Abstract:In order to minimize physiological stress, thus improving live P. yessoensis condition and survival rate, commercial hand-dived P. yessoensis, were tied-up during land base relaying, and the effects of stress reduction on storage stability were investigated. One-week supply chain from harvest to market for live scallops was designed including 2-day on-land revitalization (i.e., relaying)and subsequent 4-day chilled dry-storage. Live P. yessoensis were tied-up individually to enforced shell-valve closure pre-relaying as treatment T^b and post-relaying as treatment T^a, changes of live P. yessoensis fitness were investigated compared to the treatment-free control group named C. ATP related substances, nucleotide energy charge AEC, arginine phosphate ArP, pH and glycogen were selected as fitness indicators. Sensory assessment and visual vitality indicated by mantle retraction and mantle response were conducted as well.Results showed that both T^b and T^a had a significant effect on sustaining P. yessoensis fitness in subsequent steps in the supply chain. ① The levels of ATP, ArP, glycogen and other biochemical indicators were in this order: T^b>T^a>C. On the 6^th day, both T^b and T^a presented better fitness than the control C. ② Tying-up held a delayed advanced effect on sustaining fitness in the subsequent dry storage. Results showed that, the order of positive effects was T^b>T^a>C, and a positive correlation between mantle retraction and response time was observed. ③ Sensory analysis results also revealed the advantages of delayed effect induced by tying-up in advance. At the relaying stage, tying-up made no difference in flavor profiles between the groups. Sensory quality of all P. yessoensis tended to decline based on the sensory evaluation. However, it was observed that T^b had always shown obvious advantages in umami and sweetness than others. In summary, the tied-up closure treatment can effectively suppress the physiological stress accompanied by reduced energy consumption. Thereby, high quality live P. yessoensis can be supplied to the market. Based on the experimental results of this study, several potential improvements to current post-harvest handling and transportation of P. yessoensis are suggested.

Abstract:China has become the powerhouse of aquaculture in the world in the past 40 years. With the rapid development of aquaculture, the different kinds of troubles also keep emerging in China. In particular, the performance of unbalanced and inadequate aquaculture industry mainly exhibited the adequate supply, low quality and safety of aquatic products. Along with the farming areas of inland waters, land-based and coastal waters constantly being squeezed, the deep blue fishery is the revolutionary transformation of production mode for turning the blue ocean into blue granary. Deep blue fishery is the aquaculture production system with the integration of whole industry chain including the aquaculture, fishing and aquatic products processing. The deep blue fishery covers marine space which includes the near shore and off shore of Bohai Sea, Yellow Sea, East China Sea and South China Sea as well as open ocean and polar region. With the expansion and extension of blue granary, it combines the different key points including breed, aquaculture, fishing, processing and web with an organic whole, which plays an important role in ensuring the supply of high-quality protein, broadening the new space of culture and supporting the blue economic growth and safeguarding China's maritime rights and interests. With growing science endeavors and further industrialization practice in recent years, the deep blue fishery has made rapid development, but it still faces the gradually emerging opportunity and challenge. This paper synthetically analyzes the strategic significance and main production function of developing deep blue fishery and summarizes the prominent problems restricting its development. The major production function of deep blue fishery contained offshore industrialized farming, exploitation of biological resources in oceanic and polar regions as well as offshore logistics and information channel. We summarized the existing main problems and restrictive factors, whose focus was mainly on four aspects. Firstly, the exploitation and utilization of natural resource were not very efficient. Secondly, the overall level of equipment and technology was still relatively backward. There are, in addition, obviously insufficient total production capacity and weaker support ability for scientific research. On the basis of the development goals, the intensive scientific and technical tasks were proposed that involve analyzing the genetic resources of deep blue biology, building the industrialized green production patterns and high-quality fishing the resources originating from open ocean and polar region, researching the technology and equipment of processing links across land and oversea as well as constructing fishery boats networking system and so on. Relevant measure suggestions were also made, such as implementing the technology capability promotion project, introducing industrial development supporting policies, building diversified talents congregate highland and establishing industrial innovation garden for demonstration, which aims to provide the lesson and reference for accelerating the technological advancement of deep blue fishery and promoting the iterative upgrade of industry. In summary, the deep blue fishery is a new rising industry of China. As an efficient way of the adjustment of the industrial structure and transferring the mode of production in aquaculture, it needs strong support of the scientists, government officials and other aspects.

