Abstract:The size at first maturity was one of the most important biological characteristics for fishery population. In order to know the size at first maturity of mantis shrimp (Oratosquilla oratoria), Huxley’s traditional model and polyphsic model were established for mantis shrimp collected from fishery independent surveys by trawl net in Bohai Bay from Apr. to Aug. 2018, and the size at first maturity was estimated. Our analyses showed that the polyphasic model was more suitable for fitting the length–weight relationship for mantis shrimp. According to Huxley’s traditional model, there were two independent spot clusters for the proportional residuals, which characterized two length–weight relationship groups. According to the polyphsic growth model, the sizes at first maturity were estimated as 10.99 cm, 11.01 cm and 10.85 cm for total, female and male mantis shrimp, respectively. These data suggest that a change in growth pattern could be related to a change in energy allocation related to the reproductive activities. When mantis shrimp, especially female, were in the period of maturity, more energy was allocated for sexual maturation, and perhaps decreased energy for somatic growth.

Abstract:The necessity for fish to migrate safely is a key requirement for the existence of many fish populations. Anthropogenic constructions, such as dams and weirs, that block rivers, make it difficult, if not impossible, for fish to reach their upriver spawning grounds. Also, these constructions are also very dangerous for fish moving down the river because dams are built associated with hydroelectric power station intakes where fish are injured or killed on the gratings, pump screens, and in turbine chambers. Mild fields of pulsed, direct current (DC) electricity have been used extensively in deterring invasive fish species as well as in reservoir fishery, but directional fish guidance using electric deterrence arrays to guide fish toward desirable passage locations or away from dangerous areas has received little attention. The effectiveness of the electrified barriers is quite variable and testing is often lacking for a variety of water velocity conditions. To explore the effects of different electric parameters of electrified barriers on the avoidance behavior of the juvenile grass carp C. idella with body length of (10.22±2.01) cm and body mass of (34.25±3.62) g, a double-row type of electrified barrier based on pulsed direct current electricity was established and orthogonal designed experiment of three factors, including pulse voltage, frequency and width, four levels was adopted to optimize the blocking performance of the electrified barrier under the static water condition. To explore the effects of water flow conditions on the blocking efficiency of electrified barriers using the optimized electric parameters recommended for static water conditions, three flow conditions at a generalized model of fishway entrance were utilized to test the attractive efficiency of fishway entrance. The results showed that, under static water conditions, the working condition 7 had the highest blocking rate (88.67±1.10)% and lower average stupefaction rate and that the factors affecting blocking efficiency are pulse voltage, pulse frequency and pulse width respectively. Determined by analysis of variance and multiple comparison, the optimal electric parameters under static water conditions for blocking efficiency were the pulse voltage of 160 V/m, the pulse frequency of 6 Hz and the pulse width of 16 ms. Under the optimal electric parameters, the experimental fish had minimal injuries when subjected to electrified barriers. By employing the optimum electric parameters recommended for static water conditions, the active electrified barrier can dramatically boost the aggregation rate and average retention time ratio at the fishway entrance when the channel velocity was 0.15 m/s. When the channel velocity was 0.25 m/s and 0.35 m/s, the aggregation rate and average retention time ratio with the active electrified barrier were not enhanced significantly compared with those in the inactive electrified barrier. Therefore, the recommended electric conditions for optimal blocking effect is to set the pulse voltage of 160 V/m, the pulse frequency of 6 Hz and the pulse width of 16 ms under static conditons. The attractive effects of fishway entrance could be enhanced by the active electrified barriers with the best flowing water velocity being 0.15 m/s. These results will have important reference significance for the practical engineering of the electrified barrier arrangement. The pulsed direct current electric systems have the potential to improve fish passage at anthropogenic barriers. Additional research should investigate the effectiveness at variable electric field voltage and various water flow velocities for fish of various sizes and shapes depending on the species and its ethology.

