Abstract:

Abstract:

Abstract:Pacific saury Cololabis saira is one of the most harvested species in the temperate waters of the Northwest Pacific Ocean, and an important part of their fishery industry. In 2014, the yearly catch from mainland China, from more than 40 fishing vessels, reached 620,300 tons. The Pacific saury has also become a dominant fish species of the North Pacific Fisheries Commission (NPFC), and the conservation of saury resources has received increasing attention. It is therefore necessary to assess their stock to ensure that sustainable fishery practices occur, however, there is little previous research in this field. Based on the data of catches from 2003 to 2017, collected by the NPFC and the resource abundance data submitted by China, the stock assessment and risk analysis of alternative management strategies for the Pacific saury were carried out using a Bayesian Schaefer model. During the process, two scenarios, a standard scenario and a sensitivity analysis scenario, were considered. The Schaefer model was chosen not only because of the lack of age structure data for the Pacific saury, but also because the migration mechanisms and stock structures of the Pacific saury are very complex and insufficiently understood. Bayesian analysis is one of the methods which can be used to improve the reliability of stock assessments in data-poor situations, by utilizing information from other species with good-quality data or other known information. The results showed that compared with the results of the two scenarios, those of the posterior distribution of the three parameters are similar. Under the standard scenario, the MSY(maximum sustainable yield) is 752,600 tons. To maintain the MSY, the biomass and fishing mortality should be 2.401 million tons and 320,000 tons, respectively. While, under the sensitivity analysis scenario, the MSY is 700,300 tons. To maintain the MSY, the biomass and fishing mortality should be 2.325 million tons and 310,000 tons, respectively. The status of the Pacific saury stock is currently good and it is not under overfishing. If the harvest rate is set below 0.3, then the stock will be protected and the probability of resource collapse will be very low. The harvest rates from 2003 to 2017 are all close to 0.3, so there is reason to be optimistic for the potential of this resource. We have concluded that in the future, a harvest rate of 0.3 for Pacific saury should be set, as the best and most sustainable management strategy.

Abstract:The issue of population division of the small yellow croaker (Larimichthys polyactis) has been controversial since the 1950s. Previously used methods for studying the population classification of these marine fish populations include the mark-recapture method, catch yield statistics method, parasite labeling method, morphometric/meristic characters method, molecular biology method, and chemical fingerprints of the calcified structures method. Each of these techniques has its own reliability as well as limitations. In this study, the content of delta 13C (δ13C) and delta 18O (δ18O) in the left sagittal otolith samples of 92 Larimichthys polyactis obtained from the investigation of fishery resources in Bohai Sea and Yellow Sea, was determined using stable isotope mass spectrometry. A cluster analysis was carried out based on differences in the content of delta 13C and delta 18O among samples. The results showed that the early supplement population of Larimichthys polyactis, predominant during the autumn season, in the Yellow Sea and Bohai Sea can be divided into four major groups, which are listed as Bohai and the northern Yellow Sea population, the central Yellow Sea population, the offshore population of southern Yellow Sea, and the coastal population of southern Yellow Sea. However, there was no station between the offshore population of the southern Yellow Sea and the three other populations in the Yellow and Bohai Sea. The discriminant and cluster analysis revealed that the successful rate of discrimination was 75.9%, 80.0%, 81.0%, and 95.6% in the Bohai and northern Yellow Sea population, the central Yellow Sea population, the offshore population of southern Yellow Sea, and the coastal population of southern Yellow Sea, respectively. The overall successful rate of discrimination was recorded to be 82.6%. The population of southern Yellow Sea was subdivided into offshore and coastal populations for the first time, and no station crossing between the two populations was recorded. With this study, we propose to establish the basis for population classification of Larimichthys polyactis.

Abstract:Neon flying squid (Ommastrephes bartramii) is a short-lived species with high economic value and important ecological status. The study of squid resources plays an important role in the development of Chinese offshore fisheries. Based on the data from the Northwest Pacific squid fishery and sea surface temperature (SST) data from August to October of 20052016, and the habitat suitability index (HSI) model established by the predecessors, the size of the squid's habitat was correlated with catch per unit of fishing effort (CPUE) and the catch. We found that the average area of suitable habitat (HSI>0.6) was the largest in 2015, reaching 1,087,369 km2. In 2008, the average suitable habitat area was the smallest (618,407.5 km2). The suitable habitat distribution in the selected area can effectively reflect the resource distribution of the squid; however, there is no significant correlation between the size of the suitable habitat area and the catch and CPUE (P>0.05). The reasons may be as follows (1) the concentration of squid fishing vessels resulting in single-vessel catches that do not characterize the CPUE; (2) large-scale climate change, particularly El Niño and La Niña, affecting squid resources; (3) changes in Kuroshio and Tide also affect the amount of squid resources.

