Ru doping and interface engineering synergistically boost the electrocatalytic performance of a WP/WP2 nanosheet array for an efficient hydrogen evolution reaction.

The surface electronic structure and morphology of catalysts have a crucial impact on the electrocatalytic hydrogen evolution reaction performance. This work reports on the fabrication of a Ru-doped WP/WP2 heterojunction nanosheet array electrode via a one-step phosphating treatment of a Ru-doped WO3 precursor. Benefitting from the large electrochemical active surface of nanosheet arrays, rich WP/WP2 heterojunction interface, and trace Ru atom doping, the catalyst has a fairly low overpotential of 58.0 mV at 10 mA cm-2 and a Tafel slope of 50.71 mV dec-1 in acid solution toward the electrocatalytic HER. Further, theoretical calculations unveil that Ru atom doping and interface effect synergistically optimized the electronic structure of the catalyst and hence weakened the adsorption capacity of the catalyst surface toward hydrogen (H), which lowered the Gibbs free energy (ΔGH*) and consequently effectively improved the HER performance. This work may open new avenues for developing advanced nanoarray electrodes with efficient electrochemical energy conversion.

Exploration and origin studies of high levels of ß-glucosidase in carnivorous fishes spotted knifejaw (Oplegnathus punctatus).

In order to more efficiently utilize the abundant cellulose resources in nature, increase the utilization rate of cellulose in aquaculture, implement precise feeding and save aquaculture costs, we have conducted research on cellulase genes related to the spotted knifejaw (Oplegnathus punctatus). Cellulose, as the most abundant renewable resource, is a cornerstone in the intricate ecological balance of diverse ecosystems. While herbivorous fish are recognized for their utilization of proteins, sugars, and fats, the extent of cellulose utilization by carnivorous and omnivorous fish remains an enigma. Here, through field sampling and behavioural observations, O. punctatus' omnivorous diet has been demonstrated (stomach contents contain approximately several species of algae in the Bacillariophyta (1.12 %), Streptomyces (0.55 %), Chlorophyta (0.35 %), Rhodophyta (0.16 %), and Euglenophyta (0.19 %) phylum). Additionally, the high cellulase activity in the intestine of O. punctatus has been detected first discovery (enzyme activity up to 4800.15 U/g), indicating its ability to digest cellulose. By employing whole-genome scanning and high-throughput sequencing, a single cellulase gene (ß-glucosidase) within the genome of O. punctatus, suggesting the absence of a complete cellulose digestive system. However, microbiological analysis revealed the three crucial role of microorganisms, including Actinobacteria (25.80 %), Bacteroidetes (18.93 %), and Firmicutes phylum (0.82 %), were found to play a crucial role in the decomposition of plant cell walls, thereby facilitating plant material digestion to help the host to complete the process of cellulose digestion. Expression patterns and proteomic analysis of the ß-glucosidase were notably high in the gonads. In situ hybridization confirmed the expression of the ß-glucosidase gene in the intestinal contents and gonads, highlighting its role in supplying energy of gonads. These discoveries shed light on the dietary habits of O. punctatus and its cellulose utilization, offering insights that can inform the development of customized feeding strategies to enhance aquaculture sustainability and minimize resource expenditure.

Development of DNA Insertion-specific Markers Based on the Intergenic Region of Oplegnathus punctatus Cdkn1/srsf3 for Sex Identification.

Spotted knifejaw (Oplegnathus punctatus) is a marine economic fish with high food and ecological value, and its growth process has obvious male and female sexual dimorphism, with males growing significantly faster than females. However, the current sex identification technology is not yet mature, which will limit the growth rate of O. punctatus aquaculture and the efficiency of separate sex breeding, so the development of efficient sex molecular markers is imperative. This study identified a 926 bp DNA insertion fragment in the cdkn1/srsf3 intergenic region of O. punctatus males through whole-genome scanning, comparative genomics, and structural variant analysis. A pair of primers was designed based on the insertion information of the Y chromosome intergenic region in male individuals. Agarose gel electrophoresis revealed the amplification of two DNA fragments, 1118 bp and 192 bp, in male O. punctatus individuals. The 926 bp fragment was identified as the insertion in the intergenic region of cdkn1/srsf3 in males, while only a single 192 bp DNA fragment was amplified in females. The biological sex of the individuals identified in this manner was consistent with their known phenotypic sex. In this study, we developed a method to detect DNA insertion variants in the intergenic region of O. punctatus. Additionally, we introduced a new DNA marker for the rapid identification of the sex of O. punctatus, which enhances detection efficiency. The text has important reference significance and application value in sex identification, all-male breeding, and lineage selection. It provides new insights into the regulation of variation in the intergenic region of cdkn1/srsf3 genes and the study of RNA shearing.