Abstract:Global warming will lead to great variations in ocean environmental variables, and the spawning grounds of fishes will be changed correspondingly. To comprehensively understand the changing patterns of spawning ground suitability of Konosirus punctatus under climate change and provide a scientific basis for the conservation of spawning grounds, fishery surveys were conducted in the spawning grounds in the central and southern Yellow Sea from May to July in 2014—2018 using ring net. Spawning grounds distribution of K. punctatus was analyzed by Random Forest model. Six environmental variables were selected in the model, including sea surface temperature, sea surface salinity, depth, offshore distance, sea surface velocity from FVCOM (Finite-Volume Community Ocean Model) and chlorophyll-a concentration from NOAA. In addition, the potential distribution of the spawning grounds of K. punctatus under future climate change scenarios was also predicted. Results showed that the main environmental factors affecting the spawning grounds were different by months, and the main factors were water depth, chlorophyll a and sea surface temperature from May to July, with relative contribution of 24.49%, 28.08% and 26.26%, respectively. The suitable spawning grounds of this species will migrate northward under climate changes. Moreover, the suitability of spawning grounds in the northern coastal waters of Haizhou Bay and the deep-water areas of the southern Haizhou Bay will increase significantly. Therefore, this trend should be fully considered in the future in terms of spawning ground protection and resource development and utilization.

Abstract:Herpesviruses, as the members of the double-stranded DNA viruses, are highly disseminated in nature. Diverse viral isolates of Alloherpesviridae family are the main pathogens of aquatic animal diseases, which severely restrict the sustainable development of global aquaculture, particularly a huge impact on the fish aquaculture in China. Thus, this article provides a brief overview on virology researches of fish herpesviruses, including Cyprinid herpesvirus, Ictalurid herpesvirus, Salmonid herpesvirus and other fish herpesviruses. In detail, Cyprinivirus includes C. herpesvirus 1 (CyHV-1), C. herpesvirus 2 (CyHV-2), C. herpesvirus 3 (CyHV-3), Carassius auratus herpesvirus (CaHV), Anguillid herpesvirus 1 (AngHV-1); Ictalurivirus involves I. herpesvirus 1 (IcHV-1), I. herpesvirus 2 (IcHV-2), Acipenserid herpesvirus (AciHV-1). Salmonivirus consists mainly of S. herpesvirus 1,2,3,4,5 (SalHVs). Besides, the article also covers newly identified virus isolates including Tilapia larvae encephalitis virus, TLEV; Gadid herpesvirus 1, and so on, which threaten the health of the farmed and wild fish. This overview of fish herpesviruses discusses the diseases caused by these viruses, the biology of these pathogens, the host-virus interactions, development of detection technology and progress in the prevention strategies. This may be helpful to our understanding of the viral research trends of fish herpesviruses.

Abstract:An experiment was conducted to investigate the effects of dietary choline content on growth performance, body composition, and serum antioxidant activity of juvenile largemouth bass, Micropterus salmoides. Graded choline chloride levels of 0 (control group), 700, 1 400, 2 100 and 2 800 mg/kg were supplemented to basal diet to formulate five isonitrogen and isoenergy practical diets containing choline of 2 369.57, 2 716.90, 2 993.49, 3 443.60 and 3 799.05 mg/kg, respectively. Each diet was randomly assigned to triplicate cages of 20 fish with an initial average weight of (20.00±0.10) g for 56 days. The results showed that the weight gain rate (WGR) and specific growth rate (SGR) of the fish first increased and then decreased with the increase of dietary choline chloride, and reached the maximum when the dietary supplementation was 2 100 mg/kg, which were significantly higher than those of the control group. The survival rate (SR), hepatopancreas somatic index (HSI), viscera somatic index (VSI), and condition factor (CF) of the fish were not significantly affected by dietary choline chloride supplementation. When the dietary choline chloride supplementation reached 2 100 mg/kg or above, the lipid contents in muscle and liver of the fish were significantly decreased than those in control. Compared with the control group, the total antioxidant capacity, superoxide dismutase and catalase activities were significantly increased and the content of malondialdehyde in serum was significantly decreased in the groups which were supplemented with 1 400, 2 100 and 2 800 mg/kg choline chloride. The maximum of lysozyme activity and minimum of aspartate aminotransferase activity appeared in the group treated with dietary choline chloride of 2 100 mg/kg, which were significantly different from those of the control group. All these results indicated that the suitable dietary choline chloride supplementation could significantly improve growth performance, reduce liver fat content, and enhance the serum's antioxidant capacity. Regression analysis showed that the recommended amount of choline chloride in the practical diet of juvenile largemouth bass was 2 008.50-2 398.16 mg/kg (the dietary choline content was 3 432.09-3 530.23 mg/kg).

