Abstract:is a large marine pelagic predatory fish species in the global warm temperate ocean, which is mainly distributed near the offshore rocks and reefs of the Bohai Sea and Yellow Sea of China. In recent years, most research has focused on its breeding and breeding technology at home and abroad, whereas few studies have been conducted on its genome and group composition. The complete mitochondrial DNA was extracted from the somatic side muscles of was obtained using second generation sequencing and splicing with software of DNAStar. The sequence length was 16609 bp, and the base composition was A (26.68%), G (17.84%), C (30.12%), and T (25.36%). It contained 13 protein-coding genes, 22 tRNA genes and 2 rRNA genes. Except for , all the other genes were encoded on the heavy strand (H strand). The A+T content of the complete mitochondrial genome sequence and protein-coding genes were 52.05% and 51.085%, respectively. There was a strong bias toward A+T in the genome of . There were two repeated sequences scattered in the genes. One was located in the middle part of the sense strand of the gene sequence, and the other was located in the upper part of the antisense strand of gene sequence. All tRNA genes had typical cloverleaf structure except tRNA^Gly. Its start-stop sites and codons of protein-coding genes, except , which inhabits in the oceans of Japan. The were shorter than those of . It was preliminarily assumed that there were genetic differences between . The NJ-tree based on the complete mitochondrial DNA genomes showed the evolutionary position of relative to that of 18 other Carangidae species. The results showed that the . Furthermore, had a closer relationship than others in the tree, whereas S. nigrofasciata. This study provides basic data for solving different geographical population and kinship relations of .

Abstract:To fully determine the phylogenetic relationship and ossicle evolution of holothurians, the ossicles of 13 representative sea cucumber species in the China Sea were observed by scanning electronic microscopy and the mitochondrial 16S rDNA gene from eight specimens were amplified and sequenced. The results demonstrated that ossicles of the 13 sea cucumbers could be classified into seven types, which were termed as table, pseudo-table, button, rod, plate, rosette, and oblate grain. The length of 16S rDNA fragments amplified from eight sea cucumbers was approximately 465 bp. These fragments were enriched in AT bases with an average A+T content of 55.8%, which is in accordance with the characteristics of mitochondrial DNA in invertebrates. 16S rDNA sequences of 11 sea cucumbers obtained from GenBank were combined with sequences from our study to construct a phylogenetic tree. was regarded as a control group. Neighbor-joining (NJ) and minimum evolution (ME) methods provided almost identical results. Genetic relationships between in Holothuriidae were rather close and shapes of their ossicles were also similar, thus they could be divided into the same genus; Caudinidae, Phyllophoridae, Sclerodactylidae, and Cucumariidae were clustered with Stichopodidae, and separated from Holothuriidae. Contrary to traditional taxonomy, our study met the criteria of the newest taxonomy system, wherein Aspidochirotida was removed and Holothuroidea was redivided into seven orders, including Dendrochirotida, Synallactida, Molpadida, Persicalida, Holothuriida, Elasipodida, and Apodida. Based on molecular phylogenetic trees and morphological data of ossicles, we hypothesized that ossicles of sea cucumbers in Holothuriidae underwent slow evolution from a complex shape, such as table and button, to simple patterns, such as rosette and oblate grain. Furthermore, considering that the rod in , we concluded that ossicles in Holothuriidae underwent slow transition rather than direct evolution.

Abstract:The ubiquitin-proteasome system (UPS) is an important system for regulating protein degradation and function. In order to evaluate the effects of acute crowding stress on flesh quality and UPS in fish, we randomly distributed (initial body weight:56.88 g±10.54 g) into 6 aquarium tanks (length:200 cm, wide:100 cm, depth of water:55 cm) at two stocking density (three replicates for each group). Water temperature (17.0±0.5)℃, pH (7.5±0.3) and dissolved oxygen (7.0 mg/L) were maintained at the same level in each group. Fish serum and muscle samples were collected at 0 h, 1 h, 6 h, 12 h, 24 h, and 48 h after crowding stress as well as at 6 h and 168 h after the crowding stress was removed (treatment group stocking density changed from 100 kg/m² to 10 kg/m²). The serum cortisol, muscle texture, the mRNA expressions of , and genes related to UPS as well as the content of ubiquitinated protein in fish muscle were investigated. The results showed that the serum cortisol level significantly increased after acute crowding stress, suggesting the crowding environment led to fish stress. The serum concentration of cortisol recovered to the control level after 168 h of recovery. Crowding stress also exerted an influence on muscular texture characteristics of cultured grass carp. Muscular hardness and cohesiveness decreased significantly in grass carp suffering from cute crowding stress, and the two flesh quality indexes recovered to the level of the control group after 168 h of post-stress recovery. However, muscular adhesiveness, chewiness and resilience were significantly higher than those in the control group at the end of the experiment. Compared with the control group, the mRNA expressions of in muscle of fish stocked at the treatment group were significantly increased after 48 h of crowding stress, and then returned to the control level after 168 h of post-stress recovery. It is implied that the acute crowding environment might cause cellular stress in fish. In the UPS pathway, the mRNA levels of were significantly increased after crowding stress. The transcriptional levels of these genes did not returned to the control level after 168 h of post-stress recovery. Moreover, a significant higher content of ubiquitinated proteins occurred in the dorsal muscle of fish in the treatment group at 6 h and 12 h after crowding stress. Subsequently, there were no significant difference in ubiquitinated proteins of fish stocked at two densities, while ubiquitinated proteins in the treatment group significantly declined compared to the control group at 168 h of recovery. It was concluded that the acute crowding environment induced the stress response and altered the muscular texture as well as improved muscle UPS activity. The deleterious effects of acute crowding stress on fish physiological function and muscular texture were reversible. Post-stress recovery time should be extended more than 168 h so that the stressed fish reestablish the homeostasis on UPS.