Abstract:The phytoplankton community structure in the coastal aquaculture area of Rongcheng was analyzed based on the results of four surveys during 2016. The influence of environmental factors on the phytoplankton community in the Rongcheng coastal aquaculture area was discussed using canonical correlation analysis. The results identified a total of 66 species that belong to 29 genera of 3 phyla. The dominant species of phytoplankton include Skeletonema costatum, Melosira sulcate, Asterionellopsis glacalis, Chaetoceros tortissimus, Nitzschia pungens, and Chaetoceros lorenzianus with seasonal succession. In the spring A. glacalis increased quickly in Rongcheng Bay to make it the most important dominant species of this season, but not in Sanggou Bay, when compared with the results of previous studies. The abundance of phytoplankton varied from 16.9×104 to 251.7×104 cells/m3 over the 4 seasons, the average density of whole year was 119.3×104 cells/m3, which was the highest in summer and the lowest in autumn. The Shannon-Wiener diversity index and Pielou’s index range from 1.60 to 2.13 and 0.40 to 0.60, respectively, and the diversity of phytoplankton was the highest in the summer, and the mode of the phytoplankton structure changed with the seasons, but the levels of phytoplankton remained normal all year round. Canonical correlation analysis showed that the most important factors affecting phytoplankton community structure are dissolved oxygen, silicate, NH+4, sea surface temperature and pH. These may promote or inhibit the growth of specific species and cause the rise of dominant species. Large-scale kelp farming in the area changed the amount of nutritional salt, high density shellfish farming consumed the natural enemies of phytoplankton, and shellfish excretion also changed the composition of nutritional salts in the coastal waters; therefore, local aquaculture in the Rongcheng coastal waters may be an important factor in the pattern of phytoplankton community structure in addition to the influences of seasonal changes.

Abstract:In this study, we have evaluated the level and distribution of nutrients in the Qingdao Lancelet Reserve Area using the results of surveys of the Qingdao Lancelet Reserve Area in September (Summer) and November (Autumn), 2017. The results showed that the average level of dissolved inorganic nitrogen (DIN) in the autumn was higher than that in the summer, and the average NO2-N and NH4-N levels were 1.98 and 1.44 times higher in the autumn than in the summer, respectively. However, the average NH4-N and PO4-P levels in the summer was about 88.8% and 47.6% of that in autumn, respectively. According to the seawater quality standard, in the summer the DIN content was better than the first-level seawater quality standard, and the PO4-P content was also better than the first-level seawater quality standard; in the autumn, the DIN content was better than the first-level seawater quality standard, and PO4-P content was worse than the first-level seawater quality standard. In terms of area distribution across the Qingdao Lancelet Reserve Area, the DIN concentration distribution trends of the seawater in the summer were core area > experimental area > buffer area; the DIN concentration distributions in the autumn seawater were buffer area > experimental area > core area. The distribution trends of PO4-P content in the summer seawater were experimental area > core area > buffer area. The distribution trends of the PO4-P content in the autumn seawater were core area > experimental area > buffer area. In the summer of 2017, the N/P ratio was the same as the Redfield ratio in the Qingdao Lancelet Reserve Area, but in the autumn of 2017, the N/P ratio was lower than the Redfield ratio, with relatively low levels of DIN. According to the potential eutrophication assessment model, the Qingdao Lancelet Reserve Area’s nutrition level was poor in both the summer and autumn of 2017. Generally speaking, the Qingdao Lancelet Reserve Area was at an oligotrophic level, and the seawater quality in the Qingdao Lancelet Reserve Area was good.

Abstract:Phytoplankton are the major primary producers in the ocean and play a crucial role in the marine food chain. Understanding the dynamics of the marine phytoplankton community can provide insights into the succession process and current status of marine fishery resources. Based on the net-phytoplankton samples collected from the Bohai Sea in the summer (June and August) of 2015, we studied the phytoplankton community composition, diversity, abundance, and dominant taxa in the Bohai Sea. Compared with historical data, the phytoplankton community structure in the Bohai Sea was changed markedly. The chlorophyll-a concentration had changed slightly during recent years, but was much higher than that in the 1980s and 1990s, and the regions with lower values (<1.0 μg/L) were much smaller than those 20 years ago. In terms of the dominant taxa, the dominance of the genera Chaetoceros and Coscinodiscus was found to be slightly decreased, whereas the species Skeletonema costatum, which had been an important dominant species in the Bohai Sea, was not observed in the two months of summer in 2015. In contrast, Paralia sulcata and Pyrrophyta (Noctiluca scientillans in June and Ceratium tripos in August) were still dominant in the Bohai Sea, and the abundance and dominance of Achnanthes brevipes and Pseudo-nitzschia pungens was higher than those in the years before 2015. The diversity indices (Shannon diversity and species richness and evenness) of phytoplankton were at a moderate level. Such a trend was mainly caused by the significant change of the nutrient structure in the Bohai Sea. This may change the structure of the marine food chain and influence the growth and reproduction of commercial fishes and shrimps (e.g., Konosirus punctatus, Liza haematocheila, and Acetes chinensis) that feed on phytoplankton. Consequently, this will have potential impacts on fishery production and the structure and function of the ecosystem in the Bohai Sea.

