Abstract:

The purpose of this study is to investigate the regulatory role of dnmt3a in the sex reversal process of Chinese tongue sole， and to develop a DNA methylation editing system suitable for Chinese tongue sole. In this study， we cloned the CDS region of dnmt3a of Chinese tongue sole and analyzed structural domain features and sequence conservation between different species. We analyzed the expression pattern of dnmt3a in male， female and pseudomale Chinese tongue sole by qPCR. We also investigated the effect of a DNA methylase inhibitor 5-Aza-dC treatment on dnmt3a gene expression. The results showed that the full-length cDNA of dnmt3a was 3 063 bp， encoding 1 020 amino acids， including three core domains （PWWP domain， ADDz domain and AdoMet_MTases superfamily）. The bound structural domain （PWWP domain， ADDz domain） of dnmt3a was relatively conservative， but the catalytically active domains （AdoMet_MTases superfamily） were quite different from those of mammals and reptiles. Gene expression pattern analysis showed that the expression of dnmt3a was significantly higher in female gonads than in male and pseudo-male gonads. The relative expression of dnmt3a increased significantly after 5-Aza-dC treatment. This study indicates that dnmt3a plays an important role in the sex regulation of Chinese tongue sole by DNA methylation， which provides a reference for elucidating the sex reversal mechanism and the implementing of DNA methylation editing to target single gene in Chinese tongue sole.

Abstract:

Fish skeletal muscle is rich in mitochondria， especially in red muscle fibers. Mitochondria play an important role in maintaining the contraction of fish skeletal muscle. Tafazzin （taz） gene， as an important gene for the synthesis of mitochondrial-specific phospholipid cardiolipin， plays a key role in the production of mitochondrial ATP. Through in situ hybridization of zebrafish muscle tissue sections， the results showed the taz gene was expressed in zebrafish skeletal muscle， and specifically expressed in the I zone of myofibrils. The taz^-/- mutant was further constructed in zebrafish by CRISPR/Cas9 technology， and it was found that after taz deletion， the body length， weight， body width， and height of taz^-/- were significantly smaller than wild-type zebrafish （P<0.05）. It shows that mutation of taz gene lead to growth and developmental delay in zebrafish. The fluorescence staining of 48 hpf embryos showed that the muscle fibers from the taz^-/- mutant was looser than WT. Statistical analysis of F-actin length showed that the H-H length of taz^-/- was（1.12±0.03）μm， while the wild-type zebrafish H-H length was（0.59±0.01）μm， indicating that the length of actin was significantly longer （P<0.05）. Whole Alizarin stain of zebrafish showed the length of intermuscular bones became smaller in taz^-/- than WT. The above results indicate that taz affects the growth， actin contraction and ossification of intermuscular bones.

Abstract:

This article combines bioinformatics， quantitative real-time PCR， in situ hybridization， and HPLC techniques to investigate the sequence characteristics， spatiotemporal expression patterns， and subcellular localization of the Bco1 gene in the Chinese mitten crab （Eriocheir sinensis）. It also explores the variations in Es-Bco1 expression， color， and carotenoid content in the hepatopancreas under chronic stress caused by high pH levels. The findings reveal that the full-length of Es-Bco1 open reading frame （ORF） spans 1 614 bp and encodes 537 amino acids. It belongs to the RPE65 superfamily and exhibits a high similarity to BCO1 in the Portunus trituberculatus.（2） Es-Bco1 was expressed in multiple tissues， with high expression in the endoderm， eyestalks， and hepatopancreas； the expression of Es-Bco1 in the hepatopancreas was highest during the post-molt stage （stage AB）； the expression of Es-Bco1 in the hepatopancreas significantly increased during ovarian stages Ⅰ-Ⅲ and then significantly decreased. （3） In situ hybridization results showed that Es-Bco1 mRNA was mainly localized in the F cells （Fibrillar cell） and R cells （Resorptive cell） of the hepatopancreas during the AB stage and ovarian development stage Ⅲ. （4） After 30 days of exposure to pH 8.0 （control）， 9.0， and 10.0， the expression level of Es-Bco1 in the hepatopancreas of juvenile crabs significantly increased， while the lightness value （L^*）， yellowness value （b^*）， total carotenoid content， and β-carotene content in the hepatopancreas significantly decreased. In conclusion， Bco1 in E. sinensis is mainly expressed in the epidermal layer， eyestalks， and hepatopancreas， with high expression during the post-molt stage and ovarian stage Ⅲ. Furthermore， high pH stress can upregulate Es-Bco1 expression in the hepatopancreas and reduce carotenoid content， indicating that Bco1 plays an important role in carotenoid cleavage of E. sinensis in response to high pH stress.