Abstract:The Chinese mitten crab, , is one of the most important aquaculture species in China, and is widely distributed in Eastern Asia. This study was conducted to evaluate the genetic diversity and genetic structure of cultured and wild populations of River, and Liaohe River based on the mitochondrial DNA D-loop region. The results showed that the length of the D-loop gene segment used in this study was 477 bp, which contained a total of 234 variation sites and 131 parsimony information sites for all tested samples. The 262 samples from six populations had 110 haplotypes, which consisted of 90 unique haplotypes and 20 shared haplotypes. The haplotype diversity index () of the six populations ranged from 0.88889 to 0.96522, and the nucleotide diversity index () ranged from 0.00887 to 0.01602. The genetic diversity levels of cultured populations were HC > YC > LC, whereas the levels of wild populations were HW > LW > YW(LC and LW indicate cultured and wild population of Liaohe River respectively, HC and HW indicate cultured and wild population of Yellow River respectively, YC and YW indicate cultured and wild population of Yangtze River respectively). The genetic distance () ranged from 0.0119 to 0.0173 for the six populations. Regardless of their wild or cultured status, the genetic distance between the Liaohe and Yangtze populations was the smallest among three rivers. The genetic differentiation index () was 0.12938 among the six populations. A neutral test of the six populations showed the values of Tajima's were negative. The population's Tajima's value test showed that these groups have a complex population history, and it is speculated that has had a large-scale group expansion event. The genetic distances of the six populations were analyzed. It was found that the overall genetic distance was not large. The results of genetic differentiation showed that there was no significant difference between the LW and YC, and YC and YW populations. The results of the AMOVA analysis of the six populations showed that population genetic differences mainly occurred in the six population. The phylogenetic trees may have resulted from of a certain degree of confounding caused by the cross-regional introduction of the Chinese mitten crab population in the Liaohe River system. These results provide valuable information for the evaluation, protection, and exploitation of resources.

Abstract:The melanocortin system consists of melanocortin peptides derived from the proopiomelanocortin gene, five melanocortin receptors, two endogenous antagonists, and two ancillary proteins. It plays a role in many important physiological functions of terrestrial animals. Studies on rodents have affirmed the role of melanocortin receptor 3 () in feeding behavior and energy regulation. However, the function of in fish, including basic information, is not well understood. Thus, to determine the initial value of fish and assess the role of MC3R in fish feeding behavior and energy regulation, the full-length cDNA of was cloned. The nucleotide sequence and deduced amino acid sequence were analyzed using bioinformatics methods. Blood glucose and cortisol levels were detected, and real-time quantitative PCR was employed to characterize the tissue expression profile and expression during fasting and refeeding. The results showed that cDNA encodes a protein of 327 amino acids, which shares a high amino acid sequence identity with that of other animals and is characteristic with the typical seven transmembrane domain. Phylogenetic analyses showed that the cluster was within the MC3R clade of the Cyprinidae MC3Rs. The tissue expression analysis revealed that was highly expressed in the hypothalamus, pituitary, liver, and ovary, whereas its expression was much lower in the other detected tissues. During fasting and refeeding, mRNA expression in the hypothalamus and pituitary showed a periodic variation with higher expression near the first feeding time every day both in the experimental and control groups. Furthermore, the expression of mRNA was significantly increased and was higher than that in the control group after 72 h and 14 d fasting in the hypothalamus ( < 0.05), whereas similar results occurred in the pituitary at 72 h fasting and 6 h after refeeding ( < 0.05). In addition, an obvious change in blood glucose and cortisol was only observed with long term fasting ( is not only highly conservative in genetic information, but also in its tissue expression profile and physiological function during the evolutionary process, and may play an important role in feeding behavior and energy regulation.

Abstract:The mud crab is widely cultured in the coastal areas of southern China because of its short growth cycle, high nutrition value, large market demand, and high economic value. At present, most of the mud crab larvae come from the natural populations, which puts great pressure on its natural resources. Therefore, establishing industry-scale artificial reproduction and using artificial larvae will effectively reduce the harvest of wild resources and protect the natural resources of the mud crab. On the other hand, embryonic development is the basis of artificial reproduction and individual development. At present, the research on embryo development of mud crabs is mainly focused on morphological observation and measurement of physiological and biochemical indexes. Knowledge concerning the mechanisms regulating embryo development at molecular level is poor. Commonly, quantitative real time PCR (qRT-PCR) is used to accurately quantify mRNA expression levels. However, this technique is highly dependent on stably expressed housekeeping genes to avoid experimental errors and variations. Furthermore, the universal ideal reference gene suitable for all experiments has not been obtained. To identify the most stable internal reference genes for studying gene expression in different embryonic developmental stages of mud crabs, tubulin alpha 1a (), ribosomal protein S6 kinase (), glyceraldehyde-3-phosphate dehydrogenase (), 28S ribosomal RNA (28S), 18S ribosomal RNA (18S), and elongation factor 1A () were employed to quantify their expression by qRT-PCR. The qRT-PCR results were used to evaluate their expression stabilities by three algorithms-geNorm, NormFinder, and BestKeeper. The geNorm program analysis showed that the expression of had the highest stability. The results also suggested that it was better to use these two internal reference genes together to correct the quantitative results of target genes. NormFinder analysis showed that had the most stable expression among the nine internal candidate reference genes. BestKeeper program analysis showed that the standard deviation and coefficient of variation of were the lowest among the nine candidate genes. Combining the three internal reference gene screening softwares, , could be used to correct the expression of target genes in different embryonic developmental stages. Furthermore, we found that the expression of many published internal reference genes was not stable enough under our conditions. In our experiment, commonly used internal reference genes such as -actin, 18S, and 28S were not suitable for standardizing gene expression data in the different embryonic developmental stages of .

