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Abstract:Metabolic diseases, which are always characterized with abnormal lipid metabolism and severe fat deposition, have been commonly observed in farmed fish. However, the causes of the abnormal lipid metabolism in fish are complicated and difficult to be identified. In recent years, several studies have shown that environmental endocrine disrupting chemicals (EDCs), which are widely spread in the aquatic environment, not only have chronic toxic effects on fish development and reproduction, but also affect fish lipid metabolism and cause severe fat deposition, which would damage the quality and food safety of farmed fish. For the first time, this review systematically reviews the effects of EDCs on fish lipid metabolism. Persistent organic pollutants (POPs), heavy metals (Hg, Pb, Cd and Cu), environmental estrogens and artificially synthesized medicines (fibrates and antibiotics) are four major EDCs in water environment. In general, water or dietary exposure of these EDCs would disturb the biochemical activities and/or expressions of the enzyme proteins in the lipid metabolism pathways, including upregulating lipogenesis, inhibiting mitochondrial fatty acid β-oxidation, adipose tissue lipolysis and lipid transport cross tissues, and so on. The exposure of EDCs with high doses would also impair the functions of cellular organelles, such as mitochondria and peroxisome, which are important in the lipid metabolism. Recently, the disturbing effects of EDCs on some lipid metabolism-related nuclear receptors, such as peroxisome proliferators-activated receptors (PPARs) and sterol-regulatory element binding proteins (SREBPs), had also been found. However, it should be pointed out that among these EDCs, they also have specific mechanisms in affecting fish lipid metabolism and tissue deposition of fat. Even in the same EDC, different exposure method, duration and doses would also cause different effects in disturbing lipid metabolism in fish. In future research, more attentions should be paid on the endocrine disturbing effects of new environmental pollutants, combined effects of different EDCs, and the molecular mechanisms of EDCs effects. This review is helpful in studying EDCs in fish metabolism and also provides important theoretical supports for green and sustainable aquaculture development.

Abstract:Traditional CPUE (catch-per-unit-effort) units show diversity and complexity due to the different types of fishing methods, sizes of vessels, and characteristics of fisheries on which they are based, leading to problems with data incomparability among multiple fishing gear types. To assess the fish stocks in a specific areas of the sea, the impact of various different fishing types needs to be considered, but using traditional CPUE data makes it difficult to assess these stocks because of variations in the units used. We reviewed the relevant literature and screened out 24 types of CPUE units. The following processes were then carried out to standardize CPUE units across multiple fishing types. First, eight CPUE units appropriate for different fisheries were selected based on general criteria. Those CPUE units were then divided into two groups based on overall similarities and differences. The two main applicable CPUE units of kg/(kW·d) and kg/d were identified at this stage. Finally, the coefficient of variation (CV) of each of these two selected CPUE units was calculated. The smaller the value of the CV was, the more stabile the unit was concluded to be. The optimum unit was determined to be kg/(kW·d) based on this stability criterion. The landings of nine major fishing types in the South China Sea in each of the four seasons of 2016 were then analyzed using this optimal CPUE unit. The results of this analysis showed that the fishing capacity of different gear types were arranged in the following order: Seine > Pair trawl > gillnet > falling-net > stow net > otter trawl > shrimp trawl > pot > fishing tackle, corresponding to mean values of 29.57, 8.77, 4.96, 4.81, 4.73, 3.95, 3.11, 3.08, and 2.35 kg/(kW·d), respectively. After catch data are standardized by the optimal novel CPUE unit developed in this study, comparisons and analyses of fishing capacity among gear types, relative abundance and utilization levels of different fisheries resources, and fisheries catch statistics could be conducted with greater accuracy than was previously possible.

Abstract:Viral covert mortality disease (VCMD) is an emerging disease caused by covert mortality nodavirus (CMNV). VCMD recently resulted in severe economic losses in China due to shrimp aquaculture infections. To identify the natural hosts of CMNV in the pond culture system, samples of Carassius auratus were collected for testing purposes from the drainage channel of a shrimp farm affected by VCMD. The results of CMNV reverse transcription nested PCR showed that the RNA of C. auratus sample could be amplified and produced the expected target gene fragment. Histopathological analysis showed that CMNV infection in C. auratus caused brain nervous tissue vacuolation. Obvious karyopyknosis occurred in the corpora bigemina granular cells and cortical pyramidal cells. In situ hybridization analysis showed CMNV positive signals in regions of the brain and cardiac muscle with pathological damage. Transmission electron microscopy analysis verified the brain nervous tissue vacuolation and the presence of CMNV particles in the cardiac muscle. The results of the present study indicate that CMNV can cross the species barrier to infect fish and cause pathological damage in the target tissues. Our findings emphasize the need for paying close attention to the high risk of CMNV infections in other fish species, especially freshwater fishes.

