Abstract:Abalone is one of the important economic shellfish for marine aquaculture. In recent years, under the stress of high temperatures in summer, mass mortality of abalone has often occurred, which has brought huge economic losses to the aquaculture industry. This paper reviews the events of mass mortality of farmed abalone in recent years and summarizes the research progress on the response mechanism of abalone to high-temperature stress abalone from the perspectives of physio-biochemical indicators including growth, reproduction, survival, metabolism and enzyme activity as well as, cellular immunity, antioxidant system, heat shock protein, apoptosis, NF-κB signaling pathway, PI3K-AKT signaling pathway and other related genes expression, DNA methylation, genetic diversity, etc. summarized the research progress of the response mechanism of abalone to high-temperature stress. Existing studies have shown that high temperature stress can cause abnormal physiological and biochemical in abalone to reduce metabolic levels such as feeding, destroy the stability of abalone's internal environment, reduce abalone's ability to resist pathogen invasion and respond to external environmental stimuli, thereby adversely affecting abalone's growth and immunity, which eventually lead to the death of stressed abalone. In order to provide a reference for understanding the response mechanism of abalone to high-temperature stress, facilitate the investigation of the breeding of high-temperature-resistant varieties of abalone and preventing the occurrence of mass mortality of abalone in summer.

Abstract:Innate immunity is the first line of defense for hosts to recognize pathogens and eliminate pathogen infection. Pattern recognition receptors are the main molecules involved in the recognition of foreign pathogen invasion, including Toll-like receptors, RIG-I like receptors, NOD-like receptors and CLR-like receptors. After recognizing the molecular patterns associated with pathogens, pattern recognition receptors activate innate immune signaling pathways and induce the production of inflammatory cytokines and interferons, thereby initiating immune responses against pathogen invasion. Accumulating evidence suggests that the activation, maintenance and termination of immune responses need to be tightly regulated so that the body can maintain a certain immune strength while avoiding hyperimmune responses. MicroRNAs are small non-coding RNAs of 18-23 nt in length, which are important regulators in the innate immune response network of fish. Recently, a large number of studies have been conducted on microRNA in fish innate immunity, but there is no comprehensive and up to date review of such studies at home or abroad. In view of this, this paper reviews the research progress on miRNA in fish innate immune response in recent years, so as to provide some ideas for molecular disease-resistance breeding and disease prevention and control of fish.

Abstract:To study the sequence characteristics, the gene expression patterns under salinity stress and the targeted regulation of related miRNAs of NHE3 and NKAα1a in cobia, Rachycentron canadum, the full-length cDNA sequences of NHE3 and NKAα1a were cloned by rapid amplification of cDNA ends; the tissue-specific and salinity-adaptive expression patterns of NHE3 and NKAα1a were analyzed by real-time quantitative PCR; the double-luciferase reporter assay was used to detect the targeted regulatory relationship between NHE3 and NKAα1a and related miRNAs. The open reading frames of cobia NHE3 and NKAα1a were 2718 bp and 3075 bp in length, encoding 905 and 1024 amino acids, respectively. NHE3 and NKAα1a were expressed in all detected tissues, including gill, intestine, and heart, among which the highest expression abundance was found in gill. With the increase of salinity, the expression of NHE3 in gill decreased gradually, and there were significant differences between low-salt and high-salt adaptation. With the increase of salinity, the expression level of NKAα1a showed different trends, and it was significantly up-regulated in gill and intestine after being challenged by low-salt and high-salt conditions, while its expression level was significantly down-regulated in kidney in high-salt environment. In different salinity adaptation processes, the highest expression levels of NHE3 and NKAα1a were all found in the gill. When NHE3-pmirGLO-WT was co-transfected with miR-1335-3p, the relative luciferase activity decreased compared with the control group, and there was a very significant difference, and the similar results were found when NKAα1a-pmirGLO-WT was co-transfected with miR-1788-3p and mimic NC (control). The results of the double-luciferase reporter assay suggested that miR-1335-3p and miR-1788-3p could bind to NHE3 and NKAα1a 3'-UTR sequences, respectively, and downregulate their mRNA expression levels; NHE3 and NKAα1a were highly conserved among species; NHE3 was mainly involved in low-salt adaptation, while NKAα1a played a role in both low-salt and high-salt adaptation; miR-1335-3p and miR-1788-3p could negatively regulate their target genes NHE3 and NKAα1a, respectively, and thus participate in osmotic pressure regulation in R. canadum. The above results provided a theoretical basis for the further studies of the miRNA-mRNA osmotic pressure regulatory network in R. canadum.