Abstract:The Kumamoto oyster (Amemiya, 1928) is mainly distributed in Eastern Asia, from the southern coast of China to Korea and the Ariake Sea of Japan. Compared to other oysters, is known for its flavored meat and firm texture, and it is therefore preferred in commercial markets over other commercial oyster species. It has been one of the most important commercial species in the shellfish industry on the west coast of America since the 1950s. In China, the wild population of is abundant and is considered an important wild fishery resource. In our laboratory, two strains of have been developed for artificial hatchery breeding in recent years. Hybridization breeding is one of the important methods for developing a new strain of . Moreover, triploid marine bivalves generally have growth and survival advantages over common diploids. Therefore, hybridization for marine bivalves has gained increasing interest for scientists. In the present study, the hybrid diploids and triploids from two strains of the Chinese population and American population of were induced to evaluate the hybridization effect and triploid advantage. The conditions for larvae and adult rearing were the same throughout the entire period. The larvae were reared in indoor tanks, with a density of 4-5 individuals per milliliter water. The juveniles were farmed on the sea, with 40-45 individuals per sting of attachment. The results showed that the hybrid diploids had heterosis for cleavage rate (13.61%) and D larvae rate (5.67%) compared to that of the controls, while the larvae of hybrid diploids had negative heterosis for their shell height growth (-0.43%). However, the juveniles and adults had heterosis of 3.96% and 6.65% for their shell height and shell length, respectively. On the other hand, the hybrid triploids had a growth advantage during the entire period, with high levels of advantage in the late growth stage. The larvae had a growth advantage of 3.69% on average, and the juveniles and adults had an advantage of 12.69% and 13.64% for their shell height and shell length, respectively. The hybrid triploids had negative survival rate from 3 days to 180 days, with a highest value of -48.72% at 15 days. However, a positive survival rate of 6.70% was detected at 360 days. In contrast, the hybrid diploids had a higher survival rate compared to that of the hybrid triploids, with mean survival advantages of 10.44% and 4.59% for the larvae and adults, respectively. The hybrid triploids had a significant growth advantage in the entire period and had a positive advantage of survival rate in the adults, suggesting that the advantages of hybrid triploids resulted from triploidy advantage and partial heterosis.

Abstract:To investigate the effects of high niacin levels on lipid metabolism and body fat deposition in fish, two experiments on genetically improved farmed tilapia (GIFT, ) were designed. In experiment I, to determine whether high niacin can decrease serum lipid content in fish and its appropriate level, a model of hyperlipidemia was established by first feeding GIFT (initial body weight:15.28±0.23 g) a high-carbohydrate and high-fat diet for 40 d; subsequently, these fish were fed diets containing 500 mg/kg, 1000 mg/kg, and 2000 mg/kg niacin. The results showed that the addition of 500-2000 mg/kg niacin in the diet could reduce fish serum cholesterol and triglyceride levels, and that 1000-2000 mg/kg niacin had more highly significant effects. In experimental Ⅱ, a 2×2 factorial study was conducted to investigate the effects of two diet types (the control diet and high-carbohydrate and high-fat diet) and two niacin levels (100 mg/kg and 1000 mg/kg) on the growth, feed utilization, serum lipid level, and body composition of GIFT (initial body weight:24.45±0.07 g). The experiment lasted for 8 weeks. The results showed that neither of the diet types nor niacin levels had significant effects ( > 0.05) on the final mean weight, weight gain, specific growth rate, feed conversion ratio, feeding intake, condition factor, viscerosomatic index, mesenteric fat index, or the apparent digestibility of crude protein and crude fat, or crude fat, crude protein, moisture, and ash content of the whole fish. Apparent digestibility of dry matter and energy, and the levels of serum cholesterol, triglycerides and free fatty acid (FFA), and the crude fat contents of liver, viscera, and abdominal muscle of fish fed the high-carbohydrate and high-fat diet were significantly higher ( < 0.05) than those of the control group. The serum low density lipoprotein, cholesterol and FFA, and liver crude fat contents of fish fed the diets contain 1000 mg/kg niacin were significantly lower ( < 0.05) than those fed the diets containing 100 mg/kg niacin. There were significant interactions ( < 0.05) between dietary types and niacin levels on serum high density lipoprotein and cholesterol contents. These results indicated that the supplementation of 1000 mg/kg niacin in the diet would not affect the growth performance and feed utilization of GIFT. However, it could reduce the levels of serum lipids and liver fat content.