Abstract:A 60-d feeding trial was conducted to determine the dietary leucine requirement of juvenile sea cucumber Apostichopus japonicus with initial body weight (16.40±0.14) g. Six experimental diets were formulated with the graded leucine levels 1.29% (D1, control group), 1.63% (D2), 1.98% (D3), 2.22% (D4), 2.58% (D5) and 2.97% (D6) dry diets. The results showed that: There were no differences in survival rate among all groups (96.00%-98.67%). Both weight growth rate (WGR) and the specific growth rate (SGR) increased with increasing leucine content until reaching peak levels at 1.98% dietary leucine, but decreased thereafter. The WGR and SGR of D3, D4 and D5 groups were significantly higher than D1 group. The WGR reached maximum value of 100.84% in the D3 group. There were no significant effects on ratio of intestine weight to body wall weight (IBR) and ratio of intestine length to body length (IBL) of sea cucumber. The crude lipid contents of body wall was increased when dietary leucine content increased from 1.29% to 1.98% but decreased when the dietary leucine content exceeded 1.98%, and D3 group was significantly higher than other groups, but there were no significant effects on moisture, crude protein and crude ash contents. Both methionine and leucine content of body wall were significantly increased by dietary leucine, but there were no significant effects on total amino acids (TAA). Both lipase and protease activities of intestinal were increased with increasing levels of leucine up to 1.98% diet and then decreased. The lipase of D3 group was significantly higher than other groups, meanwhile, the protease of D2, D3 and D4 groups were significantly higher than other groups. All of alanine aminotransferase (ALT), asparate aminotransferase (AST) and total antioxidant capacity (T-AOC) activities of intestinal were increased when dietary leucine content increased from 1.29% to 1.98%. There were no significant effects on AST activity when the dietary leucine content exceeded 1.98%, but the ALT and T-AOC activities were decreased. The T-AOC activity of D3 group was significantly higher than D1, D2, D5 and D6 groups. The catalase (CAT) and superoxide dismutase (SOD) activities reached maximum value when the dietary leucine content was 2.22%. The CAT activity of D4 was significantly higher than D3, D5 and D6 groups, The SOD activity of D4 was significantly higher than D1, D2 and D6 groups. The malondialdehyde (MDA) content was decreased when dietary leucine content increased from 1.29% to 1.98% but increased when the dietary leucine content exceeded 2.22%, the MDA contents of D3 and D4 groups were significantly lower than other groups. With WGR as evaluation indicator, quadratic regression analysis showed that the optimum dietary leucine requirement of sea cucumber with body weight 16.40 g was 2.11% diet (10.37% dietary protein).

Abstract:Grass carp reovirus (GCRV) is one of the main pathogens harmful to the health of Ctenopharyngodon idella, causing severe grass carp hemorrhagic disease. To explore the difference between naturally and artificially injection infected C. idella with GCRV-II virus in clinical symptoms, pathological features, and virus distribution, we used clinical necropsy, histopathological observation, molecular biology detection, real-time fluorescent quantitative (qRT-PCR), and Western blot detection methods for experiments. We compared the clinical symptoms of naturally diseased and artificially injected C. idella, and found that the eye socket, operculum, mouth cavity, abdomen, fin base, intestine and muscle of the diseased C. idella showed obvious punctate hemorrhage. The bleeding of the latter was more serious than that of the former. Compared with histopathological sections, it was found that the infected tissues had different degrees of congestion and erythrocytes accumulation. Among them, the intestines, muscles and hepatopancreas of the artificial injection of C. idella were more severely affected, showing more serious intra-tissue bleeding and lesions. The gills and spleen of naturally diseased C. idella were more severely affected, the gills showed more serious hyperaemia and inflammatory hyperplasia, and large areas of hemosiderin agglutination lesions appeared in the spleen. The results of qRT-PCR and Western blot tests showed that GCRV was distributed in different tissues. The head kidney had a relatively high viral load in diseased fish by the two infection methods. The viral load of the hepatopancreas, intestine, and muscle was higher in artificially injection infected fish. The amount of virus is higher in the trunk kidney, gill, and spleen in naturally diseased fish. Therefore, the hepatopancreas, intestine, and muscle may be the main target organs of GCRV invasion in artificial injection infection, while the gill may be the main target organ of GCRV invasion in the case of natural disease, and the target organ for virus accumulation is the head kidney. The head kidney is the "virus library" of GCRV. This study is helpful to deeply analyze the pathogenesis of GCRV and the immune responses of C. idella, and may provide references for the prevention and treatment of C. idella hemorrhagic disease and the development of the vaccine.