Suitable habitat shifts and ecological niche overlay assessments among benthic Oplegnathus species in response to climate change.

Climate change has had a significant impact on many marine organisms. To investigate the effects of environmental changes on deep-water benthic fishes, we selected the genus Oplegnathus and applied species distribution modeling and ecological niche modeling. From the last glacial maximum to the present, the three Oplegnathus species (O. conwayi, O. robinsoni, and O. peaolopesi) distributed in the Cape of Good Hope region of southern Africa experienced fitness zone fluctuations of 39.9%, 13%, and 5.7%, respectively. In contrast, O. fasciatus and O. punctatus, which were primarily distributed in the western Pacific Ocean, had fitness zone fluctuations of -6.5% and 11.7%, respectively. Neither the O. insignis nor the O. woodward varied by more than 5% over the period. Under future environmental conditions, the range of variation in fitness zones for the three southern African Oplegnathus species was expected to be between -30.8% and -26.5%, while the range of variation in fitness zones for the two western Pacific stonefish species was expected to remain below 13%. In addition, the range of variation in the fitness zones of the O. insignis was projected to be between -2.3% and 7.1%, and the range of variation in the fitness zones of the O. woodward is projected to be between -5.7% and -2%. The results indicated that O. fasciatus and O. punctatus had a wide distribution and high expansion potential, while Oplegnathus species might have originated in western Pacific waters. Our results showed that benthic fishes were highly adaptable to extreme environments, such as the last glacial maximum. The high ecological niche overlap between Oplegnathus species in the same region suggested that they competed with each other. Future research could explore the impacts of environmental change on marine organisms and make conservation and management recommendations.

Prediction of suitable habitat shifts and assessment of ecological niche overlaps for three Tridentiger species with intertidal and subtidal characteristics under future climate changes.

To show how dramatic global climate change affects marine ecosystem species in different habitats. We used a joint species distribution model (SDM) and an ecological niche model (ENM) to investigate the suitable habitat shifts and ecological niche overlaps of the Tridentiger fishes. In the present study, the SDM results showed that 5 hotspots were identified for T. trigonocephalus and T. barbatus, and 4 hotspots for T. bifasciatus. The study on center-of-mass transfer revealed notable reductions in the habitual range of the three Tridentiger species with future climate change and no significant bipolar shifts in the center of mass. The ENM results indicated that T. trigonocephalus and T. barbatus exhibited the greatest ecological niche overlap with Schoener's D (D) and Hellinger-based I (I) values of 0.4719 and 0.7690, respectively. Both SDM and ENM results have suggested that T. trigonocephalus occupied a wider distribution and greater adaptability to future climate change. This study sought to measure the variations in the effects of global climate change on marine species in different habitats. Our study first found that intertidal species with specific life histories may be more resilient to environmental change.

Genome-wide investigation of the DMRT gene family sheds new insight into the regulation of sex differentiation in spotted knifejaw (Oplegnathus punctatus) with fusion chromosomes (Y).

The role of the DMRT family in male sex determination and differentiation is significant, but its regulatory role in spotted knifejaw with Y fusion chromosomes remains unclear. Through genome-wide scanning, transcriptome analysis, qPCR, FISH, and RNA interference (RNAi), we investigated the DMRT family and the dmrt1-based sex regulation network. Seven DMRTs were identified (DMRT1/2 (2a,2b)/6, DMRT4/5, DMRT3), and dmrt gene dispersion among chromosomes is possibly driven by three whole-genome duplications. Transcriptome analysis enriched genes were associated with sex regulation and constructed a network associated with dmrt1. qPCR and FISH results showed the expression dimorphism of sex-related genes in dmrt-related regulatory networks. RNAi experiments indicated a distinct sex regulation mode in spotted knifejaw. Dmrt1 knockdown upregulated male-related genes (sox9a, sox9b, dmrt1, amh, amhr2) and hsd11b2 expression, which is critical for androgen synthesis. Amhr2 is located on the heterozygous chromosome (Y) and is specifically localized in primary spermatocytes, and is extremely upregulated after dmrt1 knockdown which suggested besides the important role of dmrt1 in male differentiation, the amhr2 along with amhr2/amh system, also play important regulatory roles in maintaining high expression of the hsd11b2 and male differentiation. This study aims to further investigate sex regulatory mechanisms in species with fusion chromosomes.