Abstract:This study was conducted to determine the effects of three forms of manganese on growth performance, antioxidant capacity, serum biochemical indexes, and intestinal morphology of juvenile hybrid grouper (). The experimental diets were isonitrogenous and isolipidic diets with the addition of manganese sulfate (MnSO₄), manganese glycine (Mn-Gly), and manganese hydroxymethionine (Mn-MHA), respectively. The three groups containing manganese had 37.74 mg/kg, 40.66 mg/kg, and 38.15 mg/kg, respectively. Two hundred and seventy groupers[initial average weight (11.00±0.12) g] were randomly divided into three groups with three replicates at a stock density of 30, and fed with test diets for 8 weeks. The results showed that the weight gain rate in Mn-Gly and Mn-MHA groups were significantly higher than that of the MnSO₄group. The feed coefficient rate of fish fed Mn-MHA were significantly lower than those fed MnSO₄. The specific growth rate and survival rate were not significantly different among the three groups ( > 0.05). Liver malo­­naldehyde contents in the Mn-Gly and Mn-MHA groups were significantly lower than those in the MnSO₄group. In the Mn-MHA group, the activity of manganese superoxide dismutase in the liver was significantly higher than that in the MnSO₄ and Mn-Gly groups. The activity of copper-zinc superoxide dismutase in the Mn-Gly and Mn-MHA groups were significantly lower than those fed in the MnSO₄group ( < 0.05). In serum, the contents of glucose in the Mn-Gly and Mn-MHA groups were significantly higher than that of the MnSO₄group, the contents of cholesterol in the MnSO₄ and Mn-Gly groups were significantly higher than that of the Mn-MHA group (group, the plica height of proximal and mid intestine, and the muscle thickness of distal intestine were significantly increased in the Mn-MHA group ( < 0.05). In the Mn-Gly group, the plica width of mid intestine was significantly increased comparing to that of MnSO₄group, the plica height of distal intestine was significantly higher than that of the MnSO₄ and Mn-MHA groups (, Mn-Gly and Mn-MHA could significantly improve the growth performance, enhance the antioxidant capacity of liver, regulate the related metabolic response, protect the liver, and promote the development of the proximal, mid, and distal intestines of juvenile hybrid grouper.

Abstract:This study examined the effects of hypoxia and reoxygenation on antioxidant enzyme activities and the change in histological structure in with the body weight of (2.0±0.2) g. Experimental prawns were placed in a normal (control) group or hypoxia group with given dissolved oxygen of (6.0±0.2) mg/L and (2.0±0.2) mg/L, respectively. Each group was sampled in triplicate to measure the activities of antioxidant enzymes in the muscle, gill, and hepatopancreas under hypoxia at 0 h, 6 h, 12 h, and 24 h, and under reoxygenation at 1 h, 6 h, 12 h, and 24 h. The histological structures of gill, muscle, and hepatopancreas were also observed. The results showed that the activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT) enzymes in the muscle, gill, and hepatopancreas from the experimental group first increased and then declined, and the activities of the three enzymes were significantly higher than those of the control group at 12 h under hypoxia stress ( < 0.05). The activities of SOD and CAT in the muscle tissue of prawns in response to reoxygenation was fluctuated over time, and the activities of GPX under reoxygenation at 24 h was significantly lower than that of the control group ( < 0.05). The activities of SOD, CAT, and GPX in gill under hypoxia at 12 h were both significantly higher than that of the control group ( < 0.05), and there was significantly higher GPX enzyme activity under reoxygenation at 24 h than that of the control group ( < 0.05). Compared with the control group, the significantly higher SOD, CAT, and GPX activities in the hepatopancreas of prawns were observed at 6 h ( < 0.05), and the content of MDA in the hepatopancreas of prawns in response to hypoxia and reoxygenation was significantly higher than that that of the control group ( < 0.05). Observation of tissue by paraffin section revealed that hypoxia and recovery did not affect muscle tissue structure. Through the observation of the tissue section of the gill, it was found that the epithelial cells and the pillar cells were disordered after 12 h of hypoxia stress, and the secondary layer was hypertrophied. After 24 h of hypoxia, the secondary layer of hypertrophy was intensified and red blood cells inflowed. The morphology of the cells changed, and the number of cells increased, but it recovered to some extent after reoxygenation. During hypoxia stress, the number of B cells in the hepatopancreatic tissues significantly decreased, but the number and apparent volume of B cells recovered to the level of the control group after reoxygenation. The results showed that acute hypoxia can cause damage to the hepatopancreas and gill of , and affect the activities of antioxidant enzymes. Furthermore, the results showed that acute hypoxia can cause damage to the hepatopancreas and gill of , and affect the activities of antioxidant enzymes. The 24 h recovery period was not sufficient for to completely recover from hypoxia stress.

