology. In this research, the effects of bisphenol A (BPA) or 17β-estradiol (E2) exposure on the liver and testis of Cynoglossus semilaevis were investigated. In particular, this research observed the pathological alterations in the liver ( e.g., cellular swelling, hepatocyte adhesion, and vacuolation, etc.) and testis ( e.g., cellular swelling, sperm deformation, and flagellum bending, etc.). Results of the investigation revealed that exposure dose and response indicators are correlated with each other, and BPA or E2 exposure at different doses induces some degree of damage to C. semilaevis tissues on a histopathological level. Accordingly, this research provides a window for developing C. semilaevis as a model of marine fish in determining the effects of other kinds of pollutant exposure on the aquatic ecosystem and on humans. [ABSTRACT FROM AUTHOR]

This study was conducted to clarify the distribution and morphology of free neuromasts during the development of half-smooth tongue sole ( Cynoglossus semilaevis) using scanning electron microscopy. During development, (1) the apical surface of free neuromasts changed in shape from a circle to a four-point star; (2) the external structure changed from being level with the epidermis to papilla-like above the level of the epidermis; (3) the neuromast cupula changed from cylindrical to blade-shaped; (4) the free neuromasts went from occurring singly to being in clusters of a few single organs; (5) the arrangement changed from a linear array to no discernable pattern; (6) there was a significant increase in the number of free neuromasts after metamorphosis. In adult C. semilaevis, free neuromasts were only observed on the abocular side of the head. Thus, there were more free neuromasts located on the abocular side of the head with a higher concentration around the anterior nostril and mouth, which may have a mechanical sensory function to help locate food as an adaptation to a benthic mode of life. [ABSTRACT FROM AUTHOR]

A 30-day feeding trial was conducted to investigate the effects of dietary lipid levels on growth performance, activities of digestive enzymes, fatty acid composition and some lipogenesis-related gene expression of half-smooth tongue sole ( Cynoglossus semilaevis) larvae. Five isoproteic diets were formulated with graded lipid levels (6.68%, 9.84%, 13.47%, 17.89% and 21.88% dry weight) using fish oil as the main lipid source. Each diet was randomly allocated to triplicate groups of 150 larval tongue sole (35 DAH, 54 ± 1 mg). Fish were fed five times daily to apparent satiation during the feeding experiment. Results showed that, the survival rate ( SR) of larvae increased significantly firstly, and thereafter decreased significantly. The specific growth rates ( SGR) of larvae fed the diet with 13.47% lipid were significantly higher than other treatments. Larvae fed 9.84% or 13.47% dietary lipid showed higher trypsin, lipase, leucine aminopeptidase and alkaline phosphatase ( AP) activities than other treatments, whereas amylase activity nearly showed reverse trend with them. The fatty acid composition of the tongue sole larvae was well correlated with dietary fatty acid profile. Expression of acetyl-CoA carboxylase alpha (ACC1) was found to be slightly negatively correlated with dietary lipid level, and high dietary lipid level depressed the expressions of acetyl-CoA carboxylase beta (ACC2) and fatty acid synthase ( FAS) mRNA expression significantly, implying that larvae may cope with high dietary lipid mainly through down-regulating lipogenesis-related gene expression of FAS and ACC2. Besides, on the basis of SGR, the optimal dietary lipid level for larval tongue sole was estimated to be 13.56% using second-order polynomial curve. [ABSTRACT FROM AUTHOR]

