Abstract:The research trend and application of rotifer mitochondrial genome research were proposed by searching, collecting, reading and summarizing relevant literature on rotifer mitochondrial genome research to understand the current situation and existing problems of rotifer mitochondrial genome research. Meanwhile, the research of analyzing and statistics of rotifer mitochondrial genome sequence were carried out. With the development of molecular biology technology, especially sequencing technology, research on mitochondrial genome sequencing in rotifers has gradually been carried out. Currently, there are 12 records of the complete mitochondrial sequence of rotifers reported in 6 species, mainly concentrated in bdelloid rotifers and rotifers of the genus Brachionus. The mitochondrial genome of bdelloid rotifers contains one ring chromosome, while the rotifers of the genus Brachionus contain two ring chromosomes. The mitochondrial genome of all rotifers contains 13 basic mitochondrial protein coding genes, 2 rRNA coding genes, and 22 tRNA coding genes (18-32). In addition, a few rotifers, such as B. calyciflorus, contain additional copies of the cytb gene. Due to the small size of rotifers and the difficulty of cloning and culturing, relatively few researchers, and the mitochondrial genome sequencing of rotifers needs to be further deepened. The sequences obtained from mitochondrial genome research can be used for research on phylogenetic relationships of rotifers, comparative studies on mitochondrial genomes of rotifers, studies on cryptic species of rotifers, molecular identification of rotifers, and geographic genealogy of rotifers.

Abstract:The outbreak of pathogens has not only caused huge losses, but also seriously hindered the healthy and sustainable development of the artificial breeding industry. Therefore, it is urgent to develop rapid detection technology and pathogen prevention and control technology for pathogens to prevent the outbreak of diseases. Aptamer is the functional single-stranded oligonucleotide with high affinity and specificity for specific targets and screening by systematic evolution of ligands by exponential enrichment (SELEX). Based on domestic and foreign research, this paper described the advantages of aptamers and their research progress in the prevention and control of pathogenic microorganisms in farmed animals, and focused on five challenges in the application of aptamers. (1) The limitations of aptamer screening technology. (2) The lack of stability and safety of aptamers in therapeutic applications. (3) The sustainability of aptamers in organisms with targeted therapeutic effects. (4) The need to improve the accuracy of aptamers in vivo experiments. (5) The possibility of cascading aptamers with other assays to build a comprehensive testing platform. At present, the research of aptamers on cultured animal pathogens has just started, and it has broad application prospects in rapid detection and targeted therapy.

Abstract:With the continuous innovation of new material technology and the high-quality development of modern fisheries, functional fishing materials have ushered in new challenges, but also brought new opportunities to the high-quality development of modern fisheries. Functional fishing materials have played an essential role in the construction of blue granaries, the protection of the fishery ecological environment and the supply of green aquatic products. In order to develop functional fishing materials with better comprehensive performance, this paper summarizes the research status of functional fishing materials in recent years, analyzes the application progress of functional fishing materials such as antifouling materials, degradable materials, luminescent materials and antibacterial materials, as well as the existing problems and shortcomings at the present stage, and looks forward to the future development trend. In order to provide a reference for the rapid rise and industrial application of functional fishing materials.

Abstract:The comparative transcriptomic analysis was performed on natural and albino blue discus with white discus fish (Symphysodon haraldi) respectively to excavate genes related to iridophores in blue skin. It was found a total of 2, 192 different expression genes (DEGs) in natural blue fish, including 1, 270 up-regulated and 922 down-regulated genes. The DEGs were primarily enriched in purine nucleotide biosynthetic process, actomyosin structure organization, purine-containing compound biosynthetic process, oxidative phosphorylation, citrate cycle and other functions. For the albino blue discus fish compared to white one, there were 1, 859 up-regulated and 1, 309 down-regulated DEGs. Similarly, the dominant enriched pathways of these genes were oxidative phosphorylation, ribonucleoside diphosphate metabolic process, ADP metabolic process, cation binding, glycine, serine and threonine metabolism and other functions. In order to further explore candidate genes participating in iridophores appearing color, by comparing the database, a total of 32 and 38 DEGs were screened out in natural blue and albino blue discus, respectively. It could be predicted that alkal2b, gpnmb, fhl2 and pka were associated with the development of iridophores, and pgam, prtfdc1, pnp, slc23a1, slc2a9, rab38, rdh10, psat1, and paics might attend guanine synthesis and transportation in iridophores. This study might ground for in-depth analysis of the formation and regulation mechanism of blue structural color in fish.