Abstract:The Bohai Sea is a semi-enclosed bay with weak water exchange capacity and pollution levels that are increasing with the development of modern industry and agriculture. Heavy metal pollution has become an important factor, as it both directly and indirectly endangers human health. The release of heavy metals from sediments might significantly impact on the water environment and the ecological health of the sea. A survey of heavy metal content, distribution, enrichment, and pollution state of the sediments was conducted in August 2013 to determine the seas characteristics. The contents of Cu, Pb, Zn, and Cd in the surface sediment samples from 34 sites were measured, and the content and distribution characteristics of these heavy metals were studied. Single factor standard indices and potential ecological risk indices were used to evaluate the status of the heavy metal pollution and the degree of ecological risk. The results indicated that the average heavy metal content was low, and that all individual element contents were lower than the first class of GB 18668-2002. The spatial distribution of the heavy metals in the sediments showed that their contents decreased between the offshore and central regions. The Cu, Pb, and Zn surface sediment heavy metals, showed the most obvious changes with relation to their location; their coastal content was higher and was gradually reduced in samples moving towards the offshore region. The Cd content in the Yellow River estuary was high to the east and decreased along the western sides. The individual single-factors for each of the heavy metals in the surface sediments was less than 5, which indicated a low degree of pollution, and the descending order of the average single factors was Pb, Cu, Zn, As, Cd, and Hg. The single potential ecological risk factor of the six heavy metals, except for the Hg element at No. 1 (54.44) station, were less than 40 (0.9~38.80), which indicates a low level ecological risk. The descending order of the potential ecological risk factors was Hg, As, Cu, Zn, Pb, and Cd, and ranged from 0.58 to 10.50. The comprehensive potential ecological risk indices are all less than 150, and ranged from 16.39 to 79.57, which indicated low level of ecological risks. The descending order was Hg, Cd, As, Pb, Cu, and Zn. The Daqinghe River estuary had the highest risk values, and Hg was the main potential ecological risk factor in the surveyed area.

Abstract:Coccolithophores, as important primary producers in the marine ecosystem, respond sensitively to changes in environmental conditions. When coccolithophores die, the calcified plates (Coccoliths) that they secrete can reflect environmental changes. Hence, coccoliths are important indicators for studying paleoenvironmental and paleoclimatic changes. However, most studies on coccolithophore sediments have been conducted in the Atlantic and the Northeast Pacific Oceans; studies on the continental shelf in the Northwest Pacific are rarely reported. This study aims to address this shortage of long-term records for coccolithophores in the Yellow Sea. The results from these experiments can be compared with climatic changes to explore the corresponding relationship. The results will also provide fundamental data and a theoretical basis for related research. In this study, the coccolith fossils from one box core taken from a sampling position (Station N02) on the coast of the Shandong Peninsula, China, in the northwestern part of the South Yellow Sea, were used for the research. Species identification and abundance statistics were carried out and obtained for the coccolith fossils in the sediment, which scaled 140 years. Eight species of coccolithophore were found. The absolute abundance of coccoliths from the N02 Station core ranged from 5.07×106 to 14.21×106 coccoliths/g, with an average value of 9.76×106 coccoliths/g. Gephyrocapsa oceanica and Emiliania huxleyi were the two species with the highest abundance. By comparing the sediment record with the climatic data from the station, a correlation with the sea level pressure was observed. Sea level pressure can be used as an indicator for the East Asian winter monsoon. The analysis showed that when the East Asian winter monsoon was strong, the coastal currents of the Yellow Sea provided a good nutrient-salt environment for the coccolithophores at the N02 Station, resulting in a high abundance of coccoliths.

Abstract:Ecological niche model MaxEnt was applied to estimate the suitability probability of Laminaria hyperborea in the Bohai and Huanghai Seas of China. In this study, the native occurrence data of L. hyperborea and 21 key environmental variables were selected to build the ecological niche model and then redefined into occurrence zones by suitability probabilities. The contribution of each environmental variable to the model was estimated using JackKnifing techniques. The results showed that the contributions from temperature and light intensity to the spreading of L. hyperborea dominated all considered environmental parameters. In the forecasted areas, suitable probabilities were significant when the temperatures range from 718℃ and the light intensities were below 52 E/(m2∙d). Although the concentrations of N and P contributed to the prediction model, they would barely reach the limitation value for L. hyperborea in natural sea water. Additionally, our results showed that 1.67% of the entire forecasted area had a medium distribution probability, which was mainly limited within Changhai Town of Dalian City. Of the total area, 5.12% was low occurrence probability zones, mainly spreading along the east to the Liaodong Peninsula, north to the Shandong Peninsula, and northwest of the Bohai Sea. Furthermore, unbefitting and marginal suitable distribution areas represent 88.51% and 4.70% of Chinese coast, respectively. The results indicate that Changhai Town could be an ideal location for the construction of L. hyperborea beds.