Abstract:Protease inhibitors are extremely diverse proteins or peptides that inhibit the proteolytic activities of proteases. Protease inhibitors could inhibit the invasion of pathogens by inactivating pathogen proteases. The I84 protease inhibitor family is a new family in MEROPS database, and the role of its members in host defense has been studied to some extent. To investigate the distribution and function of I84 protease inhibitor family in Crassostrea gigas, in this study, 23 potential I84 family genes were identified in C. gigas. Based on phylogenetic analysis, 5 homeotic genes, Cgsi3, Cgsi5, Cgsi6, Cgsi16 and Cgsi19, were selected for gene expression and functional assessment. They were confirmed by cDNA cloning to represent expressible real genes and expressed in digestive gland, gills, adductor muscle, gonad, mantle, and hemocytes, with the highest level of expression detected in the digestive gland (P<0.05). In the larval oysters, none of the 5 selected genes was detected in zygote, and they showed different expression patterns in the remaining developmental stages. The expression level of CgSi3 increased significantly in the pediveliger stage, and then decreased. The expression level of CgSi6 increased significantly from the umbo larvae onwards. In oysters challenged with pathogen associated molecular patterns (PAMPs), gene expression pattern also differed with genes. In oysters injected with LPS and PGN, the expression level of CgSi6 changed significantly, while in those injected with Poly (I:C) and GLU the expression level of CgSi3 showed significant changes. This study revealed the gene expansion and functional differentiation of the I84 family protease inhibitors in C. gigas, and provides a basis for the comprehensive understanding of the biological functions of the I84 family protease inhibitors and the related mechanisms.

Abstract:Dead end (dnd) is a germ cell-specific molecular marker in most vertebrates, belonging to RNA-binding protein family. It is essential for the maintenance of the survival and migration of primordial germ cells (PGCs). In many species, dnd deficiency could block the migration of PGCs, and then they transdifferentiate into other cell types, resulting in complete loss of germ cells and sterility. Thus, dnd is essential for the survival and development of vertebrate germ cells. Dnd is originally identified in Danio rerio, proved that deletion of Dnd leads to abnormal polarization and migration of PGCs and loss of germ cells. Thereafter, dnd1 is characterized in Mus musculus and Dnd1-β is specifically expressed in adult testis. However, chicken Dnd homologue (CDH) is expressed in both gonads. In Xenopus laevis, dnd is only expressed in ovary. In teleosts, dnd has been identified as a PGCs marker and is specifically expressed in gonads that the expression level is higher in ovary than testis. Therefore, dnd shows distinct expression patterns among species. Although dnd plays a conserved role in maintaining the survival and migration of PGCs from teleosts to mammals, its expression pattern in gametogenesis varies with species. Thus, it is of great significance to identify the sequence characteristics, gene expression and distribution of dnd in turtles, to lay the foundation for studying on the origin and formation of PGCs, and gametogenesis of turtles. Pelodiscus sinensis is one of the oldest tetrapods and has unique scientific research value in study of animal morphological and reproductive evolution. Additionally, because of its high medicinal and economic values, P. sinensis occupies an important position in freshwater aquaculture in China. Here, in order to study the development and differentiation mechanism of turtles’ germ cells, the full-length cDNA of dnd was obtained by RACE form P. sinensis. The total length of P. sinensis dnd (Psdnd) cDNA was 1 251 bp (GenBank ID OL757532), including 254 bp 3' untranslated region and 1 017 bp open reading frame encoding 338 amino acids. Multiple alignment and phylogenetic tree analysis showed that Psdnd had 6 conserved domains, the same as homologous proteins of other species had, and the highly conserved RNA recognition domain was the main functional region. Besides, Psdnd had the highest sequence identity with and was the closest relative to Chelonia mydas dnd. RT-PCR showed that Psdnd was specifically expressed in gonads and the mRNA level was higher in ovary than testis. Chemical in situ hybridization showed that Psdnd mRNA was specifically expressed in germ cells. Particularly, Psdnd mRNA was mainly expressed in the cytoplasm of stage Ⅱ primary oocytes, and not expressed in oocytes stage Ⅳ onwards. Moreover, Psdnd mRNA signals were strongly detected in primary spermatocytes, followed by secondary spermatocytes and spermatogonia, and barely in spermatids. Our study indicates that dnd may play a key role in regulating the development of male and female germ cells in P. sinensis. This study lays the basis for further study of turtles’ germ cells development and differentiation mechanism.