A 3-month feeding trial with tongue sole Cynoglossus semilaevis broodstock was conducted before and during the spawning season to investigate the effects of dietary arachidonic acid (ARA) on the production of sex steroid hormones and gonadal gene expression of key proteins in steroidogenesis. Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels: the control diet without ARA supplementation (C, 0.58% ARA of total fatty acids (TFA)) and two diets with low (5.14% of TFA, ARA-L) or high ARA (15.44% of TFA, ARA-H) supplementation. The diets were randomly assigned to 9 tanks of 3-year-old tongue sole (10 females and 15 males in each tank). Fish were reared in a flowing seawater system and fed to apparent satiation twice daily. At the end of the feeding trial, tissue samples from mature females (MF, with spontaneous ovulation), immature females (IMF, early vitellogenesis), and mature males (MM, expressing milt) were collected to assay the production of sex steroid hormones, gonadal gene expression of sex steroid-synthesizing proteins, as well as the fatty acid profiles of gonad, liver and muscle lipids. Results showed that ARA supplementation significantly reduced the estradiol production in females, but stimulated the testosterone production in males. ARA supplementation significantly reduced the mRNA expression of aromatase in ovaries but significantly increased the gene expression of 3β-hydroxysteroid dehydrogenase (3β-HSD) in testes. In mature ovaries, diet ARA-L significantly reduced the gene expression of follicle stimulating hormone receptor (FSHR), 3β-HSD, and 17β-HSD; however, in immature ovaries, it significantly increased the gene expression of FSHR, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450ssc), 3β-HSD, and 17β-HSD. In all gonads, 17α-hydroxylase (P450c17) responded to dietary ARA differently from other sex steroid-synthesizing proteins. ARA was preferentially accumulated in tongue sole gonad lipids. ARA concentrations were highest in gonad, liver and muscle lipids of MM fish and lowest in MF fish. Compared to female tongue sole, males had higher DHA concentrations in gonad lipids, but lower concentrations in liver lipids. In conclusion, results suggest dietary ARA regulates sex steroid hormone synthesis in tongue sole broodstock, and accumulates in gonad lipids, depending on both fish gender and maturation stage. Dietary ARA supplementation appears more important for male fish than for female fish, and more important for immature females than for mature females. Statement of relevance This study is beneficial to the broodstock diet formulation. [ABSTRACT FROM AUTHOR]

In this study, a Gram-negative bacterium was isolated from diseased Cynoglossus semilaevis ( C. semilaevis ) and tentatively named strain CSG-15. It was preliminary identified as Shewanella algae ( S. algae ) based on morphological, physiological and biochemical characteristics. The sequenced 16S rRNA gene of CSG-15 strain (Genbank accession no. KX455851) was 1509 bp. And it exhibited 99.86%, 99.86% and 99.80% of identities compared with those of S. algae strains ATCC51192 (NR117771), YJ06114 (EF542799), and MAS2737 (GQ372875), respectively. Phylogenetic analysis grouped CSG-15 strain in the S. algae cluster, and showed the closest relation to S. algae ATCC51192 and YJ06114. Infection experiment showed that the median lethal dosage (LD 50 ) for CSG-15 was calculated as 1.0 × 10 6 CFU/g fish weight. The pathological observation on the intestine showed that CSG-15 strain caused noticeable histological lesions, such as inflammatory cell infiltrating and villi shedding. Antimicrobial susceptibility test showed that it was highly sensitive to most of aminoglycosides, β-lactams, tetracyclines, quinolones, macrolides aminocyclitol, sulphonamides, chloramphenicols antibiotic. Growing characteristics showed that CSG-15 could grow under the condition of temperature 26–34 °C, pH 5–9 and 20–50 ppt, and had a better adaptability to environment. The growth curve of strain CSG-15 under the condition of 30 °C, pH 7.0 and 30 ppt showed four distinct phases of bacterial growth. To the best of our knowledge, this is the first report of S. algae linked to diseased C. semilaevis . Statement of relevance In this study, a new Shewanella algae strain was isolated from diseased C. semilaevis for the first time. It was identified based on morphological, physiological, biochemical characteristics and 16S rRNA gene sequences analysis. Subsequently, antimicrobial susceptibility, pathogenicity and growing characteristics of S. algae were studied. This report can provide a scientific reference for characterization of Shewanella species, prevention and treatment of bacterial disease caused by S. algae in fish. [ABSTRACT FROM AUTHOR]