Abstract:The culture area of Pyropia sp. at Fuxin fishing port, in Rizhao City, China, were investigated from November 2016 to March 2017. The temporal and spatial distribution characteristics of the nutrient and community structures of phytoplankton and their relationships were analyzed. The main conclusions were as follows: Generally, the spatial horizontal distribution of inorganic nitrogen, phosphate and silicate concentrations showed a decreasing trend between the nearshore area and offshore sea areas. Nitrate, silicate, phosphate, dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen concentrations were significantly different in the different months. Over, all the surveyed sea area was at a mesotrophic level. The range of phytoplankton density was (0.049~3.031) × 104 cells/L and the phytoplankton growth was likely to be controlled by the silicate and phosphate. 37 species of diatom belonging to 27 genera, followed by dinoflagellates represented by 8 taxa (7 genera) and chrysophyceae by 1 taxa (1 genera) were recorded. The most common and dominant species were Skeletonema sp., Chaetoceros sp., and Coscinodiscus sp. The diversity index of phytoplankton decreased significantly in January and March, which may be caused by the sharp decrease in salinity and richness of nutrients in January, significant rises in ammonia nitrogen concentrations, and significant decrease in phosphate concentration in March. The ammonia nitrogen concentration and DIN/P ratio were both negatively correlated with the diversity index of phytoplankton. The negative relationship was significant for the non-cultured area, while it was not significant for the cultured area. It can be inferred from the above correlation analysis results that Pyropia sp. cultivation is beneficial for reducing the ammonia nitrogen levels and DIN/P ratio in the sea area, thus increasing the stability of phytoplankton community structures and the species diversity of phytoplankton, which will help to prevent the occurrence of red tides. These results provide information valuable for marine environment protection, red tide prevention and future developments of aquaculture systems.

Abstract:To develop a method for the rapid identification and classification of fishes in the middle reaches of the Yangtze River, 168 DNA sequences of the cytochrome oxidase subunit Ⅰ (COⅠ) gene collected from GenBank. 64 common freshwater fish species in 7 orders, 11 families, and 50 genera were analyzed to test the efficacy of species identification using a DNA barcode microarray. The results showed that the intraspecific genetic distances ranged from 0 to 0.0776 (average, 0.0079). The interspecific distances ranged from 0.003 to 0.0190 (average, 0.084). The interspecific genetic distance was larger than the intraspecific distance, and all 168 sequences formed species units in a neighbor-joining phylogenetic tree, indicating that the DNA barcodes could be used to identify these 64 species. Based on the DNA microarray technology, 112 probes were selected from 43 species with high specificity, accounting for 67.2% of the total species. Thus, the DNA barcode microarray provided technical support and a new way to identify fish species in the middle reaches of Yangtze River basin.

Abstract:The objective of this study was to identify microsatellites from the transcriptome sequences of Coilia ectenes using MISA software. These microsatellites could create very useful resources in the evaluation of germplasm resource and marker-assisted breeding of C. ectenes. The results showed that a total of 33,896 microsatellites were identified with repeating units, at lengths of 1~6 bases, from 71,869 unigenes. Different types of repeat SSRs had considerably different distribution characteristics. The majority of the microsatellite loci consisted of mono-, di-, and tri-nucleotide motifs (34.94%, 49.47%, and 13.34%, respectively). Dinucleotide microsatellite repeating units were the most abundant in the C. ectenes transcriptome, and the AC/GT repeating units were the most ascendant repeating unit (75.25%). The dominant repeating units for the mononucleotide and trinucleotide motifs were A/T (86.25%) and AGG/CCT (28.57%), respectively. Different nucleotide repeat motifs had different repetitions that had a reducing trend, with the increase in the number of nucleotides in repeat motifs. Among the 100 designed primer pairs, 16 pairs proved to be polymorphic microsatellite markers. In the present study, 16 polymorphic microsatellite loci were characterized to evaluate the genetic diversity of the selected C. ectenes (F3). The results showed that the average number of effective alleles (Ne), the average observed heterozygosity (Ho), the average expected heterozygosity (He), and the average Shannon´s information index (I) of the selected C.ectenes (F3) were 1.7580, 0.3414, 0.3977, and 0.6278, respectively. These results indicate that it is feasible to develop microsatellite markers based on the C. ectenes transcriptome and polymorphic microsatellite loci obtained in this study will facilitate further studies on the population genetic management and conservation of C. ectenes.