Abstract:Like all arthropods, crustaceans shed the exoskeleton periodically through their life cycle, which is called ecdysis. Molting occurs throughout the life cycle of crustaceans and significantly influences their growth, reproduction, and survival. This physiological event is regulated by several hormones, in which ecdysteroids are the important part. The effect of ecdysteroids is mediated by a heterodimer of ecdysone receptor (EcR) and retinoid X receptor (RXR) homolog, ultraspiracle (USP) in insects or RXR in crustaceans. EcR/RXR or EcR/USP complex could bind to response elements to elicit expression of early ecdysone responsive genes, such as E75, and eventually to regulate downstream transcriptional ecdysteroid cascade reaction. RXR, belonging to a nuclear receptor family, plays an important role in the regulation of molting. In recent years, RXR has been identified in several crustaceans, such as Eriocheir sinensis, Callinectes sapidu, Gecarcinus lateralis, Leptuca pugilator, Macrobrachium nipponense and so on. However, most of the studies focused on the cloning and specific expression analysis among different tissues or different molting stages, its regulation of other molting-related genes remains unclear. Therefore, this study identified a retinoid X receptor (RXR) in M. rosenbergii termed Mr-RXR and further investigated its regulation function through its mRNA expression analysis at different molting stages and RNA interference (RNAi). The full length of the Mr-RXR was 2241 bp, consisting of a 36 bp 5′ UTR (untranslated regions), a 719 bp 3′-UTR, and a 1 386 bp ORF (open reading frame). It encoded 461 amino acids with a predicted molecular weight of 50.6 ku and the theoretical isoelectric point of 7.02. Mr-RXR showed high similarity to other crustaceans with conserved DNA binding domain (DBD) and ligand binding domain (LBD). Phylogenetic analyses showed that the RXR of crustaceans clustered in a group, with the closest relationship between M. rosenbergii and M. nipponense. The expression of Mr-RXR was detected in 11 tissues of M. rosenbergii, including the stomach, gill, brain, abdominal ganglion, intestine, muscle, hepatopancreas, eyestalk, heart, testis, and ovary. The result showed that Mr-RXR was expressed in all tissues with relatively high expression level in the testis, eyestalk, heart, brain, muscle, and relatively low expression in the gill, hepatopancreas and stomach. The expression level of Mr-RXR changes at different molting stages, showing the highest level at premolt stages in both eyestalk and muscle tissues. Besides, the temporal expression of four molting-related genes, including EcR, E75, CHIT and MIH, were also examined. The expression pattern of EcR followed the same trend as Mr-RXR, while E75 and CHIT showed similar mRNA expression patterns with the highest level at premolt and postmolt in the eyestalk and muscle tissues, respectively. MIH was only expressed in eyestalk, reaching its peak at intermolt. To further investigate the function of Mr-RXR, RNAi was conducted for 12 days, which caused the death of 63% of individuals. The expression of Mr-RXR was extremely reduced and the efficiency of silence was 79% and 55% in the eyestalk and muscle, respectively. In the eyestalk, Mr-RXR dsRNA injection did not alter the expression of MIH, but significantly reduced the expression of EcR, E75and CHIT. In the muscle, however, RNAi of Mr-RXR only induced significantly declined expression of CHIT. The correlation between Mr-RXR and other molting-related genes indicated that Mr-RXR might be involved in the regulation of EcR, E75 and CHIT transcription and further mediate the molting process in M. rosenbergii. Results in this study contribute to better understanding of the mechanism of molting in crustaceans.