Abstract:Blood physiological parameters reflect the acid-base balance status and oxygen supply of organism by the ion concentration and partial pressure of gas in blood, and play an important role in the animal physiology and pathology. In order to compare three scallop species in terms of blood concentrations of K⁺, Na⁺, Ca²⁺ and Cl^-, partial blood pressures of O₂ (pO₂) and CO₂ (pCO₂), and blood acidity (pH), a blood gas analyzer was used to measure the blood physiological parameters of Chlamys farreri, Patinopecten yessoensis and Argopecten irradias. The results revealed that there were significant differences in blood physiological parameters between different species of scallops. Specifically, the values of K⁺ [(15.74±1.47) mmol/L], Na⁺ [(388.07±11.38) mmol/L], Cl⁻ concentrations [(462.43±6.88) mmol/L] and pO₂ [(140.13±15.35) mmHg] were higher in the blood of C. farreri than other two scallops. The values of Ca²⁺ and pCO₂ of P. yessoensis and C. farreri were higher than those of A. irradias, and the pH of A. irradias was highest among the three scallops. In addition, the blood pH of C. farreri was significantly positively correlated with shell height (r=0.611，P<0.05), while other physiological parameters were negatively correlated with it. With the increase of temperature, the concentration of Ca²⁺ increased significantly in the blood of C. farreri while pO₂ decreased significantly. During the temperature change, the concentrations of K⁺, Na⁺ and Cl⁻ in C. farreri increased firstly and then recovered to the initial levels, while the values of pH and pCO₂ remained relatively stable. The results provide basic information for blood physiology research and a new approach to the assessment of the physiological states of bivalves.

Abstract:Heliocidaris crassispina is one of the most important economic sea urchin species in the southern China. Its breeding season is from April to June, with high temperature and rainy, and the salinity varies greatly in the sea area. In order to determine the appropriate salinity for the early development of H. crassispina, this study was conducted to investigate the effects of different salinity (15, 20, 25, 30, 35, and 40) on the fertilization, incubation, embryonic development, larval growth, ingestion and metamorphosis of H. crassispina under laboratory conditions. The main results are as follows. The fertilization rate was above 95% under the salinity range of 20-35, but there was no fertilization with a salinity of 15 or 40. The hatching rate under salinity 30 was 89.77%, which was significantly higher than other groups, the lowest hatching rate was 46.65% under salinity 20 treatment. The embryonic developed fastest with salinity 30 exposing, 92.61% of fertilized eggs developed to the 4-cell stage in 1 h after fertilization, and all developed into the multicellular stage in 2.5 h, and 68.86% of the 2-arm larvae appeared in 27 h, which were significantly higher than other groups. Moreover, with salinity 30 treatment, the larvae develop fastest and best, and were significantly higher than other five groups, 91.67% of 4-arm larvae developed to the 8-arm larvae stage I on the 5th day, and all developed into the 8-arm larvae on the 7th day, of which 16.67% have developed to stage Ⅲ, and 83.33% of the larvae have developed to stage Ⅳ on the 13th day. The larvae with salinity 25 and 35 followed, 83.33% and 75% of stage Ⅰ larvae appeared on the 5th day, and some larvae could develop to stage Ⅳ on the 13th day, but there was a difference in individual development. Under salinity 20 or 40 condition, the larvae only developed to 8-arm larva stage Ⅰ on 13 days; further more under salinity 15 exposing, the larval development was inhibited and stayed at 4-arm larvae stage and died after 7 days. The metamorphosis rate of 8-arm stage Ⅳ larvae with salinity range of 15-40 in benthic diatoms is higher than 21.43% after 72 hours, and the salinity 30 is the highest with 54.71%. The larval post-oral and antero-lateral arms grew fastest under salinity 35 treatment on the 5th days (830.50 and 694.50 μm, respectively), which were significantly higher than other groups. But the stomach area was largest under salinity 30 with 23048.25 μm² , which was significantly higher than other five groups. And the feeding rate of 4-arm larvae and 8-arm larvae were highest under salinity 30 exposing (2780 and 3286 cell/ind·h, respectively), which were significantly higher than other groups. The study suggested that salinity has a significant impact on the growth and development of H. crassispina in early developmental stage. The optimum salinity was 30, which H. crassispina has fastest growth and best development. The suitable salinity range was 25 to 35, which H. crassispina can maintain normal growth and development. The results may provide basic data for the seed breeding technology of H. crassispina.