Expression pattern and cellular localization of pepsinogen in early development and induced by different diets in the spotted knifejaw (Oplegnathus punctatus).

To solve the high mortality rate of early-stage larval feed conversion during aquaculture in Oplegnathus punctatus, the investigation of the structural and functional characteristics of the gastric tissue was conducted. Histological results showed that the gastric gland rudiment appeared at 17 dph. The basic structure of the stomach was fully developed between 26 and 35 dph. Two pepsinogen genes, named OpPGA1 and OpPGA2, were identified in the spotted knifejaw genome. qPCR results of developmental period showed that the two genes were low in expression during early development (5 and 15 dph). At 20 dph, the two genes started to show trace expression, and at 30 dph the mRNA expression levels of OpPGA1 and OpPGA2 reached the highest levels. Results of pepsin activity detection during the development period showed lower activity was detected 22 dph, followed by a peak at 30 dph. Under different feeding inductions, OpPGA1 showed the highest expression in the basic diet group and hard-shell group, while the expression level in the phytophagous group remained consistently low. The mRNA expression level of OpPGA2 in the phytophagous group was significantly higher than in other groups. Enzyme activity determination under different feeding inductions showed slightly higher enzyme activity in the basic diet group and crustacean group. The results of in situ hybridization showed that the mRNA of both OpPGA1 and OpPGA2 genes was both expressed in gastric gland cells. These information can contribute to the development of practical feeding methods in terms of digestive physiology for the development of larvae.

Improved high-quality reference genome of red drum facilitates the processes of resistance-related gene exploration.

Sciaenops ocellatus is among the most important artificially introduced farmed fish across 11 countries and regions. However, the frequent occurrence of extreme weather events and breeding escapes have placed great pressure on local marine biodiversity and ecosystems. We reported the de novo assembly and annotation with a contig N50 of 28.30 Mb using PacBio HiFi sequencing and Hi-C technologies, which resulted in a 283-fold increase in contig N50 length and improvement in continuity and quality in complex repetitive region for S. ocellatus compared to the previous version. In total, 257.36 Mb of repetitive sequences accounted for 35.48% of the genome, and 22,845 protein-coding genes associated with a BUSCO value of 98.32%, were identified by genome annotation. Moreover, 54 hub genes rapidly responding to hypoosmotic stress were identified by WGCNA. The high-quality chromosome-scale S. ocellatus genome and candidate resistance-related gene sets will not only provide a genomic basis for genetic improvement via molecular breeding, but will also lay an important foundation for investigating the molecular regulation of rapid responses to stress.

Morphological characteristics of beak-like tooth in spotted knifejaw (Oplegnathus punctatus) and mechanisms of dental development regulation by the Wnt, BMP, FGF and SHH signalling pathways.

Oplegnathus punctatus is a fish species with beak-like tooth that feeds on algae, oysters, sea urchins, and other organisms attached to rocks. Currently, there are no research reports on the development and regulatory mechanisms of O. punctatus beak-like tooth. This present study firstly elucidated the nesting structure pattern of the beak-like tooth with dental formula (4, 15-16, 10-1) for O. punctatus. Four critical periods during early beak-like tooth development (28dph, 40dph, 50dph, 60dph) were also identified. In addition, 11 key genes (bmp2, bmpr2, smad1, wnt5a, msx, axin2, fgfr1a, fgfr2, pitx2, ptch1, cyp27a1) closely related to the development of beak-like tooth were discovered, with the highest expression levels in the initial stages of functional teeth and replacement teeth development, and expression in the mesenchymal and epithelial tissues of the teeth. Further research found that the cyp27a1 gene, related to vitamin D metabolism and calcium accumulation, was expressed in the maxilla and base of the tooth in O. punctatus. This study provides support for the biological theory of tooth development and healing and provides a reference for the adaptive evolution of tooth healing in special habitats.