Abstract:Hypoxia phenomenon in pond water is a common and prominent stress factor in aquaculture, which will severely restrict the behavior, growth, reproduction and other aspects of aquaculture animals, and even lead to large-scale death. Bax is a pro-apoptotic protein in the Bcl-2 protein family, although most studies have investigated the function of Bax in many vertebrates, little information to date was observed in the crustaceans. The full-length cDNA sequence of pro-apoptotic Bax gene was obtained by RACE (rapid-amplification of cDNA ends) PCR technology to explore the role of Bax (B-cell lymphoma-2 associated X protein) in the oriental river prawn Macrobrachium nipponense under hypoxic stress. RT-PCR was used to analyze the distribution of Bax gene in different tissues of M. nipponense. Meanwhile, real-time quantitative PCR (qPCR) and Western blot were used to detect the expression of Bax gene in different hypoxic stress stages. Bax recombinant protein and antiserum were prepared, and the localization of Bax protein was analyzed by immunohistochemistry. The present results showed that the full-length cDNA of Bax gene was 2 287 bp (NCBI accession no MZ823353), including 42 bp of 5' non-coding region (UTR), 814 bp of 3' UTR, 1 431 bp of open reading frame (ORF) encoding 476 amino acids. Sequence analysis showed that Bax was rich in highly conserved BH1, BH2 and BH3 domains. Phylogenetic tree analysis showed that Bax gene of M. nipponense was closely related to the Bax gene of Penaeus monodon. RT-PCR results showed that Bax mRNA expression was the highest in the hepatopancreas and the lowest in the brain. qPCR results indicated that Bax expression level in the gill and hepatopancreas tissues of M. nipponense was significantly higher than that of the control group under hypoxia 1-96 h. Western blot analysis also confirmed that Bax protein expression level was basically similar to gene transcription level. The recombinant Bax protein was obtained by constructing prokaryotic expression vector in vitro, which were immunized rabbits to obtain antiserum. Immunohistochemical results showed that the positive signal of Bax protein in the gill and hepatopancreas were mainly located in the gill epithelial cells and hepatocytes. Finally, flow cytometry analysis showed that the apoptosis rate of haemocytes in hypoxia 96 h group significantly higher than those in the control group, which was consistent with the expression pattern of Bax protein expression abundance and gene transcription level. These results suggest that Bax gene can promote apoptosis in different tissues of M. nipponense in response to hypoxic stress. The present study has provided theoretical reference for exploring the molecular mechanism of hypoxia sensitivity in M. nipponense.

Abstract:Hyriopsis cumingii, a pearl mussel endemic to China's freshwater waters, produces more than 70% of the country's freshwater pearls. However, the low quality of pearls is a crucial issue, among which color is one of the main factors affecting pearl quality. Carotenoids are the class of fat-soluble natural colorants, and many studies have shown that carotenoids metabolism significantly affects the color of aquatic objects, and pearl color is closely related to carotenoids. Carotenoids cannot be synthesized directly in most animals and must be ingested from food. The metabolism of carotenoids in shellfish is a complex process, and the mechanism of absorption, transport and cleavage in the body is regulated by multi-level and multi-level factors, involving many key genes. Carotenoids are important natural pigments, and it has been found that carotenoids metabolism is significantly related to shell color of shellfish. Glutathione S-transferase Pi (GSTP1), a carotenoid-binding protein, was used to elucidate the function of the HcGSTP1 gene in carotenoids transportation in H. cumingii and to explore the correlation between the expression of HcGSTP1 gene and shell color of H. cumingii. HcGSTP1 gene was cloned and identified in this study, its sequence characteristics and evolution were analyzed. The expression and localization of HcGSTP1 gene in H. cumingii were detected by qRT-PCR and in situ hybridization technology. The function and mechanism of HcGSTP1 gene were preliminarily analyzed by RNAi technology. The results showed that the full-length cDNA sequence of HcGSTP1 gene in H. cumingii was 1 317 bp, of which opening reading frame (OFR) was 618 bp, encoding 205 amino acids and containing a GST-N-pi domain and a GST-C-Pi domain. The results of qRT-PCR showed that the expression level of HcGSTP1 gene in hepatopancreas and axetopods of purple mussel was significantly higher than that in the corresponding tissues of white mussel (P<0.01), and the expression level in the marginal membrane and central membrane of purple mussel was significantly higher than that in the corresponding tissues of white mussel (P<0.05). The results of in situ hybridization (ISH) showed that the positive signals appeared in the outer fold, dorsal mantle, ventral mantle, partial middle fold, and junction of outer fold and middle fold of pallial mantle. RNAi technology results showed that the interference rate of HcGSTP1 gene expression in the fringe mantle reached 83.74% (P<0.05), and the total carotenoids content (TCC) in the fringe mantle was reduced by 30.12% (P<0.05). These experimental results preliminarily validated the vital function of HcGSTP1 gene on carotenoids transportation in H. cumingii. Furthermore, it might affect the color of shells and pearls, and would provided molecular basis for further understanding of the mechanism of carotenoids transport and color formation of shells and pearls in H. cumingii.