Sex determination is a fundamental biological process for individual sex development and population sex ratios. However, for some species, the primary sex might be altered during development, and individuals can develop into the opposite sex. Sex reversal may happen in insects, reptiles, amphibians, and fishes. In half-smooth tongue sole (Cynoglossus semilaevis ), some genetically female fish irreversibly reverse to pseudomales, resulting in higher costs in aquaculture owing to a lower growth rate of male fish during a 2-yr growth period. Here, we identified a locus with large controlling effect on sex reversal in the half-smooth tongue sole through genome-wide association study with high-density single nucleotide polymorphisms (SNPs). This SNP is located at the third intron of the F-box and leucine rich repeat protein 17 (FBXL17 )gene on the Z chromosome, and it has two alleles, A and T. Genetic females with ZAW genotypes will never reverse into phenotypic males, but those with ZTW genotypes can sometimes undergo sex reversal. This SNP explains 82.7% of the genetic variation, or 58.4% of the phenotypic variation. Based on our results, a reproductive management program could be developed to improve the phenotypic female ratio in aquaculture, and elucidate the mechanism of sex reversal in half-smooth tongue sole. We expect that these findings will have a substantial impact on the population management in many harvested species where sex reversal occurs. [ABSTRACT FROM AUTHOR]

Considerable confusion has surrounded the identity of the nominal species, Paraplagusia dollfusi Chabanaud, 1931, known only from two specimens: the holotype, collected in Gulf of Suez, Red Sea, and a second, non-type specimen (reported with the trinomial Cynoglossus (Trulla) dollfusi) captured in the Suez Canal, Red Sea. No catalogue number, illustration or photograph of the type specimen accompanied the original description, which also lacked critical information to confidently assign this species to a genus or to diagnose it from previously described tongue soles possessing similar attributes. Both the type and non-type specimen have been reported as lost for over 40 yr, further confounding attempts to resolve questions regarding the identity and status of this nominal species. During its history, C. dollfusi has been considered as a junior subjective synonym of C. sealarki Regan, 1908, a senior subjective synonym of C. cleopatridis Chabanaud, 1949, and has been misidentified as C. zanzibarensis Norman, 1939. The trinomial, Cynoglossus (Trulla) dollfusi, has also been considered as a second nominal species. Recently, specimens currently curated in the same jar in the fish collection of the Muse´um National d’Histoire Naturelle (Paris) and identified as C. zanzibarensis collected in the Red Sea were determined to be the missing holotype of P. dollfusi Chabanaud, 1931 and the second-known specimen of C. dollfusi. Their sizes, as well as their meristic and morphometric features, agree with those provided in the original description of the holotype of C. dollfusi and for those in the account of the second specimen. Rediscovery of the holotype confirms the validity of this species. Based on the holotype and non-type specimen and information from the literature, C. dollfusi is redescribed and diagnosed from other Indo-West Pacific species of the genus. Information from these two specimens also provides the necessary data to resolve historical problems regarding the identity and taxonomic placement of this species. Additionally, this new information resolves Red Sea distributional records for three other species of Cynoglossus. Conclusions from the present study indicate: a) Chabanaud erred in placing his nominal species dollfusi in the genus Paraplagusia. New data allow confident assignment of this species to Cynoglossus. b) The hypothesis that two nominal species are represented by the names P. dollfusi and Cynoglossus (Trulla) dollfusi is unsupported. Cynoglossus (Trulla) dollfusi is a new combination reflecting transfer of dollfusi from Paraplagusia to Cynoglossus. c) The hypothesis that C. dollfusi (Chabanaud, 1931) is a junior subjective synonym of C. sealarki is not supported by the data. These two species differ significantly to warrant recognizing both as valid. d) C. dollfusi has erroneously been considered the senior synonym of C. cleopatridis Chabanaud, 1949, a nominal species known only from a damaged holotype also collected in the Red Sea. Cynoglossus dollfusi was redescribed in a global revision of the genus based mostly on information from the holotype of C. cleopatridis, a decision that significantly changed the species concept of C. dollfusi from that intended in the original description. e) The hypothesis that C. cleopatridis Chabanaud, 1949 is a junior subjective synonym of C. dollfusi (Chabanaud, 1931) is rejected. The holotype of C. cleopatridis differs sufficiently in several meristic and morphometric features to demonstrate that C. dollfusi and C. cleopatridis are distinct species. f) Additional specimens are needed to more completely understand the nominal species, C. cleopatridis. g) The specimen thought to voucher C. lingua Hamilton, 1822 from the Red Sea was misidentified. It later became the holotype of C. cleopatridis, a species quite distinct from C. lingua. h) The list of cynoglossine fishes reported from the Red Sea has been updated. Red Sea records of P. dollfusi Chabanaud, 1931 should be emended to C. dollfusi (Chabanaud, 1931). The only specimens thought to voucher Red Sea records for C. sealarki, C. zanzibarensis, and C. lingua were all misidentified. Therefore, these species are removed from the list of tongue soles occurring in the Red Sea. [ABSTRACT FROM AUTHOR]