Abstract:In order to investigate the germplasm of rice flower carp cultured in the paddy fields of the northern region of Guangdong Province, 67 rice flower carp individuals were chosen at random. After measuring their morphological traits and calculating their morphological ratios, the rice flower carp were divided into two clusters according to shape. One cluster tended to have an elongated shape, and the other had a rounded shape. There were highly significant differences in the ratios DCP/LCP (depth of caudal peduncle to length of caudal peduncle), LC/LCP (length of Caudal fin to length of caudal peduncle), and DB/LS (body depth to soma length) between the long-shaped and round-shaped fish groups. The results suggested that the differences between the two groups were dependent on these three parameter values. Principal component analysis of the morphological characteristics of these rice flower carp and of six common populations reported previously was carried out. The results showed that in the PC1, which characterized the shape of the whole body, the long-shaped flower carp was similar to Cyprinus carpio var. xingguonensis, C. carpio var. specularis, and C. carpio var. Jian, and distinguished from the round-shaped rice flower carp, which clustered with C. carpio var. color and C. carpio var. wuyuannensis. In the PC2, which characterized the shape of the head, the rice flower carp of both shapes clustered together and were distinguished from C. carpio var. specularis and C. carpio var. color. The cluster analysis suggested that the long-shaped rice flower carp was similar to C. carpio var. xingguonensis, C. carpio var. specularis, and C. carpio var. Jian within one cluster, and C. carpio var. wuyuannensis and C. carpio var. color in another cluster. The round-shaped rice flower carp was positioned between the two clusters. These results indicate that rice flower carp are mixed strains. It is necessary to carry out family-wise selection on the basis of morphology. Furthermore, polymorphism analysis of a partial sequence (606 bp) of the COⅡ gene from rice flower carp showed that there were two polymorphic sites that formed four genotypes, where the proportion of polymorphic sites was only 0.33%. Compared with the seven species from Cyprinus, the phylogenetic tree based on the COⅡ gene sequences indicated that rice flower carp is one population of C. carpio. These results of the polymorphic investigation and genetic analysis in the present study lay the foundation for further breeding research on rice flower fish.

Abstract:In order to clarify the variations in population genetic patterns of Acrossocheilus wenchowensis in the Xin’an Basin, 170 individuals from 6 different geographic populations were collected. Subsequent analyses of population genetic structure and historical demography were carried out using the mitochondrial DNA cytochrome b (mtDNA cyt b) gene. The results suggested that the genetic diversity of different geographic populations varied greatly, and that of A. wenchowensis was low. Whereas different levels of genetic differentiation were detected among the 6 populations, molecular genetic variation was mainly detected within populations owing to the short divergence time. Population expansion had occurred approximately 3.35 million years ago, while the global temperature was freezing. The expansion had not been affected by low temperatures. Therefore, the Xin’an Basin may have been a potential refuge during the glacial period. Reconstruction of the ancient area suggested that the Shuaishui and Lian rivers may have been the areas of A. wenchowensis origin in the Xin’an Basin. After population diffusion, isolation, and differentiation, the current distribution patterns emerged. The identification of the original population provides a theoretical basis for the conservation of A. wenchowensis in the Xin’an Basin.

Abstract:In this study, the full-length cDNA sequence of the polymeric immunoglobulin receptor (pIgR) gene of the half-smooth tongue sole (Cynoglossus semilaevis) was obtained on the basis of its predicted sequence. The cDNA sequence was 1419 bp and included an open reading frame (1020 bp, encoding 339 amino acids), a 5¢-UTR region (109 bp), and a 3¢-UTR region (290 bp). Conserved domain analysis revealed that the pIgR protein of the half-smooth tongue sole contained one signal peptide, two immunoglobulin-like domains, and one transmembrane domain. According to the protein sequence homology alignment and phylogenetic tree analysis, the pIgR sequence of the half-smooth tongue sole had high similarity with the turbot (Scophthalmus maximus) and Japanese flounder (Paralichthys olivaceus) pIgR sequences. Real-time PCR analysis of pIgR expression in different tissues of healthy half-smooth tongue sole showed that the highest expression was in the gill and the lowest expression in muscles. After pathogen challenge with Vibrio harveyi, pIgR expression initially increased and then decreased in five tissues (liver, spleen, kidney, intestine, and gill) of the half-smooth tongue sole, with the peak time point being at 48 h in the spleen and gill, and 72 h in the liver, kidney, and intestine. Unlike in the internal organs, pIgR expression in the skin was continually upregulated. These results indicate that pIgR is involved in the immune response of the half-smooth tongue sole toward bacterial pathogens, and this finding may contribute to the discovery of an antibacterial gene marker.