Abstract:Conger eel (Conger myriaster) is one of the common fish in the East China Sea and other coastal waters, with over fishing and pollution in the marine environment, the wild resources of C. myriaster face the risk of depletion. However, there are limit studies on the reproduction and a lack of research on lipid requirements during the development of the ovary of the C. myriaster. Therefore, lipid metabolism of artificially induced ovary development tissue of lipid metabolism was analyzed in different developmental stages of ovary in this study to provide a theoretical basis for artificial reproduction of the C. myriaster. This study provides insights into the lipid metabolism of the C. myriaster during artificially induced ovarian development. The lipid compositions of the liver, ovary, muscle and plasma in distinct stages were determined using ultra-high performance liquid chromatography coupled with quadrupole-orbitrap mass spectrometry (UHPLC/Q-Orbitrap MS). The activity of metabolic enzymes in the liver was investigated as well. By analyzing the lipid components of liver, ovary, muscle, and plasma of C. myriaster at different developmental stages, 68, 27, 63 and 212 lipid markers were identified in the liver, muscle, ovary and plasma, mainly including phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylcholine (PC), triglycerides (TG) and sphingomyelin (SM). Lipids such as TG, diglyceride (DG) and ceramide (Cer) in the four tissues showed different trends during developments. In liver metabolism, the concentration of fatty acid syntheses, liver lipase and lipoprotein lipase showed a process of first increasing and then decreasing. The process was mainly involved in the metabolism of triglycerides, phospholipids and fatty acids. Studies showed that the triglycerides and phospholipids in the main tissues of the C. myriaster had changed to varying degrees during the development of the ovary, and the changes in the activities of lipid metabolism-related enzymes also corresponded to the characteristics of lipid metabolism. This experiment initially explored the lipid mobilization of main tissues during the ovary development of the C. myriaster to provide a basic reference for the artificial reproduction and sustainable development of the C. myriaster.

Abstract:Large offshore net pen aquaculture is one of the most important modes for the development of deep-sea aquaculture. Precise feeding is the key to ensureing efficient farming, nutrient digestion and absorption for farming fish. Intestine is the main area for digesting and absorbing nutrients. Thus, investigating its structure will provide a theoretical basis for accurate feeding in captivity. The intestinal tissue of five marine fishes (Verasper variegatus, Paralichthys olivaceus, Oplegnathus punctatus, Thamnaconus modestus, Mugil soiuy) reared in offshore aquaculture net pen were detected via tissue sectioning, hematoxylin-eosin (H.E) staining and optical microscope observing in this study. Meanwhile, the relative intestinal length, the height, width, the number of intestinal folds, the thickness of the circular muscle, the longitudinal muscle, the number of goblet cells, the morphological differences of different intestinal segments and correlations were evaluated. The results showed that M. soiuy had the most significant relative with intestinal length, followed by T. modestus and O. punctatus, and Verasper and P. olivaceus were the least significant relationship. The intestinal fold number, height and width of five fishes decreased from anterior intestine to posterior intestine, and the degree of intestinal fold developed M. soiuy>Verasper>O. punctatus>P. solivaceus>T. modestus. At the same time, the muscle thickness of O. punctatus intestinal tract was the largest, significantly higher than that of the other four fishes (P<0.05). While P. olivaceus and O. punctatus had the smallest, significantly lower than that of the other three fishes (P<0.05), M. soiuy and T. modestus had no significant difference (P>0.05). There were substantial differences in the number and distribution of intestinal goblet cells in the five fishes. The number of intestinal goblet cells in the five fishes was showed as sphyraenus>O. punctatus>P. olivaceus>Verasper>T. modestus. M. soiuy goblet cells were mainly distributed in the foregut and middle intestine, Verasper, P. solivaceus and O. punctatus intestinal goblet cells were mainly distributed in the foregut and posterior, and T. modestus intestine goblet cells were mainly distributed in the posterior. Correlations analysis results showed that the intestinal muscular layer of Verasper, P. olivaceus, O. punctatus, T. modestus was significantly negatively correlated with intestinal folds, and was significantly positively correlated with the number of intestinal goblet cells. M. soiuy had a significant positive correlation among intestinal parameters. In summary, the relative intestinal length, the number, height, width of intestinal folds, the thickness of the circular and the longitudinal muscles, and the distribution of goblet cells in different intestinal segments of the five fishes which were breeding suitably by offshore aquaculture net pen have significant differences among species. The aforementioned parameters indicated that five fish reared in the offshore net pen adopts different digestion and absorption strategies due to species specific. Therefore, these results provided basic data for the designing of precise feeding and feeding strategies in offshore aquaculture net pen.