Abstract:The Larimichthys crocea Daiqu group in the East China Sea was once one of the most commercially important demersal fishes unique to China's coastal waters. It is now an important target for our country to restore and rebuild the resources of L. crocea. In order to clarify the influencing factors of the decline of its resources, and reveal the selectivity of its habitat and the reasons why the resources of the L. crocea are difficult to recover, this paper took the L. crocea fishing output in Zhejiang Province from 1950 to 2020 as a sample, and analyzed the correlation between the population number changes of the L. crocea Daiqu group and major fishery events, such as knocking operation and rounding up the overwintering group in the central fishing ground, by using index analysis method, which aims to trace the causes of the decline of large yellow croaker resources; The biological characteristics and evolution of L. crocea and its adaptability to habitat were described by comprehensive literature analysis. The results showed that: (1) the main causes of the decline and depletion of L. crocea resources were caused by several unreasonable development and utilization methods, such as knocking operation, catching the incoming fishes and overfishing the wintering grounds; (2) L. crocea has the characteristics of long life span, late sexual maturity, complex population structure, and strong habitat environmental selectivity, among which temperature, salinity, flow rate, substrate and feed organisms are the key environmental factors; (3) Due to overfishing, the life history of L. crocea deviated from the original selection position, but it still belonged to K selection game. (4) In addition to human factors (such as excessive fishing intensity), the main factors affecting the recovery of L. crocea resources may also be related to the k-biased life history and habitat selection of large yellow croaker. What’s more, this study also put forward the future protection and proliferation strategies of L. crocea from the perspective of biological characteristics and habitat environmental selectivity, which provides a decision-making basis for the restoration and reconstruction of L. crocea Daiqu group in the East China Sea.

Abstract:The Yellow River Delta is rich in natural resources and has a unique ecosystem. The ecological protection and high-quality development in the Yellow River Delta have become a national strategy. Under the severe constraints of resources and environments as well as the serious degradation of ecosystems, the ecological protection and high-quality development of the Yellow River Delta urgently need the guidance and support of scientific and technological innovation. The implementation of coastal ecological farm and ranch is considered to be one of the important ways to achieve high-quality development. In order to create new models of green, low-carbon and circular coastal ecological farm and ranch in the Yellow River Delta, this paper analyzed the existing problems in coastal ecological farm and ranch, and put forward the high-quality developmental concepts and targets. At present, the unoptimized macroscopical planning, the incomplete industrial system, the imperfect innovation system, and the unstrengthened policy support of coastal ecological farm and ranch have restricted the high-quality development of coastal ecological farm and ranch in the Yellow River Delta. Furthermore, multi-driven high quality development approaches were raised as follows. Firstly, optimizing the macroscopical planning driven by water-salt scenario, that is, identify the complexity of the water-salt scenario and plan the layout reasonably; analyze the dynamics of the water-salt scenario and accomplish digital management. Secondly, highlighting the "chip" function driven by seed industry, that is, improve biodiversity based on native species protection; strengthen the cultivation of improved seed to enhance the driving force of industry; promote seed breeding to improve the coverage of seed industry. Thirdly, promoting model innovation driven by farm-aquaculture interaction, that is, connect land and sea to optimize industrial spatial layout; integrate farm and ranch, and establish linkage between Three Industries. Fourthly, realizing the intelligent upgrading of industry driven by equipment development, that is, build unmanned farms in saline and alkaline land; realize less populated farms and ranches on the tidal-flat area; create shallow sea intelligent ranches. Fifthly, innovating the collaborative paradigm driven by research-industry linkage, that is, integrate innovative elements to solve the problem of disconnection between industry and scientific research; financing through multiple channels to enhance innovation vitality. Finally, achieving industrial upgrading driven by governance policy, that is, integrate research and development resources and improve innovation ability; implement integrated development and strengthen the whole industrial chain; forward-looking layout of special research projects and innovative development modes. Therefore, stakeholders could construct new developmental models of coastal ecological farm and ranch in the Yellow River Delta with match of water-salt scenarios, integration of farm and ranch, and linkage of Three Industries, to realize the coordinated development of mechanization, intelligence, digitization and systematization. Our study is helpful to provide a reference for the high-quality development of coastal ecological farm and ranch in the Yellow River Delta.