Abstract:To investigate the effect of temperature stress on the antioxidative and nonspecific immune systems of Paramisgurnus dabryanus under transportation conditions, the liver activities of superoxide dismutase (SOD), catalase (CAT), lysozyme (LZM), and alkaline phosphatase (AKP) as well as the malondialdehyde (MDA) content, and the serum content of alanine aminotransferase (ALT) and aspartate transaminase (AST) were determined. The following results were obtained: The activities of SOD and CAT in the liver were significantly lower (P<0.05), and the MDA content was significantly higher (P<0.05), than the levels in the control group. During the recovery period, the activities of the two antioxidative enzymes in each experimental group increased gradually and the MDA content decreased gradually. There was no significant difference between the control group and each experimental group at the end of the recovery period (P>0.05). The liver activities of LZM and AKP in each experimental group were significantly lower than that of the control group (P<0.05) at the end of the stress period. During the recovery period, the LZM and AKP activities remained at the stress level at the end of the stress period, whereas their activities in the other experimental groups increased gradually and there was no significant difference (P>0.05) compared with the control group at the end of the recovery period. The changes in serum AST and ALT content during the stress period were significantly higher than those in the control group (P<0.05). During the recovery period, the AST and ALT content showed a downward trend until the end of the recovery period. In addition, the ALT content in the high-temperature group dropped to the control group level. The results showed that temperature stress significantly inhibited the antioxidative capacity and nonspecific immunity of P. dabryanus, where the high-temperature stress caused irreversible damage to the nonspecific immune function of the fish, whereas the other inhibition effects were recoverable.

Abstract:Covert mortality nodavirus (CMNV), a recently emerged RNA virus, is the pathogen responsible for viral covert mortality disease, which has caused serious losses of shrimp aquaculture in China in recent years. In order to determine the transmission, prevalence, and evolution of CMNV in the coastal provinces and cities in China, national wide survey of the molecular epidemiology of the CMNV and it’s variants was conducted, based on analysis of shrimp samples collected from 2016 and 2017 by using the methods of RT-nPCR, RT-LAMP, and TaqMan RT-qPCR in present study. The analyses found the presence of CMNV-positive specimens in the major species of cultured crustaceans, including Litopenaeus vannamei, Marsupenaeus japonicus, Fenneropenaeus chinensis, Penaeus monodon, and Macrobrachium rosenbergii. CMNV-positive specimens appeared in almost all the coastal provinces, such as Hebei, Shandong, Zhejiang, Fujian, Guangdong, and Hainan. The results based on RT-nPCR assays showed that the prevalence rates of CMNV among the collected samples were 11.8% (30/254) and 7.8% (30/387) in 2016 and 2017, respectively. The results based on RT-LAMP assays showed that the prevalence rates of CMNV were 6.7% (17/254) and 3.9% (15/387) in 2016 and 2017, respectively. The results based on TaqMan RT-qPCR assays showed that the prevalence rates of CMNV were 17.7% (45/254) and 12.4% (48/387) in 2016 and 2017, respectively. The total prevalence rates of CMNV were 26.8% (68/254) and 16.3% (63/387) in 2016 and 2017, respectively, based on the above mentioned three methods. The results based on RT-LAMP assays showed that the prevalence rate of MDNV was 9.4% (24/254) in 2016. The high prevalence of CMNV in the major shrimp species and in the main farming areas revealed that this virus still threatened shrimp aquaculture in China during 2016~2017. Moreover, mutation of the RNA-dependent RNA polymerase (RdRp) gene of CMNV will raise the risk of appearing of false-negative result in CMNV molecular tests, which is of great concern. Meanwhile, the high prevalence rates of the emerging CMNV variant, MDNV, is a reminder that close attention needs to be paid to the high risk of MDNV transmission widely in farmed crustaceans.