Abstract:Grass carp (Ctenopharyngodon idella) is the most productive freshwater aquaculture species in China, which is of great importance for Chinese aquaculture industry. Developing molecular marker assisted breeding program for C. idella has important theoretical value and practical significance. Microsatellite markers are popular in breeding studies with characterization of wide distribution, large numbers and high polymorphism. In this study, microsatellite loci were mined based on whole genome sequences of C. idella and the distribution characteristics of the loci were analyzed. In the meantime, microsatellite markers with 4-6 bases repeats with high polymorphism and high accuracy of paternity test were developed. The results showed that 677 363 microsatellite sequences were found in the 900.51 Mb genome sequence of C. idella, with a total length of 12 835 407 bp, accounting for 1.425 4% of the whole genome length. The average distance of SSR was 1 329.43 bp. The mononucleotide repeats motifs (52.85%) were the most common, followed by dinucleotide repeat (31.44%), tetranucleotide repeat (8.05%), trinucleotide repeat (6.47%), pentanucleotide repeat (1.12%), hexanucleotide repeat (0.07%). The preponderance of 1-6 base repeat motifs were A/T, AC/GT, AAT/ATT, AGAT/ATCT, AATAT/ATATT and AACCCT/AGGGTT, respectively. The distributions of copy numbers in different microsatellites repeat types showed there was a significant negative correlation between repeats motifs length and mean copy number (r = −0.8581, P = 0.0288). The copy numbers of mononucleotide repeats were focused mainly on 10-29 (98.11%), dinucleotide repeats 6-25 (96.80%), trinucleotide repeats 5-11 (95.14%), tetranucleotide repeats 5-10 (88.48%), pentanucleotide repeats 5-10 (84.93%), hexanucleotide repeats 5-7 (87.42%). The 110 loci with 4-6 base repeats were randomly selected and primers were designed. Among these loci, 50 loci were amplified successfully with mixed DNA of C. idella used as a template and 15 loci showed high polymorphsim when analyzed in its breeding parent population. Cervus 3.0 analysis results showed that average expected heterozygosity of 15 loci was 0.802-0.959. The accuracy of simulated paternity test was 100% with 95% confidence degree. These 15 loci were used to identify 192 offspring from 20 families, and all offspring matched to the correct parents successfully with the accuracy of identification being 100%. In this study, we analyzed the microsatellite characteristics of C. idella, screened out highly polymorphic microsatellite markers with 4-6 base repeats and carried our parental identification of C. idella by using these highly polymorphic microsatellite loci. At the same time, it was proved that 4-6-base repeat microsatellite is more suitable for paternity test than traditional 2-3-base repeat. The study summarized the Characteristics of whole genome microsatellites of C. idella and laid a foundation for the application of C. idella microsatellites in its breeding program.

Abstract:In recent years, the frequent outbreaks of viral hemorrhagic diseases have seriously affected the development of grass carp (Ctenopharyngodon idella) aquaculture, but its pathogenesis is still unclear. The viral hemorrhagic disease of C. idella is caused by grass carp reovirus (GCRV). Type II GCRV, as the main epidemic strain at present, is highly pathogenic to C. idella and has a high lethality rate. The VP35 protein encoded by the fragment S11 of type Ⅱ GCRV is the outer capsid protein. VP35 protein may play an important role in binding to receptors to promote virus entry into host cells, and may also promote virus replication by interacting with intracellular proteins. In order to explore the role of VP35 protein in virus replication, the S11 gene was amplified and inserted into the vector pCMV-3×flag to construct the S11 plasmid, which was transfected into C. idella kidney (CIK) cells, and then infected with type Ⅱ GCRV. After infection, the supernatant and cells were collected. First, real-time fluorescent quantitative PCR was used to detect S6 mRNA in cell samples. The results showed that overexpression of VP35 promoted the replication of type Ⅱ GCRV at the level of viral mRNA by about two-fold. Then the S6 gene was amplified and inserted into the vector pET-32a (+) to construct a recombinant plasmid, and the recombinant protein His-VP4 were purified and polyclonal antibodies was prepared to determine the effects of VP35 on type Ⅱ GCRV at viral protein level. The results showed that overexpression of VP35 promoted the replication of type Ⅱ GCRV at the level of viral protein. Finally, the pET-32a-S6 plasmid was used as a positive standard plasmid to establish an absolute quantitative detection method for the gene copy number of type Ⅱ GCRV. The pET32a-S6 plasmid was diluted 10-fold, and then used as a template, qPCR was used to detect the expression of the S6 gene, and a standard curve was drawn. The quantitative method was used to determine the effects of VP35 on type Ⅱ GCRV particles in supernatants. The results showed that overexpression of VP35 increased the copy number of type Ⅱ GCRV. This study proved from three dimensions that overexpression of VP35 protein promoted type Ⅱ GCRV replication, which is helpful for in-depth analysis of the function of VP35 protein, and laid a foundation for the subsequent exploration of the mechanism of VP35 protein in promoting virus proliferation, provided a protein-level detection method for further study of type II GCRV virus, and a new technical means for rapid and accurate quantification of virus titer.

