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Abstract:Ommastrephes bartramiii, a neon flying squid, is an economically important oceanic cephalopod, which is widely distributed in the North Pacific Ocean. In China, it is one of the most important fishing targets of distant-water squid jigging vessels. Because of its short life cycle, the fishing seasons and its main fishing seasons have obvious year difference. Therefore, analyzing the characteristics of the O. bartramii fishing season and predicting the main fishing season are helpful for the rational development and sustainable harvest of O. bartramii. We analyzed fishery data for neon flying squid from China squid jigging fisheries during 2013 to 2017. The daily catch per fishing effort (CPUEday) was used to provide the abundance index and was considered as an indicator for judging the division of main fishing seasons. The quantile method was used to identify the main fishing seasons. And the grey wave forecasting method is also used to establish the grey model group [GM (1,1) model] based on the date series of the actual main fishing seasons. The results showed that the earliest catch of neon flying squid is May 12 with catches lasting until the end of the year. The primary period of the fishing season is from August to November each year. The first main fishing peak occurs in August. The average relative error of the grey wave forecasting GM (1,1) model group is 6.83%, the average relative error of the date series forecast during the main fishing season is 8.19%, and the average relative error of the validation data is 15.82%. It is concluded that this grey model can be used to predict the main fishing season for neon flying squid in the North Pacific Ocean. The findings of this study not only provide technical support for efficient and rational capture of distant-water fishery enterprises, but also provide a useful tool for prediction of the main fishing seasons for marine capture fisheries.

Abstract:Marine microplastic pollution has become a global environmental problem. Understanding the status of microplastic pollution in living organisms is fundamental for assessing the biological effects on ecosystems. This study investigates the microplastic pollution status in tissues (digestive tract, gill and muscle) of ten common species in Xiangshan Bay. The results show that microplastics are widely present in all ten species. A total of 131 microplastics were detected in 61.0% of the organisms, with an average abundance of (1.3±1.5) items/individual. A total of nine microplastic types were detected. The majority of the plastics were rayon (RY; 74.0%), polyethylene terephthalate (PET; 14.5%), polypropylene (PP; 3.8%) and polyamide (PA; 3.1%). Fiber, fragment, and granule microplastic shapes were detected, accounting for 95.4%, 3.1%, and 1.5% of the total microplastics, respectively. Rayon and fiber were present in all species investigated. The size of the microplastics ranged from 110 μm to 4796 μm [mean value: (1246±1119) μm], with the size of ≤1000 μm accounting for 55.2% of the microplastics. PE, PP, and PS microplastics, as well as the typical foamed microplastics produced by breeding facilities, are detected less frequently and in a lower abundance in living organisms. Our findings provide the knowledge and data to improve our understanding of the status of microplastic pollution in marine organisms and assists in evaluating their biological effects in coastal ecosystems.

Abstract:In order to explore the nutritional value, feeding habits and seasonal changes in the main catches from Lüsi fishing ground, we measured fatty acid composition of the main catches collected through a fishery resources survey in May 2018, August 2018, and October 2018. We analyzed feeding habits based on fatty acid biomarkers. The results of the eight main catches showed that the value for PUFA/SFA was 0.88~1.79 and that for n-3/n-6 was 2.56~3.18. C16:1n7, Σ15+Σ17 increased significantly in summer (P<0.05). The EPA+DHA, PUFA/SFA, n-3/n-6, C20:4n6, C22:6n3, and Σ22+Σ24 increased and C20:1+C22:1 decreased significantly in autumn (P<0.05). Previous studies have shown that the nutritional value of each catch is high and was significantly higher in autumn than in spring and summer. The nutritional value of Collichthys lucidus and Larimichthys polyactis was the highest. DHA/EPA and cluster analysis divided the catches into three groups: Parapenaeopsis hardwickii, Metapenaeus joyneri and Charybdis japonica; Coilia mystus, Johnius belangerii, C. lucidus and L. polyactis; Pampus argenteus. P. hardwickii, M. joyneri and C. japonica preferred phytoplankton and benthos. L. polyactis and C. mystus preferred zooplankton. P. argenteus preferred phytoplankton and zooplankton. C. lucidus and J. belangerii had no obvious preferences. In general, food source on diatoms and bacteria increased significantly in summer. In autumn, food source significantly increased on benthos, dinoflagellates, and terrestrial plants and it decreased on zooplankton.