Abstract:Glycine decarboxylase is a key glycolytic enzyme that is involved in both the glycolytic and gluconeogenic pathways. In this study, the glycine decarboxylase gene from the Chinese shrimp Fenneropenaeus chinensis (FcGLDC) was cloned and sequenced for the first time. The full-length cDNA sequence of FcGLDC was 3481 bp long and contained a 17 bp 5¢-UTR, an 86 bp 3¢-UTR, and a 2829-bp open reading frame that encoded a 942 amino acid peptide with a calculated molecular mass of 104.66 kDa and theoretical isoelectric point of 6.51. The full-length FcGLDC DNA sequence was 4964 bp long and contained 12 exons and 11 introns. Multiple sequence alignment showed its high similarity with the glycine decarboxylase genes from other arthropod species: Zootermopsis nevadensis (71%), Pediculus humanus corporis (68%), and Aedes albopictus (68%). Phylogenetic analysis revealed that FcGLDC was in the same class with those from the other arthropods. The FcGLDC transcript showed the highest expression in muscles and the lowest expression in the gill. Stimulation of the shrimp with white spot syndrome virus (WSSV) resulted in changes in FcGLDC expression profiles in the hepatopancreas, gill, and muscles. In the gill, the transcript level was approximately 4.47-fold higher than that of the control group (P<0.05) at 24 h post injection (hpi). In the hepatopancreas, no significant difference was observed between the WSSV-challenged group and the control group (P>0.05). In the muscles, the transcript levels increased significantly, by approximately 19.98-fold at 24 hpi and 4.21-fold at 72 hpi, relative to the control group levels (P<0.05). Four single nucleotide polymorphisms were identified, using direct sequencing and time-of-flight mass spectrometry. Association analysis indicated that there was no significant association between the genotype and WSSV resistance (P>0.05). These results show that FcGLDC is inducible and may be involved in the shrimp’s immune response to pathogens.

Abstract:This study was done to assess regional differences among abalone from different habitats and develop a new and efficient method to identify abalone from different habitats of origin. To do this, the content and composition of 13 major elements and trace elements (Na, K, Mg, Ca, Fe, Zn, Cu, Ni, As, Al, Mn, Cr, and Se) in the muscle tissue of 18 kinds of abalone samples from the four major breeding provinces of Guangdong, Fujian, Shandong, and Liaoning, China, were determined and analyzed using principal component analysis (PCA). The results showed that the elemental content differed among the 18 abalone samples. The variation in Manganese (Mn) was the largest [the coefficient of variation (CV) was 74% among samples], followed by Nickel (Ni) (CV = 65%), and then by Selenium (Se) (CV = 60%); all the rest of the analyzed elements had CVs higher than 10%. At the same time, after using the PCA method to reduce the dimensions of these data, six elements were effectively extracted from among the 13 elements examined that cumulatively explained 89.87% of the variance among samples. These characteristic elements of abalone from different habitats were Ca, Se, Na, Fe, Mn, K, and Ni, and a comprehensive model of the six principal components including them was established as follows: F = 0.2777F1 + 0.2652F2 + 0.1295F3 + 0.1066F4 + 0.0656F5 + 0.0541F6, where F1 represents the first principal component, and F2~F6 represent the second to sixth principal components, respectively. On the basis of the comprehensive PCA score, the top six samples were samples No. 2, 6, 17, 13, 7, and 15, and the lowest one was sample No. 5. Among these, sample No. 2 had a higher content of all characteristic elements and better quality than all others. The PCA approach was found to be quite suitable for the evaluation of the nutritive quality of abalone. The establishment of this PCA model provided an empirical basis for the theoretical determination of the origin of abalone samples.