Abstract:Deception Island is a volcanic island located southwest of the South Shetland Islands in Antarctica with more than 20 eruptions over the last two centuries. Under the significantly influence of the island's active volcanoes, the adjacent water temperature is high, and the concentrations of iron, manganese, silicon, and other elements are significantly greater, with rich biological resources. Environmental DNA (eDNA) analysis constitutes a promising tool to study the distribution and diversity of fishes. This technique is based on organisms leaving DNA in the environment, which can be extracted and sequenced to identify the species from which it originates. This study explored the potential use of eDNA metabarcoding from seawater samples to detect fish species diversity in Deception Island. The fish species composition and diversity characteristics in the waters of Deception Island were detected by high-throughput sequencing of eDNA in this study. Overall, a total of 31 species (1 order 6 families 23 genera) of Antarctic fishes were detected in the environmental samples from five sampling stations around Deception Island, and most of them were identified in previous surveys of Antarctic fishes using traditional methods. Some rare fish which were considered difficult to be caught by traditional fishing methods were detected by eDNA, such as Chionobathyscus dewitti, Akarotaxis nudiceps. OTU abundance was ranked from the largest to the smallest in taxa at the family level, with Channichthyidae and Nototheniidae accounting for the highest proportions. The dominant fish species were Champsocephalus gunnari, Notothenia rossii, Pseudochaenichthys georgianus, Bovichtus sp1., Bovichtus sp2., Pagothenia borchgrevinki, C. dewitti, Notothenia coriiceps, Eleginops maclovinus. Among the identified fish species from eDNA analysis, C. gunnari and N. rossii had the highest abundance (53.52% and 28.27%). The sampling stations were divided into nearshore and distant stations according to the distance from Deception Island or South Shetland to evaluate the diversity of fish communities in different habitats. The alpha diversity index of fish communities was calculated using Chao1, ACE index to characterize richness, Shannon and Simpson diversity index, and Pielou’s evenness. Moreover, the overall composition pattern of the data was analyzed by PCoA. The α and β diversity significantly differed between nearshore and distant sites, but the fish species composition was similar between distant sites. This research demonstrated the utility of eDNA for species diversity in fish communities, knowledge of which was essential for standardized monitoring of Southern Ocean's biodiversity. The eDNA technology was less intrusive to the environment and could provide rapid detection of fish species in the water of Deception Island, complementing to traditional survey methods. In addition, our findings can provide data support for fish diversity monitoring and fisheries resource management and conservation in Deception Island.

Abstract:As an irreplaceable and important ecosystem, island reef waters meet the needs of fish communities for growth, reproduction, development and protection from natural predators. They are good habitats for many species. Environmental DNA (eDNA) metabarcoding technology, which combines universal primers with high-throughput sequencing (high-throughput sequencing, HTS) technology, facilitates the amplification of eDNA from multiple target groups and has great potential in establishing or improving the assessment of species diversity. Zhoushan archipelago is the largest archipelago in China, which consisting of 2 085 islands. A total of 27 water samples were collected from nine stations in Zhoushan and its adjacent waters in May 2019 in this study to better understand the species composition of the major fish communities in Zhoushan and its adjacent waters and to monitor and protect their diversity. eDNA metabarcoding technique was used to determine the fish community composition. The results showed that 52 species of fish were detected in Zhoushan and its adjacent waters, belonging to 19 orders, 36 families and 49 genera. Four species were only annotated to genus-level. Perciformes and Scombriformes account for the highest proportion, 28.85% and 15.38%, respectively. The dominant species in different sea areas were quite different. The distribution trends of the Shannon, Simpson, and Pielou indices were basically the same. They all showed the trend as Zhoushan offshore waters > Yangtze River estuary > Zhoushan offshore waters. The variation of eDNA in different water layers could be roughly divided into three trends, and the trend of most fish species' sequence abundance between water layers was highly consistent with their habitat preference. In addition, by comparing the results with other scholars, it was found that the eDNA metabarcoding results in the same sea area at the same time varied greatly, which indicated that the repeatability of the eDNA technology was less reproducible and should be used with caution in the field of fisheries resources monitoring. Therefore, eDNA technology can only partially replace traditional survey methods at present. In the future, eDNA metabarcoding can be used as an adjunct to fishery resource monitoring to improve detection efficiency and reduce interference with ecosystems. This study can provide new ideas and methods for the study of fish communities in island reef waters.