Symphurus longirostris, a new, cryptic tonguefish, was discovered by combining evidence from both morphological characters and the genetic divergence data of partial sequences of the 16S rRNA and COI genes. This dwarf species, reaching sizes to 65.5 mm standard length (SL), is described from 37 specimens collected from shallow waters around southern and central Japan. Compared with congeners, S. longirostris shares many morphological similarities with those of S. microrhynchus, S. holothuriae, and several undescribed species that are morphologically similar to S. microrhynchus. Symphurus longirostris differs from all congeners by the following combination of characters: a predominant 1-2-2-2-2 ID pattern; 12 caudal-fin rays; 9 abdominal vertebrae; 45-48 total vertebrae; four hypurals; 81-88 dorsal-fin rays; 68-74 anal-fin rays; 56-66 longitudinal scale rows; 21-26 transverse scales; 11-14 scale rows on the head posterior to lower orbit; a well-developed fleshy ridge on the ocular-side lower jaw; a membrane covering both eyes that is continuous with the anterior nostril; distinct spots present in the dermis at the bases of the anterior dorsal- and anal-fin rays; the dorsalmost aspect of the peritoneum bluish black; the upper head lobe larger than lower head lobe; relatively short lengths of the head (HL 20.5-22.6 % of SL) and postorbital region (POL 13.0-14.9 % of SL); relatively long snout (SNL 18.7-24.4 % of HL); and relatively long predorsal length (PDL 23.8-32.7 % of HL) compared with corresponding features in S. microrhynchus and S. holothuriae. Analysis of morphological and molecular features in this description of S. longirostris will also help to clarify the status of the poorly known species, S. microrhynchus and S. holothuriae. This study is the beginning of a taxonomic revision of shallow-water species of Symphurus from the Indo-West Pacific. [ABSTRACT FROM AUTHOR]

The effect of graded levels of dietary taurine on growth, enzyme activities and pretrypsinogen (Ptry) mRNA expression in the tongue sole postlarvae was evaluated in this study. Four microdiets supplemented with 0 (T0), 5 (T0.5), 10 (T1.0) or 20 (T2.0) g kg−1 taurine were prepared. These diets were fed to the postlarvae with an average initial body dry weight of 3.32 ± 0.06 mg for 28 days. Survival and growth performance of the tongue sole postlarvae were significantly ( P < 0.05) influenced by dietary taurine. Survival rate of fish fed with 20 g kg−1 dietary taurine was significantly lower than other treatments. The growth of fish initially increased with increasing dietary taurine level and then decreased. Postlarvae fed with 10 g kg−1 dietary taurine showed the best growth performance. Trypsin activities showed a significant increase with increasing dietary taurine level and then reached a plateau, while amylase activities and alkaline phosphatase activities increased in the start with increasing dietary taurine and then decreased. Ptry mRNA expression was stimulated by dietary taurine. Excessive dietary taurine (20 g kg−1) had adverse effects on survival, growth, digestive enzyme activities of the experimental fish. The suggested dietary taurine supplementation in microbound diets was 10 g kg−1 for the tongue sole postlarvae. [ABSTRACT FROM AUTHOR]