Abstract:Fish coloration has long been a scientific research hotspot, owing not only to complex biological mechanisms associated with the prominent phenotypic characteristics, but also to high evolutionary significance for adaptation. Lately, an increasing number of researches have focused on lncRNA, due to their involvement in biological regulatory function. However, studies on lncRNAs in non-model organism such as Cynoglossus semilaevis are still lacking, particularly on skin melanostic mechanism. C. semilaevis is an important farmed marine fish in China and is easy to present the melanistic problem of blind side skin in the process of artificial cultivation. The blind side pigment abnormalities would spread with varying degrees of areas. It has not been known how pigment is correctly transported to the corresponding skin in C. semilaevis so far. In order to investigate the blind side melanized mechanism of lncRNA and mRNA in C. semilaevi, this experiment predicted that lnc-XR_003049606.1 targets pmelb through trans-acting according to the results of the transcriptome analysis. Bioinformatics analysis revealed that the full length of the cDNA of pmelb was 1 755 bp, encoding 584 amino acids, with a predicted protein molecular weight of 63.94 ku and a theoretical isoelectric point of 5.12. The predicted secondary protein structure contains a Pleckstrin homology domain, a Bruton's tyrosine kinase Cys-rich motif, a Src homology 3 domains, a Src homology 2 domains and a tyrosine kinase catalytic domain. Phylogenetic tree analysis showed that pmelb was clustered with corresponding genes in other fishes. The amino acid homology analysis showed that pmelb had the highest similarity with Scophthalmus maximus and Paralichthys olivaceus (68.05% and 66.28%, respectively). Analysis of the spatio-temporal expression patterns on lnc-XR_003049606.1 and pmelb revealed that lnc-XR_003049606.1 was expressed in the skin and liver of 1-year-old tongue sole, with expression peaking in the skin at 60 days and then decreasing over time, whereas pmelb was mainly expressed in the skin, with expression increasing and then decreasing over the timeline. This study provided an idea for further screening the key genes that play a role in the process of blind side hypermelanotic skin in C. semilaevi.

Abstract:Genome editing is an important means of genetic modification of organisms. It has been widely used in a broad spectrum of fields, such as functional genomics, animal model generation, genetic improvement of animals and plants, and gene therapy. In recent years, the emergence of CRISPR/Cas9 technology has sparked a revolution in biological research. Efficient, accurate and low-cost CRISPR technology has become a useful tool to explore gene functions and elucidate life phenomena, and its application in molluscs is expanding rapidly. In this review, we introduced the developmental course and working mechanisms of gene editing technology, and its application and prospects in molluscs, which might promote further application of genome editing in more molluscan researches, and provide information for identification of gene functions, determining genes related to economic trait, and genetic improvement.