Abstract:

In order to study the correlation between phenotypic traits and dry meat yield of Ruditapes philippinarum in different seasons， 270 individuals in spring， 141 individuals in summer， and 55 individuals in autumn were sampled in Xiangshan Bay， respectively. The shell length （X₁）， shell height （X₂）， shell width （X₃）， back edge length （X₄）， frond edge length （X₅）， live body mass （X₆）， soft part mass （X₇）， and shell mass （X₈） were measured. The dry meat weight （X₉） was then obtained by dehydrating the soft part mass. SL/SH（X₁₀）， SL/SW（X₁₁）， SH/SW（X₁₂）， FEL/BEL（X₁₃） and dry meat yield were calculated. Correlation analysis， path analysis， determination coefficient analysis， and regression analysis were conducted to identify the main traits affecting the meat yield of the clams and to establish regression equations. The results showed that the coefficient of variation for the soft part mass of the autumn populations was the highest， while the coefficient of variation for morphological traits was relatively lower. In summer， the number of phenotypic traits significantly correlated with dry meat yield were the highest. Path analysis indicated that shell length， shell height， and shell width were important factors affecting dry meat yield. In particular， shell width had a significant positive impact on the meat yield of the R. philippinarum， especially in autumn and spring. In summer， the ratio of shell height to shell width had a significant negative impact on dry meat yield. The regression equation for the dry meat yield of the spring population is： Y=-9.765+0.888X₁-1.470X₆-0.379X₄+0.609X₃， R²=0.157. The regression equation for the dry meat yield of the summer population is： Y=5.89+0.884X₂-5.473X₁₂-0.413X₅， R²=0.474. The regression equation for the dry meat yield of the autumn population is： Y=35.286-11.076X₁₁， R²=0.161. These research findings provide theoretical reference for the selection of high meat yield strains in R. philippinarum.

Abstract:

To explore potential strategies for red swamp crayfish （Procambarus clarkii） in controlling weeds in rice fields， it was hypothesized that P. clarkii could directly consume weed seeds. Quantitative feeding experiments were conducted using feed as the control group （Cg） to assess the feeding capacity of P. clarkii on seeds of five common rice field weeds （Ludwigia prostrata， Lp； Leptochloa chinensis， Lc； Echinochloa crusgalli， Ec； Eclipta prostrata， Ep and Ammannia baccifera， Ab）， along with its antioxidant performance and gut microbiota response. Results indicated significant differences in daily consumption and consumption rates of different weed seeds fed by P. clarkii （P<0.05）. The mean daily consumption of Lc， Ab， Lp， Ec and Ep seeds was 0.033， 0.027， 0.059， 0.047 and 0.031 g/ind.， respectively. P. clarkii showed significantly higher consumption of Lp seeds compared to Lc， Ab， and Ep （P<0.05）， and higher consumption of Ec seeds compared to Ab seeds （P<0.05）. However， consumption of weed seeds by P. clarkii was significantly lower than that of the control group （0.1 g/ind.）. The GSH-Px enzyme activity in the hepatopancreas of P. clarkii did not show significant differences among treatment groups （P>0.05）. The MDA content in Ec group was significantly higher than in the other treatment groups （P<0.05）， measuring 7.41 nmol/mgprot； there were no significant differences among the other treatment groups （P>0.05）. The SOD enzyme activity in the Ab group was significantly higher compared to the Lc， Ep， and Cg groups （P<0.05）. The CAT enzyme activity was significantly higher in the Ab group compared to the Ep group （P<0.05）. In the Lp group， the SOD enzyme activity was significantly higher compared to the Lc and Cg groups （P<0.05）. There were no significant differences in α-diversity indices of gut microbiota among different treatment groups. The dominant phyla in the gut microbiota of P. clarkii were Proteobacteria， Tenericutes， Actinobacteria， and Firmicutes， collectively comprising over 99% relative abundance across all treatment groups. Specifically， the relative abundance of Actinobacteria was significantly higher in the Lp and Ec groups， at 9.72% and 5.74%， respectively， compared to other groups. Dominant genera included Acinetobacter， Citrobacter， Aeromonas， Rhodobacter， Shewanella， Clavibacter， Pseudomonas， Lactobacillus， and Arthrobacter. In conclusion， P. clarkii can directly consume seeds of common weeds in rice fields， showing a preference for seeds of Lp and Ec seeds. However， excessive consumption of Ec seeds can lead to oxidative damage in the organism， while seeds of Ab and Lc are consumed in smaller quantities. The gut microbiota of Procambarus clarkii exhibits strong environmental adaptability and can process a variety of complex plant materials. These findings provide valuable insights into understanding the changes in weed biodiversity in rice-crayfish co-culture systems.