Tea polyphenols, astaxanthin, and melittin can significantly enhance the immune response of juvenile spotted knifejaw (Oplegnathus punctatus).

The frequent occurrence of diseases seriously hampers the sustainable development of the spotted knifejaw (Oplegnathus punctatus) breeding industry. Our previous genome-wide scan and cross-species comparative genomic analysis revealed that the immune gene family (Toll-like receptors, TLR) members of O. punctatus underwent a significant contraction event (tlr1, tlr2, tlr14, tlr5, and tlr23). To address immune genetic contraction may result in reduced immunity, we investigated whether adding different doses (0, 200, 400, 600, and 800 mg/kg) of immune enhancers (tea polyphenols, astaxanthin, and melittin) to the bait after 30 days of continuous feeding could stimulate the immune response of O. punctatus. We found that the expression of tlr1, tlr14, tlr23 genes in immune organs (spleen and head kidney) was stimulated when tea polyphenols were added at 600 mg/kg. The tlr2 (400 mg/kg), tlr14 (200 mg/kg), tlr5 (200 mg/kg), and tlr23 (200 mg/kg) genes expression of intestine were elevated in the tea polyphenol group. When the addition of astaxanthin is 600 mg/kg, it can effectively stimulate the expression of tlr14 gene in immune organs (liver, spleen and head kidney). In the astaxanthin group, the expression of the genes tlr1 (400 mg/kg), tlr14 (600 mg/kg), tlr5 (400 mg/kg) and tlr23 (400 mg/kg) reached their highest expression in the intestine. Besides, the addition of 400 mg/kg of melittin can effectively induce the expression of tlr genes in the liver, spleen and head kidney, except the tlr5 gene. The tlr-related genes expression in the intestine was not significantly elevated in the melittin group. We hypothesize that the immune enhancers could enhance the immunity of O. punctatus by increasing the expression of tlr genes, and thereby leading to increased resistance to diseases. Meanwhile, our findings further demonstrated that significant increases in weight gain rate (WGR), visceral index (VSI), and feed conversion rate (FCR) were observed at 400 mg/kg, 200 mg/kg and 200 mg/kg of tea polyphenols, astaxanthin and melittin in the diet, respectively. Overall, our study provided valuable insights for future immunity enhancement and viral infection prevention in O. punctatus, as well as offered guidance for the healthy development of the O. punctatus breeding industry.

Genome-Wide Scan Reveals Toll-Like Receptor Contraction Events in Oplegnathidae.

The striped knifejaw (Oplegnathus fasciatus) and spotted knifejaw (Oplegnathus punctatus) are prominent members of the Oplegnathidae family and are rocky reef-loving fishes with high ecological and economic value. However, the frequent occurrence of diseases in these fishes has severely restricted the development of their breeding industry. Toll-like receptors (TLRs) play an important role in resistance to pathogens as part of innate immunity. Genome-wide scans and cross-species comparative analysis revealed 10 TLRs in O. fasciatus (OfTLRs) and only 5 in O. punctatus (OpTLRs). In contrast to those of mammals and other fishes, the TLR family of Oplegnathidae underwent significant contraction events, especially in O. punctatus (only TLR1, TLR2, TLR14, TLR5, and TLR21 were retained). A phylogenetic tree divided the 10 OfTLRs into 5 subfamilies: TLR1, TLR3, TLR5, TLR7, and TLR11. The five OpTLR genes were divided into three different subfamilies: TLR1, TLR5, and TLR11. Quantitative real-time PCR revealed that all OpTLRs were expressed in the examined tissues, especially the immune system-related tissues, such as the spleen, gill, head kidney, and middle kidney. The expression of OpTLRs was high at the early stage of development (5 days posthatching [dph]) and decreased gradually until 30 dph. We speculated that maternal immunity or the developmental function of TLRs played an important protective role in the early stage. However, from 30 to 60 dph, TLR expression was low. At this time, juvenile fish are susceptible to viruses and begin to show TLR self-expression with weak immunity. Artificial immunity enhancement is needed to improve the environmental resistance of juvenile fish. In summary, our results not only provide valuable basic data for future studies of the TLR gene family in Oplegnathidae fish but also lay a solid foundation for Oplegnathidae fish research.