Abstract:Accurate understanding of the changes in fish resources and growth characteristic in important tributaries in the Three Gorges Reservoir can provide a scientific basis for fishery management and resource conservation in the region. This study was based on fishery information collected in 36 important tributaries of the Three Gorges Reservoir area in November and December 2015 and May, June, and September 2016. The growth and development status of eight species of dominant fish was evaluated using the FiSAT Ⅱ software developed by the Food and Agriculture Organization of the United Nations (FAO). These species were Carassius auratus, Saurogobio dabryi, Pseudobagrus nitidus, . The growth and death parameters were estimated using the body length frequency distribution method (ELEFAN I), and the resource change trend was evaluated according to the Beverton-Holt model. The results showed the following. The body length and body weight of the eight species of fish were in a power function, and the growth index () was between 2.74 and 3.11, which is an approximate constant velocity growth. The growth coefficient () values of the eight species of fish were all greater than 0.2, which indicated a rapid growth type. The growth performance index ( was the highest at 5.25, and was the lowest at only 2.83. The development rates of (0.4) were less than 0.5 and less than ; the development rates of the remaining six species were 0.5 and above. The length of the opening of Cyprinus carpio, Pseudobagrus vachelli, Saurogobio dabryi, Pseudobagrus nitidus, Hemiculter leucisculus, and should be controlled at 289 mm, 253 mm, 134 mm, 102 mm, 71 mm, and 52 mm, respectively, and fish resources can be effectively restored. From these results, we can conclude that the development of important tributary fish resources in the Three Gorges reservoir area was excessive. The growth rate of omnivorous and carnivorous fish was increasing, but the benthic food fish were decreasing. We conclude that the upper reaches of the Yangtze River should focus on the protection of endemic species and the maintenance of biodiversity. Key waters should be forbidden from fishing throughout the year, so aquatic organisms can play out their ecological roles and improve the stability of the Yangtze River aquatic ecosystem.

Abstract:Fish stock assessment usually requires a wide range of supporting data, including an abundance index, production, age structure. However, some data are hardly available in many fisheries because of limited research funding and social attention. Therefore, many fisheries, particularly small-scale fisheries, often do not have sufficient data to support fish stock assessment and are considered data-limited or data-poor. An increasing amount of literature has been focused on the development of data-poor stock assessment methods in recent decades, among which electronic length frequency analysis (ELEFAN) is a prevalent method that uses length frequency distribution data to assess the status of fisheries. One crucial application of the ELEFAN is the estimation of growth parameters in the Von Bertalanffy growth function (VBGF). However, the method is based on certain optimization algorithms and cannot provide information on its precision or confidence intervals for growth parameters, which implies that the reliability of ELEFAN needs to be tested in future studies. This study used a bootstrap approach to evaluate the uncertainty of the ELEFAN method based on the survey data of in Haizhou Bay. This species is one of the dominant species in Haizhou Bay and plays an important role in the food web and ecosystem of the Yellow Sea. Although the declines in fishery resources have drawn increasing attention in many regions of the world, relevant studies have commonly focused on large-scale fisheries, whereas small-scale fisheries, such as that of , has been largely overlooked. Therefore, the biological characteristics of this species and their temporal changes is not well understood. This study was focused on the temporal changes in VBGF growth parameters of in Haizhou Bay at different survey periods. We conducted annual bottom trawl surveys in Haizhou Bay in the spring and autumn from 2013 to 2018, and used the ELEFAN method to estimate the VBGF growth parameters infinite length ( In addition, the bootstrapped ELEFAN was used to evaluate the variation in the growth parameters, and the difference was compared between 2013-2015 and 2016-2018. We analyzed the robustness of ELEFAN with respect to three aspects:(1) the effect of bin size of body length on parameter estimation, (2) the selection of different optimization algorithms (Simulated Annealing, SA; Genetic Algorithm, GA; Response Surface Analysis, RSA), and (3) the confidence intervals of parameter estimation through the bootstrap approach. The results showed that the VBGF growth parameters of in Haizhou Bay changed significantly during 2013-2018, and the decreased infinite length () indicated that there was a significant trend of miniaturization. The bin size of body length significantly affected the goodness of model fit and improper bin size settings might lead to unreasonable parameter estimations. Bootstrapped ELEFAN provided robust parameter estimations compared to the conventional ELEFAN approach, and the bootstrapped results were less affected by the randomness of sample data. The Genetic Algorithm could benefit from parallel computing in the TropfishR package, which significantly sped up computation. This study improved the understanding of population dynamics of . In particular, the changes of growth characteristics of this species may have a substantial impact on the Haizhou Bay ecosystem. We demonstrated that bootstrapped ELEFAN performed well and could be applied to the prevalent data-poor and small-scale fisheries.

