Aquaculture species diversification in China

China has been the top aquaculture producer in the world since 2002.Over 800 species and 240 improved varieties have been used in China’s aquaculture,which is the most diverse collection of species on this planet.Species diversification,along with other aquaculture technologies,contributes significantly to the increase of China’s aquaculture production,whereas the use of too many species in aquaculture has resulted in some issues related to the environment and sustainability.We provide an updated overview of the species currently used in Chinese aquaculture in this paper.We examine critically the main drivers of species diversification in China with examples.We also introduce Chinese approaches to improve and certify new species and varieties for commercial production.We believe that further species diversification is not a priority in China’s aquaculture,while further improvement of aquaculture technologies for major and native species is essential for green,profitable,and sustainable(GPS)aquaculture.The implications of China’s experiences with species diversification for global aquaculture species diversification are discussed.

Glycolysis and gluconeogenesis are involved of glucose metabolism adaptation during fasting and re-feeding in black carp(Mylopharyngodon piceus)

Both in nature and in aquaculture,fish may experience periods of food scarcity or hunger.The metabolic regulation of fish when nutritional state changes is a complex process that involves many factors.To study glucose metabolism adaptability during fasting and re-feeding in the black carp(Mylopharyngodon piceus),we measured changes in some biochemical indicators related to glucose metabolism.Five fish were sampled on days 0,1,3,5,and 10 of fasting(F,S1,S3,S5,and S10,respectively)and days 1,3,and 5 of re-feeding(RF1,RF3,and RF5,respectively).The serum glucose concentration decreased significantly at S1,reached the lowest point at S10,and increased significantly at RF1(P<0.05).The concentration of liver glycogen decreased significantly at S1 and reached the lowest level at S3,whereas the muscle glycogen level decreased significantly at S5 and reached the lowest value at S10(P<0.05).Both liver and muscle glycogen levels returned to the pre-fasting level at RF5(P<0.05).Regarding glycolysis,the concentrations of pyruvate kinase(PK)and hexokinase(HK)decreased significantly at S5 and increased significantly at RF5 and RF1,respectively(P<0.05).The concentrations of glucokinase(GCK)and insulin decreased significantly at S1 and increased significantly at RF1 and RF3,respectively(P<0.05).The mRNA expression levels of liver GCK and glucose transporter 2(GLUT2)decreased significantly at S1 and increased significantly at RF1 and RF5,respectively(P<0.05).As for gluconeogenesis,the concentration of glucose-6-phosphatase(G6PC)increased significantly at S1 and decreased significantly at RF1(P<0.05).The concentrations of glucagon and glucocorticoid(GC)increased significantly at S3 and significantly decreased at RF1 and RF5,respectively(P<0.05).The mRNA expression levels of liver G6PC and phosphoenolpyruvate carboxykinase(PEPCK)increased significantly at S3 and S1,and both decreased significantly at RF1(P<0.05).These results indicate that coordination between glycolysis and gluconeogenesis might be crucial for glucose homeostasis during fasting and re-feeding in the black carp.

Effects of biological flocculation technology(BFT)on water quality dynamics and immune response of grass carp(Ctenopharyngodon idella)

The biofloc technology(BFT)offers benefits in improving feed utilization and reducing the feed conversion ratio compared to the recirculating aquaculture system(RAS).In this study,high-throughput 16S rRNA gene sequencing was employed to investigate and compare the bacterial communities in these aquaculture systems and the gut microbiota of grass carp reared in them.We observed a significant distinction between the microbial communities of the aquaculture systems and the intestinal microbiota of grass carp.The genera cetobacterium and bacillus were more abundant in the BFT system,accounting for only 0.05% and 0.25% in the RAS.Our study also demonstrated that BFT could influence the intestinal microorganisms of grass carp(Ctenopharyngodon Idella)by reducing the relative abundance of burkholderia-caballeronia-paraburkholderia and increasing that of cetobacterium.Based on bugBase community predictions,the potential pathogenicity in BFT and grass carp intestine was lower than in RAS.Regarding gene expression in the grass carp intestine,immunosuppressive genes showed higher expression,while pro-inflammatory genes exhibited lower expression in grass carp reared in BFT.Furthermore,the final average length and weight of grass carp in the BFT system were significantly higher than those in the RAS.This study provides valuable insights into gut microbiome ecology in relation to two grass carp aquaculture systems,which could be effectively applied in grass carp management to promote health and improve water quality.