Identification of Male-Specific Molecular Marker and Development of PCR-Based Genetic Sex Identification Technique in Spotted Knifejaw (Oplegnathus punctatus).

Spotted knifejaw (Oplegnathus punctatus) is a marine teleost species that is economically important for aquaculture and marine pasture proliferation and shows obvious bisexual growth dimorphism, but molecular sex markers are currently lacking. A 290 bp (base pair) insertion with two fragments (230 bp and 60 bp) was identified in male individuals of O. punctatus based on whole-genome sequencing scanning and structural variation analyses. The gene annotation results showed that the insertion event occurred in the Igfn1 gene of male O. punctatus. The results of amino acid analysis further showed that the insertion event resulted in the functional variation of Igfn1 in male O. punctatus, and recombination caused the inactivation of Igfn1. According to the male-specific insertion information, we designed a PCR-based genetic amplification technique for rapid sex identification in O. punctatus. The results of agarose gel electrophoresis showed that two DNA fragments of 635 bp and 925 bp were amplified in male O. punctatus, while only a single DNA fragment of 635 bp was amplified in female individuals. The sex of individuals identified by this method was consistent with their known phenotypic sex, which will improve sex identification efficiency. This method provides a new DNA marker for rapid sex identification in O. punctatus, which has great significance and application value in monosex breeding and provides new insights for the study of Igfn1 gene recombination and inactivation in male O. punctatus.

Genome-wide identification, characterization and expression analysis of the BMP family associated with beak-like teeth in Oplegnathus.

Bone morphogenetic proteins (BMPs), which belong to the transforming growth factor beta (TGF-ß) family, are critical for the control of developmental processes such as dorsal-ventral axis formation, somite and tooth formation, skeletal development, and limb formation. Despite Oplegnathus having typical healing beak-like teeth and tooth development showing a trend from discrete to healing, the potential role of BMPs in the development of the beak-like teeth is incompletely understood. In the present study, 19 and 16 BMP genes were found in O. fasciatus and O. punctatus, respectively, and divided into the BMP2/4/16, BMP5/6/7/8, BMP9/10, BMP12/13/14, BMP3/15 and BMP11 subfamilies. Similar TGFb and TGF_ß gene domains and conserved protein motifs were found in the same subfamily; furthermore, two common tandem repeat genes (BMP9 and BMP3a-1) were identified in both Oplegnathus fasciatus and Oplegnathus punctatus. Selection pressure analysis revealed 13 amino acid sites in the transmembrane region of BMP3, BMP7, and BMP9 proteins of O. fasciatus and O. punctatus, which may be related to the diversity and functional differentiation of genes within the BMP family. The qPCR-based developmental/temporal expression patterns of BMPs showed a trend of high expression at 30 days past hatching (dph), which exactly corresponds to the ossification period of the bones and beak-like teeth in Oplegnathus. Tissue-specific expression was found for the BMP4 gene, which was upregulated in the epithelial and mesenchymal tissues of the beak-like teeth, suggesting that it also plays a regulatory role in the development of the beak-like teeth in O. punctatus. Our investigation not only provides a scientific basis for comprehensively understanding the BMP gene family but also helps screen the key genes responsible for beak-like tooth healing in O. punctatus and sheds light on the developmental regulatory mechanism.

Identification of Male-Specific Molecular Markers by Recombination of RhoGEF10 Gene in Spotted Knifejaw (Oplegnathus punctatus).

The spotted knifejaw (Oplegnathus punctatus) is a marine economic fish with high ecological value, food value, and fishing value, and its growth has obvious sex dimorphism. The rapid identification of its sex is beneficial to the development of sex determination and breeding. In this study, the method of comparative genomics and PCR amplification was used to further establish a rapid detection method for the recombinant RhoGEF10 gene in O. punctatus, which can quickly, accurately, and efficiently identify the sex of the O. punctatus to be tested. The homologous comparison results of male and female individuals showed that the DNA fragment length of the RhoGEF10 gene on the X1 chromosome was 326 bp, and the DNA fragment length on the Y chromosome was 879 bp. Therefore, it can be concluded that there is an insert fragment of 553 bp on the Y chromosome. PCR amplification results showed that the two DNA fragments of 879 bp and 326 bp were amplified in the Y chromosome and X1 chromosome of the male O. punctatus (X1X2Y), respectively, and the 879 bp fragment was a unique marker fragment of the recombinant RhoGEF10 gene; The female O. punctatus (X1X1X2X2) only a single DNA fragment of 326 bp was amplified. At the same time, the inserted fragment of the male individual resulted in partial inactivation of the RhoGEF10 protein, which in turn resulted in a slowing of peripheral nerve conduction velocity and thinning of the myelin sheath in male O. punctatus. The method shortens the time for accurate identification of the O. punctatus RhoGEF10 gene recombination and improves the detection efficiency. It is of great significance and application value in the research of nerve conduction and myelin development, male and female sex identification, the preparation of high male seedlings, and family selection based on the RhoGEF10 gene in the O. punctatus.