Abstract:Phenotypic variation within a species can be associated with varying environmental conditions in their habitats. Understanding the variations in species’ phenotypes helps to understand their resource utilization and ecological niche. The jumbo squid, Dosidicus gigas, is a keystone species of the Eastern Pacific Ocean, which is widely distributed and exhibits large phenotypic variation under environmental influences. To investigate whether different environmental conditions lead to morphological changes in the beak of D. gigas, the animal’s important feeding apparatus, a total of 244 D. gigas’ beaks were collected from the eastern equatorial Pacific Ocean from Jun to August in 2017, 129 and 115 specimens were from the western and eastern waters of the Galapagos Archipelago, respectively. Traditional morphometrics and geometric morphometrics methods were applied to quantify the external morphology of the beak. A total of twelve external morphological parameters were measured through traditional morphometrics, and twenty landmarks were set on the one-side image of upper and lower beaks and digitized for geometric morphometrics analysis. The results showed that 11 external standard morphological parameters of beaks were significantly different between different cohorts except for upper hood length (UCLs) (P<0.05). Although the coefficients of difference were all less than 1.28. Geometric morphometric analysis showed significant differences (P<0.001) in the size and shape of upper and lower beaks between the two cohorts, with different allometric growth patterns. The morphological differences were mainly reflected in the rostrum and lateral wall of the upper beak, and the rostrum and wing of the lower beak. Stepwise discrimination analysis based on land-mark geometric morphometrics showed high success rates for both upper and lower beaks, which were 89.61% and 85.88%, respectively. D. gigas from the eastern waters had smaller beaks with more curved and sharper rostrum, larger lateral walls, and wider but shorter wings compared to those from the western waters, which may be attributed to the environmental conditions and food types of the habitat. Such resource allocation-related phenotypic plasticity could be considered as a response to the environmental characteristics of their habitats, which may likely facilitate their survival.

