Abstract:Developing modern aquaculture seed industry, and leading the green development of aquaculture, will secure the sustainable aquaculture industry in the future. New aquaculture varieties with high quality, high efficiency, multi-resistance and safety advantages should be encouraged to breed and popularize in aquaculture seed industry, and shift from pure high-production yield to high quality, high efficiency, feed saving, drug saving, stress resistant and wide adaptability varieties suitable for ecological and intensive aquaculture mode. In this paper, some problems existing in aquaculture seed industry were analyzed, and indicated that the foundation of high quality, high efficiency and multi-resistance aquaculture varieties is stress resistance. Arrangement of topics related to stress resistance select breeding technology, including stress response, stress recovery, stress coping style and the case studies of stress coping style in animal and poultry seed industry were discussed, the concept of environmental restricted breeding and the future direction of comprehensive stress resistance breeding technology were introduced。This study may lay the foundation to promote sustainable aquaculture in China.

Abstract:To elucidate the growth characteristics and reproductive strategy of the Pacific oyster Crassostrea gigas "Haida No. 3", the relationship between environmental factors and seasonal growth variations, gonadal development, the general nutrient components of the mantle, gonadal-visceral mass, gill and adductor muscle were examined from November 2016 to October 2017. Results indicated that in winter (from January to February), the growth of C. gigas "Haida No. 3" was slow and its gonad was in the resting stage. With the increase in water temperature (from March to April), gametogenesis began and the gonads of both sexes developed synchronously. The high growth rate of shell and the significant increase of wet weight were observed from April to May. During summer, the growth rate of shell declined along with gamete development. In July, C. gigas "Haida No. 3" lost weight due to gametes emissions. In autumn, the shell height and wet weight increased significantly. The biochemical analyses showed glycogen content of all tissues decreased significantly during sexual maturation, whereas the protein and lipid content in gonadal increased as the gametes matured. It indicated that carbohydrates provide energy for gamete development, lipids and proteins are major structural substances of gametes. During the autumn, protein was rich in the four tissues and provides the material basis for the rapid growth. Moreover, the major function of mantle is to secrete shell, its significant increases in glycogen and lipid content from August to September indicating that the rapid growth of the body requires a certain amount of energy reserve. The present study demonstrated that the growth and reproduction activities of C. gigas "Haida No. 3" are affected by seasonal changes in seawater temperature and are closely related to the nutrient composition of tissues. Organism experience the rapid growth period in spring and autumn, while summer is the spawning season. Glycogen is the main source of energy for growth and reproduction, lipids are the major structural substances of gametes, and protein is the material basis of rapid growth.

Abstract:The changes in the spermatozoa number in spermatangia and seminal receptacles at different times after copulation, and the structure of the seminal receptacle were examined by using experimental ecology and tissue section techniques to reveal the mechanism of sperm storage in seminal receptacle and sperm utilization during oviposition. The results showed that paired seminal receptacles were located in the raised ventral portion of the buccal membrane, and opened inside the buccal membrane. The entire seminal receptacle was connected by a central duct, which had many folds and cilia on its inner surface. Each seminal receptacle had 12-20 sperm storage bulbs surrounded by circular muscles. A large number of spermatozoa were stored in sperm storage bulbs, and the heads of most spermatozoa faced toward the inner surface of sperm storage bulbs. After one copulation, the utilization of spermatozoa in spermatangia and seminal receptacles could be divided into three stages:① the utilization of spermatozoa mainly from spermatangia (1-2 d after copulation); ② the transition from the utilization of spermatozoa in spermatangia to spermatozoa in seminal receptacles (2-3 d after copulation); ③ the utilization of spermatozoa mainly from seminal receptacles (more than 3 d after copulation). These results suggest that spermatozoa released from the spermatangia reached the seminal receptacles through the folds on the surface of the female buccal membrane. Spermatozoa entered the sperm storage bulbs through self-movement and cilia fluttering on the inner surface of the central duct. The distribution of spermatozoa inside the sperm storage bulbs was highly regular, and the heads of most spermatozoa faced toward the inner surface of the sperm storage bulbs. During spawning, females preferred to use spermatozoa from spermatangia to fertilize their eggs. When spermatozoa in spermatangia were insufficient, spermatozoa in seminal receptacles were released gradually by muscle contraction and cilia fluttering, and ova were fertilized externally near the female buccal membrane.