First observation of the mating, egg-laying and hatching behaviour of a captive female Kong skate, Okamejei kenojei (Müller & Henle, 1841).

This study provides a novel record of the reproductive behaviour of the Kong skate (Okamejei kenojei) in captivity. These skates were found to mate and deposit eggs at a temperature of 16.5 ± 0.5°C. The results showed that 76.13% of the eggs possessed one yolk, 0.77% of the eggs possessed two yolks and 23.11% of the eggs had no yolk (N = 1043). The deposition of non-yolk and double-yolk eggs was random. A total of 100 eggs were collected. After nearly 92 ± 5 days of incubation, 28 eggs failed to hatch, and 72 skates were successfully hatched with a female-to-male ratio of 1:1 (P > 0.05). The results enrich our knowledge of the reproduction in cartilaginous fishes and can inform management and conservation strategies for this species.

Insights into the Effect of Sulfur Incorporation into Tungsten Diphosphide for Improved Hydrogen Evolution Reaction.

Exploring the highly active and stable nonprecious metal electrocatalysts is particularly important for the advancement of water electrolysis, whereas it remains a challenge to efficiently improve the intrinsic electrocatalytic activity. Herein, we reasonably constructed a self-supporting nanosheet array material with sulfur incorporated into WP2. Because of the tunability of electronic configuration and the formation of partial metal phase sulfides, the optimized catalyst exhibits a low overpotential of 115 mV at 10 mA cm-2, along with superb durability over 24 h in acidic media. Furthermore, theoretical calculations reveal that sulfur substitution effectively manipulates the local electronic configuration of WP2, which reduces the interaction between the catalyst surface and hydrogen atoms, thus improving the intrinsic activity of the hydrogen evolution reaction. This work provides valuable insight into the rational fabrication of highly efficient flexible electrode materials based on resourceful electrocatalysts for electrochemical water splitting.

Chromosome-Level Genome Reveals the Origin of Neo-Y Chromosome in the Male Barred Knifejaw Oplegnathus fasciatus.

The barred knifejaw, Oplegnathus fasciatus, is characterized by an X1X2Y system with a neo-Y chromosome for males. Here, a chromosome-level genome was assembled to investigate the origin of neo-Y chromosome to the male O. fasciatus. Twenty-three chromosomes corresponding to the male karyotypes were scaffolded to 762-Mb genome with a contig N50 length of 2.18 Mb. A large neo-Y chromosome (Ch9) in the male O. fasciatus genome was also assembled and exhibited high identity to those of the female chromosomes Ch8 and Ch10. Chromosome rearrangements events were detected in the neo-chromosome Ch9. Our results suggested that a centric fusion of acrocentric chromosomes Ch8 and Ch10 should be responsible for the formation of the X1X2Y system. The high-quality genome will not only provide a solid foundation for further sex-determining mechanism research in the X1X2Y system but also facilitate the artificial breeding aiming to improve the yield and disease resistance for Oplegnathus.

Deciphering the Origin and Evolution of the X1X2Y System in Two Closely-Related Oplegnathus Species (Oplegnathidae and Centrarchiformes).