Abstract:Along with the development of economy and the living standard of residents, the discharge of industrial and agricultural wastewater and municipal domestic sewage has a serious impact on the water quality of the Pearl River Delta. Bacterial communities are important components in riverine ecosystem and play key roles in the degradation and transformation of various pollutions in river environment. Bacterioplanktonic community responds to changes in biotic and abiotic factors that are amplified during spring and summer these wet seasons, however, whether communities respond to environmental disturbance in dry seasons remains unknown. In this study, we collected surface water samples from the Pearl River Delta (112.18°E-113.51°E, 22.38°N-23.17°N) in November 2017 and January 2018, using high-throughput sequencing of 16S rDNA gene amplicons on the Illumina Miseq platform, to investigate the bacterioplanktonic community's composition and their environmental impact factors of the Pearl River Delta in winter. Total DNA was extracted from water samples by using DNA extraction kit (Magen Hipure Spil DNA Kit), and DNA concentration was determined by Qubit^® dsDNA HS Assay Kit. The targeted V3-V4 regions were amplified with the primers set (341f-CCTACGRRBGCASCAGKVRVGAA; 806r-GGACTACNVGGGTWTCTAATCC). The purified PCR products were sequenced on Illumina MiSeq (Illumina, San Diego, CA, USA) platform, and raw reads were screened by QⅡME (1.9.1), with the removal of chimeric sequences by UNCHIME. Operational taxonomic units (OTUs) were generated by Vsearch (1.9.6) with similarity at 97%, and aligned against reference database SILVA (http://www.arb-sliva.de). Αlpha diversity indices such as Shannon and Chao 1 index, and beta diversity based on Bray-Curtis difference coefficients were calculated in R (3.5.2) software (http://www.r-project.org) according to normalized OTU abundance. Non-metric multidimensional scaling (NMDS) was used to test communities dissimilarity, and analysis of similarities (ANOSIM) was used to test the similarity among different communities, by using vegan (2.5.2) package. Redundancy analysis (RDA) was used to analyze the relationship between bacterial community and environmental factors by using vegan (2.5.2) and ggplot2. Pearson correlation analysis was carried out with SPSS (19.0) statistical software (IBM Corporation, USA) to determine the relationship between environmental factors and the diversity of planktonic bacteria (Shannon index and Simpson index) and the abundance of specific bacteria. The results showed that Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria were abundant phyla in Pearl River Delta. γ- was the most abundant class among the communities, followed by Actinobacteria and α-Proteobacteria. The bacterioplanktonic community showed a relatively high diversity in the Pearl River Delta in winter, with no significant differences observed in bacterioplanktonic community's composition among all sampling sites. Pearson correlation analysis showed that the abundance of γ-Proteobacteria (P < 0.01) was positively correlated with temperature, while the diversity index was negatively correlated with PH (Shannon, < 0.007) and the abundance of α-Proteobacteria ( < 0.05) was negatively correlated with dissolved oxygen. RDA showed that temperature, pH were the main driving factors affecting the structure of bacterioplanktonic community. Temperature was identified as the main environmental factor affecting planktonic bacteria community. Previous studies shown the composition of bacterial community was driven more by temperature and the average cell size of planktonic bacteria community decreased with the increase of temperature. In addition, temperature was related to the diversity of estuarine ecosystems. Seasonal temperature variation was also considered to be the main variable affecting the dynamics of sediment bacterial community in the Pearl River Estuary. The pH was another major environmental factor affecting the structure and diversity of bacterial communities. pH was generally considered as an indicator of , in the study, negative correlation was observed between pH and Actinobacter (=0.016), which was consistent with the results of other studies. These results might provide fundamental information on bacterioplanktonic community composition and environmental factors in winter Pearl River Delta.

Abstract:To explore the method of microchemistry marking on the otolith of Japanese flounder, , during the process of proliferation and release, the juveniles with a total length of (1.56±0.16) cm were immersed at four different concentrations (0.5, 2, 8, and 32 mg/L) of SrCl₂·6H₂O for 72 h to detect the Sr sedimentation effect. During the immersion period, half of the water was exchanged by fresh seawater daily, and SrCl₂·6H₂O were added to maintain constant concentration for each group. The exogenous Sr sedimentation in otoliths was detected by X-ray electron probe microanalyzer (EPMA). Results of line transect analysis showed that the strontium marking on otoliths could not be formed after the immersion of two concentrations (0.5 mg/L and 2 mg/L). The Sr high area appeared in the 8 mg/L concentration group with a 5.49-8.49 peak value, and the mean value of the Sr/Ca (Sr:Ca×1000) ratio was 4.50-6.60. Furthermore, in the 32 mg/L group, the mean value of the Sr/Ca ratio was 6.61±0.86, and the peak value of Sr was 5.62-11.04. This means that otoliths of can be marked with strontium by the method of SrCl₂·6H₂O immersion. However, in the 8 mg/L concentration group there were also unlabeled samples. and the mean value of Sr/Ca was lower than that of the 32 mg/L group. In the 32 mg/L group, the strontium marking rate was 100%, and the mean value of the Sr/Ca ratio was 6.61±0.86, which was significantly different ( < 0.05) compared with that of the control group. The EPMA mapping analysis showed that the red "high strontium marking ring" in the otolith appeared in the 8 mg/L group and 32 mg/L group, and the color of the "high strontium marking ring" was deepened with increasing of concentration. One-way analysis results showed that the total length and weight was not significantly different between the experimental groups and the control group (O immersion did not affect the growth of young fish. A Chi-square test ( > 0.05) showed there were no significant differences in mortality rate among the different concentration groups. Overall, 32 mg/L SrCl₂·6H₂O was the best marker concentration.