Abstract:Aiming to improve the growth and survival performance of "Pingyou No. 2" flounder in different aquaculture areas, in this study, broodstocks which were selected based on the results of genetic parameter estimation and genome selection for growth and resistance traits, wre used to produce "Pingyou No. 2" families. In total, 28 families were produced. Then these families were cultured in different sites (Site 1:Hebei; Site 2:Shandong). Genotype by environment interactions for growth and survival traits were estimated based on mixed linear models. The average daily gain was 1.5 g/d and 1.2 g/d in Site 1 and Site 2 respectively, and the survival rate was 81.4% and 82.2% in Site 1 and Site 2 respectively. Both traits showed a superior performance in two sites. The genetic correlations for harvest body weight and survival traits between both environments were 0.57 and 0.82 respectively, indicating that there was a significant genetic by environment interaction effect for harvest body weight, but not for survival. These results suggest that "Pingyou No. 2" flounder showed good growth and resistance performance in different sites. The harvest body weight and survival traits still have certain selective potential. Hence, to ensure a good demonstration and extension results, it is necessary to improve and optimize the seed production techniques (e.g., seeds with good environmental adaptability) for achieving the advantage of fast growth and high survival rate of olive flounder in different aquaculture environments.

Abstract:Hybridization is the most widely used and an effective way of artificial breeding in aquaculture. This study using Epinephelus lanceolatus as female parent, E. moara as male parent by artificial insemination technology has conducted the interspecific cross experiment, and developmental sequence of fertilized egg, and growth of larvae, juveniles and young fish were observed and studied, and then with the phenotypic of traits, the parent and the hybrid F₁ generation "Yunlong grouper" (E. moara ♀×E. lanceolatus ♂) were compared. Results showed that the embryo was oval, transparent, floating, the fertilized eggs size (0.787±0.013) mm, each egg has one oil globule in the center. At sea-water temperature of 24℃, salinity 30, pH 7.8, embryos can develop normally, according to the data, six periods including 25 stages of embryos were recorded,which were fertilized egg, cleavage, blastula, gastrula, organogenesis and hatching period. The length of newly hatched larvae (1.595±0.015) mm shows the feasibility of the cross;3 days after hatching, the yolk membranes disappeared and became the late larva, with a total length of (2.530±0.023) mm. 52 days after hatching, entering the juvenile stage, the total length (17.500±1.915) mm, the length of the second dorsal fin spine (5.795±0.049) mm, and the length of the first pelvic fin (2.992±0.911) mm. When the dorsal fin spine contracted to the minimum value (4.460±0.600) mm, scales began to appear and body color began to darken. The second dorsal fin spine and the first pelvic fin spine completely degenerated. The body shape was similar to that of the adult fish. The whole body was covered with scales. The growth comparison results showed that the growth rate of the direct and reciprocal cross F₁ generation was between those of the parents, which was faster than that of E. moara, and slower than that of E. lanceolatus, and the growth rate of the reciprocal cross F₁ generation was slower than that of the direct F₁ generation. The results provide a basis for the formation of hybrid heterosis traits and genetic analysis of grouper.