Abstract:

Compared with Pyropia haitanensis cultivated in southern China， Pyropia suborbiculata has stronger high-temperature resistance， but its round algae are not suitable for production. Therefore， several long-type mutants were isolated from the wild-type strain of P. suborbiculata by artificial mutagenesis. In this study， the blades of the long-type mutant （CCT-2） of P. suborbiculata were induced by ⁶⁰Co-γ ray， and a new strain （PS-M1） with fast growth was screened from its progeny with growth rate as the main breeding index. The PS-M1 blades cultured at 23 ℃ for 60 days had a mean length of 68.1 cm and a length-width ratio of 26.3， which were 2.7 and 2.4 times of CCT-2， respectively. The blades of PS-M1 and CCT-2 cultured at 23 ℃ for 30 days and then cultured at 30 ℃ for another 30 days， their mean length had increased by 6.4 and 3.0 times， respectively. The survival rates of conchospores of PS-M1 and CCT-2 were 47.4 and 42.2%， respectively， after 14 days of culture at 30 ℃， with no significant difference between them. The blades cultured at 23 ℃ for 45 days had a mean chlorophyll a content of 6.5 mg/g and phycobiliprotein content of 64.9 mg/g in PS-M1， which were 20.4% and 22.9% higher than those of CCT-2， respectively. The thickness of PS-M1 was 33.6 μm， which was 15.8% thinner than that of CCT-2. The total numbers of conchospores released by PS-M1 was up to 2.223 million per shell for 10 consecutive days， which was 4.8 times that of CCT-2. In conclusion， compared with long-type mutant （CCT-2）， the new strain （PS-M1） of P. suborbiculata has a higher growth rate， better resistance to high-temperature and also shows obvious advantages in main pigments protein contents， and number of conchospores releasing， which has potential to be applied in commercial cultivation.

Abstract:

In order to compare the differences between the CO₂ fluxes at the water-air interface between the aquaculture areas and the non-aquaculture areas of Eriocheir sinensis on the lake surface and the factors affecting the CO₂ fluxes. The experiment was carried out at Luoma Lake from August 4 to August 5， 2023， where CO₂ fluxes were measured at the water-air interface between the aquaculture areas and the non-aquaculture areas of Eriocheir sinensis of the lake by using the PS-9000 Portable Automatic Measurement System of Carbon Fluxes and the synchronized measurement of the meteorological factors and water quality indices were analyzed at the same time. The results showed that the average value of CO₂ fluxes in the aquaculture area was 0.012 μmol/（m²·s）， which showed an overall CO₂ emission source， and the CO₂ fluxes in the non-aquaculture area was -0.006 μmol/（m²·s）， which showed an overall CO₂ sink. However， both aquaculture and non-aquaculture areas exhibit CO₂ as a source during the day and a sink at night. Multiple stepwise regression analyses showed that the main environmental factors affecting CO₂ fluxes differed between aquaculture and non-aquaculture areas， with air temperature and pH being the the former and total phosphorus， nitrate nitrogen and total organic carbon being the the latter. The results of the study revealed the characteristics and influencing factors of CO₂ fluxes at the water-gas interface between aquaculture and non-aquaculture areas of Eriocheir sinensis in lake， which provides data support for an in-depth understanding of the CO₂ fluxes characteristics of different aquaculture functional areas of freshwater lakes.

Abstract:

To explore the effect of rice-crayfish farming on the stability of soil organic carbon and enzyme activity， a comparative experiment was conducted between rice-crayfish farming model and rice monoculture model using Oryza sativa “Shen Liang You 3117” and Procambarus clarkii as material in 2021 and 2022. The results showed that， compared to the rice monoculture model （RM）， the soil LOC Ⅰ content in the rice-crayfish farming model （RC） increased by 25.85% to 39.13%， the soil MBC content increased by 96.54% to 105.73%， and the soil POC content increased by 92.24% to 132.32% （P<0.05）. Meanwhile， the activity of soil β-XYS in RC decreased by 29.35% to 59.74%， β-GC activity decreased by 17.16% to 53.10%， and ACP activity decreased by 41.64% to 59.12% （P<0.05）. Pearson analysis revealed that soil LOC Ⅰ ， ROC， MBC， and POC were positive correlated with pH， TN， and TOC （P<0.05）， while DOC and C/N ratio were negative correlated with pH and TN （P<0.05）. The rice-crayfish farming model increased the soil pH and TN， reduced the activity of β-XYS and ACP， enhanced the activity of NAG in the soil， and thus increased the content of active organic carbon in the soil.

