Abstract:It is difficult to distinguish the gynogenetic fish from common one by morphology and physiology of grass carp(Ctenopharyngodon idella).To establish a molecular method of distinguishing the two groups,an artificially induced gynogenetic grass carp group was produced by activating grass carp eggs by the ultraviolet light(UV)irradiated common carp(Cyprinus carpio)sperm and subsequently blocking the release of the second polar body(PB2).Eight microsallite markers were detected,among which five markers were selected to establish a microsatellite identification method.33 alleles were amplified on 8 loci.The average value of observed homozygosity and polymorphism information content(PIC)were 0.203 1 and 0.552 8 in the common group,and those were 0.716 1 and 0.357 2 in the gynogenetic group,respectively.The genetic similarity between the two groups was 0.873 3.And then five microsatellite markers were used for genetic identification of gynogenetic grass carp.The total numbers of alleles at these five loci were between 5 and 7 for 48 gynogenetic grass carp,while those were between 8 and 10 for 48 common grass carp.So we can completely distinguish the two groups of grass carp according to the number of alleles amplified at the five loci.The probability of identification of the gynogenetic grass carp reached 99.92%,premised on the theory of probability calculation.In conclusion,the genetic homozygosity in the gynogenetic group was much higher than that in the common group,and therefore the gynogenesis technique was an effective method to quickly establish pure line and fix merits.Using polymorphic microsatellite markers can distinguish gynogenetic group(or highly inbred population)from common group according to the variation of genetic homozygosity.

Abstract:In order to understand the structure and function of heart type fatty acid binding protein H-FABP,the full-length cDNA sequence of H-FABP gene was cloned from obscure puffer(Takifugu obscurus)by using SMART RACE technique.The entire H-FABP cDNA was 772 bp,containing a 402 bp open reading frame encoding a protein with 133 amino acids.Bioinformatics analysis indicated that the H-FABP gene had a conserved domain of lipocalin family and several phosphorylation sites.Phylogenetic analysis indicated that the H-FABP gene of Takifugu obscurus was closely related to Takifugu rubripes,followed by that of Perciformes.Real-time PCR revealed that H-FABP gene was ubiquitously expressed in all tested tissues.The highest expression of H-FABP was tested in the liver,followed by muscle and heart.This indicates that H-FABP is mainly involved in fatty acid oxidation process.To evaluate the feasibility of using soybean oil as a dietary lipid,juvenile fish were fed with four formulated diets differing in lipid composition,with soybean oil accounting for 0,25%,50% and 75% of total dietary lipid respectively.After feeding for 8 weeks,the expression of H-FABP gene in the liver of the fish oil group was significantly higher than those in 50% soybean oil group and 75% soybean oil group(P<0.05).However,there was no significant difference(P >0.05)between the 25% soybean oil group and the fish oil group.The expression of H-FABP gene in the liver decreased with the increasing of the proportion of soybean oil in diets,indicating that fish oil rich in n-3 polyunsaturated fatty acids can promote fatty acid oxidation and prevent fatty liver.Therefore,in order not to affect the liver fat metabolism of obscure puffer,the proportion of soybean oil instead of fish oil should be less than 50%.

Abstract:Edwardsiellosis caused by Edwardsiella tarda is one of the most serious diseases in the eel culture industry.Bacterial ghosts,which have native surface antigenic structures and can induce humoral and cellular immune response,have become an important candidate of vaccine development.In present study,immune efficacy of E.tarda ghosts vaccine for European eel was detected in 3 kinds of inoculation routes.Results indicate that antibody titer of European eel shows significant increase after immunization with E.tarda ghost(ETG)and Formalin killed cell(FKC),but there is no significant difference between ETG group and FKC group.The relative protective survival(RPS)of ETG by intraperitoneal injection and immersion and oral administration are 75.0%,52.5%,37.5% respectively,is higher than FKC's 55.0%,40.0%,32.5% respectively.Moreover,the beginning of death time of eel immunization with ETG has a delay compared with FKC.Above results indicate that immune efficacy of ETG was superior to FKC.In particular RPS of ETG is 52.5% by oral administration.Considering easily operating and less stress,oral immunization of ETG has a favorable application prospect in preventing Edwardsiellosis of eel industry.