An overview of disruptive technologies for aquaculture

The world wild fish stocks are being depleted in an ever-increasing speed.Aquaculture is the only way to ensure sufficient seafood for the world.Conventional aquaculture can be traced back to 4000 years in China and has been very successful in the past three decades.However,aquaculture has faced serious challenges,including only a few improved species,labour-intensiveness,environmental pollution,diseases and lack of traceability of products.Aquaculture needs disruptive technologies to increase fish production.Novel and disruptive technologies,including genome editing,artificial intelligence,offshore farming,recirculating aquaculture systems,alternative proteins and oils to replace fish meals and fish oils,oral vaccination,blockchain for marketing and internet of things,may provide solutions for sustainable and profitable aquaculture.This review briefly introduces these emerging and disruptive technologies to open up a forum for an in-depth discussion on how to integrate these technologies into aquaculture to improve its sustainability and profitability.

Current status of research on aquaculture genetics and genomicsinformation from ISGA 2018

The ISGA(International Symposium on Genetics in Aquaculture)is an important conference in the field of aquaculture genetics,which is held every three years.This year,the meeting was hosted by James Cook University,in Cairns.The conference sessions included biotechnology and functional genomics,sex control,genomic prediction,selective breeding and quantitative genetics,industrial use of genetics,genome technology,genetics of diseases and stress,genetics of nutrition,epigenetics,genomics and metabolomes,population genetics and ethics,food safety,as well as environmental risks.Many new and interesting unpublished data,including those for new aquaculture species,marker-assisted selection,genomic selection and genome editing using Crispr/Cas9 technologies,were reported at the conference.In this brief review,we highlight the novel and interesting researches on aquaculture genetics and genomics to give readers an overview of the current status and trends of aquaculture genetics and genomics research.

A multiplex microsatellite PCR method for evaluating genetic diversity in grass carp(Ctenopharyngodon idellus)

Grass carp is one of the most important cultured fishes all over the world.The genetic diversity of grass carp plays an important role whatever in selective breeding progress or ecological conservation purposes.However,some genetic diversity researches were not accuracy and cannot be compared with each other due to different molecular markers,sample size and detection methods.In this study,we constructed five multiplex PCR assays contained 20 microsatellites with highly polymorphism and heterozygosity for evaluating genetic information of grass carp.We used nine cultured populations consisting of 507 individuals to detect stability of the five multiplex PCR assays.The results showed that the number of alleles(Na),effective number of alleles(Ne),observed heterozygosity(Ho),expected heterozygosity(He)and polymorphism information content(PIC)of the 20 microsatellite loci were relative high compared with the genetic diversity parameters of microsatellite loci developed by other researchers.Six loci were significantly deviated from Hardy-Weinberg equilibrium(P<0.01).And with exception of the Shaoguan,Indian and Nepal cultured population,all other cultured populations showed very high genetic diversity.Through the test of grass carp populations,we developed an effective and accurate multiplex SSR-PCR assays that can be as statistical powerful tool for detecting genetic information of grass carp.

Genetic diversity and population structure of the Chinese lake gudgeon (Sarcocheilichthys sinensis) using microsatellite markers

The Chinese lake gudgeon is a small benthopelagic freshwater fish.It is presently threatened by human activities and environmental factors in China.Understanding the genetic diversity and population structure is fundamental for implementation of appropriate conservation measures and a sustainable management program.However,little is reported about the current genetic diversity and population structure.Here,we used ten microsatellite markers to genotype 175 individuals from six populations.Low levels of genetic diversity were found in all six tested populations.The Xiang river population showed the highest level of genetic diversity.Genetic differentiation was very low but significant among the Changyang,Changqidang and Mayang populations,but the Qiandao lake,Gan river,Xiang river populations all showed significant and strong differentiation from the other three populations.Contemporary gene flow was observed in among Changyang,Changqidang and Mayang populations and between Gan and Xiang river populations,respectively.This is the first genetic study to report the genetic diversity and population structure of S.sinensis and the results will be used to develop management and conservation strategies.