Abstract:

The effects of different temperatures （20， 25， and 30 ℃） and different feeds （shrimp flake， commercial prawn feed， and Chlorella pyrenoidosa） on the growth and reproduction performances of Neocaridina denticulata were investigated with the 7-day-old N. denticulata postlarvae. The results showed that the survival rate of N. denticulata decreased with the increasing temperature. The survival rate at 20 ℃ （93.33%±7.20%） was significantly higher than that at 30 ℃ （P<0.05）. Temperature had no significant effect on the body length， mass， and specific growth rate of N. denticulata during the 91-day- cultivation （P>0.05）. The development of N. denticulata accelerated significantly at the increasing temperature. The first time of berried female at 30 ℃， 25 ℃， and 20 ℃ appeared at （39.25±3.20）， （55.00±1.00）， and （162.33±1.53） day， respectively. However， the body length， mass， and egg number of the berried female at 20 ℃ were significantly higher than those at 25 ℃ and 30 ℃ （P<0.05）. There were no significant differences in body length， mass， and egg number between the 25 ℃ and 30 ℃ groups （P>0.05）. There was no significant difference （P>0.05） in the relative reproductive capacity of N. denticulata among the three treatments. The hatching time of postlarva significantly decreased with the increasing temperature. The biological zero and the effective accumulated temperature on gonad development in N. denticulata were 16.57 ℃ and 507.54（℃·d） respectively. The biological zero and the effective accumulated temperature on embryonic development were 6.69 ℃ and 279.98（℃·d） respectively. The growth and survival rates of the N. denticulata fed with Chlorella pyrenoidosa were significantly inferior to those fed with shrimp flake and commercial prawn feed （P<0.05）. Compared to that fed with Chlorella pyrenoidosa， the berried female N. denticulata fed commercial prawn feed displayed significantly higher body length， mass， egg number， and relative reproductive capacity （P<0.05）. In summary， around 25 ℃ is the suitable temperature and commercial prawn feed is a suitable feed for the cultivation of N. denticulata.

Abstract:

Monosex cultivation of Chinese mitten crab is a potentially promising aquaculture method. Customizing gender-specific diets based on the nutritional requirements of males and females is a crucial prerequisite for precise feeding. This study employed a 2×2 factorial experimental design （2 diets × 2 genders） and conducted an 80-day aquaculture experiment in outdoor pond enclosures. The research investigated the effects of gender-specific fattening diets on the cultivation performance， physiological metabolism， and biochemical composition of pre-adult male and female Chinese mitten crabs （Eriocheir sinensis）. The experiment consisted of four groups： males fed with male-specific diet （MM）， males fed with female-specific diet （MF）， females fed with female-specific diet （FF）， and females fed with male-specific diet （FM）. Each group had four replicate enclosures. The results show that： Feeds had no significant effect on the growth， survival rate， yield， and feed conversion （P>0.05）. However， gender had a significant impact on growth， yield， and feed conversion at day 80 （P<0.05）； The hepatosomatic index（HSI） and gonadosomatic index（GSI） of the FF group were higher than those of the FM group， and the GSI difference was significant on the 80th day （P<0.05）. The total fat content in the hepatopancreas was significantly higher in the FF group than in the FM group （P<0.05）. However， there were no significant differences in conventional biochemical components in edible tissues between the dietary groups （P>0.05）； Concerning antioxidant and immune indicators， the glutathione peroxidase（GSH-Px） activity in the hepatopancreas was significantly higher in the MM group than in the other groups （P<0.05）， while the FF group had the highest total superoxide dismutase（T-SOD） activity in the hepatopancreas. Both diet and gender factors significantly influenced acid phosphatase（ACP） activity in the serum （P<0.05）； Regarding protein and lipid metabolism， the MM group had the highest trypsin activity in the hepatopancreas and the lowest lipase activity. The FF group had significantly higher triglyceride（TG） content in the hepatopancreas （P<0.05）. The FF group had the highest levels of total protein（TP）， TG， total cholesterol（TC）， low-density lipoprotein cholesterol（LDL-C） and high-density lipoprotein cholesterol （HDL-C） in the serum. In conclusion， male crabs fed fed male-specific diet demonstrated enhanced antioxidant and immune capacity， promoting protein deposition； female crabs fed female-specific diet accelerated ovarian development and increased triglyceride deposition in the hepatopancreas.

Abstract:

To evaluate the effects of crisp culture on the growth， serum biochemical indexes and intestinal health of tilapia， Nile tilapia（Orechromis niloticus）（665±34） g were fed with faba bean， crisp feed （approximately 50% faba bean） and ordinary feed. The growth， serum biochemistry， intestinal tissue morphology， tight junction protein， digestive enzyme， antioxidant enzyme， inflammatory gene and intestinal flora of tilapia were investigated at 40 d and 80 d. The results showed that： The body mass/length and weight gain rate in the faba bean/crisp feed group were significantly lower than those in the ordinary feed group. The serum lysozyme （LYZ） in the faba bean group was significantly higher than that in the ordinary feed group. There was no significant difference in serum alkaline phosphatase （AKP） between the faba bean group and ordinary feed group. The serum aspartate aminotransferase （AST） and alanine aminotransferase （ALT） increased at 80 days in faba bean group. There was no significant difference in serum ALT， AST and AKP between the crisp feed group and ordinary feed group， whereas LYZ was significantly higher in the crisp feed group. The length of intestinal villi in the faba bean/crisp feed group was shorter than that in the ordinary feed group. The expressions of tight junction protein genes Occludin/ZO-3 /Claudin-3 decreased significantly and the expression of Claudin-12 increased significantlyin the faba bean group. There was no significant difference in the expressions of the above genes between the crisp feed group and ordinary feed group. The activities of α-amylase and lipase in faba bean group decreased， and the activity of lipase in crisped feed group decreased only at 40 d. The content of malondialdehyde （MDA） in faba bean group significantly increased， and the total antioxidant capacity （T-AOC） significantly increased at 80 d. There was no significant difference in MDA content between the crisp feed group and ordinary feed group， but T-AOC significantly decreased. The expressions of pro-inflammatory genes IFN-γ， TNF-α and anti-inflammatory gene IgM were significantly higher in the faba bean /crisp feed group than those in the ordinary feed group. The expressions of anti-inflammatory genes TGF-β1 and IL-10 decreased in the faba bean group， but the TGF-β1 and IL-10 significantly increased in crisp feed group. The ACE， Chao1， Simpson and Shannon indexes of intestinal microorganisms in the crisped feed group were close to those in the ordinary feed group but higher than those in the broad bean group. The abundance of Lachnospiraceae and Lactobacillus in the crisped feed group decreased， while the abundance of Mycobacteria and multiple Clostridium increased. The abundance of Firmicutes， Fusobacteria and Cetobacterium in the broad bean group decreased， whereas the abundance of Proteobacteria and Mycobacteria increased. Compared with 40 d， there were no significant changes in most indexes in the crisp feed group at 80 d. In conclusion， feeding tilapia with faba bean or crisp feed （approximately 50% faba bean） inhibited growth and intestinal antioxidant capacity， shortened intestinal villi， induced intestinal inflammatory reactions， reduced the abundance of beneficial bacteria and increased the abundance of pathogenic bacteria in the intestine. However， the adverse effects of crisp feed were weaker than those of faba bean. The crisp feed had no significant effect on intestinal digestive enzyme activity， cell membrane permeability and anti-inflammatory system. Faba bean had significant negative effects on the above indexes.

Abstract:

Bighead carp （Aristichthys nobilis）is an important economic cultured fish. Its muscle quality is affected by different aquaculture environments. Moreover， the effect of different aquaculture models on the muscle quality of bighead crap is unclear. To explore this， we selected six bighead carp， randomly and respectively， from three different aquaculture environments： paddy field （DT）， pond （CT）， and reservoir （SK）. We analyzed their muscle composition， measuring moisture， crude ash， crude protein， crude fat， and volatile flavor compounds using methods like atmospheric drying， high-temperature ashing， Kjeldahl nitrogen determination， acid hydrolysis， and gas chromatography-mass spectrometry. The results showed that the crude protein content of CT and DT was significantly higher than that of SK （P<0.05）. Additionally， the crude fat content of CT was significantly higher than that of DT and SK （P<0.05）.The muscles from all groups are rich in various constant and trace elements required by the human body， among which the contents of iron， manganese， sodium， and selenium are significantly higher in DT than in CT and SK （P<0.05）. The distribution of fatty acids differed among the groups types of bighead carp， with CT having a higher content of monounsaturated fatty acids（31.20%）， DT showing higher saturated fatty acids（46.05%）， and SK having higher polyunsaturated fatty acids（29.83%）. The ∑n-3/∑n-6 polyunsaturated fatty acid ratio was highest in DT， followed by SK and CT. We also observed similar total amino acid content among the 18 amino acids analyzed， the total amino acid content in the muscles of all three bighead carp was similar， and the proportion of total essential amino acids （EAA） to total amino acids was above 39%， surpassing the WHO/FAO model standard of 35.38%. The essential amino acid index （EAAI） was above 86 for all three groups， with DT exhibiting higher values than ST and CT. Notably， DT was found to have a better flavor profile with higher aldehyde volatile substances and lacking ketone volatile substances. Overall， the study highlighted the nutrient richness and balanced amino acid and fatty acid profiles in bighead carp muscles， making them a superior protein source across the different breeding modes. This study illstrates the nutritional benefits and balanced amino acid and fatty acid profiles in bighead carp muscles across different farming models， offering insights for consumer selection and foundational data to enhance muscle quality in bighead carp.