Abstract:The relationship between five morphological traits [body length (X1), body width (X2), body height (X3), head length (X4), and caudal peduncle height (X5)] and the body weight (Y) of 12-month-old Oujiang color common carp (Cyprinus carpio var. color), with four different body color patterns [red and black (RB), white and black (WB), whole red (WR), and whole white (WW)] were investigated using correlation analysis, regression analysis, and path analysis. The results showed that the coefficient of variation of all the studied traits was highest in the WR fish, demonstrating that the WR had the greatest potential for selective breeding. For the four different color patterns, the correlation coefficients among the morphological traits and body weight were all extremely significant (P≤0.01), and the greatest correlation coefficient was found between the body height and body weight. The multiple regression equations obtained with the stepwise regression method for the four body color patterns were listed as Y1 = –517.069+12.628X1 +67.916X2 +94.885 X5 (RB); Y2 =–525.711+38.085X2 +68.869X3 +72.206X5 (BW); Y3=–502.952+90.980X2 +18.172X4 +113.965X5 (WR); Y4 = –537.119+22.932X1 +55.113X2 +48.203X5 (WW). The path coefficient analysis showed the highest direct effect of body width on the weight in the RB (0.387) and WR (0.504) fishes, and body height on weight in the WB fishes (0.546), and body length on weight in the WW fishes (0.508). The current study indicated that the morphological differences among the four body color patterns of the Oujiang color common carp had different degrees of influence on the morphological traits of body weight. Consequently, this study provides important insights that can be utilized for selective breeding of Oujiang color common carp in the future.

Abstract:Black rockfish (Sebastes schlegelii) is an economically important marine fish. Our team constructed a three-generation breeding population of Sebastes schlegelii by combining population selection with family breeding. In order to understand the phenotypic correlation between the main morphological traits and body weight and the differences among the three-generation breeding population of S. schlegelii, the body weight (Y, g) and eleven other morphometric traits (cm), e.g., total length (X1), body length (X2), body height (X3), head length (X4), tail length (X5), caudal peduncle length (X6), caudal peduncle height (X7), tongue length (X8), trunk length (X9), eye diameter (X10), and head length behind the eyes (X11), were correlated on the three-generation continuous breeding population of 8-month-old S. schlegelii. Path analysis and gray correlation analysis were conducted to define the effect of major morphometric traits on body weight in the three-generation continuous breeding population. The results showed that all the correlation coefficients between morphometric traits and body weight achieved highly significant levels (P<0.01) or significant levels (P<0.05). The results of path analysis showed that the path coefficients between body height and trunk length were highly significant (P<0.01) in F1 and F2. The path coefficients of body height and caudal peduncle length were also highly significant (P<0.01) in F3. The multiple regression equation between the morphological traits and body weight for the three-generation breeding population were established as Y(F1)=−47.383+17.097X3+7.308X9, Y(F2)=−34.615+15.779X3+ 3.901X9, Y(F3)=−54.496+21.966X3+7.283X6. The results of gray correlation analysis showed that there was a certain difference in the size and order of the gray correlation between the body weight and morphological traits of the three-generation breeding population. However, the grey degree between body weight and body height, and the total length and body length, was the highest. The morphological traits affecting body weight were found to be different by two analytical methods, and there were obvious differences among the three-generation population. The first controlling trait was body height, indicating that body height is a predominant morphometric trait affecting body weight. This research may provide an essential reference for determining the measurement index of S. schlegelii in selective breeding.

Abstract:Grass carps are seriously threatened by GCRV (grass carp reovirus) that can cause high mortality to fingerling and yearling grass carps. Grass carp snout fibroblast cells (PSF) are highly sensitive to GCRV. Junctional adhesion molecule A (JAM-A), an immunoglobulin superfamily member, acts as a viral cell receptor. In our previous study, the cDNA sequences of grass carp jam-a1, jam-a2, and jam-a3 (named gcjam-a1, gcjam-a2, and gcjam-a3) were cloned. Based on this, qRT-PCR was used to analyze the expression pattern of gcjam-as at different embryonic and juvenile development stages and in GCRV-GD108-infected PSF cells. The results showed that the expression pattern of gcjam-a1, 2, and 3 differed during the embryonic development stages. mRNA expression of gcjam-a1 could be detected in unfertilized eggs and at a lower level from the fertilized egg stage to 1 dph (day post hatch). However, the mRNA was highly expressed at 1~3 dph and high levels were maintained from 3 dph to the end of the experiment (15 dph). The expression of gcjam-a2 and gcjam-a3 was very low at different embryonic development stages compared to that of gcjam-a1. gcjam-as were only slightly expressed in non-infected PSF cells. After GCRV-GD108 infection, the expression of S7 in PSF cells increased significantly, and the expression of gcjam-as in PSF cells also increased to different levels after GCRV-GD108 infection. Upregulation of the gcjam-as was in the order: gcjam-a1> gcjam-a2>gcjam-a3. The results showed that the expression of jam-as was related to GCRV infection in PSF cells and that the expression of jam-a1 was most influenced by GCRV-GD108 infection. It is also expressed in early embryonic development, suggesting that jam-a1 is the most relevant to GCRV infection. This study will lay the foundation for further research on GCRV receptors.