Abstract:The aim of this study was to explore the effects of different management methods on the sedimentation of particulate matter, related sediments, and water quality indicators in sea cucumber (Apostichopus japonicus) ponds. Nine sea cucumber culture ponds (divided into three groups: water quality regulator, natural tide, and microporous aeration) were used. The average sedimentary and horizontal distribution characteristics of particulate matter were measured in spring, summer, autumn and winter as well as the organic matter content of the mud, total number of Vibrio, nutrient concentrations in the water, phytoplankton biomass, and net primary productivity were analyzed. The results showed no significant difference in the seasonal and horizontal distribution of the average sediment concentrations between natural tide ponds and microporous aeration ponds. The average sediment concentrations in the water quality regulator ponds was (30.33±2.46) g/(m2∙d) in summer, which was significantly higher than in the other two types of ponds, while in winter it was (7.49±1.17) g/(m2∙d) and was significantly lower than in the other two types of ponds (P<0.05). The horizontal distribution characteristics of the average sediment concentrations in the water quality regulator ponds were more than those of the other two groups of ponds. During the same season, the organic matter content, and the total number of Vibrio in the water quality regulator pond sediment were at the lowest level among the three groups, with the microporous aeration ponds being the second lowest, and the natural tide ponds being the highest. The results of this study show that traditional sea cucumber farming is based on the management of natural tides and auxiliary suitable equipment can affect the sedimentation rate of particulate matter, accelerate the exchange of nutrients between the bottom sediment and the water of the sea cucumber ponds, and improve the water and bottom sediment environment.

Abstract:Schizothorax kolzovi, which belongs to Cypriniformes, Cyprinidae and Schizothoracinae, is a wild fish species of high economic value, distributed in the Jinsha, Yalong, and upper Wujiang Rivers of the Yangtze River system and the Beipan River in the Pearl River system in China. To assess the genetic diversity and germplasm resources of S. kolzovi in the Wujiang River, Guizhou, the genetic structure and diversity were analyzed in the 30 individuals of the species from the river by the methods of amplified fragment length polymorphism (AFLP). With 7 pairs of selected primers through the pre-experiment, 5~73 DNA fragments were amplified in the 30 individuals, ranging from 69 to 500 bp. A total of 856 loci were detected, including 796 polymorphic loci accounting for 92.99% of the total. The population contained 30 genotypes, and the mean values of the observed number of alleles (Na), effective number of alleles (Ne), Nei diversity index (H), and Shannon information index (I) were 1.933 6, 1.338 8, 0.212 2, and 0.338 7, respectively. The genetic distance between individuals ranged from 0.169 1 to 0.531 9, with an average of 0.306 8. The unweighted pair group method with arithmetic mean (UPGMA) and neighbor-joining (NJ) phylogenetic trees of the 30 individuals contained 2 branches and had the similar topological structure. The S. kolzovi population in the Wujiang River contained rich genetic diversity. However, hydropower station dams, river pollution, and overfishing have reduced the distribution of S. kolzovi, and its population size has declined. Therefore, this species is ecologically threatened, and the population and germplasm resources of S. kolzovi in the Wujiang River needs to be protected.

Abstract:To study the genetic diversity of Triplophysa yarkandensis in the Tarim River basin, high-throughput sequencing was used to sequence the genome of T. yarkandensis. We screened for qualified microsatellite loci and designed 100 primers pairs for PCR. A high-throughput sequencing platform was used to randomly sequence the genome of Riplophysa yarkandensis and eligible microsatellite loci were selected to design primers for PCR. Finally, 39 primers pairs with polymorphisms were selected. Fifteen pairs were randomly selected to be amplified in the five river populations of T. yarkandensis. The results showed that the average and effective alleles of the five T. yarkandensis populations were 48.467 and 15.181, respectively. The observed heterozygosity (Ho) and expected heterozygosity (He) were 0.578 and 0.929, respectively. The polymorphism information content (PIC) was 0.893. The index of gene differentiation (Fst) was 0.102. The highest number of alleles was in Che'erchen Lake (18.143), and the lowest number of alleles was in the Akesu River (10.429). The observed heterozygosity of the Akesu River group was the highest (0.706), while the observed heterozygosity of the Taitema Lake group was the lowest (0.517). The polymorphic information content of the Algan population was the highest (0.877), and the polymorphic information content of the Akesu River population was the lowest (0.760). The genetic distance between the Akesu River and Tainan River populations was the smallest (0.606), while the genetic distance between the Algan River and Tainan River populations was the largest (1.901). The genetic similarity between the Algan and Tainan River populations was low (0.149), and the genetic similarity between the Akesu and Tainan River populations was high (0.545). Genetic structuring showed that Che'erchen and Taitema Lakes, Akesu and Tainan Rivers, and the Algan group clustered in one branch. The results of this study show that there are differences among T. yarkandensis populations in the Tarim River, but gene exchange is ongoing.