Abstract:

To comprehend the fish assemblage characteristics of the rocky reef habitats in the sea area of Dachen Islands， we collected fish samples from the subtidal rocky reef habitats using gillnets with multiple mesh， once per season from September 2020 to April 2021. Multiple statistical methods， including Jaccard similarity index， relative importance index， α-diversity index， clustering and ordination， and canonical correspondence analysis， were employed to investigate the characteristics of fish assemblages in this habitat and their relationship with environmental factors. A total of 49 fish species were collected from the subtidal rocky reef habitats of Dachen Islands. These species belong to 10 orders， 27 families， and 40 genera. The highest proportions were found in the Sciaenidae family （22.45%） and the Engraulidae family （10.20%）. Eleven dominant species appeared throughout the year， with Sebastiscus marmoratus， Johnius distinctus， and Stephanolepis cirrhifer exhibiting high dominance. The multivariate statistics results indicate significant spatial and temporal differences in fish communities in subtidal reef habitats on Dachen Islands. Different degrees of dissimilarity between various site types were observed， with the aquaculture areas and eastern rocky reefs forming assemblages that differed significantly from other areas （P<0.05）. Additionally， significant seasonal variations were observed （P<0.05）， with the highest biological diversity observed in summer and the lowest in winter. Canonical correspondence analysis identifies salinity and temperature as the most significant factors influencing fish assemblages in the rocky reef habitats of Dachen Islands. On a local scale， the study reveals that rocky reef habitats around aquaculture disturbance areas exhibit more stable and diverse fish assemblage patterns. The negative impact of aquaculture activities on fish assemblages is currently not significant， and fish within these habitats may have already developed adaptive strategies to cope with human disturbances. But in general， the fish assemblage composition of subtidal reefs was simple and structurally fragile， emphasizing the urgent need for targeted conservation and management measures.

Abstract:

In order to investigate the species characteristics of coral reef fishes in the four islands in Yongle Atoll （Jinqing Island， Antelope Reef， Quanfu Island， and Yinyu Island） of Xisha Islands， this study was conducted on the coral reef fishes of the four islands from 2020 to 2023 by using hand-fishing， diving fishing， and underwater video methods. The species composition， similarity， and taxonomic diversity of coral reef fishes in the four islands were analyzed， incorporating data from the survey conducted on Yinyu Island from 2020 to 2021. Additionally， the feeding type and individual size of coral reef fishes in the four islands were examined in conjunction with relevant literature. The findings indicate that： （1） There are 260 species of coral reef fishes in the four islands of Yongle Atoll in recent years， belonging to 40 families in 10 orders of 2 classes. Perciformes emerges as the predominant order， with Labridae， Pomacentridae， and Chaetodontidae exhibiting the highest number of species. （2） The coral reef fishes from the four islands of Yongle Atoll were primarily composed of carnivorous fishes， with a prevalence of medium and small fishes and the coefficient of similarity was significantly lower for large fish than for small and medium fish， indicating that the four reefs have been affected by fishing to varying extents. （3） The proportions of carnivorous fish and large fish displayed the following order： Jinqing Island > Antelope Reef > Quanfu Island > Yinyu Island， and the average classification difference index （Δ⁺） followed the sequence： Jinqing Island （54.94） > Antelope Reef （53.30） > Quanfu Island （52.63） > Yinyu Island （52.05）， which suggested a significant difference in the degree of human disturbance levels among four islands， with the disturbance ranking as Jinqing Island < Antelope Reef < Quanfu Island < Yinyu Island. The study conducted an in-depth analysis of the coral reef fish composition at the four islands in Yongle Atoll， analyzed the influence of human disturbance， which will offer a theoretical basis for promoting the sustainable development of coral reef fish resources in the Xisha Islands and provide references for the conservation and management of coral reef fish.

Abstract:

In order to investigate the deterioration of sensory quality and physicochemical indexes among different fine-segmented fish， and screen out the parts that are susceptible to deterioration， silver carp （Hypophthalmichthys molitrix） and tilapia （Oreochromis niloticus） were finely segmented into dorsal meat， abdomen meat， belly meat and tail meat. The samples were analyzed for organoleptic evaluation， biochemical indexes and textural characteristics before and after storage. The results showed that the sensory evaluation of all parts of the two fish decreased to different degrees after 7 d of storage， and the odor of the belly of silver carp was the most deteriorated. 0 d of silver carp dorsal meat and tail meat had similar volatile odors， and the separation of PCA increased on the 7th day. During the 7-day storage period， there was no significant difference in the brightness of the different parts of silver carp， and only the brightness of the dorsal meat of tilapia increased significantly from 36.29 to 42.57. The drip loss and centrifugal loss of silver carp were higher than tilapia， and the texture profile of silver carp were more likely to deteriorate. From the comprehensive analysis of freshness indexes， the contents of TVB-N， K value， and TVC value of silver carp dorsal， tail meat， tilapia belly， tail meat were significantly increased， and the POV of chub belly meat increased significantly from 0.09 mmol/kg to 0.16 mmol/kg （P<0.05）. Total free amino acids increased significantly in rib meat， belly meat and tail meat of silver carp. Overall， the sensory and freshness qualities of silver carp belly and tail meat were more susceptible to deterioration， and tilapia backbone meat deteriorated the fastest in terms of sensory quality and textural characteristics. This study provides data support for fine segmentation of freshwater fish and establishment of rapid evaluation methods.