Abstract:A shrimp hatchery of Litopenaeus vannamei was infected by an unknown disease during the zoea stage with declined feeding, reduced activity, and increased mortality. In order to diagnose and explore the pathogenic factors causing the zoea disease, we collected samples from two diseased rearing ponds at zoea stage 3 (Z3) and zoea stage 1 (Z1), respectively. PCR detection for nine known pathogens, including WSSV (White spot syndrome virus), IHHNV (Infectious hypodermal and hematopoietic necrosis virus), VpAHPND (Acute hepatopancreatic necrosis disease caused by Vibrio parahaemolyticus), TSV (Taura syndrome virus), IMNV (Infectious myonecrosis virus), YHV (Yellow head virus), EHP (Microsporidian Enterocytozoon hepatopenaei), CMNV (Covert mortality nodavirus), and SHIV (Shrimp hemocyte iridescent virus) showed negative results. Histopathological diagnosis showed unknown brown particles in the epithelial cells of the hepatopancreatic tubules. The results of bacterial isolation and identification for potential pathogens resulted in only two isolates of Vibrio alginolyticus on 2216E media. The average survival rate of gnotobiotic brine shrimp (Artemia franciscana) nauplii immersion- challenged with these isolates were 58% and 83% respectively. The microbial communities were profiled by high-throughput sequencing of the V3~V4 hypervariable region of 16S rRNA gene using the Illumina HiSeq sequencing platform. Meta-16S-sequencing revealed the microbial diversities and their relative abundance in the zoea stage of L. vannamei. The results showed that Proteobacteria, Bacteroidetes, and Firmicutes were the most dominant phyla in the entire bacterial community from both samples, but their relative abundance was obviously different. At the genus level, Vibrio was the most abundant genus in both samples, at 74.3% and 60.5%, respectively, and the relative abundance of Tenacibaculum (21.9%) was the second highest genus in the Z1 stage sample. Collectively, the information regarding the management of larval rearing and the above results of the case study imply that the disease may be caused by an opportunistic infection with some strains of V. alginolyticus having moderate pathogenicity under the dystrophia of larva caused by quality degradation of larval feed due to the expiration of storage.

Abstract:To explore the growth and development patterns during the early life period of Octopus vulgaris, the morphological characteristics of larva, juvenile, and young O. vulgaris under industrialized breeding conditions were observed and recorded. From hatching to 49 days of age, eight larvae were sampled randomly every two days, and total length, arm length, mantle length, mantle width, body weight, and sucker number in the longest arm were measured. In conditions of water salinity of 30~32 and 18.6℃~26.0℃, the average full length of the newly hatched larva was (3.05±0.11) mm; the yolk sac of newly hatched larvae was absorbed by the larvae themselves before hatching or within 9 hours after hatching; the 1-day-old larva just began to feed and the 17-day-old larva could feed on shrimp; at the age of 35 days, the larvae were ready for benthonic living; the body color of 60-day-old larva changed from transparent to milky white; at the age of 80 days, the body color of the larva is the same as that of the adult; the organs of 100-day-old larva were mature except for the gonads, and the morphological characteristics were consistent with those of the adult. The results showed that O. vulgaris larva (1~49 days of age) body weight exhibited a cubic function growth relationship with total length, represented by the equation: y=5×10–5x3–0.0009x2+0.0072x–0.0132; total length exhibited a linear growth relationship with arm length, represented by the equation: y=–0.0012x3+0.0492x2+0.0243x+0.2179; total length, body weight, arm length, mantle length, and mantle width exhibited a cubic function growth relationship with days respectively, with the regression equations: y=–0.0001x3+0.0105x2–0.0122x+3.0562, y=–2×10–7x3+4× 10–5x2–0.0004x+0.0034, y=–0.0004x3+0.0247x2–0.1037x+0.8214, y=–0.0004x3+0.0124x2+0.0749x+1.4757, and y=–3×10–5x3+0.0025x2+0.0354x+1.4026. We divided the early period of O. vulgaris into four developmental stages: Larvae octopus, juvenile paralarvae octopus, juvenile benthonic octopus, and young octopus. Each stage was determined by feeding style (endogenous or exogenous), morphological and biological characteristics, and ratio between arm lengths and mantle length.