Abstract:At the early stage, the shell of the strain F1 of “Shenzi No.1” Hyriopsis cumingii is transparent, so the workload involved in selection and improving the breeding efficiency can be reduced at this stage. In this study, seven different selection methods were tested with different selection orders and retention rates of objective traits. When shell length (SL) was the first trait selected and a deep purple shell (PN) was the secondarily selected trait, the different methods used were SL 50% × PN 20%, SL 30% × PN 33%, and SL 20% × PN 50%. However, when the selection order was the opposite of this, the selection methods used were PN50% × SL 20%, PN 30% × SL 33%, and PN 20% × SL 50%. Moreover, according to conventional experience, juveniles with a deep purple shell and large size were selected simultaneously in a seventh control gorup. This was done to compare the experimental results of this control group with those of the other six methods. The total retention rate of each method was 10%. After five months of culture, the growth traits (shell length, shell height, shell width, body weight, mantle weight, and shell weight) and the inner shell color parameters (L, a, b, and dE) of the selected mussels were measured to evaluate the early selection effects of these seven methods. The results showed that the different selection methods led to differences in the effects of early selection. The growth traits of individuals selected by the PN 50% × SL 20% and PN 20% × SL 50% methods were the best, while the selection effect of the SL 30% × PN 33% method was the worst. However, when the deep purple shell was selected as the objective trait, the other three methods (SL 50% × PN 20%, SL 30% × PN 33% and SL 20% × PN 50%) were better than the above methods. The selection effect of the SL30% × PN 33% method was the worst for the growth traits. The traits of H. cumingii selected by the traditional method were not prominent in any of the experimental groups. The method of taking SL as the first selection trait was SL × PN, while the method of taking PN as the first selection trait was PN × SL. In the early stage, the SL × PN method can be used to select for clams with a deep purple shell color, while the PN × SL method can be used to select for larger clams. The results showed that the selection order had a significant impact on the selection effect. In addition, when the traits with higher expectations were selected at the end, the effect of the selection was better. Further more, both the retention rate and the compound selection response affected the selection effect.

Abstract:The early growth characteristics of Octopus ocellatus larvae raised under culture conditions were analyzed. Ten larvae were sampled at different periods from post-hatching to when larvae were 50-days-old, and their body weight, total length, arm length, and mantle length were measured. We described the growth characteristics of O. ocellatus, to define the different phases characterizing this species’ post-hatching development. The larval stages of O. ocellatus were divided into a planktonic stage and a benthic stage, with benthic life beginning at the age of 11 d. At water temperatures of 22℃~24℃, the cultured larvae could grow from an average total length of 10.03 mm on the first day post-hatching to a benthic octopus with an average length of 16.21 mm by the 11th day post-hatching. The results showed that the body weight of planktonic O. ocellatus increased with time according to a cubic function, the equation of which was: y = 0.0001x3 – 0.0019x2 + 0.0098x + 0.0409. On the other hand, benthic O. ocellatus body weight increased according to an exponential function, the equation of which was: y = 0.0284e0.092x. The total length of O. ocellatus larvae exhibited a cubic relationship with body weight, the equation of which was: y = –8e–07x3 + 0.001x2 – 0.011x + 0.099. Total length was linearly related with arm length, as represented by the equation: y = 1.314x + 4.952. Body weight, total length, and arm length exhibited cubic growth functions over time, as represented by the equations: y = 6e–05x3 – 0.003x2 + 0.036x – 0.03, y = 0.0004x3 + 0.002x2 + 0.307x + 10.604, and y = 0.0004x3 – 0.007x2 + 0.364x + 4.205, respectively. The larval body is transparent, and the visceral mass of the larva is a golden color during the first day post-hatching. As the individual grows, the color deepens to a yellowish brown. Newly hatched O. ocellatus usually have 14 to 16 suckers, and with the constant growth of the larval wrist the number of wrist suckers gradually increases. The new suckers appear at the end of the wrist, each beginning as a small, raised bulge that then increases in size until a new sucker is formed.