Abstract:

The objective of this study is to extract C-phycocyanin from Spirulina platensis using four different extraction methods and to investigate its structural， physicochemical， functional properties， and antioxidant activity. The four extraction methods include oscillatory extraction （OE）， high-speed homogenate extraction （HHE）， ultrasonic extraction （UE）， and repeated freeze-thaw extraction （RFE）. The results showed that the purity of C-phycocyanin obtained by the four extraction methods reached the standard of reagent grade. The purity of C-phycocyanin obtained by repeated freeze-thawing and high-speed homogenization methods reached 2.68 and 2.37， respectively. FTIR analysis showed that C-phycocyanin α-helix obtained by repeated freezing and thawing had the highest content， indicating that its secondary structure was the most stable. The physicochemical and functional properties of C-phycocyanin showed that its solubility， emulsification ability， foaming ability， water holding capacity， oil holding capacity， minimum gel concentration and surface hydrophobicity all showed the following characteristics： repeated freeze-thaw extraction > high-speed homogenate extraction > ultrasonic extraction > oscillating extraction （P<0.05）. As shown by SDS-PAGE profiles， C-phycocyanin obtained by all extraction methods contained two helical subunits， α and β . The results of antioxidant experiments showed that C-phycocyanin had strong antioxidant properties. The ability of C-phycocyanin to scour DPPH and ABTS free radicals obtained by the four extraction methods was shown as repeated freeze-thaw extraction， high-speed homogenate extraction， ultrasonic extraction， oscillation extraction. In conclusion， C-phycocyanin extracted by repeated freezing and thawing has the highest purity， the most stable secondary structure， the best solubility， emulsification ability， foamability， water holding capacity， oil holding capacity， minimum gel concentration and surface hydrophobicity， and strong antioxidant ability. These results provide theoretical support and research basis for expanding the application of C-phycocyanin in food， medicine and cosmetics.

Abstract:

In order to explore the conditions for the catalytic synthesis of α-arbutin by recombinant marine sucrose phosphorylase Suc75290 from the ocean and its separation and purification conditions， sucrose and hydroquinone were used as substrates， and marine sucrose phosphorylase Suc75290 was used as a catalyst to synthesize α-arbutin. The macroporous adsorption resin HP20 was used to separate and purify α-arbutin and hydroquinone in the reaction solution. The results showed that the optimum conditions for the synthesis of α-arbutin catalyzed by marine sucrose phosphorylase Suc75290 were as follows ： MES-NaOH buffer with pH value of 7， reaction temperature of 40°C， optimum hydroquinone concentration of 38.5 g/L， optimum molar ratio of sucrose to hydroquinone of 5∶1 （ sucrose concentration of 600 g/L）， optimum enzyme dosage of 300 U/mL， and optimum reaction time of 28 h. The conversion rate of hydroquinone was 96.70%， and the content of α-arbutin was 64.3 g/L （238.7 mmol/L）. The macroporous resin adsorption method was used for separation， and deionized water was used as the loading buffer. The optimal separation conditions were determined as follows： the loading volume was 10 mL， the loading flow rate was 0.5 mL/min， the eluent was 30% ethanol， and the elution flow rate was 1 mL/min. 50 mg of α-arbutin was obtained after rotary evaporation， and the purity was 99.9%. In summary， the optimization of the conditions for the synthesis of high-concentration α-arbutin using marine sucrose phosphorylase Suc75290 and the study on the separation and purification process of α-arbutin provide an application basis for the development and utilization of high-purity α-arbutin.