Abstract:Stress is unavoidable in the aquaculture environment. Upon exposure to stress, the host stress hormones profoundly affect the pathogenicity of bacteria. It has been demonstrated that the inter-kingdom communication between bacteria and their hosts is mediated by catecholamines hormones epinephrine (Epi)/ norepinephrine (NE), and transduced by QseBC two-component system (TCS). In bacteria, QseBC TCS is a widely used signal transduction mechanism that facilitates in eliciting an adaptive response to various environmental stimuli. It consists of a membrane-associated sensor histidine kinase (HK) QseC and a cytoplasmic response regulator (RR) QseB. In most cases, QseC senses and recognizes environmental signals, following activation via self-phosphorylation at a conserved histidine residue. The phosphoryl group is then transferred to a conserved aspartate residue of QseB. The activated response regulator then exerts its regulation on bacterial virulence. Aeromonas hydrophila is a common aquatic bacterium and can cause motile Aeromonad septicemia (MAS) in aquatic animals especially fish. Recently, QseC has been reported to regulate the virulence of A. hydrophila in response to NE. However, the specific role of QseB in NE-enhanced virulence of A. hydrophila remains poorly understood. In this study, we constructed a qseB gene deletion mutant of A. hydrophila NJ-35 (ΔqseB) and examined the virulence both in vitro and in vivo in the presence or absence of NE (100 μmol/L). The results showed that the deletion of qseB gene significantly reduced the growth-promoting effect of NE on A. hydrophila compared to the wild type strain NJ-35. Meanwhile, the biofilm formation ability of the ΔqseB mutant was remarkably lower than that of the wild type strain NJ-35 in the presence of NE, while no significant difference was observed when bacteria were cultured without NE. Also, the hemolytic activities of ΔqseB exhibited significant decrease compared to the wild type strain NJ-35 with NE treatment. However, there were no significant differences in the motility and lipase activity between the ΔqseB mutant and wild type strain NJ-35 with or without NE. Additionally, the ΔqseB mutant displayed a dramatically decreased virulence in the experimental infection of Oreochromisc oaureus. In conclusion, our data suggest that the biofilm formation and hemolytic activity enhanced by NE may be dependent on the phosphorylated QseB in A. hydrophila NJ-35, indicating that QseB plays an important role in the outbreak of hemorrhagic septicemia disease induced by fish stress. Our study further reveals the pathogenesis of A. hydrophila in response to NE and may provide a new theoretical basis for the research on communication between bacteria and their hosts.

Abstract:The present study was conducted to validate the acetylation site of STAT3 and its relationship with SIRTs deacetylase family in Pelteobagrus fulvidraco. The STAT3 overexpression plasmids containing Flag tag and the SIRTs overexpression plasmids containing HA and GFP tags were constructed, and mutants were constructed for the possible acetylated sites of STAT3. Then, STAT3 was transfected and the mutants, STAT3 and SIRTs were co-transfected into HEK 293T cells, and the detection was carried out by immunoblotting, immunoprecipitation and immunofluorescence techniques. The results showed that STAT3 is a cytoplasmic protein. Compared with wild-type STAT3, the acetylation level of mutant K685R was significantly reduced. The acetylation levels of mutants K49R, K87R, K680R, K712R and K714R had no significant changes compared with wild-type STAT3. The immunoprecipitation and immunofluorescence showed that SIRT2 and SIRT7 interacted with STAT3 and catalyzed the deacetylation of STAT3, while SIRT5 did not interact with STAT3, and there was no significant change in acetylation level. The study revealed the acetylation site of STAT3 and the relationship between STAT3 and SIRTs in P. fulvidraco.