Abstract:Hyriopsis cumingii is a unique freshwater pearl mussel in our country. It occupies an important position in the aquaculture industry. In the actual breeding process, male individuals have a more obvious advantage in pearl production than female individuals. Therefore, research on the sex determination of H. cumingii is crucial. Previous studies have found that Sox9 gene plays a role in male sex determination in many species, kinase X gene is an important gene in the synthesis of protein kinase (PKA), and PKA plays a vital role in many physiological and biochemical processes, especially in the process of spermatogenesis. In this process, PKA has a very obvious effect on sperm capacitation. The kinase X gene and Sox9 gene are both located in cAMP-PKA pathway. And the relationship of the kinase X gene and Sox9 gene is upstream and downstream. It is speculated that the Sox9 gene may be regulated by PKA. The results showed that the kinase X gene was 1 652 bp in length, the 3' UTR was 314 bp, while the length of the 5' UTR was 45 bp, encoding 430 amino acids, and there was an STKYc structure domain which was located at 381-1179 bp, kinase X gene has a transmembrane domain and the Molecular weight (Mw) of the kinase X protein was 49.00 ku and the theoretical Isoelectric point (pI) was 8.22, among which Leu(L) was the most abundant amino acid, accounting for 9.8%; the homology analysis showed that H. cumingii had a high similarity with other shellfishes such as Mizuhopecten yessoensis, Chlamys farreri. The phylogenetic tree showed that H. cumingii had a close relationship with Crassocras gigas and Crassostrea virginica, but had a long genetic distance with mammals. The fluorescence quantitative PCR results showed that the kinase X gene was expressed in 6 tissues including gonads, gill, adductor muscle, foot, mantle, liver of the 2-year-old H. cumingii , and the kinase X gene was expressed the highest in the male gonads while expressed the lowest in the female liver. And in 1-3 years of H. cumingii, the expression of kinase X gene in male was all higher than that in female, and the difference between male and female was extremely significant. Among them, the expression of kinase X gene in 2-year-old H. cumingii was highest among 1-3 years. Due to the high expression of the kinase X gene of the 2-year-old H. cumingii near the sexual maturity stage, the sperm occurrence rate was high; after 7 days of interference, the expression of kinase X gene decreased. RNA interference results show that the synthesized 3 interference chains had a certain interference efficiency on the kinase X gene, and the interference rate of the interference chain 1 was the highest. The interference rate was 83.1% in females and 81.9% in males, while interference chain 2 had an interference rate of 76.0% in females and 25.7% in males; interference chain 3 had an interference rate of 24.0% in females and 67.7% in males. At the same time, the Sox9 gene expression decreased by 90.3% in females and 56.6% in males after the interference of interfere chain 1. This improved the synthesis of kinase X gene was positively correlated with the synthesis of Sox9 gene. It was speculated that the two may work together to participate in the sex determination process through the cAMP-PKA-mediated signaling pathway. In this experiment, through preliminary functional exploration of the kinase X gene, it was found that there was the upstream and downstream relationship between kinase X gene and Sox9 gene and the two were positively correlated, and it effectively interfered with the kinase X gene, which is important in cAPM-PKA of H. cumingii. This study provides a theoretical basis for the study of sex determination and male parthenogenesis of H. cumingii.

Abstract:Among vertebrates, fishes show an exceptional range of reproductive strategies, which can be roughly divided into three categories: gonochorism, sequential hermaphrodite and partheonogenesis. In general, gonads can differentiate into ovaries or testes after sex determination, and remain unchanged throughout the life cycle. In contrast, some hermaphroditic fishes can change their sex from male to female (protandrous), female to male (protogynous), or serially (bi-directional sex change) in their life cycle. Hermaphroditic fishes have various forms of sex change, which is an ideal model to investigate the sex determination and differentiation in vertebrates. Therefore, this paper reviews the recent research progress on the sex differentiation and determination of hermaphroditic fishes from the aspects of gonadal change, sex hormone secretion, neuroendocrine, sex differentiation and molecular regulation of determining genes, so as to provide a reference for further research on the sex regulation mechanism of the fish.