Abstract:The nutrient content of abalone viscera is similar to that of muscle. It contains rich proteins and various biologically active substances. However, the abalone viscera are often abandoned when processing or during consumption of abalone. This is not only a great waste, but also causes pollution to the environment. In recent years, with the exploration and research of marine active substances, abalone viscera have also been studied and developed. Intestinal microorganisms are known as "external organs" of the host, they are directly involved in the host's nutrition, immunity, metabolism, and so on. They play important roles in maintaining the health of the host. A few studies have reported the in vitro and in vivo antioxidant activity of abalone polysaccharides and polypeptides; however, the effects of abalone active substances on the intestinal microorganism have not been previously reported. In this paper, the intestinal microbiota of tilapia and the influence of feeding abalone visceral crude polysaccharide (CAVP) on the intestinal microbiota were studied by PCR-DGGE and Illumina MiSeq sequencing. A total of 13 bacterial phyla were detected in the intestines of tilapia:Fusobacteria (77.84%) was the dominant phylum, Bacteroidetes (8.59%), Chlamydiae (6.18%), Proteobacteria (5.84%), and Actinobacteria (1.20%) were the subdominant phyla. Saccharibacteria, Firmicutes, Planctomycetes, Verrucomicrobia, TM6_Dependentiae, Cyanobacteria, Spirochaetae, Acidobacteria, and some unknown groups were also detected. At the genus level, (5.80%), (1.13%) were the subdominant genera. There was also an unknown genus of the family Porphyromonadaceae, accounting for 8.29%. In addition, , and some unknown genera were also detected. The addition of CAVP diet had an obvious influence on the intestinal microbiota of tilapia because the CAVP-treated samples and the control samples without CAVP clustered separately. After feeding CAVP, the abundance of Actinobacteria, Saccharibacteria, Verrucomicrobia, and TM6_Dependentiae decreased significantly ( and Neochlamydia, Acinetobacter, Mycobacterium, Alsobacter, Aquicella, Pseudomonas, Aeromonas, and Mycobacterium, Alsobacter, Aquicella, and P < 0.05). After feeding CAVP, the abundance of some pathogens, such as Mycobacterium abscessus, Acinetobabacter baumannii, Aeromonas sharmana, Tsukamurella tyrosinosolvens, and Mycobacterium abscessus and decreased significantly compared with that of the control (Cetobacterium, increased. This study investigated the effects of CAVP on the host with regard to intestinal microbes; it provides insight into the efficient evaluation of marine active substances, and also lays a theoretical foundation for the development and utilization of bioactive substances and the development of prebiotics from abalone viscera. In addition, this study is of importance in recycling abalone viscera and reducing environmental pollution.

Abstract:Turbot () is an economically important marine fish species cultured in China. However, disease is a major problem in the turbot aquaculture fishery, causing high mortality. In August 2017, a disease outbreak among turbot in a marine farm in Tianjin led to a cumulative mortality rate of 25%. The main symptom of the disease was abundant white granulomas in the internal organs of the turbot. To define the causative pathogens, bacteria were isolated from the spleen and kidneys of diseased fish using conventional methods. An artificial infection experiment was conducted to determine the pathogenicity of the isolated strain. The 16S rDNA, gene sequences, as well as morphological and biochemical characteristics of the strain, were examined. In addition, histopathological analysis was performed on the diseased turbot. Abundant white granulomas were observed in the spleen, kidneys, livers, and intestinal tracts of diseased fish. The hepatocytes in the livers of the diseased fish were damaged, and several irregular vacuolations were observed. Some of the spleen cells were enlarged and necrotic, and epithelial cells from the renal tubule showed vacuolar degeneration and necrosis. Furthermore, in the center of the pregranulomas, as well as kidney and spleen macrophages contained several phagocytized red, rod-shaped acid-fast bacteria. Strain myco-10 was isolated from spleens of diseased fish. Healthy turbot were subjected to bacterial challenge tests by intraperitoneal injection of 3×10⁸cfu/fish of the isolated myco-10. The accumulative mortality rate was 66.7% within 30 days post-infection. Diseased turbot displayed symptoms similar to those observed in naturally infected individuals. Strain myco-10 showed positive pigmentation production after exposure to visible light, Tween-80 hydrolysis, urease, catalase at 68℃, and arylsulfatase, and negative results in terms of nitrate reductase and growth on 5% NaCl. Phylogenetic trees were constructed by matching 16S rDNA, spp. registered in GenBank. The results showed that strain myco-10 clustered with . Strain myco-10 was determined to be based on bacterial morphology, analytical profile index identification, and 16S rDNA, genes sequences. The results of this study suggest that is the causal agent of granulomas in the internal organs of turbot. To the best of our knowledge, this is the first report on spp. causing disease in turbot in China. Our findings will be useful as a reference for the prevention and control of mycobacteriosis in cultured turbot.

Abstract:In April 2016, a serious infectious disease characterized by hemorrhage of the gill, swim bladder, and internal organs emerged in a farm in Sichuan Province. Histopathological observation showed that the spring viremia of carp virus (SVCV) infection in could cause pathological damages in multiple organs, which exhibited hemorrhage, degeneration, necrosis, and infiltration of the inflammation cells, especially in the liver, spleen, kidney, gill, and intestine. The filtrated homogenate was inoculated into the epithelioma papulosum cyprini (EPC) cells, and the typical cytopathic effect (CPE) was formed after three blind passages. Diseased tissue suspension filtered from bacteria and EPC-grown virus were used to inoculate healthy developed similar clinical symptoms to those described above and suffered 60% and 50% mortality, whereas the control group remained normal. Transmission electron microscopy (TEM) of EPC cells infected with ZLP160415 found that the virus was bullet-shaped, 90-150 nm long, and 40-60 nm wide. RT-PCR of tissue homogenates from the fish naturally infected, the fish artificially infected, and the infected cells were performed, and the results showed that all were SVCV-positive. Based on phylogenetic analysis of glycoprotein genes, the isolate ZLP160415 was classified into the Ia genogroup. From the combination of epidemiology, pathologic lesions, virus isolation and identification, artificial infection, and TEM examination, it was concluded that the SVCV was the pathogen of the disease.