Abstract:Grass carp (Ctenopharyngodon idella) is the most productive aquaculture fish in the world. With the development of C. idella culture, diseases have occurred from time to time, and the disease caused by Aeromonas hydrophila infection lead to serious economic losses. miRNA is a kind of endogenous non-coding small molecule RNA with a length of about 22 nt, which can bind to 3'-UTR (3'-untranslated regions) of target mRNA to inhibit the translation of target mRNA or degrade target mRNA. As a new type of gene expression regulation molecule, miRNA can participate in the regulation of different types of biological processes such as cancer occurrence, immunity, development, cell differentiation, apoptosis and immune defense. The degree of complementarity corresponds to different forms of action. When miRNA and target mRNA 3'-UTR have incomplete complementary binding, protein production is inhibited at the translation level. When miRNA completely complements the target mRNA 3'-UTR, degradation generally occurs after transcription. At present, more than 30 000 miRNA molecules have been found in more than 200 species. In all kinds of aquatic animals, miRNAs perform a variety of biological functions in their bodies. For example, some miRNAs are closely related to the regulation of immune response in bony fish after virus or bacterial infection. During Vibrio anguillarum infection in ayu, miR-155 promotes pro-inflammatory functions and augments apoptosis of monocytes/macrophages. In addition, some studies have found that miRNAs such as miR-148, miR-214 and miR-19a can also inhibit the expression of MyD88, which can negatively regulate the inflammatory response caused by bacteria. In this study, the target genes of miR-23a were screened and determined to study its mechanism after A. hydrophila infection. In order to explore the regulatory mechanism of miR-23a in C. idella kidney (CIK) cells infected with A. hydrophila, the expression of miR-23a in CIK cells infected with A. hydrophila was determined by real-time quantitative PCR(qPCR). The target genes of miR-23a were predicted by RNAhybrid software and identified by dual-luciferase reporter assay system. Finally, the regulation of miR-23a on downstream genes was analyzed. The study found that the expression of miR-23a changed significantly at different time points of infection. In the dual-luciferase reporter assay and experiments of miR-23a agomir/antagomir transfection, the target genes were reversely regulated, and tbk1, glut1 were identified as the target genes of miR-23a. The expression of ldha, ldhba, pdha1a and pdha1b were suppressed after overexpression of miR-23a. These results showed that miR-23a was involved in the regulation of immune response in CIK cells after A. hydrophila infection. tbk1 and glut1 are the target genes of miR-23a. miR-23a can affect the expression of downstream genes by targeting GLUT1. The above results provide important ideas for the role of miR-23a in the regulation of immune response in bony fishes, and provide more theoretical basis for further understanding of miRNA-mediated multiple target genes to regulate the innate immunity of fish.