Abstract:Species diversity is closely related to the composition of rare and common species in the community. However, their contribution to community species diversity remains controversial, studying the relationship between rare species and species diversity is helpful to better understand the mechanism of community construction. We calculated the α-diversity and β-diversity of the community, combined with geographic range(gri), habitat specificity index (hsi) and population size index (psi) recognition community rare species to investigate the effects of rare and common species on α-diversity and β-diversity of macrobenthos community, and to reveal the basic process of community construction, mangrove macrobenthos in Aojiang Estuary were as the research object in this experiment. Meanwhile, the species were sorted according to their rarity, forming two species sequences of rare species - common species and common species - rare species. On this basis, the relative contributions of rare and common species to species diversity were determined by comparing the changes in species diversity (α-diversity and β-diversity) by adding species one by one. The results showed that a total of 47 species of macrobenthos were identified in the mangroves of Aojiang Estuary from 2017 to 2020. The α diversity of mangroves in spring and autumn was higher than that in summer and winter. The β diversity was similar in four seasons, mainly dominated by nested components. The α-diversity increased first and then decreased with the addition of species to Shannon-Wiener diversity index and richness index in rare species-common species sequence, while evenness index only increased first and then decreased in 2020, and the rest showed a downward trend. Shannon-Wiener diversity index and richness index showed an increasing trend, while evenness index showed a decreasing trend with the addition of species in the common-rare species sequence. β-diversity increased with the addition of species to community heterogeneity (β_SOR) and nested component (β_NES), while turnover component (β_SIM) decreased in the rare species to common species sequence. In the sequence of common species and rare species, β_SOR, β_SIM, and β_NES increased with the addition of species. In conclusion, rarity index could accurately and effectively identify rare species in the community, the rare species contributed more to community α diversity and affected the turnover component of community β diversity, while the common species had a greater impact on the nested component. Therefore, different ecological conservation strategies should be adopted for different species, these results of this study provide theoretical support for mangrove ecological protection in Aojiang Estuary to better protect the mangrove ecosystem in this region.

Abstract:Biofloc technology (BFT) regulates the carbon-to-nitrogen ratio to promote the growth of heterotrophic bacteria, which assimilates ammonia nitrogen in the water into microbial nitrogen, reducing the accumulation of ammonia nitrogen during aquaculture and forming a biofloc consisting of bacteria, organic particles, extracellular polymers, and plankton. It is widely used in Litopenaeus vannamei culture. In practical production, relying solely on monitoring indicators such as pH, dissolved oxygen, total ammoniacal nitrogen (TAN), and nitrite nitrogen (NO₂^--N) cannot comprehensively reflect the real-time formation progress and health status of biofloc. This limitation poses challenges to effective biofloc control, demanding the identification of more appropriate monitoring indicators to ensure biofloc stability. Within the biofloc culture system, foam is a surface feature. Therefore, studying the relationship between biofloc and foam, and identifying effective monitoring indicators is crucial for achieving adequate control over the operational status of the biofloc system. This approach is important in maintaining biofloc stability and ensuring safe production during aquaculture. This study employed three commercial biofloc culture systems for L. vannamei and conducted a 100-day experiment focusing on plankton and foam. Parameters such as foam volume, water surface tension, and water environment parameters were measured. By tracking and monitoring the changes in foam volume, the relationship between plankton, foam, and the operational status of the biofloc culture system was analyzed. This allowed for determining of the biofloc's operational condition through the patterns of foam volume. Pearson correlation coefficient was employed to analyze the correlation between foam volume, water surface tension, biofloc mass, water quality factors, and other parameters, investigating the relationship between foam volume and operation status of biofloc. The results revealed that water surface tension did not significantly affect foam. It also showed a positive correlation between foam volume and total ammoniacal nitrogen (TAN) with a correlation coefficient of 0.571. According to the existing evaluation system, when TAN peaked and began to decline, it signified the biofloc entering stage 2. Additionally, the date for the foam volume changed from increasing to decreasing was highly correlated with the date for biofloc began to form, with a time difference of less than five days. With the formation of formation, the foam volume gradually decreased. Therefore, when foam volume started to decline from its peak could serve as an auxiliary indicator to determine the initiation of biofloc development. When the biofloc was stable, and water quality conditions were favorable, the foam volume remained at a relatively low level. A consistently low and stable foam volume could be used as an indicator to assess the stability of the biofloc. This experiment maintained the foam volume during stable biofloc operation below 0.011 0 m³/t (0.011 0 m³ of foam per ton of water). The research results can be valuable for better control of biofloc and provide essential guidance for promoting the L. vannamei culture in biofloc technology.