Abstract:Myostatin (Mstn) is one of the main regulatory factors of embryonic muscle formation and adult muscle growth in vertebrates, which inhibits muscle growth and development by inhibiting the expansion and differentiation of muscle cells. Our previous researches have preliminarily suggested that Mstn involved in myogenesis and muscle growth probably as a negative regulator in Fenneropenaeus chinensis like vertebrates. In order to screen genes related to muscle growth regulated by Mstn in F. chinensis and understand the mechanism of muscle growth regulation, RNA-Seq technology was used to sequence control group injected PBS and experimental group injected siRNA for inhibition of Mstn expression. The results showed that a total of 36,605 unigenes were produced and 19,628 genes were annotated by transcriptome analysis. Under the inhibition of Mstn expression by RNAi, a total of 1657 differentially expressed genes were screened, of which 805 genes were significantly up regulated and 852 genes were significantly down regulated. Referring to the previous reports of TGF-β/Smad and MAPK pathways as well as function of differential genes, 29 genes related to muscle growth regulated by Mstn were preliminarily screened. In these genes, 16 genes were involved in TGF-β/Smad and Mapk pathways. Among the 16 genes, only the ActRI was detected to be slightly up-regulated and other genes showed different degrees of down-regulation. The other screened 13 genes were involved in molting, muscle growth and other processes related muscle such as muscle contractions, of which the genes correlated with promoting muscle growth were detected up-regulation. The results of this study provided further evidence for our previous studies that Mstn probably negatively regulates muscle growth in a similar way to vertebrate in F. chinensis. Our results will also provide important theoretical basis for the regulation mechanism of muscle development in invertebrate.

Abstract:Cluster analysis has been widely used for pattern recognition, machine learning, and in other fields. The K-means dynamic clustering algorithm is simple and efficient, which is why it is one of the most commonly used methods of cluster analysis. The beak of cephalopods, comprising hard tissue, has been widely used to determine species and identify populations owing to its stable structure, corrosion resistance, easily observed growth lines, and abundant characteristic information, causing it to have great application prospects. In this study, the K-means dynamic clustering algorithm was used on 150 pairs of Sthenoteuthis oualaniensis beaks within the mantle length range of 120~200 mm. Samples were collected from the northwest Indian Ocean, the tropical eastern Pacific Ocean and the South China Sea from 2014 to 2019. The results showed that S. oualaniensis from the northwest Indian Ocean had the largest beaks, followed by the tropical eastern Pacific Ocean, and those in the South China Sea. The K-means dynamic clustering algorithm showed that S. oualaniensis from the three areas can be well distinguished. We used z-scores to normalize the data the created a 2D beak morphological parameter matrix to randomize the data before we conducted a K-means dynamic clustering analysis with Manhattan distance and Euclidean distance. The total correct discrimination rate was 86.7% and 88.7%, respectively. This study also identified that the geographic regional differences in beak morphology are unlikely to be due to sampling bias. From the location of the clustering center, we concluded that the Manhattan and Euclidean distance algorithms and outlying points will generate deviations from the clustering center. The K-means dynamic clustering algorithm for beaks of the S. oualaniensis has great reference value. We identified improvements that optimize the K-means algorithm to expand capability for universal use. These improvements and a retrieval system will improve our capabilities to identify S. oualaniensis species.

Abstract:To study the effect of different dissolved oxygen (DO) concentrations on the gill morphology and enzyme activity of a hypoxia-tolerant new strain F5 of Megalobrama amblycephala, we placed the new strain in fish tanks with low oxygen [DO: (1.7±0.2) mg/L] and high oxygen [DO: (19.3±0.5) mg/L] concentrations for 0 d, 4 d, 7 d, and recovery [DO: (7.8±0.3) mg/L]. The morphology of the gill tissue was observed from paraffin sections and malondialdehyde (MDA) content, catalase (CAT), succinate dehydrogenase (SDH), and lactate dehydrogenase (LDH) activities in the gills, hepatopancreas, intestines, and muscle were determined. The results of the paraffin sections showed that with longer hypoxia time, the interlaminar cell mass of the branchial filaments of the new strain decreased, whereas the surface area of the branchial filaments increased and recovered after 7 days of constant oxygen. Under hyperoxic conditions, the substratum intercellular mass increased and the surface area of the branchial patches decreased. The results of the enzyme activity test showed that the changes of CAT activity and MDA content in different tissues had no obvious regularity with the extension of treatment time under both hypoxic and hyperoxic conditions; however, there were significant differences (P<0.05). LDH activity increased significantly and SDH activity decreased significantly under hypoxic conditions (P<0.05), whereas LDH activity decreased and SDH increased significantly under hyperoxic conditions (P<0.05). This study provided baseline data on the effect of DO on the gill tissue and enzyme activity of different tissues and laid the foundation for the breeding of new strains of M. amblycephala.

Abstract:The “land-sea-land” breeding pattern has become an important strategy for the rearing of Chinese sturgeon. In this study, juvenile Chinese sturgeon (Acipenser sinensis) in freshwater culture were utilized as the research object and an acclimation experiment was performed using continuous saltwater rearing conditions. To understand the adaptability changes of organs during osmoregulation, a comparative study was conducted on the structure of the gills, kidneys, and intestinal tissues of juvenile Chinese sturgeon grown in different salinities during seawater acclimation. The results showed that the survival rate of juvenile Chinese sturgeon in the seawater was 100%. During seawater acclimation, the breadth of the gill lamella significantly decreased (P<0.05), whereas the spacing of the gill lamella and chloride cell diameter significantly increased (P<0.05), suggesting that these juvenile Chinese sturgeon from a freshwater environment gradually adapted to a seawater environment by changing their gill lamella breadth and the space between the adjacent gill lamella, sped up their body and oxygen exchange capacity with the outside water conditions, and increased the chloride secretory cell sizes to improve the level of cell metabolism to cope in a water environment with high osmotic pressure. The glomerular diameter of the juvenile Chinese sturgeon decreased during seawater acclimation (P<0.05), and the number of glomerular decreased slightly; therefore, the juvenile Chinese sturgeon decreased the loss of body water by reducing the filtration function of their kidneys to adapt to the changes in osmotic pressure of the external environment. However, no obvious changes were observed in the intestinal tissue structure. The results showed that the juvenile Chinese sturgeon had strong seawater adaptability and osmotic adjustment of organs that adapted to the changes in seawater salinity by changing the breadth and spacing of their gill lamella, the size of the chlorine secretory cells, and the size and number of the glomerular.