Abstract:Microplastic pollution in the ocean is a global environmental problem, and the microplastic pollution in the waters around Antarctica is a crucial part of it. However, there are few studies on microplastics in the Antarctic, most of which focus on the seawater and penguin excrement near the Antarctic. Studies on microplastics in the Antarctic fish are few, especially in Pleuragramma antarcticum. P. antarcticum is the most abundant pelagic fish living in the Antarctic continental shelf waters and plays a role of linkage in the Antarctic Marine ecosystem, so it is necessary for conserving this resource to explore microplastic pollution in P. antarcticum in the waters around South Shetland Islands, Antarctica. After thawing the samples from Antarctica and recording biological information, the gastrointestinal tract was extracted. At 60 ℃, 10% KOH was used for digestion in a constant temperature shaker for more than 24 hours. After the solution was basically clarified, a 0.45 μm filter membrane was used for filtration. Suspected microplastics were picked out after filtration under a stereomicroscope, and then qualitatively detected by Fourier infrared spectrometer. Finally, the microplastic morphology was photographed by a Scanning Electron Microscope (SEM). The results showed that the average abundance of microplastics in P. antarcticum was (0.36±0.51) item/individual in the waters near South Shetland Islands. There was a positive correlation between the abundance of microplastics in the gastrointestinal contents and the body length of the fish. In general, the occurrence of microplastics in P. antarcticum was slightly higher in the northern Southern Shetland Islands than in the southern Bransfield Strait, but the overall pollution levels were relatively low. The microplastics in the P. antarcticum could be divided into fibrous and fragmentary types, and most of them were fibrous. The color of microplastics was mainly blue, followed by black, and red and transparent colors were less common. The average particle size of microplastics was (584.6±419.2) μm, 84.6% of which was less than 1 000 μm. Polyester microplastics accounted for nearly 80% of the microplastics in the P. antarcticum, most of which were polyethylene terephthalate (PET). Fishing nets and discharge of sewage from crew might be its main source. The surface characteristics of microplastics were analyzed by SEM which indicated that the fracture area of microplastics was rough and the specific surface area increased significantly. The SEM images of two kinds of fibrous microplastics illustrated the changes of microplastics in organisms. Due to the large specific surface area, it was easy to combine with other pollutants, carry toxic and harmful substances into the ecosystem, and then enter human life through the food chain. Therefore, it is still necessary to pay attention to the ecological effects caused by microplastics pollution. The results of this study enrich the basic data of microplastics research in Antarctic marine life and could be used as background data to provide a scientific basis for further research on microplastics in the Antarctic ecosystem.

Abstract:To understand the spatio-temporal distribution characteristics of Hexagrammos otakii in Haizhou Bay and its influencing factors, a spatio-temporal species distribution model was constructed based on the bottom trawl fishery resource surveys and environmental observation data conducted in Haizhou Bay from autumn 2013–2019 and used to analyze the relationship between its distribution and environmental factors. The residual independence and heterogeneity of the model were compared with those of the generalized additive model (GAM) by residual analysis, and the prediction performance of the model was tested by cross-validation, and finally the distribution was predicted and the habitat suitability index (HSI) and the center of gravity of resource distribution were calculated by the delta method. The deviation explanation rate of the spatio-temporal model was 65.50%, and model analysis showed that the most important environmental factor influencing the distribution of H. otakii was water depth (22.11%), followed by bottom water temperature (12.98%), while bottom salinity (0.09%) had less influence. There was a positive correlation between water depth and its distribution, a negative correlation between bottom water temperature and its distribution, and a weak positive linear relationship between bottom salinity and its distribution. The residual independence and heterogeneity of the spatiotemporal model was stronger than that of GAM, with a cross-validation regression line slope of 0.90±0.38. The model predictions showed that H. otakii mainly distributed in the sea area north of 34.5°N and east of 120.0°E. its high HSI value area tended to shrink year by year, and the center of gravity of resource distribution was shifting to the northeastern sea area, which might be the result of the combined effect of climate change and fishing pressure. This study analyzes the spatio-temporal distribution of H. otakii in Haizhou Bay, which is important for understanding the distribution dynamics of H. otakii and scientific fisheries management.