Oplegnathus fasciatus and O. punctatus (Teleostei: Centrarchiformes: Oplegnathidae), are commercially important rocky reef fishes, endemic to East Asia. Both species present an X1X2Y sex chromosome system. Here, we investigated the evolutionary forces behind the origin and differentiation of these sex chromosomes, with the aim to elucidate whether they had a single or convergent origin. To achieve this, conventional and molecular cytogenetic protocols, involving the mapping of repetitive DNA markers, comparative genomic hybridization (CGH), and whole chromosome painting (WCP) were applied. Both species presented similar 2n, karyotype structure and hybridization patterns of repetitive DNA classes. 5S rDNA loci, besides being placed on the autosomal pair 22, resided in the terminal region of the long arms of both X1 chromosomes in females, and on the X1 and Y chromosomes in males. Furthermore, WCP experiments with a probe derived from the Y chromosome of O. fasciatus (OFAS-Y) entirely painted the X1 and X2 chromosomes in females and the X1, X2, and Y chromosomes in males of both species. CGH failed to reveal any sign of sequence differentiation on the Y chromosome in both species, thereby suggesting the shared early stage of neo-Y chromosome differentiation. Altogether, the present findings confirmed the origin of the X1X2Y sex chromosomes via Y-autosome centric fusion and strongly suggested their common origin.

Genome sequence of the barred knifejaw Oplegnathus fasciatus (Temminck & Schlegel, 1844): the first chromosome-level draft genome in the family Oplegnathidae.

BACKGROUND: The barred knifejaw (Oplegnathus fasciatus), a member of the Oplegnathidae family of the Centrarchiformes, is a commercially important rocky reef fish native to East Asia. Oplegnathus fasciatus has become an important fishery resource for offshore cage aquaculture and fish stocking of marine ranching in China, Japan, and Korea. Recently, sexual dimorphism in growth with neo-sex chromosome and widespread biotic diseases in O. fasciatus have been increasing concern in the industry. However, adequate genome resources for gaining insight into sex-determining mechanisms and establishing genetically resistant breeding systems for O. fasciatus are lacking. Here, we analyzed the entire genome of a female O. fasciatus fish using long-read sequencing and Hi-C data to generate chromosome-length scaffolds and a highly contiguous genome assembly. FINDINGS: We assembled the O. fasciatus genome with a total of 245.0 Gb of raw reads that were generated using both Pacific Bioscience (PacBio) Sequel and Illumina HiSeq 2000 platforms. The final draft genome assembly was approximately 778.7 Mb, which reached a high level of continuity with a contig N50 of 2.1 Mb. The genome size was consistent with the estimated genome size (777.5 Mb) based on k-mer analysis. We combined Hi-C data with a draft genome assembly to generate chromosome-length scaffolds. Twenty-four scaffolds corresponding to the 24 chromosomes were assembled to a final size of 768.8 Mb with a contig N50 of 2.1 Mb and a scaffold N50 of 33.5 Mb using 1,372 contigs. The identified repeat sequences accounted for 33.9% of the entire genome, and 24 003 protein-coding genes with an average of 10.1 exons per gene were annotated using de novo methods, with RNA sequencing data and homologies to other teleosts. According to phylogenetic analysis using protein-coding genes, O. fasciatus is closely related to Larimichthys crocea, with O. fasciatus diverging from their common ancestor approximately 70.5-88.5 million years ago. CONCLUSIONS: We generated a high-quality draft genome for O. fasciatus using long-read PacBio sequencing technology, which represents the first chromosome-level reference genome for Oplegnathidae species. Assembly of this genome assists research into fish sex-determining mechanisms and can serve as a resource for accelerating genome-assisted improvements in resistant breeding systems.

The expression pattern of hsp70 plays a critical role in thermal tolerance of marine demersal fish: Multilevel responses of Paralichthys olivaceus and its hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic and acute heat stress.

Ocean warming has multifaceted impacts on marine organisms. This study investigated the different responses of Paralichthys olivaceus and the hybrids (P. olivaceus ♀ × P. dentatus ♂) to chronic and acute heat stress. By comparing their survival, behavioural and histological changes, we found that the hybrids possess a better thermal tolerance with a higher cumulative survival rate (CSR), relatively fewer behavioural changes and less gill damage. Moreover, we analysed the relationship between thermal tolerance and the hsp70 expression pattern and found that thermal tolerant species (the hybrids) exhibited higher threshold induction temperature, shorter durations, stronger magnitudes and a delay in hsp70 expression. We speculated that the expression mode of hsp70, rather than itself, plays a critical role in thermal tolerance. These findings would improve the understanding of hsp70 in future marine climate research and help clarify the profound effects of rising temperature on marine demersal fishes.