Abstract:To study the relationships among tissues, organ weights, and body weight of tilapia (Oreochromis niloticus) and obtain organ coefficients, 40 adult male GIFT tilapia with body weights of 600~900 g were randomly selected, and their body weight and weights of the heart, liver, kidney, spleen, intestine, gill, skin, gallbladder, scales, muscle, and carcass (fish head, fins, and fish bones) were measured, as well as the total weight of each fish after dissection. Correlation analysis was performed on the body weight and organ weights of the various tissues, an optimal regression model was established, and model extrapolation was verified using approximately 500 g of tilapia tissue organ weights. The results showed that the organ coefficients of the heart, liver, kidney, spleen, intestine, gill, skin, gallbladder, scales, muscle, and carcass of GIFT tilapia were 0.12±0.02, 1.22±0.20, 0.11±0.03, 0.13±0.05, 1.58±0.30, 2.85±0.17, 3.31±0.38, 1.05±0.24, 2.89±0.41, 51.60±2.09, and 29.66±2.00, respectively, and all the measured tissue and organ weights and body weight were significantly positively correlated (P<0.001). This was consistent with the univariate linear regression model (y=bx) and the predicted error of the model for the heart, liver, kidney, spleen, skin, and muscle of the tilapia was within 8%. These results provide baseline data for fish physiology, toxicology, and the construction of a physiologically-based pharmacokinetics model for veterinary medicine of fish.

Abstract:To explore the effects of morphological traits on the body mass of Leiocassis longirostris, 115 × 14-month-old samples were randomly selected. A total of 12 morphological traits including body mass, total length, standard length, body height, body width, head length, head height, head width, snout length, caudal peduncle length, caudal peduncle depth, and trunk length were measured and analyzed using correlation analysis, path analysis, and multiple regression analysis. The results showed that the correlation among these 12 morphological traits were all very significant (P<0.01). The path analysis results showed that there were five morphological traits, including total length, standard length, head width, snout length, and caudal peduncle depth that reached a significant level (P<0.05). Among these, total length had the greatest direct effect on body mass. The common determinant coefficient of total length, standard length, head width, snout length, and caudal peduncle depth was 0.911, which was consistent with the results of the path analysis, indicating that these five morphological traits were the main factors affecting the body mass of L. longirostris. The multiple regression analysis established a linear regression equation with body mass (Y) as the dependent variable and total length (X1), standard length (X2), head width (X7), snout length (X8), and caudal peduncle depth (X10) as the independent variables, which was presented as Y=‒301.368+5.888X1+5.988X2+21.482X7+16.408X8+34.878X10 The results of this study provide a theoretical basis for the breeding of growth-related traits of L. longirostris and is of great significance for the breeding of individuals of this species.

Abstract:Here we clarify the effects of gradually changing hypoxia and reoxygenation on respiratory metabolism and antioxidant capacity in Exopalaemon carinicauda. In the present study, we investigated oxygen consumption and reoxygenation in a respiratory chamber in which we first created a low-oxygen environment by preventing aeration and isolating the air, following which the chamber was aerated and reoxygenated. Continuously aerated groups were used as the control groups. Water and shrimp tissue samples were taken after 0, 1, 2, 4, 5 h of hypoxia and 1, 4, 8 h of reoxygenation from the beginning of the experiment. Further, we recorded the dissolved oxygen concentration of the water and the activities of the main respiratory metabolism enzyme and the antioxidant enzyme in shrimp tissues at different time points. The results indicated that over time, the dissolved oxygen concentration in the experimental group significantly decreased and was significantly lower than that in the control group (P<0.05). The dissolved oxygen concentration in the control group remained stable. After reoxygenation, the dissolved oxygen concentration in the experimental group quickly returned to the control level. Over time, cytochrome c oxidase (CCO) and succinate dehydrogenase (SDH) activities in the gill, hepatopancreas, and muscle tissue from the experimental group continuously decreased, lactic dehydrogenase (LDH) and fumaric reductase (FRD) activities continuously increased. In addition, the value of SDH/FRD showed a gradually decreasing trend. During reoxygenation, SDH, LDH, and FRD activities gradually returned to the levels of the control group in three organizations; CCO activity in muscle continuously increased but was significantly lower than that in the control group at 8 h (P<0.05). Furthermore, the value of SDH/FRD also showed a gradually increasing trend. Over time, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione s-transferase (GST) in the gill, hepatopancreas, and muscle tissue showed a trend of first increasing and then decreasing, but the activities of peroxidase (POD) continuously decreased in the hepatopancreas, while fluctuating in both, the gill and the muscle tissue. During reoxygenation, the activities of SOD and CAT in the gill, hepatopancreas, and muscle tissue all showed a trend of first increasing and then decreasing, but showed no significant difference with the control group at 8 h (P>0.05). With the increase of recovery time, the activities of GPX and GST in the three tissues returned to the level of the control group, but the activities of POD in gill and muscle tissue were significantly lower than those in the control group under reoxygenation at 8 h. The results show that with the continuous decrease in dissolved oxygen concentration, the aerobic metabolic level of E. carinicauda gradually decreased, and the anaerobic metabolic capacity gradually increased, while during reoxygenation, the aerobic metabolic capacity gradually recovered. Antioxidant enzymes such as SOD, CAT, POD, GPX, and GST may play an important role in responding to oxidative damage during hypoxia and reoxygenation.