Abstract:Pseudorasbora parva was originally distributed in Jinshajiang and Nanpanjiang in Yunnan. However, it has been widely distributed in all major river systems and has become an invasive fish in other four river systems in Yunnan. In order to reveal the difference of genetic diversity and genetic differentiation of P. parva between Yunnan after the invasion and the native region, we collected 220 samples distributed in 13 different sites of Lancang River, Nujiang, Honghe and Irrawaddy River in Yunnan, and 6 native populations in Yellow River, Yangtze River, and Pearl River. Here we analysed a 1 072 base pair fragment of the mitochondrial cytochrome b gene (Cyt b) to examine the genetic diversity and genetic structure. A total of 72 mutation sites and 25 Cyt b haplotypes were identified. The haplotype diversity and nucleotide diversity of the four river systems in Yunnan were 0.828±0.014 and 0.005 44±0.001 18, respectively. Haplotype diversity of the introduced populations from the four river systems in Yunnan was higher than that of the native populations. The haplotype maximum likelihood tree and haplotype network map show that the haplotypes of the Yellow River population are special, while haplotypes in the invasive populations in Yunnan were mixed with those in Yangtze River and Pearl River. It is speculated that P. parva in Yunnan mainly came from the Yangtze River and the Pearl River, which was consistent with the history of introduction of economic fish in Yunnan Province. Analysis of molecular variance (AMOVA) revealed significant genetic subdivision among individuals within populations and among populations within rivers but not among rivers, indicating distribution of genetic diversity was inconsistent with contemporary hydrological structure. That may be the human effect who introduced them from many native regions. The results of Fu's Fs neutral test showed that there was no expansion of the invasive population of P. parva in Yunnan. In the subsequent management of the invasive population of P. parva in Yunnan, it is necessary to avoid the exchange of special haplotype groups with other regional groups, and to reduce the introduction of fish from different river systems. In addition, the development of new ways to utilize P. parva may be a useful way to control their population and reduce the damage to indigenous species and fishery culture in Yunnan.

Abstract:Based on the trawl data of fishery resources collected from comprehensive surveys from May 2016 to February 2017 in Yueqing Bay, species composition, biodiversity index, community structure and its relationship with environmental factors were examined by cluster analysis, multivariate statistical analysis and redundancy analysis. The results showed that a total of 43 species of crustacean were identified, which belonged to 28 genera, 18 families and 2 orders. Portunus trituberculatus, Charybdis japonica and Parapenaeopsis hardwickii were annual dominant species. The species number of crustacean was the greatest in summer and the least in winter which varied significantly in four seasons, while the composition of dominant species changed slightly. The research about crustacean species at different depth indicated that the richest crustacean were at depths of 5~10 m while fewer species at depths of less than 5 m and more than 10 m. The results of One-Way ANOVA showed that the richness index (D) of crustacean community at different depth were distributed significantly, and there were no significant differences in evenness index (J') and diversity index (H'). Redundancy analysis suggested that temperature, depth and turbidity were the most important environmental factors affecting the crustacean species composition and community structure characteristics. In particular, the depth has a great influence on the community structure of crustacean.

Abstract:In this study, using twelve novel microsatellite markers, we established a paternity test technology for Acanthopagrus latus based on a mixed family of A. latus including 112 parent individuals and 393 offspring individuals. Genetic diversity data demonstrated that there were 119 alleles observed and the mean number of alleles (N_a), observed heterozygosity (H_o), expected heterozygosity (H_e) and polymorphism information content (PIC) were 9.91, 0.651, 0.661, 0.621, respectively. Paternity analysis showed that the combined probability of exclusion reached 99.58% when both parents were unknown (confidence level, 95%) by 12 loci. And, the combined probability of exclusion reached 99.1% when both parents were unknown (confidence level, 95%) by 8 loci. Consequently, the 8 high polymorphic microsatellite markers (AL49, AL37, AL01, AL20, AL14, AL18, AL15 and AL51) made up the system of paternity test for A. latus. The cumulative exclusion rate of their parents was 99.1% without parents' gender by 8 loci. The rate of assignment success for the real data set was only 89.31%. In conclusion, the combination of this novel 12 microsatellite markers in our study provided highly effective testing tools for the paternity identification, population breeding and molecular-assisted family management in A. Latus.