Abstract:Fishes of the family Muraenidae, commonly known as morays, are of commercial importance to fisheries worldwide. Morphologically, classification and identification in Muraenidae fish remain problematic because many closely-related species share common overlapping color patterns. Additionally, colorations and patterns in some Muraenidae species change greatly during their lives, making the juveniles quite distinct from their adult forms. To analyze the phylogenetic relationships of the Muraenidae fish based on the molecular level, and to clarify the species taxonomic controversies, 16S rRNA sequences of 26 Muraenidae species of 9 genera from China Sea were obtained by PCR amplification in this study. Combined with other Muraenidae sequences obtained from GenBank, the base composition, conserved sites, variable sites and genetic distance of the sequences were analyzed using Mega 7.0 software and the molecular phylogenetic trees were constructed by maximum likelihood and Bayesian inference methods. Results showed that: In the genetic distance results, the genetic distance values of 35 Muraenidae species ranged from 0.009 to 0.309. The maximum value (0.309) was found between species Gymnothorax pesudothyrsoideus and Scuticaria tigrina, while the minimum value (0.009) was between G. kidako and G. niphostigmus. Within the genetic distance among 10 genera，the maximum inter-genera value (0.187-0.279) was found between genera Gymnothorax and Uropterygius, while the minimum value (0.045-0.131) was between genera Enchelycore and Muraena. Additionally, certain inter-species distance values within the same genus were large and even exceeded the inter-genera values. Like some species in the genera Gymnothorax, Echidna and Enchelycore, it indicated that the genetic differentiation level in some species had exceeded the inter-genera levels. In the phylogenetic tree, Muraenidae species formed two major groups: subfamily Uropterygiinae and subfamily Muraeninae groups. Uropterygiinae group comprised two genera Uropterygius and Scuticaria, while Muraeninae group comprised 8 genera including Gymnothorax, Echidna, Enchelycore, Gymnomuraena, etc., which was consistent with the current morphological classification result. In Uropterygiinae group, two genera Uropterygius and Scuticaria formed a parallel sister branch. In Muraeninae group, species G. zebra formed a separate branch and was located at the base of the group, and the remaining species were clustered into another large branch. Within this branch, genera like Gymnothorax, Echidna, Enchelycore and Muraena could not form monophyletic group. Species in these genera were clustered together in different positions of the phylogenetic tree, revealing their polyphyletic evolutionary status, which was consistent with the recent molecular phylogenetic studies. For the species/genera that were in morphological classificational controversy, our phylogenetic results supported the view that G. zebra was classified into genus Gymnomuraena as a monotypic species. Scuticaria tigrina was classified into genus Scuticaria and its phylogenetic status was sister to the genus Uropterygius. Species Pseudechidna brummeri showed distant relationship with genus Strophidon, which might be separated from Strophidon and classified into genus Pseudechidna. Enchelycore pardalis was closely related with genus Muraena at the molecular level, but morphologically, certain Enchelycore basic characteristics also existed in the species. Whether it could be classified into genus Muraena, further comprehensive molecular and morphological studies are needed for confirmation.

Abstract:There is large catch of fishery in China, due to the rich nutrients, high moisture content, and protease activity in fish meat, fresh fish meat is more inclined to spoilage and deterioration after death than other meats, which reduces its utilization rate. Therefore, it is necessary to take effective preservation measures. Fermentation, as a traditional food processing and preservation skill, can be used to improve the taste and flavor of food, increase its nutritional value and edible safety quality. Fermentation uses microorganisms to convert carbohydrates into lactic acid. The accumulation of organic acids causes pH value to drop and inhibits the growth of spoilage bacteria. The enzymatic hydrolysis of microorganisms promotes protein denaturation and degradation, fat degradation and oxidation in fish meat, promotes texture improvement, nutritional value enhancement, and unique flavor generation of freshwater fish products, thereby realizing the value-added utilization of freshwater fish products. Fermented fish is a fish product that uses various enzymes in the fish and environmental microorganisms to form inhibitory metabolites through microorganisms based on pickling, reducing water activity, and preventing spoilage. Fermented food has a long history in China. Traditional fermented fish products have a simple production process and can be completed under ordinary household conditions. The process is mostly natural fermentation and manual operation, so there are more family-style workshops. The fish meat is inoculated and fermented with a good starter to prolong the storage time at room temperature and produce a good flavor. As one of the most common starters, lactic acid bacteria play an important role in the fermentation of various fish products. At present, there are many studies on the application of lactic acid bacteria in the fermentation of fish products, but there are few reports on the application of Lactobacillus plantarum, Pediococcus pentosus and L. paracasei in the fermentation of grass carp (Ctenopharyngodon idella), respectively. In this study, the number of microorganisms and physicochemical properties of fermented C. idella were determined in order to investigate the effects of different lactic acid bacteria during fermentation of C. idella and to further improve the quality of fermented fish products. In order to investigate the effect of different lactic acid bacteria on the quality of C. idella during fermentation, the microorganism, pH value, total acid, moisture content, whiteness, amino acid nitrogen, thiobarbituric acid, and volatile base nitrogen of C. idella dorsal meat were analyzed with different fermentation time (0-15 d). The results showed that compared with the natural fermentation, lactic acid bacteria grew rapidly in C. idella meat after inoculation, so the pH value decreased to 4.03±0.02 and the total acid content increased to (23.70±1.06) g/kg, which could effectively inhibit the reproduction of spoilage bacteria. At the same time, the whiteness of C. idella meat was improved. The content of amino acid nitrogen in C. idella meat was increased. The moisture content and the production of volatile basic nitrogen were reduced. Among them, at the end of fermentation, P. pentosaceus had the greatest impact on the decline of moisture content. Compared with the other two groups, LP group had higher whiteness and lower TVB-N value, but its ANN content was significantly lower than the other two groups, and L. plantarum had poor ability to degrade protein. In conclusion, inoculating lactic acid bacteria fermentation can reduce the lag time of fermentation start, delay the deterioration of C. idella meat, improve the nutritional value and color, and improve the quality of fermented C. idella.