Cloning,prokaryotic expression,purification,and functional verification of the insulin gene in black carp(Mylopharyngodon piceus)

In this paper,we studied the structure,expression and function of black carp insulin gene.The complete Mylopharyngodon piceus insulin(Mp-Ins)gene is 1,965 bp long and includes a 1,499 bp 5ʹ-untranslated region(UTR),a 139 bp 3′-UTR with a poly(A)tail,and an open reading frame(ORF)of 327 bp.The predicted molecular weight of the recombinant Mp-Ins(rMp-Ins)protein is 11.87 kDa.The mRNA expression of Mp-Ins is upregulated in the brain and liver.After the injection of rMp-Ins,Mp-Ins mRNA transcript abundance was significantly upregulated in the liver.The rMp-Ins protein could inhibit the concentration of glycogen phosphorylase(GP),growth hormone(GH),fatty acid synthase(FAS),and insulin-like growth factors-1(IGF-1),and it also significantly increased the concentration of PI3K.Additionally,the injection of rMp-Ins did not have a significant impact on the glucose-6-phosphatase(G6Pase)content in blood.In situ hybridization results showed that the positive signal of the Mp-Ins gene was mainly concentrated in the cell nucleus of brain tissue and the cell membrane of liver tissue and muscle tissue.Together,these results demonstrated that Mp-Ins plays an important role in growth and metabolism in M.piceus.

Liver DNA methylation and transcriptome between 1- and 3-year-old grass carp

Diseases of grass carps often occur in juveniles but not in adults that may have established disease resistance during development.We performed both DNA bisulfite and transcriptome sequencing on liver libraries of 1-and 3-year-old grass carps.Differential DNA-methylation analysis exhibited a declined methylation level through development.Functional annotation revealed that identified differentially methylated genes(DMGs)and differentially expressed genes were enriched in immune-related pathways such as PI3K-Akt signaling pathway and its related pathways.Both differentially methylated and differentially expressed genes were clustered into the growth-and immune-related function networks.Subcellular localization analysis indicated that the DMGs localized on cell membrane were significantly enriched in calcium signaling pathway and neuroactive ligand-receptor interaction pathway,implying the importance of G protein-coupled receptors to development.These findings will broaden our understanding of the key genes and pathways that affect the immune system at different development stages and the developing protective strategies in grass carp.

Transcriptomic analysis reveals growth-related genes in juvenile grass carp,Ctenopharyngodon idella

Grass carp has the highest production yield among all the farmed fish species around the world.But the molecular and genetic basis of growth traits is inadequately understood in this fish.In the present study,we apply whole-transcriptome sequencing to identify genes whose expression is different between fast and slow growing grass carp.We identified 1178 differentially expressed genes(DEGs),among which 270 were upregulated in the fast growing group and 908 upregulated in the slow growing group.The GO enrichment analysis revealed that DEGs was significantly enriched in protein synthesis and export machinery,cell division and development and metabolism,suggesting that cell division and metabolism may play key roles in development processes of fish.KEGG pathway analysis showed that MAPK signaling pathway may play a prominent role in growth difference.In addition,the majority of genes in immune responses related pathway were upregulated in the slow growing individuals.These results provide some valuable resources for understanding the molecular mechanisms of growth traits in fish.

Exposure to microplastics induces lower survival,oxidative stress,disordered microbiota and altered metabolism in the intestines of grass carp(Ctenopharyngodon idella)

There are major gaps in illustrating the risk to freshwater fish that are exposed to environmental microplastics(MPs),even though MPs in freshwater environments has drawn much concern.To explore the potentially negative effects of microplastics on freshwater fish,grass carp(averaging 9.215±0.035g)were exposed to microplastics(32-40μm in diameter)at two environmental concentrations(100 and 1000μg/L)for 21 days,and evaluated for physio-biochemical performance,gut microbiome,and metabolome responses.After exposure,microplastics were detected in the intestine and within basal nuclei and goblet cells hyperplasia.Antioxidant enzyme activities(superoxide dismutase and catalase)also significantly decreased within the intestines(P<0.05).Through 16S rRNA gene sequencing analysis,a decrease in diversity and richness was observed in the MPs-H and MPs-L groups.The abundance of opportunistic pathogens increased and beneficial bacteria decreased in both MP treatments.For example,Acinetobacter and Bosea proportions were higher in the MPs-L group,while Bacteroides and Shewanella increased in the MPs-H group.Furthermore,abundance of Lactobacillus decreased both in the MPs-H and MPs-L groups.Metabolomics analysis revealed primary bile acid biosynthesis metabolism upregulated in the MPs-L and purine metabolism downregulated in the MPs-H group.Additionally,an integration analysis of the gut microbiome and metabolomics identified significant associations between several bacteria taxa and metabolites related to intestinal repair.Taken together,these results highlighted the negative effects on intestinal morphology,oxidative stress,and microbiome and emphasized the relationship between microbiota and metabolites in response to microplastics,which could provide comprehensive insights into the potential risks of MPs on freshwater fish intestines.