Abstract:A growth experiment was conducted to determine the optimal dietary protein to energy (P/E) ratio for juvenile tiger puffer (Takifugu rubripes) (initial average weight 14.95 g). Nine practical diets were formulated to contain three protein levels (36%, 42% and 48%), and three lipid levels (8%, 12% and 16%) in order to produce a range of P/E ratios (from 17.06 to 24.20 mg/kJ). Fish meal and soybean meal were used as main protein sources, and fish oil were used as the main oil source. Each diet was randomly assigned to triplicate groups of 30 fish with (14.95±0.37) g, stocked in polyethylene tanks (0.7 m×0.7 m× 0.4 m) supplied with a flow through seawater. Fish were fed by hand to apparent satiation twice daily (08:00 and 17:00). During the feeding trial, water temperature ranged from 24℃ to 28℃, salinity from 30 to 31, pH from 7.4 to 8.2, and dissolved oxygen from 5 to 7 mg/L. Juvenile tiger puffer was fed the experimental diets for 56 days. Based on two-way analysis of variance, the protein level, lipid level and protein to energy ratio of feed significantly affected the final weight, feed efficiency ratio (FER) and specific growth rate (SGR) (P<0.05). Those three growth parameters in the 42% and 48% protein groups was significantly higher than that in the 36% protein group (P<0.05), but there was no significant difference in the 42% and 48% protein groups (P>0.05). Those three growth parameters in the 8% lipid group was significantly lower than that of the 12% lipid group (P<0.05), while no significant difference was observed between the 12% and 16% lipid groups (P>0.05). In addition, there was no significant interaction between feed protein and fat levels on growth-related indexes. One-way analysis of variance showed that the final weight, FER, and SGR were the highest in the Diet8 (48/12) treatment, which were significantly higher than those in the Diet1 (36/8), Diet2 (36/12), and Diet3 (36/16) treatments (P<0.05), and was no significant difference compared with the Diet4 (42/8), Diet5 (42/12), Diet6 (42/16), and Diet7 (48/8) treatments (P>0.05). Considering growth performance and protein saving effect, these results suggest that the diet containing 42% protein and 12% lipid with P/E of 20.75 mg/kJ is optimal for juvenile tiger puffer.

Abstract:The purpose of this study was to investigate the effects of dietary vitamin C on the immunity, antioxidant capacity, and stress tolerance of juvenile Lateolabrax maculatus under acute cooling stress. An 8-week feeding trial was conducted with experimental diets containing 6.85, 46.90, 88.24, 167.43, 329.21, and 658.69 mg/kg vitamin C (Vc). Some fish were then exposed to acute cooling stress for 24 h and 48 h (transferred from 33℃ water to 27℃ water). The results showed that the serum levels of Complement 3 (C3) in each group after cooling were higher than before cooling, while the levels of serum Complement 4 (C4) showed the opposite pattern. When dietary Vc was 6.85~167.43 mg/kg, the levels of serum immunoglobulin M (IgM) at 24 h and 48 h were higher than at 0 h (P<0.05). However, there were no differences among the treatments with higher dietary Vc supplementation (329.21~658.69 mg/kg; P>0.05). After cute cooling for 48 h, the levels of serum lysozyme (LZM) were lower than at 0 h, but the Vc-supplemented groups were higher than the control group (P<0.05). The concentration of hepatic malondialdehyde (MDA) were higher in all groups after cooling stress than before cooling stress, but decreased with increasing levels of dietary Vc (P<0.05). Total superoxide dismutase (T-SOD) activity initially increased but then decreased with greater cooling time, and the glutathione (GSH) content increased with increasing dietary Vc supplementation. Heme oxygenase-1 (HO-1) activity in the 6.85 mg/kg Vc group was higher after cooling stress, but the groups supplemented with 88.24 to 167.43 mg/kg Vc had lower activities after cooling (P<0.05). The levels of heat shock proteins (HSP70) were higher before acute cooling, and when cooled for 48 h, HSP70 levels in the Vc -supplemented groups were lower than the control group (P<0.05). These results suggest that dietary Vc supplementation (46.90~167.43 mg/kg) may improve antioxidant capacity, reduce lipid peroxidation, and enhance the resistance to acute cooling in L. maculatus.