Abstract:Japanese flounder(Paralichthys olivaceus)is a widely cultured economic marine fish species in China because of its fast growth,high value and good taste.As a consequence,more and more fish farmers participate in Japanese flounder aquaculture in recent years.However,high density of breeding makes it easy to cause water quality deterioration and a variety of diseases,and diseases of the cultured fish have occurred frequently and infectious disease brought huge economic losses.What is more serious is that this limits the profitability and development of Japanese flounder aquaculture.Therefore,to breed new flounder strain with enhanced disease resistance and growth rate is an important task in marine fish aquaculture.In this paper,we focused on the detection of different disease resistance ability,during the course of Edwardsiella tarda infection,56 families were established.Among them,32 families were used in the experiment of infecting E.tarda.The purpose of this experiment was to screen families with high disease resistance to E.tarda so that we could solve the problems caused by the traditional methods of treating disease,such as drug residues,environmental pollution and drug resistance.Disease resistance was evaluated in 32 families through intraperitoneal injection of bacterial E.tarda.Before formal challenge experiment,we did a preliminary infection experiment to measure the half lethal concentration of E.tarda to Japanese flounder.According to the results of preliminary experiments,we determined the half lethal concentration(LD₅₀)to be(3.69×10)⁵ CFU/mL.Then 75 fishes were randomly taken from each family and injected with the bacteria according to the half lethal concentration of solution,0.2 mL/10 g body weight.Water temperature should be controlled at(19±1)℃.4 800 fishes from 32 families were challenged with E.tarda through intraperitoneal injection.Through the analysis we know that their survival rate was between 8.2%-66.1% with an average rate of 31.2%.Results demonstrated that there was significant difference in disease resistance among different families(P<0.05).Six families showed high disease resistance to E.tarda.Moreover,we found that the families from family F0768 which had been considered to be highly resistant to Vibrio anguillarum in 2007 showed high disease resistance to E.tarda.So we speculate that the family F0768 has a good disease resistance to both of the bacteria.This study laid the foundation for the selection of E.tarda and V.anguillarum resistant Japanese flounder strains,which is of importance and has application value for the study of molecular mechanism of bacteria resistance and the selective breeding of disease-resistant new species.

Abstract:Australian redclaw crayfish,Cherax quadricarinatus,belongs to Decapoda order,and Parastacidae family.Because it grows rapidly and can reach commercial size in a few months at optimal conditions,it has been one of the most important economy shrimps in China.However,the physiological mechanisms of redclaw crayfish have not been well studied,especially the basic information of key nutrients and the related enzymes or proteins are missing.Cathepsin L(CatL)is an important enzyme related to digesting process in crustaceans,however,its molecular structure and correlation with dietary nutrients have not been investigated.In the present study,in order to obtain insights into the regulatory effects of key dietary nutrients on expression of CatL gene,the CatL gene of C.quadricarinatus was cloned first using RACE-PCR methods.The tissue-specific CatL gene expression was also performed,and the C.quadricarinatus were fed with artificial diets containing different levels of vitamin C(0,100,200,400,800,1 600,3 200 mg/kg)for 8 weeks,and the expression of CqCatL mRNA in different tissues and different groups were examined.The CatL cDNA was isolated from the hepatopancreas of C.quadricarinatus using RACE-PCR methods,which was designated CqCatL(Genbank accession number:KJ913663).The full-length cDNA of CqCatL obtained from the present study was 1 810 bp in length with an open reading frame of 1 026 bp,encoding a putative peptide of 341 amino acids,and the predicted molecular mass and isoelectric point were 37.63 ku and 5.17.By alignment,the amino acid sequence of CqCatL of C.quadricarinatus showed high homology with those of other animals.For example,the deduced amino acids sequence of C.quadricarinatus CqCatL shared 79% homology with Penaeus monodon,and 74%,59%,59%,58% and 58% with Macrobrachium nipponense,Eriocheir sinensis,Metapenaeus ensis,Metapenaeus ensis and Litopenaeus vannamei,respectively.This suggested that CqCatL was highly conservative.The tissue-specific expression pattern study indicated that CqCatL mRNA was widely expressed in hemocytes,gill,hepatopancreas,muscle,ovary,intestine,stomach,heart,brain and antennal gland,indicating CqCatL may play important roles in many tissues of the C.quadricarinatus.The highest expression was observed in hepatopancreas,and the second was seen in hemocytes,while only very low expressions of CqCatL mRNA were found in intestine and antennal gland.After feeding with seven levels of vitamin C,the mRNA expression of CqCatL was the highest in the 400 mg/kg dietary vitamin C group and significantly higher than the other groups.The results showed that CqCatL might play an important role in the physiological process of C.quadricarinatus,and its gene expression and functions were likely regulated by nutrients,such as vitamin C.