Abstract:In order to understand the status and dynamics of fish community in Gehu Lake, the fishes at 16 stations in Lake Gehu were seasonally sampled using multi-mesh gillnets and traps from August, 2017 to May, 2018. Meanwhile, water temperature (WT), water depth (WD), transparency (SD), pH, chlorophyll a (Chl.a), total nitrogen (TN), total phosphorus (TP) were measured. Using these data, fish community structural characteristics, the spatial and temporal distribution pattern and its relationship with environmental factors were analyzed. A total of thirty-six fish species, belonging to 4 orders and 8 families, were collected from Lake Gehu. According to index of relative importance (IRI), Japanese grenadier anchovy (Coilia nasus) was the predominant species, silver carp (Hypophthalmichthys molitrix) and crucian carp (Carassius auratus) were the common species. Sedentary fishes (83.3%) predominated in species number among the three ecological groups and omnivorous fishes (47.2%) prevailed among the five feeding functional groups. The fish species composition in Lake Gehu did not differ monthly and spatially. The Two-Way analysis of variance (ANOVA) showed that number per catch effort (NPUE), richness index (R), Shannon-Wiener's diversity index (H′) and evenness index (J) significantly differed but biomass per catch effort (BPUE) did not differ monthly, and all the five structural features except R did not significantly differ between lake areas. Redundancy analysis revealed that WT and TP were the key factors influencing the spatial and temporal distribution of fish species of Lake Gehu. The results suggested that since 1950s the fish diversity has declined markedly and the species and product composition have changed greatly, which is speculated to be responsible for sharp degradation of macrophyte vegetation, overfishing, disconnection between lake and river, and breeding and enhancement.

Abstract:Changes in abundance and distribution during the fish larvae and juveniles period can affect the size of fish replenishment groups and, consequently, rusult in changes in the size of fish populations.The study of early-stage fish resources has great value for understanding fish stocks recruitment and the assessment of fishery resources. In this study, 47 stations(119°00'-123°00'E, 31°00'-35°00'N) were investigated in the nearshore waters of the southern Yellow Sea from March 2019 to January 2020. Fish larvae were monthly collected using a larval fish net(1.3 m diameter at the mouth, 6.0 m length, 0.5 mm mesh aperture) during the high tide to reveal the spatial-temporal distribution and drifting trends of larval and juvenile Collichthys lucidus. The environmental factors (surface water temperature, surface salinity, water depth) of the surveyed waters were also measured, and the spatial and temporal distribution characteristics and drift trends of the abundance of C. lucidus fish larvae and juveniles were analyzed. The relationship between environmental factors and fish larvae distribution was analyzed by a GAM model. A total of 2385 fish larvae were collected from June to October, with the highest abundance in June (165.15 ind./100 m³) and a decreasing trend month by month. Each month's most dominant developmental stages changed from pre-flexion larvae to juveniles in the order of months, except that only one post-flexion larva was collected in October. The results of the GAM model showed that the deviation of abundance was explained by latitude and longitude with the highest rate of 52.3%, followed by month and surface salinity. We conclude that the inshore waters of the southern Yellow Sea were nursery ground for C. lucidus, with its eggs and pre-flexion larvae dispersed passively. Then, the post-flexion larvae and juveniles drift inshore with growth and development under the influence of environmental factors such as surface salinity, surface water temperature, and water depth. Juveniles dominated in September and subsequently disappeared from the samples, implying potential recruitment success.

Abstract:As the carrier and transmitter of genetic information, the chromosome is the most important component in eukaryotic cells. Karyotype analysis is an intuitive way to understand characters of chromosomes in eukaryote. Understanding karyotypes of fish is of great significance for studies on genetics, variation, classification, systematic evolution, sex determination, cross breeding and environmental pollution monitoring. As an important aquaculture fish family in China, Siluriformes are the good models to study evolution of fish chromosomes and differentiation of sex chromosomes. In the present study, progresses of karyotype studies on 35 catfishes in China, including their hybrids and polyploids, were reviewed when characteristics of the karyotypes and evolutionary relationships of chromosomes among different taxa were analyzed. Finally, development trends of catfish karyotype studies were forecasted. The number of chromosomes in Siluriformes varied from 24 to 100, with 30 of the 35 catfishes owning chromosome numbers in the range of 48~60, and chromosome polymorphisms were reported in five fishes. Moreover, visible sex chromosomes were detected in seven of the 35 fishes. This study will provide useful references for future chromosomal and genomic studies on Siluriformes, and will also be helpful for evolutionary studies of teleost.