Abstract:Gillnet is extensively used as fishing tool throughout the world. However, it has high species- and size-selectivity for fishes because of net mesh size. The selectivity caused by net mesh size will inevitably reduce comparability on attributes of fish assemblages sampled with non-standard gillnets. Therefore, the standard of fish sampling with multi-mesh gillnets has been universally established and applied in North America and Europe since more than ten years ago. The standard will enhance the comparability across large space and long time scale. Unfortunately, there is so far no analogous standard in China. In this study, using two types of multi-mesh gillnets (benthic and floating) with 12 mesh sizes of 1.0, 1.25, 1.6, 2.0, 2.5, 3.1, 3.9, 4.8, 5.8, 7.0, 8.6 and 11.0 cm, we sampled fishes from June to December, 2019 in Dongguan ecological park wetland, an important component of the Dongguan National Urban Wetland Park wetland. The differences in attributes of catch community between two type of gillnets and among different nets mesh sizes were explored. We hope that this study will help to establish Chinese standard of fish sampling with multi-gillnets. Meanwhile, we revealed the structural characteristics of catch community in the wetland to provide scientific basis for its management. The results showed that a total of 13 fish species were collected, and Toxabramis houdemeri and Oreochromis mossambica were the dominant species in terms of relative importance index. The former species accounted for 84.8 percent of the abundance of the whole catch community and the latter one contributed 40.2 percent to its biomass, respectively. There was a significant difference between benthic and floating gillnets in catch species composition, but there were no significant difference in number per unit effort (NPUE), biomass per unit effort (BPUE) and species number; floating gillnet had significantly lower NPUE of two tilapia species (O. mossambica and Oreochromis nilotica) than benthic gillnet, but T. houdemeri did not significantly differ in NPUE between the two type of gillnets. Two species clusters of catches sampled by nets with 12 different mesh sizes were obtained using cluster analysis (CA) and non-metric multidimensional scaling (NMDS); one species cluster was composed of catches collected by nets with mesh size of 1.0-2.0 cm with indicator species of T. houdemeri, and another species cluster consisted of catches sampled by nets with mesh size of 2.5-11.0 cm with indicator species of O. mossambica and O. nilotica. Meanwhile, two size clusters of all catches were also obtained using CA and NMDS; one size cluster was made up of catches sampled with 1.0-3.9 cm mesh-size nets and another size cluster comprised catches collected with 4.8-11.0 cm mesh-size nets. With increasing mesh size, the average body length of catch increased linearly, while NPUE decreased by power function. To more scientifically estimate the fish community structure in inland waters, adding nets with mesh size of 1 to 2 cm to the multi-mesh gillnet and combining use of benthic and floating gillnets would be recommended in the future.

Abstract:It is urgently necessary to produce low-cadmium (Cd) rice in Cd-polluted paddy soil. Integrated rice-fishing culture is an efficient complex ecological agricultural production mode, which combines the culture of rice with culture of economic aquatic animals, owning both economical and ecological benefit. In order to investigate the control efficiency on Cd accumulation in rice in the rice-fish coculture system, the newly hybrid crucian carp WR-Ⅱ { [Carassius cuvieri (♀)×C. auratus var. red (♂)] (♀)×C. cuvieri (♂) } was used as an example in the rice-fish coculture system, and the cadmium (Cd) concentration in rice grains, WR-Ⅱ and environmental medium were compared between the rice-fish coculture system and the rice monoculture system, as well as the quality traits of rice grains and the characteristics of WR-Ⅱ were analyzed. The results showed that the average weight of WR-Ⅱ (331.4±74.3) g in the rice-fish coculture system increased by 1.7 times compared to the fingerling (133.1±22.4) g; there existed no significant difference in the nutrient quality traits of rice grains between the two culture systems; the average value of total soil Cd concentration (0.472 mg/kg, pH=5.5) was a little higher than the pollution threshold (0.40 mg/kg, 5.5≤pH≤6.5), and there was no significant difference observed in the total Cd concentration in paddy soil and in the soil pH between the two culture systems; a low level of Cd accumulation (0.060±0.032) mg/kg was found in viscera of the WR-Ⅱ, while this value in fish muscle was lower than the minimum detection limit value (0.003) mg/kg for Cd; the average Cd concentration in rice grains in the rice monoculture system was 0.311 mg/kg (0.239-0.381) mg/kg, reaching 1.6 times of National Food Safety Standards Limits of Cd for Foods in China (0.2) mg/kg; while this value (0.034) mg/kg in rice grains in the rice-fish coculture system was much lower than 0.2 mg/kg, and was down 89.1% compared to that in rice monoculture system; there was significantly positive correlation (P<0.01, r=0.802) between the Cd concentration in rice grains and total soil Cd concentration in rice monoculture system, but not in rice-fish coculture system. Our results indicated that the WR-Ⅱwas a great species for rice-fish coculture system, which can inhibit the biological activity of Cd in soil, and in turn effectively reduced the rice in Cd uptake in this system, yielding low Cd and quality rice grains and fish, as well as outstanding economic benefits. The results of this study provide useful guidance and important data on Cd accumulation in rice for the promotion and development of integrated farming of rice and fish.