Abstract:In order to study the effects of the marine bioactive peptide on the formation of marine bacterial biofilm and settlement of the marine mussel juveniles, this study investigated Mytilus coruscus juvenile response stimulated by agarose encapsulation with different concentrations of M. galloprovincialis peptide and observed its induction capacity on M. coruscus juvenile settlement. Then, two strains of marine bacteria with different settlement induction abilities were selected including Pseudoalteromonas marina and Leisingera aquaemixtae. Different concentrations of M. galloprovincialis peptide were added into the bacterial fluid during biofilm formation. The effects of M. galloprovincialis peptide on biofilm formation and biological characteristics were analyzed. Meanwhile, the effect of biofilm changes on M. coruscus juvenile settlement was studied. The result of M. coruscus juvenile settlement bioassays showed that M. galloprovincialis peptide could significantly induce M. coruscus juvenile settlement (P<0.05). Besides, the effect of 1.0 g/L M. galloprovincialis peptide which was added during the formation of biofilm on settlement induction of M. coruscus juveniles was the most significant (P<0.05) and the effect of 10.0 g/L M. galloprovincialis peptide on settlement of M. coruscus juveniles was lowest (P<0.05). In further experiment on biofilms, such as biofilm bacterial density counting, biofilm thickness measurement and confocal laser scanning of extracellular products of biofilms, it was found that the induction effect of 1.0 g/L M. galloprovincialis peptide was most significant (P<0.05) and 1.0 g/L M. galloprovincialis peptide significantly increased the bacterial density and exoprotein content of biofilms (P<0.05). However, 10.0 g/L M. galloprovincialis peptide was significantly decreased the bacterial density and protein content of biofilms (P<0.05). The results showed that M. galloprovincialis peptide could directly affect the settlement of M. coruscus juveniles and indirectly affect the settlement of M. coruscus juveniles by affecting the biofilm formation level and exoprotein content of marine bacterial biofilms. These results provided a new insight for exploring the role of marine bioactive peptides in settlement of M. coruscus juveniles. This study provided a new approach for studying the physiological function of bioactive peptides from marine shellfish.