Abstract:Bacillus velezensis is a novel species in the Bacillus genus which exhibits a broad spectrum of antimicrobial activities because it produces various secondary metabolites. The current research on B. velezensis mainly focuses on its use for the promotion of the growth of animals and plants, for antagonizing pathogens, and on investigating its gene cluster which plays significant roles in biological control, drug research and development, and food fermentation. The aims of this study are to explore the gene clusters related to antagonistic substances of B. velezensis LF01 strain based on the whole genome sequencing, and to evaluate the biological safety and biocontrol effect of the antagonistic substances of LF01 strain. In this study, the whole genome of LF01 strain was sequenced based on the third generation Nanopore sequencing platform, and its taxonomic status was identified based on ANI and DDH online analysis, and the genetic evolution at genome level. The gene clusters related to antagonistic substances of LF01 strain was analyzed based on antiSMASH software. The hydrolysis activity of LF01 strain to carbohydrate was analyzed based on CAZyme database. The toxicity of the antagonistic substances of LF01 strain to Oreochromis niloticus and Danio rerio was evaluated by intraperitoneal injection. The biocontrol effect of the antagonistic substances of LF01 strain to O. niloticus was evaluated by artificial infection after 5 d of feeding O. niloticus. The complete genome of LF01 strain had a total length of 3974023 bp and the GC content was 46.56%, and it contains 3843 coding genes. Compared to B. velezensis, the ANI and DDH values of LF01 strain were ≥97.66% and ≥80.10%, respectively. Furthermore, the genomic evolution analysis showed that LF01 strain was clustered with B. velezensis. These results indicated that LF01 strain was identified as B. velezensis at the genomic level. The LF01 strain contains nine gene clusters related to antagonistic substances, including bacillaene, bacillibactin, bacillomycin D, bacilysin, difficidin, fengycin, macrolactin H, plantazolicin and surfactin, which accounts for 8.83% of the total genome sequences. In addition, LF01 strain contains a large number of CAZymes related to the degradation of cellulose, hemicellulose, starch, chitin, pectin, peptidoglycan and glucan. The antagonistic substances of the LF01 strain showed high biological safety to O. niloticus and D. rerio, and they significantly enhanced the resistance of O. niloticus against S. agalactiae infection. In conclusion, LF01 strain contains a large number of gene clusters for biosynthesis of secondary metabolites related to antagonistic substances. The antagonistic substances were found to be safe for O. niloticus and D. rerio, and feeding O. niloticus with them significantly improved the diseases resistance of fish. Therefore, the antagonistic substances of LF01 strain have a broad development and application prospect as biocontrol agents to improve bacteria diseases control in aquaculture.

Abstract:Marine fishing vessels are now under localized management, but their offshore production has the characteristics of operating in waters under cross-regional jurisdiction. Traditionally, local fishing vessels generally have significant local characteristics because they follow local fishing experience and traditional fishing habits in inshore waters. However, with the steelization and large-scale of fishing vessels, the operating space of marine fishing continues to expand, so to understand and grasp whether the current marine fishing has regional characteristics differences, it has indispensable scientific and theoretical guiding significance for fishery sampling statistical survey and accurate fishery management. In this paper, the double-towing fishing vessels in Zhejiang, a major marine fishery province, are selected as the research object. Through a large sample random sampling survey, the annual production data of double-towing fishing vessels in three prefecture-level regions of Zhejiang Province are obtained, and the regional differences of fishing capacity (CPUE, catch per unit of effort) and catch structure are analyzed. The results show that except for September, there are significant regional differences in fishing capacity among the three regions, and Ningbo is relatively close to Taizhou, and there are significant differences in catch structure among the three regions in the whole year. Taizhou area is relatively independent and has its own category, while the similarity between Ningbo and Zhoushan is relatively high. Considering the interaction between fishing capacity and catch structure, the difference among the three regions is more significant. Although the production activities of China’s marine fishing vessels are wider and more flexible than those of 40 years ago, the differences in regional characteristics of fishing operations are still obvious, indicating that China’s marine fishery management should be more accurate. in order to continuously improve the level of spatial scientific management of marine fisheries in China.