Abstract:Conger myriaster is a commercially important species in China. The population structure of C. myriaster remains a mystery and the spawning activities of C. myriaster are not well known because larvae and adults of this species have separate habitats and its spawning grounds have not been discovered. Several hypotheses on the population structure and spawning grounds of C. myriaster have been proposed. Takai described that this species has a single population with a single spawning site. On the other hand, there are also some indications of the possibility of multiple spawning populations. So it is important to clarify the population structure of C. myriaster to provide basics for future detailed examination on its life history. If this species has multiple populations, there may be some morphological and genetic differences in the samples collected from different sea areas at the same time. In the present study, we combined morphological and genetic methods to understand the morphological and genetic differences of C. myriaster in the two different localities of Zhoushan (East China Sea) and Qingdao (Yellow Sea). The morphological studies were conducted by using one-way ANOVA, discriminant analysis and principal component analysis. Genetic analysis of the mitochondrial DNA (mtDNA) sequence was carried out. Results from morphological studies indicated that there were intermuscular bones of "I" type in the muscle of the C. myriaster from Zhoushan group but not in Qingdao group. The results of multivariate statistical analysis showed that there were significant differences in seven morphological measurements (preanal length, head width, snout length, rictus length, eye diameter, predorsal length) of C. myriaster from different groups, and these measurements were all over the body. In principal component analysis, C. myriaster from different groups could be distinguished by a scatter plot based on the first two principal components. Discriminant analysis results showed that the correct diserimi-nation rates of Qingdao and Zhoushan groups were 100% and 94.7%, respectively. The results of multivariate statistical analysis methods showed that there were significant differences in morphology between the two groups. But according to the Mayr's 75% rule, most differences in morphology between the two groups were characterized under-subspecies. Genetic results suggested that there was no significant difference in genetic diversity between samples collected from different locations on the level of mtDNA. The neighbor-joining tree showed no genealogical clade. The pairwise fixation index F_ST revealed no significant genetic difference between the two groups. The present study provides morphological and genetic basis for the taxonomic status of the C. myriaster population in China. It also provides useful information for the population assessment, management and conservation of C. myriaster.

Abstract:In this study, eleven representative seaweeds were sampled in raft-mussel-culture area, Gouqi Island during the flourishing period of seaweeds. And biological parameters of seaweeds and amphipods associated with each seaweed species were measured. Results showed that the population characteristics of Gammaridea and Caprellidae attached on different seaweed species were significantly different. Both of the highest population density and the largest body size of Gammaridea appeared on Pachydictyon coriaceum. And the highest population density and the largest body size of Caprellidae appeared on Ganonema farinosum and Grateloupia constricata, respectively. Moreover, seaweed species with relatively lower biomass tended to support higher population density of Gammaridea and Caprellidae and smaller size of Caprellidae, but had no significant effect on size of Gammaridea. Furthermore, seaweed with higher surface area to biomass ratio tended to support higher density and larger body size of Gammaridea, but had no significant effect on density or body size of Caprellidae. In a word, our investigation indicated that seaweeds community paly different functional roles in structuring seaweed-associated amphipods population characteristics in mussel raft culture area, which were determined by the diverse seaweed biological traits.

Abstract:Using high-throughput sequencing,we characterized 20 pairs of polymorphic microsatellite primers from Crassostrea sikamea genome, and we examined the markers in a wild population. A total of 330 alleles were found in 25 microsatellites.The observed number of alleles (N_a) ranged 6-39 in average of 16.500 0,and the effective number of alleles(N_e) ranged 1.352 9-33.361 7. The observed and expected heterozygosity values range 0.200 0-1.000 0 and 0.265 6-0.987 7, respectively.The Shannon Weiner index ranged 0.648 3-3.585 8 and Polymorphic information content (PIC) ranged 0.254 5-0.969 2. 16 microsatellite markers accord with Hardy-Weinberg equilibrium. Using these loci to analyze the genetic diversity of a cultured population, the average number of alleles was 10.25; the average number of N_e was 5.843 4. The observed heterozygosity (H_o) average was 0.639 1; the expected heterozygosity (H_e) average was 0.763 6; the Shannon-wiener index (I) average was 1.791 4; and the polymorphic information content (PIC) average was 0.720 7. It was found that the genetic diversity of C. sikamea cultured population was lower than that of the wild population, but it maintained a high-genetic diversity. The results of this study indicate that in the artificial breeding process of C. sikamea, the use of a large number of parents for breeding can effectively prevent the decline of genetic diversity of the cultured population, but artificial breeding also has a certain impact on the genetic diversity of the cultured population. The 20 loci were surveyed the cross-species proportions in C. angulate, C. gigas, C. hongkongensis, C. ariakensis, Saccostrea cucullata, Ostrea mordax and Hyotissa hyotis. Loci XB1-6, XB1-39, and XB1-45 can amplify the target band in 8 species, and the XB1-41 can only amplify the target band in C. sikamea.