Abstract:Cordyceps confragosa is an entomopathogenic fungus that was isolated and identified from the disease Perca fluviavilis. The anamorphic stage, Lecanicillium lecanii, has been widely used as an insect biocontrol agent in agriculture. To date, whole-genome sequencing of C. confragosa isolated from fish has never been reported. This study used the Illumina PE150 sequencing platform to whole-genome sequence CHL02 strain, and the sequencing data were assembled and analyzed by the corresponding software. Gene prediction and functional annotation were conducted, secondary metabolite synthesis gene clusters were predicted, and pathogen-host interactions and comparative genomic analyses were performed. The sequencing results showed that the CHL02 genome is 36.17 Mb with a GC content of 53.09%. There were 8093 identified genes, 1618 TEs (Transposable elements), 4572 tandem repeats, and 114 transfer RNAs (tRNAs). A total of 7724 genes were annotated, 1985 of which were obtained by KOG annotation, and 2687 genes were involved in metabolic processes in the Gene Ontology (GO) cluster analysis. Twenty-two secondary metabolite synthesis gene clusters were predicted, and 1162 genes were involved in the pathogen-host interaction mechanisms. Gene cluster analysis and the phylogenetic tree showed high homology with the reference strain C. confragosa RCEF 1005 of insect origin. This study, for the first time, reported the whole genome sequencing and comparative analysis of C. confragosa CHL02 isolated from P. fluviavilis. These results provide an important theoretical foundation for further research into the mechanisms of perch pathogen infections.

Abstract:Dalian is the principal farming region for the economic alga Undaria pinnatifida, producing 65% of the national annual biomass. In late October 2019, insect pests caused serious damage to seedlings of U. pinnatifida in this region. We performed field investigation excursions and analyzed pest samples through the sequencing of the mitochondrial COⅠ gene. The results showed that explosive growth of Caprella danilevskii was the major cause. Caprella spp. are considered common biofouling organisms that usually inhabit the surface of maricultural algae and maricultural facilities, such as cultural rope and oyster nets. Steadily increasing seawater temperatures and the drifting brown alga Sargassum horneri biomass also played a role in the explosion of the pests. To the best of our knowledge, this is the first description of the morphological characteristics of different Caprella spp. collected in the same area in China. Caprella spp. are commonly found on the surface of cultured seaweed and marine aquaculture facilities, which has caused enormous losses to the Sargassum fusiforme farming industry in Fujian Province and Gracilaria lemaneaformis farming industry in Shandong Province for the past few years. We conclude with a proposal for dispersing or killing Caprella species through a traditional ammonium bicarbonate fertilizer application method. Sequence analysis revealed that these COⅠ gene fragments were 479 bp in length and showed an obvious AT-skewness. The transition/transversion bias (1.130) was much higher than the critical value (0.4), which could offer effective phylogenetic information. There was no insertion or deletion that occurred in each fragment. The average inter-species genetic distance was 0.231 (0.210~0.279) and the average intra-species genetic distance was 0.014 (0~0.030). The phylogenetic relationships among Caprella species were represented. The results proved that the cloned COⅠ gene contains rich information on gene variations. This gene is conserved in intra-species and is different among species. It is a suitable DNA barcode for identifying species in the genus Caprella.

Abstract:In order to study the physiological and ecological toxicity of polychlorinated biphenyls (PCBs) of marine microalgae, the growth, photosynthetic pigment content, glutathione S-transferase (GST), superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, and ultrastructure of Dicrateria zhanjiangensis were compared over 7 days under 2,2ʹ,4,4ʹ,5,5ʹ-hexachlorobiphenyl (PCB153) stress. The results showed that PCB153 stress had significant effects on the growth, photosynthetic pigment content, antioxidant and detoxification related indexes of D. zhanjiangensis (P<0.05). Increasing PCB153 concentration increased the inhibition of PCB153 on the growth of D. zhanjiangensis. In the 250 μg/L stress group, all the algae cells died on day five. The content of chlorophyll a, chlorophyll c, carotenoid, total light, and pigment had decreased significantly after the PCB153 stress (P<0.05). The decreasing photosynthetic pigment level was enhanced by the increase in PCB153 concentration. The MDA content of algal cells in all stress groups increased after the PCB153 stress. SOD and GST enzyme activities were significantly increased by low concentration PCB153 (<25 μg/L). Both enzyme activities were significantly inhibited by high concentrations of PCB153 (>25 μg/L). Under short-term low concentrations of PCB153 stress, the ultrastructure of the cells changed. To be specific, the organelle morphology altered and shrunk. Under high concentrations of PCB153 stress, the integrity of the cell membrane was destroyed, leading to cell rupture, autolysis and death. PCB153 can inhibit the growth and synthesis of photosynthetic pigments of D. zhanjiangensis. Low concentrations of PCB153 can activate the antioxidant and detoxification system. This activation improves self-protection capabilities. High concentrations of PCB153 can aggravate lipid peroxidation and destroy the normal function of antioxidant and detoxification systems, causing cell rupture and death.