Abstract:This experiment investigated the effects of high carbohydrate diets supplemented with arginine on growth performance, body composition, plasma biochemistry, antioxidant activity, glucose metabolism and immune-related genes in juvenile hybrid snakehead [Channa maculata (♀)×C. argus (♂)]. The 450 hybrid snakehead with initial body weight of (22.02±0.02) g were randomly divided into three groups with three replicates of 50 fishes each and fed three experimental diets with carbohydrate levels of 21.34%, 27.45% and 27.38%, respectively, and were recorded as LC, HC and Arg groups for eight weeks. The results showed that compared with low-carbohydrate diet (LC group), high-carbohydrate diet (HC group) significantly decreased the weight gain rate (WGR), specific growth rate (SGR), and protein deposition rate (PDR), and increased the feed ratio (FCR). The addition of arginine group (Arg group) significantly decreased FCR. Significantly improved the WGR, SGR, PDR, whole fish plasma protein and crude protein content. Compared with the LC group, the plasma and liver malondialdehyde (MDA) content and liver tumor necrosis factor-α (TNF-α) expression were significantly increased in the HC group. Intestinal total antioxidant capacity (T-AOC) and peroxidase (POD) and glutathione peroxidase (GSH-Px) and liver POD and GSH-Px activity, hepatic phosphoenolpyruvate carboxylase (PEPCK), glucose transporter protein-2 (GLUT-2), transforming growth factor (TGF-β) and heat shock protein 70 (HSP70) gene expression quantity dropped significantly. Oxidative stress and liver inflammation suggested liver disease in hybrid snakehead fed a high carbohydrate diet. Feeding the diet supplemented with Arg could enhance the antioxidant capacity of the liver by reducing the content of MDA and strengthening the activities of T-AOC, POD, GSH-Px and superoxide dismutase (SOD). Compared with the HC group, the expressions of pro-inflammatory factors interleukin-8 (IL-8), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were significantly decreased, and the expressions of anti-inflammatory factors TGF-β, HSP70 and heat shock protein 90 (HSP90) were significantly increased in C. maculata (♀)×C. argus (♂) fed with Arg diet. These results suggest the liver inflammatory response was relieved after dietary supplementation with Arg. Studies have shown that, Arg promoted insulin production and glycogenolysis by up-regulating the expression of insulin-related genes protein kinase B (AKT), insulin receptor subset-1 (IRS-1) and phosphatidylinositol-3 kinase (PI3K) and glucose metabolism-related genes PEPCK, glucose-6 phosphatase (G6P) and pyruvate kinase (PK) in the liver. Thus, it regulates hepatic glucose metabolism in fish. In conclusion, a high carbohydrate (HC group) diet induced oxidative stress and inflammation in C. maculata (♀)×C. argus (♂), while Arg supplementation enhanced antioxidant activity, alleviated inflammation, and promoted glucose metabolism.

Abstract:Bifenthrin (BF) is widely used in agricultural production due to its excellent environmental stability and insecticidal activity, resulting in its widespread residue in the environment. In recent years, BF has been frequently detected in coastal areas of China, which would harm aquatic organisms. Extracellular traps play an important role in innate immunity in molluscs. However, knowledge of the formation of ETs is still limited in the marine mollusks induced by environmental contaminants so far. This study aimed to investigate the effects of bifenthrin on the formation of extracellular traps in hemocytes of Haliotis discus hannai. Here, H. discus hannai, with an average shell length of approximately 60 mm, was collected from a local farm and maintained in aerated seawater (temperature 20-22 °C; salinity 28-30) for a week before processing. Then hemocytes were obtained and stimulated by BF (0, 0.01, 0.10 and 1.00 mg/L) for an hour. The results showed that the cell viability of hemocytes decreased to 90.40%, 80.22% and 72.28%, respectively, in a dose-dependent manner. Meanwhile, observed formation of ETs outside hemocytes induced by BF, quantitative analysis revealed the amount of ETs formation significantly increases in a dose-dependent manne, compared to the control group. A more abundant structure of ETs could be induced by 1 mg/L BF. Furthermore, the mRNA expressions of phosphatidylinositol 3 kinase (PI3K) and protein kinase B (Akt) were significantly upregulated in a similar trend in response to the BF-induced reactive oxygen species (ROS) burst and hypoxia inducible factor 1α (HIF-1α) increased significantly (except 0.10 mg/L). Notably, we detected an increase of ROS production during ETs. Quantitative analysis revealed that ROS production increased significantly with the increased BF concentration, as well as in a dose-dependent manner. Furthermore, the formation of ETs was blocked with the inhibition of ROS production by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor (DPI). Meanwhile, the mRNA expression of pyruvate kinase (PK) and hexokinase (HK) was significantly elevated, indicating that during the formation of extracellular traps, part of the energy was supplied by the glycolytic pathway. In summary, stimulation by bifenthrin causes toxic effects on H. discus hannai hemocytes, which in turn exert immune functions through the formation of ETs. The ROS-mediated mediates the formation of ETs, and the PI3K/AKT signaling pathway. HIF-1α, is involved in the formation of ETs, meanwhile energetically supplied by glycolysis. This study preliminarily explored the response of hemocytes of H. discus hannai under BF stress to ETs, to provied a reference for further research on the immune response of hemocytes in shellfish and expand the understanding of environmental pesticide residues on cellular immune toxicity.