Abstract:The neon flying squid (Ommastrephes bartramii) is a dominate economic species in the north Pacific Ocean. Marine environment variation has a profound impact on the marine organisms and their growth. As a short lifespan oceanic cephalopod, O. bartramii is highly susceptible to the climate change in different degrees, such as the Pacific Decadal Oscillation (PDO), El Niño and La Niña. Consequently, investigation on growth of O. bartramii affected by variable marine environment becomes an important and basic part for cephalopod research. Based on 6091 samples of O. bartramii collected in fishing season (from August to October) from 2009 to 2012 and 2015 to 2016 in the north Pacific Ocean, the growth of O. bartramii was studied combined with the marine environmental factors in the present study. The results indicated that significant difference of fishery biological characteristics was found between different gender and marine environment years. Viewed from the difference of the dominated mantle length (ML) and body weight (BW) group, maximum values of both ML and BW occurred in 2016, while minimum values occurred in 2010 and 2015. The b values of ML-BW relationship in all sampling years were significantly different with 3, which showed allometric growth. The mature stage of both female and male squids concentrated in stage II, and the proportion of mature female squid was less than that of male squids. The maturation of ML of O. bartramii was positively correlated with the Pacific Decadal Oscillation index with one-year lag. Samples in El Niño years were greater than those in La Niña years, and individuals in El Niño year with very strong intensity were the smallest. The El Niño event with very strong intensity caused low sea surface temperature (SST) and low Chlorophyll a (Chl. a) concentration which was not beneficial to the growth and their gonad development of O. bartramii. Higher SST and Chl. a concentration provided favorable environment for O. bartramii, resulting in a greater body size and early maturation. The present study suggested that the growth and gonad development had significant difference among different marine environment years, and the synthetic actions of PDO, El Niño/La Niña, SST and Chl. a concentration were the dominate factors that affected the growth of O. bartramii.

Abstract:The excavation and utilization of excellent germplasm resources are pivotal in ensuring the supply of China’s high-quality aquatic protein. As Larimichthys crocea owns China’s highest production in marine aquaculture, and its germplasm resources serve as an indispensable material basis for the healthy and sustainable development of L. crocea breeding industry, it is of great strategic significance to carry out the collection, preservation, identification, evaluation, protection and utilization of L. crocea germplasm resources systematically. This paper has reviewed the history and present situation of germplasm protection and utilization of L. crocea, and analyzed the main current problems from the aspects of scientific research, breeding technology system, industry, and talents. Besides, based on the scientific and technological innovation of L. crocea seed industry and the creation of new varieties, the development direction creating major new species with such traits as disease resistance, stress resistance, high yield, high quality, and high compound feed conversion rate was proposed to substantially expand the coverage of improved L. crocea and provide a fine bread guarantee for the healthy development of L. crocea industry.

Abstract:In order to evaluate the genetic parameters of body length, weight and WSSV resistance of Litopenaeus vannamei more accurately, 8 microsatellite loci were used to genotype mother and offspring of 69 families of L. vannamei, and the pedigree reconstruction and the calculation of the molecular relationship correlation were carried out by using the genotyping information. The reconstructed pedigree, the molecular affinity and the physical pedigree were used to construct the additive genetic correlation matrix. Then, the genetic parameters of body length, body weight and WSSV resistance were evaluated. Finally, through the cross validation method, the prediction ability and accuracy of genetic parameter evaluation were compared. The results of genotyping showed that 166 alleles were detected in 8 microsatellite loci; the number of alleles in each locus was 12-45; the average number of alleles in each locus in parent and offspring population was 9.50 and 18.13; the average observed heterozygosity was 0.618 and 0.709; the average expected heterozygosity was 0.749 and 0.775; the average polymorphism information content was 0.711 and 0.750, respectively, and all of loci showed high polymorphism. The heritability of reconstructed pedigree, molecular affinity and physical pedigree analysis showed that the heritability of body length was 0.119±0.031, 0.120±0.032, 0.132±0.030; the heritability of body weight was 0.176±0.039, 0.182±0.040, 0.172±0.034; and the heritability of resistance to WSSV was 0.135±0.033, 0.134±0.033 and 0.098±0.031, respectively. In the heritability of body length, body weight and resistance to WSSV, the standard deviation of molecular affinity was smaller than that of reconstructed pedigree and physical pedigree. Through cross validation, the prediction ability and accuracy of the three genetic parameters evaluation from high to low are molecular affinity, reconstructed pedigree and physical pedigree. The results showed that it was more accurate to evaluate the body length, body weight and WSSV resistance of L. vannamei by using microsatellite molecular markers than using physical pedigree. In the method of evaluating heritability by using microsatellite molecular markers, it was more effective to directly use the genetic correlation of offspring. This study provides a more accurate method for the evaluation of genetic parameters of L. vannamei and a reference for further breeding.