Abstract:This study was conducted to explore the ecological advantages in the rice-fish co-culture systems in Hani Terrace. High-throughput sequencing technique was used to analyse the bacterial diversity of water, surface soil, root soil and carp intestine (16S rDNA) between rice-carp co-culture (RC) and rice-monoculture (CK) models. The results showed that Proteobacteria, Actinomycetes, Firmicutes, Chlorobacteria, Acidobacteria, Bacteroidetes, Nitrospira and Bacteroidetes were the dominant phyla of the rice-fish co-culture systems. Compared with CK group, the relative abundance of Chlorobacteria and Firmicutes in RC surface soil significantly increased, and the significantly increased genera mainly included Anaerolineaceae_norank, Aminicenantes_p_norank, Chloroflexi_p_unclassified, Clostridium_sensu_stricto_1, Clostridium_sensu_stricto_12, Syntrophaceae_f_norank, Gemmatimonadaceae_f_norank. The relative abundance of Chlorobacteria in root soil was significantly increased in RC group compared with CK group, and the significantly increased genera included Anaerolineaceae_norank, Sideroxydans, Aminicenantes_p_norank, Chloroflexi_p_unclassified, Gemmatimonadaceae_f_norank . The dominant phyla of intestine bacterial communities in RC group were Firmicutes and Proteobacteria, and the relative abundance of Firmicutes was 58.59%. The pH, total nitrogen, ammonia-N, nitrate-N, hydrolysis nitrogen, total phosphorus, available phosphorus and soil organic carbon contents were lower in the surface soil of RC group than the CK group, and the pH, total P and available P were significantly reduced. Sobs and PD indexes of bacteria in surface and root soil of RC group were also increased, and these two indexes were significantly increased in the surface soil of RC group. In brief, the introduction of fish to rice farming ecosystems changed the physico-chemical properties and bacterial community structure of surface soils, and also affected the microbiota community structure of root soil and fish intestine to a certain extent. Our preliminary results provide microbial ecological evidences for the advantages of rice-carp co-culture over rice monoculture system.

Abstract:In order to understand the structural characteristics of MR and its role in anti-infective immune responses in Leptobarbus hoevenii, we cloned and sequenced the MR of L. hoevenii. Subsequently, real-time polymerase chain reaction (qRT-PCR) assay was used to measure the expression of the MR in the tissues of L. hoevenii with or without F. columnare infection. The results showed that the MR of L. hoevenii (LhMR) open reading frame was 4 296 bp, encoding 1 431 amino acids (aa). The amino acid sequence and molecular structure of LhMR are highly similar to the MRs from other animals, i.e., containing an extracellular ricin-like β-type clover domain (RICIN), a fibronectin type II domain (FNII) and eight tandem C Lectin-like domains (CLECTs), a transmembrane region and a short intracellular region. The mRNA of LhMR was widely expressed in 11 tested tissues, including spleen, kidney, heart, brain, skin, muscle, gills, liver, post intestine, fore intestine and mid intestine, with the highest expression level in the spleen. The mRNA expression of LhMR was significantly increased in the spleen, intestine, kidney and gills of L. hoevenii infected by F. columnare measured by qRT-PCR. Furthermore, the protein expression of LhMR was also increased in the spleen, kidney and gill of L. hoevenii infected by F. columnare revealed by immunochemistry assay. By Hematoxylin eosin staining, there were various pathological changes observed in the body kidney, intestine, liver and gills. In the body kidney, there were blood cells infiltrated in the renal tubules with necrosis in epithelial cells. The wall of intestine became thinner with diffused necrosis. Numerous vacuoles were observed in the liver cells. Gill lamella showed swollen, disordered, necrosis and detached. The results revealed that LhMR plays an important role in the immune responses of L. hoevenii infected by F. columnare and this will provide some reference for prevention and therapy strategies against columnaris disease.