Abstract:To determine the dietary manganese (Mn) requirement of juvenile largemouth bass, Micropterus salmoides, 0, 4, 8, 16, 32 and 64 mg/kg Mn were added as the form of MnSO₄·H₂O into the semi-purified diet containing 5.2 mg/kg Mn, to obtain six diets with graded Mn level of 5.2, 9.6, 13.5, 20.7, 38.3 and 67.9 mg/kg, respectively. M. salmoides with initial body weight of (16.00±0.07) g were fed one of the six diets for 10 weeks. The results showed that adding Mn to the basal diet significantly increased the weight gain rate (WGR), and reduced feed conversion ratio (FCR) of M. salmoides, which tended to stabilize when dietary Mn reached 13.5 mg/kg. With the increase of dietary Mn, the serum activity of T-SOD and Mn-SOD, and Mn content in whole fish and vertebrae increased, and then kept relatively stable when dietary Mn reached 20.7 mg/kg, but the serum MDA content showed a decreasing trend. In addition, the iron content in whole body, iron and zinc contents in vertebra, and the Mn retention in whole body decreased with the increasing dietary Mn. In conclusion, the supplementation of Mn in semi-purified diet improved the weight gain and feed utilization, promoted serum antioxidant capacity and Mn retention in whole body and vertebra. Based on the WGR, FCR, Mn in whole body and vertebra, the broken-line analysis indicated that the dietary requirement of Mn for M. salmoides was 18.3, 20.5, 21.1 and 23.4 mg/kg dry matter, respectively.

Abstract:In order to investigate the fate of enrofloxacin in aquatic environment, the pharmacokinetics and metabolism of enrofloxacin in silver crucian carp (Carassius auratus gibelio) were monitored after oral administration of medicated feed in the simulated aquaculture system, and the pattern of metabolism and distribution of enrofloxacin in the water body and sediment. Fish were fed enrofloxacin-medicated feed at a multiple dose of 18 mg/kg twice a day for a period of 6 days. The peak concentration (C_max) of enrofloxacin in C. auratus gibelio was intestine > kidney > muscle > gill > liver > plasma, the C_max were 14.15, 13.31, 14.15, 7.48, 7.94 mg/kg and 2.94 mg/L, respectively. The metabolite ciprofloxacin could be detected in all tissues, and the percentages of C_max of ciprofloxacin to C_max of enrofloxacin were 5.10%, 1.70%, 6.28%, 2.97%, 2.90% and 6.53%, respectively. The order of body clearance (CL_z) of enrofloxacin in the tissues was plasma > liver > intestine > gill > muscle > kidney. With the increase of administration times, the enrofloxacin concentration in water went up rapidly and the peak value (5.23 μg/L) was reached at 6 hours after the last administration; it began to decline afterwards, but the metabolite ciprofloxacin could not be detected in water. The enrofloxacin concentration in the sediment first showed an upward trend, and reached the peak value (796 μg/kg) at 240 h, then it decreased slightly and fell to 587 μg/kg at 480 h. The metabolite ciprofloxacin concentration in the sediment showed a gradual upward trend, and the residue was 382 μg/kg at 480 h. The percentage of ciprofloxacin to enrofloxacin concentration in the sediment was 27.5%-65.1%. The antibacterial residues after medicated-diet administration mainly existed in the sediment of the aquaculture ecosystem, and the percentage of antibacterial residues in the sediment was 41.86%-46.69%, and the residues eliminated slowly. We should pay close attention to the ecological safety risk of the antibacterial residues in the sediment after medicated-diet administration. This study provides technical support for scientific medicine production in aquaculture and theoretical data for ecological security assessment.