CD59 is a complement regulatory protein that inhibits the formation of membrane attack complex of complement. In this study, we examined the expression and activity of tongue sole ( Cynoglossus semilaevis ) CD59 (CsCD59). CsCD59 possesses the conserved structural features of CD59 and shares 33%–46% sequence identities with other fish CD59. Expression of CsCD59 was high in liver, spleen, and muscle, and was stimulated by infection of bacterial pathogens. Recombinant CsCD59 (rCsCD59) exhibited an apparent inhibition effect on the activation of tongue sole serum complement. ELISA and microscopy detected binding of rCsCD59 to a number of Gram-negative and Gram-positive bacteria. Interaction with rCsCD59 did not affect bacterial viability but significantly enhanced bacterial resistance against the killing effect of fish serum. Together these results indicate that fish CD59 may to some degrees facilitate a general escape of bacteria from complement-mediated immunity. [ABSTRACT FROM AUTHOR]

Measurements and observations of juvenile hatchery-reared three-lined tonguefish Cynoglossus abbreviatus were performed to examine morphological abnormalities, focusing on five asymmetric characters: eye position, body coloration, presence of a nasal tube, presence of dentition, and premaxillary length. Hatchery-reared juveniles were classified into a normal type similar to wild fish, an ambicolored type (with eyes on both sides of the body), and an intermediate type showing characteristics between the other two types. The ambicolored and intermediate types are considered metamorphosis-related malformations of flatfishes. Pseudoalbinism and reversal, which are commonly observed in hatchery-reared flatfishes, were not found in this study. The most significant result of the present study on hatchery-reared three-lined tonguefish is that the eye position and body coloration of the intermediate-type individuals were between the normal and ambicolored types. Eye migration and body coloration on the blind side of the intermediate type did not synchronize. [ABSTRACT FROM AUTHOR]

A cultured female half-smooth tongue sole ( Cynoglossus semilaevis) was crossed with a wild male, yielding the first filial generation of pseudo-testcrossing from which 200 fish were randomly selected to locate the Vibrio anguillarum resistance trait in half-smooth tongue sole at its microsatellite linkage map. In total, 129 microsatellites were arrayed into 18 linkage groups, ≥4 each. The map reconstructed was 852.85 cM in length with an average spacing of 7.68 cM, covering 72.07% of that expected (1 183.35 cM). The V. anguillarum resistance trait was a composite rather than a unit trait, which was tentatively partitioned into Survival time in Hours After V. anguillarum Infection (SHAVI) and Immunity of V. Anguillarum Infection (IVAI). Above a logarithm of the odds (LOD) threshold of 2.5, 18 loci relative to SHAVI and 3 relative to IVAI were identified. The 3 loci relative to IVAI explained 18.78%, 5.87% and 6.50% of the total phenotypic variation in immunity. The microsatellites bounding the 3 quantitative trait loci (QTLs) of IVAI may in future aid to the selection of V. anguillarum-immune half-smooth tongue sole varieties, and facilitate cloning the gene(s) controlling such immunity. [ABSTRACT FROM AUTHOR]