Abstract:

In this study， the characteristics of biofilm formation of single and mixed strains of Vibrio parahaemolyticus with different virulence genotypes from freshwater products under pure culture conditions and bile salts stress were investigated. The amount of biofilm formation and cell viability were detected by crystal violet staining and CCK-8 method， and the structure of biofilm was visually observed by confocal laser scanning microscopy （CLSM）. Bicinchoninic acid （BCA） method and phenol-sulfuric acid method were used to quantitatively analyze the contents of extracellular protein and extracellular polysaccharide before and after bile salts treatment. The results showed that bile salts treatment inhibited the formation of V. parahaemolyticus biofilm， significantly decreased the amount of biofilm formation and cell viability， and affected the degree of aggregation and disorganization of biofilm system， and disrupted the biofilm structure， while affecting the synthesis and secretion of extracellular protein and extracellular polysaccharide. Strains containing tdh gene can form more and more stable biofilms， and the mixed strains showed greater adaptability to bile salts stimulation and were able to respond rapidly to counteract this stress， thus ensuring more stable survival of the strains. This study provides a new theoretical support for the formation and control of V. parahaemolyticus mixed biofilms， which is of great significance for exploring the impact of V. parahaemolyticus carriage in freshwater products on food safety and human health， and provides an important reference for further research on its adaptive mechanism and prevention and control in the human gut.

Abstract:

Vibrio parahaemolyticus is a Gram-negative rod-shaped bacterium with flagella， widely distributed in estuaries and oceans， and is one of the major pathogenic bacteria in aquaculture. For future development of attenuated vaccine of V. parahaemolyticus， in this study we knocked out hemoD gene in V. parahaemolyticus using homologous recombination. Compared with wild type of V. parahaemolyticus， ΔhemoD strain showed a decrease in hemolytic activity by 45.7%， a decrease in the ability of biofilm formation by 36.2%， and no significant change in growth rate. When co-cultured with Tetrahymena thermophila， the injury of Tetrahymena by ΔhemoD strain was less with more Tetrahymena survived， and hence engulfed more cells of ΔhemoD strain than the wild strain of V. parahaemolyticus. The whiteleg shrimp Penaeus vannamei was further used for pathogenicity evaluation. The P. vannamei werechallenged with strain ΔhemoD and wild type strain of V. anguillarum through administration， respectively， the LD₅₀ of ΔhemoD strain was 5.06 times higher than that of the wild type strain. Compared with wild type of V. parahaemolyticus， the colonization ability of ΔhemoD strain in the intestinal tract of P. vannamei was obviously weakened， and the damage ability to hepatopancreas was reduced， and the phenomena of hepatopancreatic cytolysis and vacuolisation were less serious. These results indicate that the ΔhemoD strain has a reduced pathogenicity to P. vannamei. Onthe whole， we constructed an attenuated strain of V. parahaemolyticus， which will be developed as a potential attenuated vaccine.

Abstract:

The research on underwater object detection algorithms is a prerequisite for achieving intelligent fishing with underwater robots. The problems of fuzzy object， numerous small objects and mutual occlusion in underwater object detection pose challenges to the realization of accurate object detection. This paper proposes a YOLO-U algorithm for underwater object detection based on YOLOv7-tiny. The algorithm introduces a RepViT backbone network with structural reparameterization and fuses an ESE channel attention mechanism to enhance the feature extraction capability for underwater fuzzy objects. Additionally， a feature pyramid network CAFPN with shallow coordinate information feature fusion is designed to further enhance the sensitivity of the detection model to directional and positional information， and integrate feature information of different scales to improve the detection ability of small objects. Furthermore， the WIoUv2 bounding box loss function is employed to effectively reduce the contribution of easy examples to the loss value. This allows the model to focus on occluded objects and further improve the detection accuracy for occluded objects. The YOLO-U algorithm achieves a mAP50 of 84.6% on the URPC2021 dataset， which is an improvement of 2.1%， 5.2%， and 2.8% compared to YOLOv7-tiny， YOLOv5s， and YOLOv8s， respectively. The detection results show that the algorithm can effectively improve the detection accuracy of underwater objects and further improve the detection performance of underwater fuzzy objects， small objects， and occluded objects.

Abstract:

In order to study the application of the distribution law of fishing grounds in shrimp and crab farming， and to solve the problem of over-concentration of feeding in traditional shrimp and crab farming feeding devices， this study completed the mechanical structure and intelligent control system design of the mobile autonomous feeding device through the research of overall structural layout， storage tank， feeding device， garbage collection device， control system and power device， conducted stability and motion feasibility analysis， trial-produced a feeding device prototype and conducted underwater three-dimensional feeding tests. The device can carry 5 kg of bait and feed underwater three-dimensionally through the propulsion device and the Ballast tank. It can simulate the behavior pattern of shrimps in natural waters and optimize the distribution of feed， thereby creating a feeding environment closer to natural ecological conditions. The test results show that the device can feed at 6 different depths underwater， with a feeding speed of 4.9 kg/min， which can meet the needs of intelligent three-dimensional feeding and collect floating garbage generated during the breeding process. The feeding device can feed flexibly and evenly， and can replace manual feeding to reduce labor intensity. At the same time， the intelligent device can be used to record various parameters such as water bodies， shrimps and crabs for research on the distribution of fisheries， assist in the application of fishery distribution laws in aquaculture， and provide new ideas for intelligent and precise farming.