Abstract:samples were collected during the migration flood season of 2017. After dissection, six samples of were selected as the infected group, and six samples that were uninfected were selected as the control group to determine the effect of C. nasus. A total of twenty-three bacterial phyla were identified. Twenty-two phyla were identified in the control group and eighteen phyla were identified in the infected group, among which Verrucomicrobia was only detected in the infected group. The main bacteria phyla in the intestinal tract of were Proteobacteria, Firmicutes, and Tenericutes, with a total relative abundance of more than 85%. The average content of Firmicutes, Fusobacteria, and Fibrobacteres in the infected group was higher than that in the control group, and the relative abundance of other bacteria phyla was lower than that in the control group, but there was no significant difference between the two groups ( > 0.05). Comparison of the relative abundance of bacteria at the family level showed that the proportions of Clostridiaceae, Peptostreptococcaceae, Lactobacillaceae from Firmicutes, and Enterobacteriaceae in the Proteobacteria were higher than those in the control group. Abundance of Peptostreptococcaceae, Lactobacillaceae, and Enterobacteriaceae in the 130 families identified were higher than those in the control group. Porphyromonadaceae and were significantly more abundant in the intestinal tract of the infected group ( < 0.05). At the community diversity level, there was no significant difference in Shannon index, Chao1 index, and Simpson index between the two groups ( infection on the community structure and species diversity of intestinal microorganisms were not significant, there were significant differences in the composition of specific species.

Abstract:, which occurs in the coastal waters of China, including the Yellow and East China Seas, is a delicious seafood and has great economic value. In the past few years, resources have rapidly declined, as a result of the use of a smaller net mesh sizes of the fishing gear, which has resulted in large numbers of fish fry being caught. To better develop and protect resources, the goal of this study was to determine the differences in selectivity of various mesh sizes and hanging ratios for were collected by using a simulated cover-net method in a flume tank. A logistic curve was fitted as a selectivity model to obtain selective curves of different mesh sizes and hanging ratios. Selective parameters were estimated by MLE (Maximum Likelihood Estimate). The results indicated that the selection length (Sebastes schlegelii when the mesh sizes were 63 mm, 82 mm, and 93 mm. Selection rangers (SRs) were 2.05, 3.6, and 3.85, and selection factors (SFs) were 2.83, 2.72, and 2.70, respectively. The SR increased with an increase in the mesh size, whereas the SF decreased. When three groups of hanging ratios (0.5, 0.6, and 0.707) for 82 mm mesh size were chosen to study the impact of hanging ratios, the respective of s were 21.47 cm, 23.90 cm, and 22.02 cm, SRs were 3.23, 3.6, and 3.38, and SFs were 2.65, 2.91, 2.68, respectively. With an increase in the hanging ratio of meshes, the , SR, and SF increased first and then decreased, and obtained a maximum value at the hanging ratio of 0.6. It was concluded that the suitable size of fishing gear for protecting masked greenling resources was a 7 cm mesh size and a hanging ratio of 0.6.

Abstract:) is an important large red algae (laver) that not only tastes delicious but also possesses several health-beneficial effects, such as antilipidemic and anti-ageing effects. In addition, blades have a strong ability to absorb nitrogen and phosphorus and fix carbon, and its cultivation also plays an important role in the restoration and improvement of eutrophication in shallow seas. Herein, we introduce the germplasm resources of in China and review the advances in its breeding technique, objectives, and achievements. At present, there are 24 species and varieties of laver in China, and they are mainly distributed from the south of the Huanghai and Bohai Seas to the southeast coast of Guangdong, and a few species are also common in Taiwan and Hainan Island. In the Huanghai and Bohai Seas, are the main species, and in the southeast coast, are the main species. Based on the natural groups and habitat environment, there are two cultivation areas, namely, the north and south of the Yangtze River cultivating , respectively. Although the problem of seed quantity has been solved by traditional seedling methods, the problem of seed quality has not been resolved because inbreeding could easily decrease the quality of a cultivated germplasm. Therefore, genetic breeding of is of great significance to promote its yield and quality. The breeding techniques of have been improved with the progress in science and technology and with the accumulation of cultivation experience, through the initial field selection (selective breeding), mutation breeding and cross breeding, which are based on cell biology, and genetic engineering breeding. The purpose of genetic breeding of is to provide varieties that meet the needs of production and development; therefore, the breeding objectives should also change with changes in production and market demand. In the early stage of breeding, yield and quality were used as key indicators to identify whether a variety is good. With changes in climate and marine environment, it is of great significance to cultivate varieties of with high-temperature and low-salt resistance. At present, Chinese has cultivated 6 new varities of P. yezoensis. Finally, we put forward some problems in the development of laver industry in China, assuming that superior seed selection and industrial development are interrelated. Overall, the paper provide useful information for further studies in genetics and breeding.

Abstract:N₂O emissions from aquaculture activities are attracting increasing attention. This paper compares the results of experimental studies on N₂O emissions from aquaculture and estimation studies based on material balance, analyzes the state of nitrogen emission from different aquaculture modes, and constructs strategies to reduce N₂O emissions. The results showed that the N₂O emission coefficients measured in actual culture processes were lower than those in wastewater treatment processes. The efficiency of nitrogen utilization and the pathways of the unused nitrogen from different farming modes were quite different. In addition, the nitrogen treatment approach of the recirculation aquaculture system was the closest to that of the wastewater treatment plant, but the recirculation aquaculture production accounted for a low proportion of the global aquaculture production. Additionally, being fed is not required during the production of approximately half of the aquaculture yield. Therefore, the results based on the N₂O emission coefficient of the wastewater treatment plant and the total N₂O emission of aquaculture production will be significantly larger. Currently, there is still a lack of basic research on the production of N₂O in aquaculture. Therefore, this paper does not establish relevant estimates. Future studies should conduct systematic research on the production of N₂O in aquaculture activities to provide theoretical support for the objective assessment of N₂O emissions from aquaculture activities.