Caspases are a family of proteases involved in many important biological processes including apoptosis and inflammation. In this study, we analyzed in a comparative manner the expression patterns and immune effects of four different types of caspases, i.e. caspase-1 (CsCas1), caspase-2 (CsCas2), caspase-3 (CsCas3), and caspase-9 (CsCas9), from the teleost fish tongue sole ( Cynoglossus semilaevis ). CsCas1, CsCas2, CsCas3, and CsCas9 share 35.4%–58.5%, 61.2%–75.3%, 52.3%–65.6%, and 63.0%–76.2% overall sequence identities, respectively, with their counterparts in teleost species. CsCas1, CsCas2, CsCas3, and CsCas9 possess the caspase domain and catalytic site conserved in known caspases. The expressions of the four caspases were detected in a wide range of tissues, however, the expression levels varied between different tissues and caspases. Following bacterial infection, the expressions of the four caspases were upregulated or downregulated to significant extents in a time- and tissue-dependent manner. In vivo analysis showed that overexpression of each of the caspases in tongue sole significantly enhanced the ability of the fish to resist bacterial dissemination in and colonization of tissues. These results indicate an involvement of fish caspases in bacteria-induced immune response and demonstrate for the first time that caspase-1, 2, 3, and 9 are essential to the optimal defense against bacterial infection in fish. [ABSTRACT FROM AUTHOR]

Membrane progestin receptors (mPRs) play an important role in the regulation of oocyte meiotic maturation in fish. However, details of the molecular endocrine mechanism regulating oocyte maturation in multiple spawning fish with asynchronous ovarian development remain unclear. The cDNA encoding a novel progestin and adipoQ receptor with structural similarity to mPRα (Paqr7), herein called Paqr7b, was cloned and sequenced from the ovary of half-smooth tongue sole Cynoglossus semilaevis . Phylogenetic analysis showed that Paqr7b represents an evolutionary intermediate between mPRα and mPRβ and shares high homology with other similar Paqr proteins in other teleost species. However, the tongue sole Paqr7b protein showed much greater homology to teleost mPRαs (average 52%) than mPRβs (average 40%), suggesting it may have arisen from gene duplication of mPRα . paqr7b and paqr7 mRNA exhibited similar patterns of tissue expression. The mRNA and protein of Paqr7b were ubiquitously detected in all tissues analyzed, including the ovary. Moreover, in situ hybridization results revealed that paqr7b was expressed in stage V oocytes, as well as in scattered cells in the pituitary. The expression of paqr7b mRNA in brain and ovary significantly increased from ovarian development stage II to stage V ( P < 0.05), and was maximal at stage V, and then sharply decreased at stage VI. The transcript level of paqr7b mRNA in the pituitary also peaked at stage V ( P < 0.05). Treatment of tongue sole ovarian follicles with gonadotropin consistently increased the expression level of Paqr7b protein and mRNA in both a dose- and stage-dependent manner. Microinjection of tongue sole oocytes with a morpholino antisense oligonucleotide to Paqr7b blocked the progestin induction of oocyte maturation. Our findings demonstrate an important role of Paqr7b in the regulation of oocyte maturation in tongue sole and suggest the receptor may also influence other aspects of reproduction, such as pituitary function. [ABSTRACT FROM AUTHOR]

In this study, we performed a comprehensive analysis of the transcriptome of one- and two-year-old male and female brains of Cynoglossus semilaevis by high-throughput Illumina sequencing. A total of 77,066 transcripts, corresponding to 21,475 unigenes, were obtained with a N50 value of 4349 bp. Of these unigenes, 33 genes were found to have significant differential expression and potentially associated with growth, from which 18 genes were down-regulated and 12 genes were up-regulated in two-year-old males, most of these genes had no significant differences in expression among one-year-old males and females and two-year-old females. A similar analysis was conducted to look for genes associated with reproduction; 25 genes were identified, among them, five genes were found to be down regulated and 20 genes up regulated in two-year-old males, again, most of the genes had no significant expression differences among the other three. The performance of up regulated genes in Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis was significantly different between two-year-old males and females. Males had a high gene expression in genetic information processing, while female's highly expressed genes were mainly enriched on organismal systems. Our work identified a set of sex-biased genes potentially associated with growth and reproduction that might be the candidate factors affecting sexual dimorphism of tongue sole, laying the foundation to understand the complex process of sex determination of this economic valuable species. [ABSTRACT FROM AUTHOR]