Abstract:With the development of fishery economy, fishing gear materials, such as cotton, which are generally biodegradable, have been replaced by synthetic materials, such as polyethylene, polypropylene, and polyamide, which are difficult to be degraded. Moreover, fishing nets made from synthetic fibers, are not able to degrade in marine environment for decades. When they are lost or abandoned at sea, they will continue to trap fish and other animals, becoming "ghost fishing" gears. In face of the threats of "white pollution" and "ghost fishing" resulting from the use of non-degradable fishing equipment, the development of biodegradable fishing materials has become one of an effective path towards the sustainable development of the fisheries. Starch is widely present in nature, renewable, and can be used as a biodegradable material. However, due to poor processing and mechanical properties, they are often blended with other polymer materials. It is noted that the purpose of accelerating or slowing down the degradation of composite materials can be achieved by adding nanomaterials to modify biodegradable materials. Based on this, the starch (STR)/high-density polyethylene (HDPE)/montmorillonite (MMT) nanocomposite fibers were prepared by melt-spinning method, and the effect of nano-MMT on the thermal properties, mechanical properties, dynamic mechanical properties and degradation behavior under seawater of nanocomposite fibers was studied. The results showed that the melting temperature (T_m) of the nanocomposite fibers was reduced, the crystallinity of the nanocomposite fibers increased, and their breaking strength decreased as well. What’s more, the addition of MMT significantly reduced the glassy storage modulus and internal loss of polyethylene, but it had little effect on the starch. After 4 months of seawater degradation, compared with that of STR/HDPE fibers, the weight loss rates of STR/HDPE/MMT nanocomposite fibers increased by about 5%, and the loss of fiber diameter increased by about 11%. This indicated that MMT accelerated the degradation process of STR/HDPE fibers. This paper systematically studies the seawater degradation properties of the MMT modified starch-based nanocomposite fibers, which can provide reference for the development and application of biodegradable materials for marine industries such as fisheries.

Abstract:The aquaculture industry is now in a state of changing, from traditional to modern, from extensive to accuracy aquaculture, with Recirculating Aquaculture System as a creative and efficient aquaculture model. In order to investigate the effects of inlet system optimization on the internal flow field characteristics of aquaculture tanks, analyzes the hydrodynamic features of aquaculture tank applying different inlet structure layout, so as to provide a theoretical basis for the inlet structure design of Recirculating Aquaculture System.Under the application of Computational Fluid Dynamics simulation (CFD), a three-dimensional numerical turbulence model of the square arc angle aquaculture tank was constructed. The single tube inlet system was located in the middle of the arc wall of the aquaculture tank (hereinafter referred to as: arc wall single tube), and adjusted to various inlet-diameter ratios (parameter C/B, the ratio of the horizontal distance C from the center of the jet tube to the tank wall, to the length B on the shorter side of the tank) and different jet angles to study the flow field characteristics in the tank system. From the experiment it is found that the internal flow field features of single tube aquaculture tank are significantly affected by the inlet angle and diameter ratio of the inlet system, and the optimized jet angle of each inlet diameter ratio of square arc angle aquaculture tank differs with each other. The layout of the inflow system of the aquaculture tank involves the two parameters of inlet diameter ratio and jet angle in a comprehensive way, and make sure them are matching. According to the relative inflow distance data, the results show that with the increase of inlet diameter ratio, the optimal average velocity curve of water body first increases and then decreases. When the inlet diameter ratio is 0.09 and the jet angle is 25°, the velocity is the maximum. The optimal angular velocity of inlet diameter ratio 0.09 is about 28.13% higher than that of inlet diameter ratio 0.01. When the relative inflow distance reaches 0.07-0.11, the uniformity coefficient reaches the peak value when the jet angle is 25°. According to the comprehensive analysis of the internal flow velocity, flow field uniformity and internal characteristic diagram of the flow field in the aquaculture tank,under the condition that the inlet diameter ratio C/B=0.07-0.09 and the jet angle is 25°, the internal flow pattern of the aquaculture tank is generally better than other working conditions, the flow environment of the aquaculture tank achieves the best, and the correstanking flow conditions accommodate the needs of Recirculating Aquaculture System better, reducing energy consumption and building a steady flow system. This research will provide a basis for influent system of Recirculating Aquaculture System designing and the optimization of its flow field features.