Abstract:This experiment was to investigate the effects of fish protein hydrolysate on growth, feed utilization, body composition, and morphological structure of muscle fibers in turbot (Scophthalmus maximus L.). Six isonitrogenous and isolipidic diets were formulated and fed to fish. The experimental diets contained two control groups with no fish protein hydrolysate, positive control group including 44% fish meal, negative control group including 22% fish meal. Four experimental groups with different levels of fish protein hydrolysate and fish meal, PH4.5A group contained 22% fish meal and 4.5% fish protein hydrolysate, PH4.5B group contained 17% fish meal and 4.5% fish protein hydrolysate, PH18A group contained 22% fish meal and 18% fish protein hydrolysate, and PH18B group contained 0.5% fish meal and 18% fish protein hydrolysate. The results showed that there were no significant differences in the weight gain rate and specific growth rate between PH4.5A and PH18B groups (P>0.05), while PH4.5A group and PH18B group were significantly higher than that of PH4.5B group and negative control group (P<0.05) and significantly lower than that of PH18A and positive control groups (P<0.05). There were no significant differences in the feed efficiency, protein efficiency and protein retention efficiency between PH18A and positive control groups (P>0.05), while PH18A and positive control groups were significantly higher than that of PH18B, PH4.5A and negative control group (P<0.05). Contrary to feed efficiency, there were no significant differences in the feed intake among PH18A，PH18B and positive control groups (P>0.05), while these groups were significantly lower than that of PH4.5A, PH4.5B and negative control groups (P<0.05). There were no differences in the contents of crude protein and crude lipid between PH4.5B and negative control groups (P>0.05), while these groups were significantly lower than that of PH18A and positive control groups (P<0.05). There were no significant differences in total amino acids, essential amino acids and non-essential amino acids in the muscles among six groups (P>0.05). The muscle fiber cross-sectional area in PH18A group was significantly higher than that of PH18B, positive control, PH4.5A, negative control, PH4.5B groups (P<0.05), and PH18B group was significantly higher than PH4.5B group (P<0.05). The muscle fiber density of PH18A group and PH18B group was significantly lower than that of PH4.5B group (P<0.05). The above results show that both 18% and 4.5% fish protein hydrolysate added to high plant protein feeds can promote the growth of turbot and increase the feed efficiency and protein deposition rate of turbot, and growth and feed utilization in fish given 18% fish protein hydrolysate diet showed better than that of fish given 4.5% fish protein hydrolysate diets. For the morphological structure of muscle fiber, 18% fish protein hydrolysate in diets can increase the cross-sectional area of muscle fiber and reduce the muscle fiber density, while 4.5% of the fish protein hydrolysate did not affect significantly the cross-sectional area of the muscle fiber and the fiber density.

Abstract:This investigation aimed to compare the effects of ice crystals, endogenous proteases, and oxidation on the quality of obscure pufferfish (Takifugu obscurus) fillets during frozen storage, and detemine the dominant factors impacting their quality deterioration. The fillets were immersed in 1) liquid nitrogen, 2) iodoacetic acid solution, or 3) antioxidant mixtures (tea polyphenol and ascorbic acid solution), designed to inhibit the formation and growth of large ice crystals, activities of endogenous proteases, and the oxidization of proteins and lipids during storage, respectively. Therefore, the roles of these three factors in changing the quality of the frozen pufferfish fillets were differentiated. The hardness, thawing loss, cooking loss, total volatile basic nitrogen (TVB-N), K value, activity of Ca2+-ATPase, myofibril fragmentation index (MFI), and myofibril lengths were evaluated as quality indicators. The results showed that controlling the growth of ice crystals on the frozen pufferfish fillets had the greatest impacts on quality. After 24 weeks, the hardness of frozen pufferfish fillets with smaller ice crystals was about 26.8 % and 20.5 %, higher than that with the inhibition of endogenous proteolytic activities and oxidation, respectively. When it came to the thawing loss, it was about 44.2% and 44.8% lower with quick-freezing than in the other two groups. In addition, the TVB-N, K value, and activity of Ca2+- ATPase with the treatment of liquid nitrogen before freezing changed more slowly. In this group, the values of the quality indicators were 10.5 mg/100 g, 6.8 %, and 1.43 μmol Pi/mg/10 min after 24 weeks, respectively. As a result, ice crystals, endogenous proteases and oxidation have all contributed to the deterioration of frozen pufferfish fillets. Among them, the formation of ice crystals was the dominant factor for quality loss in frozen pufferfish fillets and the effects from the endogenous proteases and oxidation on the quality of pufferfish fillets followed, and there was no significant differences between these two factors.