Abstract:Fructose 1,6-bisphosphatase (FBP) is the rate-limiting enzyme in the gluconeogenesis process. When animals and plants are exposed to adverse environmental conditions, such as temperature stress, FBP participates in the gluconeogenesis pathway to maintain the body’s sugar balance, playing an important role in animal and plant stress resistance. In this study, we obtained the FBP gene of the pearl oyster Pinctada fucata martensii (Pm-FBP) using the RACE technique and detected the expression level of this gene in six tissues of P. fucata martensii as well as its temporal expression pattern in the gill at 17℃ (low-temperature group), 22℃ (control group), and 32℃ (high-temperature group). According to the results of sequence analysis, the full-length Pm-FBP sequence was 1381 bp long, including a 54 bp 5¢ UTR and a 62 bp 3¢ UTR. The open reading frame was 1020 bp long, encoding a peptide of 339 amino acids with a predicted molecular mass of 37.13 kDa. The isoelectric point of Pm-FBP was 6.02. Pm-FBP had a Pfam FBPase conserved domain, 6 potential O-linked glycosylation sites (Ser36, Ser56, Ser57, Ser76, Ser80, and Thr115), a potential N-glycosylation site, a metal-binding site (Asp-Pro-Ile/Leu-Asp- Gly/Ser-Thr/Ser), and 46 phosphorylation sites. Multiple sequence alignment showed that Pm-FBP had the highest homology with the corresponding gene in Crassostrea gigas, with a similarity value of 83%. The phylogenetic tree indicated that Pm-FBP was clustered with shellfish such as C. gigas, and then clustered with other mollusks, and arthropods and vertebrates were clustered together, and the evolutionary tree was clustered into three branches. Real-time fluorescence quantitative results showed that Pm-FBP was expressed in the adductor muscle, gill, gonads, hepatopancreas, foot, mantle, and other tissues. The gonads had the highest expression of Pm-FBP, followed by the hepatopancreas and gill. Time-series analysis showed that Pm-FBP expression first increased and then decreased, reaching the maximum at 72 h, which indicates that it may be involved in the response of P. fucata martensii to temperature stress. The Pm-FBP expression levels in the high-temperature and low-temperature groups decreased significantly at 120 h, suggesting that Pm-FBP may play an important role in short-term temperature stress. The results of this study provide reference data for further exploration of the adaptability of P. fucata martensii under temperature stress.

Abstract:Pyropia is one of the most economically important seaweeds, which is mainly cultured in China. In recent years, water quality deterioration caused by long-term and intensive culture have led to problems for Pyropia aquaculture, such as disease outbreaks, decreased yields, and lower product quality. Microorganisms are important components of the environment and have important effects on the growth of other organisms. In this study, the microbial community structure in a Pyropia yezoensis aquafarm in Changdao, China, was studied using 16S rDNA-based high-throughput sequencing technology. Whether there were correlations between different environmental factors and the abundance of some predominant bacterial taxa was also tested to explore the environmental impacts of Pyropia farming. The results showed that microbial diversity was rich in the surveyed marine area. The abundance of Proteobacteria was the highest among all of the identified bacterial phyla. When the Pyropia farming area was compared with nearby non-farming areas, it was found that the highest abundances of microbial species occurred in the near-shore area (CDCNS), followed by the Pyropia farming area (CDPF), and the microbial diversity was the lowest in the offshore area (CDCOS). Cluster analysis of the samples was carried out based on Bray-Curtis similarity coefficient values calculated among them. The microbial community structure of CDCNS and CDCOS formed a clade that was separated from CDPF. Furthermore, the twenty genera with the highest abundances were used for a further cluster analysis, and the results showed that CDCNS and CDCOS clustered together, with more genera being especially abundant in CDPF. The predominant bacteria from CDPF included Muricauda, Pseudomonas, Halomonas, Erythrobacter, and Marinobacter. Suspected pathogenic bacteria of Pyropia, such as Pseudoalteromonas tetraodonis and Pseudoalteromonas citrea, were not identified in the surveyed areas. Indeed, the abundance of the genus Pseudoalteromonas was lower than 0.1%, suggesting that the environment was safe for Pyropia farming. Dissolved oxygen (DO) and pH decreased gradually from CDCNS to CDCOS, and TSS increased gradually from CDCNS to CDCOS. The content of NH4+-N was the lowest in CDPF and the highest in CDCOS, while the salinity was the highest in CDPF. Correlation analyses showed that there were relationships between environmental factors and environmental microorganisms. The abundance of Ammoniphilus was positively correlated with the content of NH4+-N, which was the lowest in CDPF and the highest in CDCOS. The distribution of Halomonas was related to salinity, and the abundance of Halomonas was significantly higher in CDPF than in the other two areas. Halomonas functions in denitrification, and thus can promote the conversion of N from an oxidized state to reduced forms that are more easily absorbed by algae. In conclusion, this study represented the first report of the structure of the microbial community in a Pyropia aquafarm and its correlation with environmental factors. The results showed that farming Pyropia had significant influences on the environmental microbial community, which were closely related to variations in environmental factors caused by Pyropia farming. Such changes in environmental factors and microbial structure had corresponding effects on Pyropia growth. The mechanisms of these interactions between environmental microorganisms and Pyropia growth should be further investigated in the future.