Abstract:In this study, we measured the growth and pigment content of Betaphycus gelatinae under different inorganic nitrogen concentrations (50, 100, 200, 400, and 800 μmol/L), inorganic phosphorus concentrations (2.5, 5, 10, 20, 40, and 80 μmol/L), and different ratios of NH4+-N and NO3–-N (0/100, 25/75, 50/50, 75/25, and 100/0). The best nutrient conditions for the growth of B. gelatinae were thus evaluated. The results showed that the optimum nutrient conditions for the growth of B. gelatinae were an inorganic nitrogen concentration of 0~200 μmol/L, inorganic phosphorus concentration of 2.5~10 μmol/L, and NH4+-N to NO3–-N ratio of 25/75. Within the range of suitable nutrient conditions, B. gelatinae achieved high weight gain. When the inorganic nitrogen concentration exceeded 200 μmol/L, inorganic phosphorus concentration exceeded 10 μmol/L, or the ratio of NH4+-N to NO3–-N was higher than 50/50, the growth of B. gelatinae was slow but tolerance to adverse growth conditions was observed at the beginning of cultivation. However, with the extension of culture time, the growth of B. gelatinae became abnormal; severe white rot of algal bodies and a sharp decrease in weight gain was observed. Overall, our findings indicate that B. gelatinae grows faster under relatively low nutrient conditions and provide a theoretical basis for large-scale multiplication cultivation of B. gelatinae.

Abstract:Red rot and Oplidiopsis disease are the main diseases that occur during the farming of Pyropia (Bangiales, Rhodophyta) cultivated in the sea, which cause large areas of Pyropia to rot. Oplidiopsis disease is caused by Oplidiopsis sp., which is a biotrophic parasitic oomycete and there is currently no in vitro culture method for this species. The pathogen can only be identified by high-resolution microscopic observation and molecular methods. Experimental infection is typically undertaken by culturing diseased Pyropia with normal blades. In January 2019, 2000 acres of Pyropia disease occurred in a P. yezoensis cultivation area in Dafeng District, Yancheng City, Jiangsu Province, causing a large decrease of the P. yezoensis yield. We performed an investigation and pathogen identification of this disease. By macroscopic observation and studying the histopathology characteristics of the diseased thalli using a microscope, the Pyropia symptoms were found to be the same as that of the Oplidiopsis disease. The main symptoms were as follows: Pink spots appeared at the edge, base, and middle of the thallus at the beginning of the infection, which gradually faded and expanded as the disease progressed. During the late infection stage, the entire thallus became lighter and the tissue broke down and fell off. One to four spheroid parasitic oomycetes were found in one Pyropia cell, which contained multiple oil drop-like substances. Diseased thalli or their homogenates were used for experimental infection, with all causing Oplidiopsis disease symptoms in normal thalli at 10℃ and 20℃. To identify the pathogen, cox1 gene sequencing and phylogenetic analysis of the naturally and experimentally infected thalli were performed. The results showed that the pathogen sequences were clustered with O. porphyrae, O. pyropiae and O. porphyrae var. koreana with 100% similarity. In summary, the disease of P. yezoensis in Dafeng District was found to be caused by Oplidiopsis sp.

Abstract:“Salmon” is the trade name of salmon and trout, these are internationally recognized high-grade aquatic products. In recent years, the large-scale supply of rainbow trout has had a great impact on the world salmon trade, triggering a war of “real” and “fake” salmon. The public impression is that the high quality and high market price of the famous Atlantic salmon (Salmo salar) from Atlantic Ocean is not comparable to the cultured freshwater rainbow trout (Oncorhynchus mykiss). Thus, it is important to have knowledge about the species of salmon available in the aquatic market and whether the species information indicated on the label is true. It is very difficult for ordinary consumers to identify the species of salmon in the market. DNA barcoding has been widely used in the study of species taxonomy. It is a powerful technology for rapid and accurate identification of species. In this study, DNA barcoding was used to investigate the consistency between label information and the actual species of salmon in products across six large supermarkets and aquatic markets in Qingdao. Of the 74 salmon samples collected, 61 were S. salar, accounting for 82.43%; 11 were O. mykiss, accounting for 14.86%; and O. keta and O. kisutch accounted for 1.35%. Although the survey data shows that Atlantic salmon is the main salmon product in Qingdao, we identified that 14.86% of labels on salmon products were inconsistent with the test results, and more than 40% of the salmon products did not provide origin information. Thus, there are still some adulteration and food safety risks in aquatic salmon products. Market supervision of this internationally recognized high-end aquatic product needs to be strengthened. The relevant departments should urgently formulate product standards and testing standards to ensure the safety and traceability of salmon quality before inferior species affect the high public impression of salmon products.