Abstract:In order to effectively prevent the harm of bacteria and other pathogenic microorganisms to S. broughtonii, we observed the response process of the lysozyme activity in different tissues of S. broughtonii infected by Vibrio anguillarum, and explored the immune function of the lysozyme in the body of S. broughtonii. In this experiment, 20-month-old S. broughtonii individuals were infected by injecting live bacteria, and 16 individuals were randomly selected. And 1 mL (about 1×10⁹ bacteria) V. anguillarum suspension was injected into the axe foot of each individual as the infection group. 16 randomly selected individuals were not injected with V. anguillarum as the control group. The two groups were cultivated in clean seawater for 4, 12, 24 and 48 h. In each group, randomly selected 4 S. broughtonii individuals were dissected for the blood, mantle, gill, axe foot, hepatopancrea and adductor muscle tissues. The concentration of lysozyme was determined by ELISA kit. The results showed that for the invasion of V. anguillarum, the lysozyme content in the blood of S. broughtonii rapidly increased from the normal low value and maintained a high level, indicating that the blood is one of the main immune tissues of S. broughtonii body defending against pathogen. In the case of no infection, S. broughtonii mantle always maintained a high lysozyme concentration to prevent the interference of the external water environment. The concentration of lysozyme in infected gills and axe foot are significantly higher than the normal values after the injection for 24 hours, indicating that the mantle, gills and axe foot were the first barriers for S. broughtonii body to contact with the outside world which can also respond to the invasion of pathogenic bacteria, but the response was delayed compared with the blood. The lysozyme content of hepatopancrea and adductor muscle did not change significantly. And it was speculated that hepatopancrea and adductor muscle were not important immune tissues or organs of S. broughtonii. The results of this study can provide relevant parameters for the study of disease resistance and immune mechanism of S. broughtonii.

Abstract:The susceptibility of Pyropia haitanensis and its bacteria to chloramphenicol, oleandomycin and cefotaxime was studied. They were combined with ampicillin, kanamycin and gentamicin to optimize the sterilization effect of P. haitanensis thalli. The effects were evaluated by plate count, qRT-PCR and 16S rRNA sequencing analysis. The results show that when P. haitanensis thalli was treated with ampicillin (300 mg/L), kanamycin (100 mg/L) and gentamicin (100 mg/L) mixture for 18 h, and then treated with chloramphenicol (50 mg/L), cefotaxime (200 mg/L) and oleandomycin (50 mg/L) mixture for 4 days, the health rate of the thalli is above 96.3%, and the inhibition rate of bacteria reached 99.9%. According to the results of qRT-PCR and 16S rRNA, the number of bacteria in this antibiotic combination was nearly reduced by half as compared with the first three antibiotic combination, and the bacteria abundance and diversity index were also significantly decreased. Among them, Pseudoalteromonas, Altererythrobacter, Salinimonas and Marinobacter were specifically inhibited. These results indicated that the optimal combination of multiple antibiotics could significantly affect the community structure of epiphytes on the thalli, which could be inhibited to the minimum, but still could not achieve the absolute sterilization.

Abstract:In order to understand the expression profile of JAK (Lv-JAK) and STAT (Lv-STAT) genes in Litopenaeus vannamei during the infection of pathogenic bacteria, relative expressions of Lv-JAK and Lv-STAT genes were analyzed in this study. Relative expression profile of Lv-JAK and Lv-STAT in different tissues and during the infection of Bacillus thuringiensis were analyzed by semi-quantitative PCR and quantitative real-time PCR,respectively. The results showed that transcript of Lv-JAK and Lv-STAT was mainly detected in gill, intestine and heart. The relative expressions of Lv-JAK and Lv-STAT were significantly up-regulated in gill tissues at the middle and late stages of B. thuringiensis infection (24~72 h). In intestine, the relative expression of Lv-JAK was significantly up-regulated at 6 and 24 h, while that of Lv-STAT was significantly up-regulated at 24 and 72 h. These studies indicated that JAK and STAT participated in the innate immune response induced by B. thuringiensis in L. vannamei. Understanding the expression profile of JAK and STAT in response to B. thuringiensis infection will be helpful to study the function and regulatory mechanism of shrimp JAK/STAT signaling pathway in response to bacterial infection.