Abstract:Conventional bacteriological culture techniques and molecular identification methods were used to reveal the composition and structure of the intestinal microflora in sea cucumber (Apostichopus japonicus) larvae at different developmental stages and the microflora in the aquaculture environment (feeds and aquaculture water), and then the correlations between these were analyzed. The results of bacterial culture from sea cucumber larvae showed that there were no culturable bacteria during the stages preceding the development of the mouth (gonads, eggs, zygotes, and gastrula), but culturable bacteria did occurr after larvae developed a mouth and began feeding. From the auricularia to doliolaria larval stages, the number of culturable bacteria in the gastrointestinal (GI) tract was low. After the larvae reached one month of age, the abundance of culturable bacteria in the GI tract increased significantly, and the highest level (108 CFU/g) was reached in four-month-old juveniles. The proportion of culturable bacteria that were made up of culturable Vibrio species ranged from 2.2% to 77.3% across the different developmental stages. The results of bacterial culture from the environment showed that there was no significant change in the bacterial content in the aquaculture water over time. However, as the ingredients in the feed used for different early developmental stages of sea cucumber changed, there were significant differences in the bacterial content in these feeds. Sixty-five dominant strains isolated from the aquaculture system were identified by sequencing their 16S rDNA. They were classified into 14 genera and 43 species. Correlation analyses revealed that over the course of the development of the sea cucumber larvae, the bacteria obtained from their feed likely had a great impact on the microbial flora in their GI tracts. This study laid the foundation for the analysis of the formation processes and succession patterns of GI tract microflora in sea cucumber, as well as for the screening and application of probiotics in aquaculture.

Abstract:Vibrio parahaemolyticus (VP), which is ubiquitous in the marine environment, is one of the key foodborne pathogens affecting humans. It is thus of great significance for both scientific research and public safety that we understand how and what environmental factors affect its growth. To determine the functional relationship between a combination of environmental factors and VP growth, in this study the effects of temperature, salinity, pH, phosphate, nitrate, and ammonium on the growth of this kind of bacteria were investigated using response surface methodology (RSM). First, a Box-Behnken design was used to optimize the three critical internal factors of temperature, salinity and pH for this species, using optical density (OD600 nm) as a marker for the growth of VP. It was found that for these factors, the optimum parameters were 34.5℃, 3%, and 8.0, respectively. Based on these results, the combined effects of phosphate, nitrate, and ammonium on the growth of VP were then further studied with the same method to develop a response model. The coefficient of determination (R2) of the model equation was 0.9217, while the correction coefficient (R2) was 0.8211. The regression model had an F-value of 9.16, and was thus statistically significant (P=0.004). These results indicated that the model proposed herein had satisfactory accuracy. Results obtained from verified testing were also in good agreement with those obtained with the model. Clearly, phosphate, nitrate, and ammonium all exhibited negative effects on the growth of VP. These outcomes are beneficial to the culture of VP, and even to the establishment of early warning systems for marine environments and seafood safety.

Abstract:To better understand the quality characteristics of traditional dried salted Spanish mackerel, the dried salted Spanish mackerel product with the best organoleptic qualities among seven commercial products was chosen, and then its basic physical and chemical characteristics were analyzed, including its salt content, nitrite content, total volatile basic nitrogen (T-VBN) content, thiobarbituric acid reactive substances (TBARS) value, and so on. Furthermore, the dominant strains of bacteria, which have important impacts on the fermentation process and flavor formation, were isolated, purified, and identified from the dried salted Spanish mackerel product. The physiological and biochemical characteristics of these dominant bacterial strains were also studied in detail. The results showed that the water content of the traditional dried salted Spanish mackerel was 54.40%, and the salt content was 3.1%，which means that the analyzed product can be classified as a semi-dry and low-salt product. The nitrite content was 5.07 mg/kg, so the sample met relevant food safety standards. The TVB-N content of the dried salted fish product was 40.12 mg/100 g, which exceeds the TVB-N content limit of common fresh and frozen marine fish (30.00 mg/100 g), so these results indicated that the degree of protein degradation during fermentation was significant. The TBARS value was 10.00 mg/kg, which is slightly higher than the recommended standard (8.00 mg/kg); however, the degree of lipid oxidation in the sample was within the range of sensory acceptability because of its low moisture content. In addition, according to the results of plate counts of bacterial colonies, bacteria were inferred to be the dominant microorganisms in the traditional dried salted Spanish mackerel rather than yeasts or molds. On the basis of analyses of 16S rDNA sequences, the dominant strains of bacteria in the product were identified as Lactobacillus sakei, Enterobacter aerogenes, Lysinibacillus macroides, and Enterobacter xiangfangensis. Among these, Lactobacillus sakei was further identified as possessing the typical characteristics of a fermentative species, and thus probably plays a major role in the fermentation of dried salted Spanish mackerel.