Abstract:The Chinese giant salamander (Andrias davidianus) is the largest extant amphibian species in the world, with significant scientific, ecological and economi values. According to the Chinese law, wild populations of A. davidianus are treated as the class Ⅱ state protected species, while the second and subsequent generations of captive-bred A. davidianus can be utilized as aquatic products or resources for the food and pharmaceutical industry. As one of the endemic and rare animals in China that possess both conservation and utilization values, the process about germplasm resources of A. davidianus has raised considerable concern. Although with multiple conservative status, the current situation of wild A. davidianus is still unoptimistic. The present practices and effects on the conservation of A. davidianus through in-situ conservation in terms of nature reserves and ex-situ conservation by artificial enhancement and translocation are yet to be evaluated. In contrast, with the increasing development of artificial culture and expanding of the husbandry scales, the captive-bred A. davidianus has become one of the new aquaculture species with good market prospects. However, the disease control is still one of the bottleneck problems during the process of captive breeding. A. davidianus is one of the high-valued aquaculture species with high protein and low fat, and additionally, its bioactive substances and efficacies are being revealed gradually. However, by restrictions of the market, industry, and the input of scientific research, the scale of captive A. davidianus is still very limited, thus the scope and depth of its utilization need to be greatly strengthened. Based on the studies from previous papers and the practices from our team, in this study we reviewed the conservation and utilization of the germplasm resources of A. davidianus, from the aspects of basic biology, habitat characteristics, genetic diversity, conservation, captive breeding, disease, nutrition, bioactive substances, industrial utilization, etc. By summarizing the successful experiences and identifying the problems, this paper aims to provide a valuable reference for studying the genetic germplasm resources, planning the conservation strategies, developing and sustainable utilization, as well as enhancing the public awareness of this precious species in the future.

Abstract:Flavobacterium psychrophilum, the causative agent of bacterial cold-water disease and rainbow trout fry syndrome, is currently an important pathogen causing great economic loss to the salmonid industry worldwide. Recently, the genomic evolution and pathogenic mechanisms of F. psychrophilum have been widely studied in many countries. However, these studies that originated from China are still rarely reported. In order to better understand the genomic evolution and pathogenesis of F. psychrophilum in China, the virulent strain CH06 was subjected to whole genome sequencing and analyzed using comparative genomics, and virulence-associated genes were predicted. The result of whole genome sequencing showed that the CH06 genome consists of a single circular chromosome of 2 836 981 base pairs (bp) harboring 2 437 protein-coding genes with an overall G+C content of 32.56%. The results of ANI analysis showed that ANI values between CH06 and 12 F. psychrophilum strains are higher than 99%, indicating that CH06 belongs to F. psychrophilum. Analysis of the genome sequence reveals that CH06 consists of 5 insertion sequences, 4 genomic islands and 3 prophage sequences, indicating that these mobile genetic elements led to the genome evolution of CH06. Collinear and phylogenetic analysis showed that CH06 is more closely related to CSF259-93 and FPG101. Secretion system analysis showed that CH06 carried type I (T1SS) and type IX (T9SS) secretion system. Among the coding proteins, 56 proteins are predicted to be secreted by the T9SS. Furthermore, CH06 was predicted to encode 11 histidine kinases (HKs) and 16 response regulators (RRs), revealing that CH06 has evolved sophisticated regulation mechanisms to export virulence factors across the bacterial cell envelope to sense and respond to environmental changes. In this study, the genomic evolution and virulence-associated genes of CH06 are analyzed, providing a basis for research on the genomic evolution and pathogenic mechanisms of this fish pathogen in China.