Abstract:To evaluate the differences of spoilage potential of Shewanella and Aeromonas in refrigerated seafood, growth curves and production of trimethylamine (TMA), biogenic amines and total volatile basic nitrogen (TVB-N) in S. baltica and A. salmonicida isolated from Larimichthys crocea were measured at 28℃ and 4℃. And trimethylamine reductase (torA) gene in the two strains were amplified, and similarity, physicochemical properties and spatial structures of TorA protein were compared by bioinformatics. A. salmonicida grew faster at 28℃, while S. baltica grew faster at 4℃. Compared with more amount of cadaverine in A. salmonicida, S. baltica produced the higher levels of TMA, biogenic amines, and TVB-N in refrigerated fish juice. The torA genes of 2 490 bp and 1 959 bp were amplified from S. baltica and A. salmonicida respectively, and similarity of TorA protein in its same genus was higher than 97%, and similarity between the two strains was only 36.90%. The molecular weight and isoelectric point of TorA protein in S. baltica were about 92.3 ku and 6.52, while those were about 90.6 ku and 6.74 in A. salmonicida. The highest amino acid of the predicted protein was glycine and alanine in two strains respectively, resulting in the significant difference of protein spatial structure. The expression levels of torA and ornithine decarboxylase ODC genes in S. baltica were 1.26 and 19.04 times compared to A. salmonicida. Thus, S. baltica and A. salmonicida are psychrophilic spoilage strains in marine products, in which S. baltica has stronger ability to produce amine metabolites due to specific physicochemical properties of TorA protein and its high expression. The study provides theoretical support for revealing the mechanism of microbial spoilage in seafood.

Abstract:A 10-week feeding trial was conducted to investigate the effects of dietary arginine levels on the growth performance and immunity of Epinephelus coioides. Seven isonitrogenous and isolipid diets were formulated with arginine contents of 2.13%, 2.42%, 2.71%, 2.95%, 3.20%, 3.48% and 3.74% (dry matter) respectively. Randomly selected healthy groupers[initial weight (80.11±0.03) g] were divided into 7 groups, with 3 replicates in each group and 25 fish per replicate. It was found that the weight gain rate (WGR) and specific growth rate (SGR) of 2.71% group were significantly higher than 2.13% and 2.42% groups, and the feed coefficient (FCR) was significantly lower than that 2.13% group. The protein efficiency rate of the 2.71% group was significantly higher than those of 2.13% and 3.48% groups, and the protein deposition rate of the 2.71% group was not significantly different from that of 2.95% group, which was significantly higher than that of other groups. Broken-line model analysis of weight growth rate against dietary arginine levels indicated that the optimum requirement of arginine for maximum growth of subadult grouper was 2.73%, corresponding to 5.40% of dietary protein on a dry weight basis. There was no significant difference between 3.20% serum insulin (INS) and 3.48% groups, which were significantly higher than other groups. The level of TOR gene in muscle of 3.48% group was significantly higher than those of 2.13%, 2.42% and 2.71% groups. The expression of b^0,+ AT gene in the hindgut of 2.42% group was the highest, which was significantly higher than that of other groups. There was no significant difference in the expression of b^0,+ AT gene of kidney between 2.95% and 3.20% groups, which was significantly higher than that of other groups. In conclusion, the appropriate level of feed arginine can stimulate the secretion of IGF-I of E. coioides to promote the synthesis of protein and improve the expression of immune genes of the intestine, kidney and liver of fish to improve the body immunity, and ultimately promote the growth of fish.