Abstract:Shrimp shells contain a number of components, including chitin, proteins, and minerals. Chitooligosaccharides, derivatives of chitin, are homo- or hetero-oligomers of N-acetyl-glucosamine and d-glucosamine that are linked by β-1,4-glycosidic bonds. The production of chitooligosaccharides from shrimp shells involves demineralization, deproteinization, deacetylation, and depolymerization. The traditional chemical processes involved in the extraction of chitosan from shrimp shells mostly use HCl for the demineralization and NaOH for the deproteinization and deacetylation processes; the chitosan is then oxidatively degraded to chitooligosaccharide. Although these methods are highly economic and effective, they present several disadvantages, such as energy wastage, long processing times, and environmental pollution. Chitooligosaccharides have been widely used in agriculture and it has been proven that their degree of deacetylation (DDA) affects the physiology of the plants. However, limited attention has been paid to understanding the relationship between the DDA of a chitooligosaccharide and its effects on plant resistance to tobacco mosaic virus (TMV). In the present study, an eco-friendly method was established for the production of chitooligosaccharides by using H3PO4 for the demineralization and KOH for the deproteinization and deacetylation processes. Additionally, we studied the effects of chitooligosaccharides with different DDAs on the resistance to TMV. The effects of chitooligosaccharides with different DDAs on inactivating TMV in vitro and inhibiting its multiplication were detected by the Evans blue method. Changes in the activities of defensive enzymes induced by chitooligosaccharides with different DDAs were tested with tobacco leaves. The degrees of demineralization and deproteinization were 94.04%±0.52% and 85.65%±1.06%, respectively. Chitosans and chitooligosaccharides with different DDAs were obtained by microwave-assisted KOH metathesis and oxidative degradation. The DDAs of the obtained chitooligosaccharides were 63.79%, 72.12%, 79.34%, and 88.15%, and their molecular weights were approximately 1500 Da. The chitooligosaccharides with 79.34% and 88.15% DDAs improved leaf resistance to TMV by inactivating the virus in vitro, inhibiting its multiplication, and increasing the activities of the CAT, POD, and PPO enzymes. The liquid waste generated during the demineralization, deproteinization, and deacetylation processes was found to be rich in phosphorus, potassium, and nitrogen, the main constituents of fertilizers. The chitooligosaccharides with 79.34% and 88.15% DDAs could thus be applied as resistance inducers. Therefore, the liquid waste and the chitooligosaccharides generated could be recovered and used in fertilizers, which would significantly decrease environmental pollution and improve the economic value of shrimp shells.

Abstract:Antarctic krill (Euphausia superba) stocks produce large biomasses and contain useful, high-quality proteins. Krill protein has been suggested to be a good source of protein for humans, due to its well-balanced amino acid composition and high biological value. In this study, minced Antarctic krill was studied. The effects of freezing and thawing cycles on changes in the content of adenosine triphosphate (ATP) and related compounds and free amino acids in minced Antarctic krill were investigated. Changes in taste components during freezing and thawing cycles were also analyzed. Results showed that with increasing freezing and thawing cycle times, the degradation of ATP and related compounds increased rapidly, the content of umami nucleotides gradually decreased, and the content of bitter nucleotides gradually increased. The flavor/bitter ratio was 3.32 at the first freeze-thaw cycle, and then after two freeze-thaw cycles the flavor/bitter ratio decreased significantly (P < 0.05). At the same time, the K value increased rapidly, which indicated that the freshness had dropped sharply. After a third freeze-thaw cycle, the K value increased significantly (P < 0.05). The K value was (86.88±3.58)% at the fourth freeze-thaw cycle, meaning that the minced Antarctic krill was no longer fresh. After the fourth freeze-thaw cycle, the K value did not significantly change. The total content of free amino acids increased as the number of freeze-thaw cycles increased. However, the proportional content of umami amino acids and sweet amino acids decreased, while that of bitter amino acids gradually increased. The total taste activity value of bitter amino acids was the highest during the freeze-thaw cycles, which indicated that bitter amino acids made the greatest contribution to the resultant taste. This led to the further deterioration of the taste components of minced Antarctic krill. Therefore, it was concluded that the number of freeze-thaw cycles should be controlled to be within two to better preserve the flavor of minced Antarctic krill.