Abstract:This study aimed to compare the taste compounds of different grades of Chinese mitten crab (Grade A: 200 g; Grade B: 150 g; Grade C: 125 g). The taste profiles of the different grades were distinguished by an electronic tongue. Free amino acids, 5´-nucleotides, organic acids, and inorganic ions were analyzed by an automatic amino acid analyzer, high-performance liquid chromatography (HPLC), and an ion chromatography, and the taste activity value (TAV) and equivalent umami concentration (EUC) were also calculated. Grade A crabs had the highest sweetness amino acid content, and grade C crabs had the highest umami amino acid content. The taste nucleotides were the highest in the grade C crabs. For the organic acids, only lactic acid and citric acid were detected, and Grade A crabs > Grade B crabs > Grade C crabs. Grade C crabs had the highest phosphate (PO43–) content, which was significantly (P<0.05) higher than Grade A and Grade B crabs. The TAV values of alanine, glycine, histidine, arginine, phenylalanine, proline, potassium (K+), chlorine (Cl–), and PO43– in the different grades were greater than 1 and contributed to Chinese mitten crab taste. Grade C crabs had the highest EUC value. Based on the contents of umami FAA, umami nucleotide, inorganic ions, and EUC value, the umami of grade C crabs was superior.

Abstract:With recent advances in detection technology the volatile substances in green algae, brown algae, red algae, and other algae have been identified. However, few studies have investigated the volatile substances of laver (genus Porphyra), especially, the analysis of the flavor change in Porphyra yezoensis after roasting. To address this issue, the electronic nose, FlavourSpec® flavor analyzer and SPME-GC-MS were used to compare the volatile components of P. yezoensis before and after roasting. The results of the electronic nose analysis showed that there were some differences in the volatile components derived from P. yezoensis before and after roasting. The two main components were the same, but the contribution of hydrocarbon compounds to the main components were different. Thus, the electronic nose was capable of discriminating the flavor differences in P. yezoensis before and after roasting. Flavor analysis showed that the volatile components of P. yezoensis before and after roasting were significantly different. The contents of nonanal, octanal, hexanal, valeraldehyde, benzaldehyde, and 2-ethyl-furan, were relatively higher in P. yezoensis. After roasting, the contents of methyl-pyrazine, 1-pentanol, furfural, 3-methyl-butanol, and 3-methyl-butanal were higher. The characteristic flavor and relative content of pyrazines also increased after roasting. The SPME-GC-MS analysis showed that the total volatile flavor compounds of laver samples before and after roasting were 83 and 86, respectively. The major volatile compounds of P. yezoensis were aldehydes, alcohols, ketones, and alkanes. The pyrazines consisted of methyl pyrazine, 2,5-dimethyl-pyrazine, 2-ethyl-5-methyl-pyrazine, 3-ethyl-2,5-dimethyl-pyrazine and 2-ethyl-6-methyl- pyrazine. These compounds increased significantly after roasting. In summary, the main flavor substances of P. yezoensis varied significantly after roasting, especially the content of pyrazines (increased significantly). This research clarifies how the roast flavor is generated, allowing us to optimize our processing technology. Future research is required to understand the mechanisms underlying the formation of flavor.

Abstract:Owing to its non-toxicity, excellent biodegradability, film-forming property, and biocompatibility, sodium alginate (SA) is used as a common and promising raw material for biopolymer films. However, pure SA films tend to have defects in performance and functionality; therefore, blend films, consisting of two or more types of components, are more widely used as precursors for biopolymer films. To investigate the synergy between SA and Enteromorpha polysaccharide (EP), a degradable composite film was fabricated by blending SA and EP with glycerol as a plasticizer. The effect of different polysaccharide mass ratios, total mixed solution concentrations, and glycerol contents on the tensile strength, elongation at break, water vapor permeation, and water solubility of the films was investigated. In addition, the microstructure of the films was characterized through Fourier transform infrared spectroscopy and scanning electron microscopy. Results showed a good compatibility and synergy between SA and EP. Moreover, no obvious phase separation was observed in all SA/EP composite films. The component mass ratio, total concentration, and glycerol content had a significant influence on the properties of composite films. Among these factors, mass ratio had the most significant influence on the films. The addition of an appropriate amount of EP improved the tensile strength and elongation at break of the SA film and reduced its water vapor transmission rate; however, it slightly increased the water solubility of the SA/EP composite film. When the component mass ratio was modified from 10:0 to 8:2, the tensile strength increased from 99.22 MPa to 108.41 MPa, the elongation at break increased from 5.14% to 6.20%, and the water vapor transmission rate decreased from 6.445×10–11 g/(m·s·Pa) to 6.027×10–11 g/(m·s·Pa), which were the comprehensive optimal mechanical and barrier properties of the films. The total concentration and glycerol content of the SA/EP composite films were further optimized. The best total concentration and glycerol content were 1.6% (m/v) and 0.9% (m/v), respectively. The results demonstrate that the addition of EP enhanced the mechanical and barrier properties of the SA films and that there is a relatively strong synergistic effect between SA and EP.