Abstract:Heat treatment is the leading and most traditional means of cooking and sterilizing meats from aquatic products and poultry product for the processing industry. The meat protein composition and structures are briefly described in this manuscript and the denaturing of the different proteins during the heat treatments are discussed. Most of the sarcoplasmic proteins either from aquatic or poultry meat aggregate between 40℃ and 60℃, but some coagulation can occur at up to 90℃. The unfolding of myofibrillar proteins in solution begins at 30℃~32℃, followed by protein–protein associations at 36℃~40℃, and subsequent gelation at 45℃~50℃ (conc.>0.5% by weight). At temperatures between 53℃ and 63℃, collagen denaturation occurs, followed by collagen fibre shrinkage. If the collagen fibres are not stabilised by heat-resistant intermolecular bonds, they dissolve and form gelatine on further heating. In addition, the structural changes and quality changes of different kinds of meat due to the heat treatment are discussed. In most cases, after meat is heated to a certain temperature, its microscopic structure shrinks, the sarcomere length shortens, the water holding capacity decreases, and the shear force which represents hardness rises once or twice. Minced meat products including surimi products, hamburger patties and emulsified sausages have disordered muscle system structures due to the effect of heat processing. Compared with emulsified sausage, hamburger patties have a higher occurrence rate of whole fiber and fiber fragments, and their content is as high as 50%~70%, and resulting in greater shrinkage after heating. Compared to poultry product, surimi products showed to be much more complicated. Salt soluble proteins in fish muscle would reform a cubic network containing water when it was heated to be surimi products due to the formation of disulfide bridge, hydrophobic interaction and hydrogen bond, etc. In emulsified sausage, the myofibrillar protein is extracted due to the crushing and stirring of muscle, resulting in a dense protein network gel during heat treatments, and water can be effectively maintained through capillary force. Understanding the structural changes of different meat proteins and the mechanism of quality changes during heat treatments can provide a theoretical basis for formulating a more reasonable meat processing methods.

Abstract:Antarctic krill (Euphausia superba) is a species of krill found in the Southern Ocean, and an important strategic resource of China, whose growth and reproduction are susceptible to the Antarctic water environment. Due to their huge biomass (estimated to be 125 to 725 million tons), nutrient contents, and active ingredients, Antarctic krill can be widely used in functional food, aquaculture, medicine, and other fields. As an important extractive, astaxanthin has high antioxidant activity and could play an important role in anti-oxidation, anti-inflammatory, anti-tumor, and immunity enhancement treatments, as well as in the prevention of cardiovascular diseases. However, astaxanthin has poor stability and poor water solubility, as the molecules are easily damaged by oxygen, light, and heat. In order to reduce the oxidation rate of astaxanthin and improve the storage stability of astaxanthin, the use of maltodextrin and hydroxypropyl-β-cyclodextrin (HP-β-CD) as the wall material for the microencapsulation of the Antarctic krill astaxanthin by spray drying and the physical and chemical properties of the product after microencapsulation were studied. The results showed that when the mass ratio of maltodextrin to HP-β-CD wall material was 1:3, the mass fraction of astaxanthin was 4.76%, the mass fraction of polysorbate-80 was 0.87%, and the solids concentration was 0.20 g/ml; the microencapsulation efficiency of astaxanthin microcapsules was 98.77%. The water content of the prepared astaxanthin microcapsule was (3.11±0.11)%, the solubility was (94.32±0.08)%, and the angle of rest was (34.16±0.24)°. Stability experiments showed that compared to the non-microencapsulated astaxanthin crystals, astaxanthin microcapsules at high temperatures, the retention rate of astaxanthin increased from 28.72% to 78.32%; under natural light conditions. The astaxanthin retention rate increased from 45.27% to 84.88%; under aerobic conditions and the retention rate of prime increased from 20.76% to 74.97%. The above-mentioned results indicated that microencapsulation can significantly improve the solubility and stability of astaxanthin, which can provide technical support for the preparation of astaxanthin microencapsulated products.

Abstract:With the highest annual production among flatfish, turbot (Scophthalmus maximus) is reared as the major industrial aquaculture marine fish species in North China. In the culture process, members of this species are subject to infection with a variety of pathogens. In 2017, massive death of reared turbot occurred in a farm in Lianyungang City, Jiangsu Province. Externally, no clinical signs were observed for most of the diseased fish. However, after dissection, splenic and renal tubercles were found in all the diseased fish. Homogeneous colonies were isolated from diseased or moribund fish and were named as SM-Myco001. Healthy turbot were subjected to challenge tests by intraperitoneal injection using SM-Myco001. SM-Myco001 was found capable of causing death in turbot, especially at a higher water temperature (22℃). The diseased turbot displayed clinical signs, such as splenic and renal tubercles, similar to those observed in naturally infected fish. SM-Myco001 was identified as Mycobacterium marinum based on bacterial morphology, analytical profile index identification, and 16S rRNA gene sequencing. This study suggests that a strain of M. marinum is the causal agent of splenic and renal tubercle disease in turbot. As a first report, to our knowledge, this study provides a new perspective on disease control in the flat fish aquaculture industry in China.