Abstract:In order to study the immunogenic and protective effects of Sip-GAPDH from Streptococcus agalactiae recombined chimeric DNA vaccine for Oreochromis niloticus,we cloned Sip and GAPDH gene by PCR,and then obtained the Sip-GAPDH fusion gene using the splicing overlap extension technology(SOEing).The Sip-GAPDH fusion gene was inserted into pcDNA3.1(+)vector and confirmed by restriction endonuclease digestion,PCR amplification and sequencing,and O.niloticus were immunized with the recombined plasmid(designated as pcDNA-Sip-GAPDH)by intramuscular injection.The pcDNA-Sip-GAPDH expression in tissues(including muscle,brain,head kidney,spleen,gill and liver)was analyzed by PCR and RT-PCR at 7 and 28 d after immunization.To reveal the serum antibody titer,expression of immunogenes(IgM,IL-1β and CD8)and relative percentage survival(RPS),we used the enzyme-linked immunosorbent assay(ELISA),real-time PCR and bacterial challenge in vitro to demonstrate the DNA vaccine is a potential candidate for vaccine development of O.niloticus. The results indicated that pcDNA-Sip expression could be found in all studied tissues and antibody titer rose to peak(1:4 096)at 21 d after immunization.Quantitative real-time PCR(qRT-PCR)analysis showed that IgM,IL-1β and CD8 had relatively high expression levels in the head kidney,thymus,spleen.After S.agalactiae infection,transcripts of IgM,IL-1β and CD8 increased and reached its peak 12 h in thymus and head kidney,and 48 h in spleen,respectively.Additionally,the relative percentage survival(RPS)value was 93.3% according to the mortality by S.agalactiae challenge.All the results suggested that the chimeric DNA vaccine is an effective vaccine candidate against S.agalactiae infection.

Abstract:The influence of temperature on growth and the expression levels of sex steroids were studied in juvenile half-smooth tongue sole(Cynoglossus semilaevis Günther,1873).Tongue soles at 32 days post-fertilization(dpf)were exposed to temperatures ranging from 19 to 27 ℃.Measurements of length and body weight of all individuals in each temperature group were conducted 32-142 dpf.Student-Newman-Keuls software was used to analyze the growth rhythm of juveniles and relativity of temperature and length and body weight of half-smooth tongue sole. Results showed that the juveniles of 98 dpf grew fastest in 25 ℃ group but grew fastest in 23 ℃ group when cultured between 129-142 dpf.The specific growth rates of body weight of half-smooth tongue sole were 4.42 and 4.6 respectively at 23 and 25 ℃ and obviously higher than other temperature groups.The Pearson correlation coefficients between temperature and total length and body weight were 0.271 and 0.260,respectively.Moreover,the relationships of temperature(T)and length(L)and body weight(W)were given by the equations L=1.637 6T^0.3782(R²=0.082)and W=0.0285T^1.0781(R²=0.075),respectively.The expression of sex steroid hormones in fertilized egg and juveniles of 3-142 dpf at 23 ℃ were detected.The results showed that the concentrations of testosterone(T)and 17β-estradiol(E₂)were very high in fertilized eggs,but decreased gradually and reached their lowest levels at 32 dpf(4.6 ng/mg for T and 5.43 pg/g for E₂)and then increased to their highest levels(average 40.80-94.70 ng/mg for T and 42.04-105.80 pg/g for E₂)at 46 dpf,but decreased again later.In all temperature groups,the concentrations of T and E₂ increased obviously at 32-46 dpf and reached highest levels at 46 dpf.The concentrations of T and E₂ in 19 and 21 ℃ groups were much higher than that in other groups and there were no significant differences in these groups.The concentrations of sex steroid hormones decreased significantly at 98 dpf in all temperature groups and the expression of E₂ had no significant differences,but the expression of T were higher in 19 and 27 ℃ groups than that in other groups.Therefore,it was speculated that the gonad of juvenile half-smooth tongue sole began to differentiate when the body length was(4.99±0.75)cm at 4 dpf and 19 and 27 ℃ may be the temperature which could promote the juvenile to masculinization.

Abstract:After nonionic ammonia stress(0.1 mg/L and 0.5 mg/L),changes of activities of hexokinase(HK),pyruvate kinase(PK),lactic dehydrogenase(LDH),and succinate dehydrogenase(SDH)were compared between L.vannamei long-term cultured in freshwater and in seawater.Results showed that:(1)nonionic ammonia in lower concentration induced the HK activity in gills of freshwater shrimps to a significantly higher level,while nonionic ammonia in higher concentration induced a significantly higher level of HK activity in gills of freshwater and seawater shrimps.After stress,no significant change was observed in HK activity in muscles of freshwater and seawater shrimps.(2)After nonionic ammonia stress,an increase was observed in PK activity in gills of all shrimps,and PK activity returned to the normal level at the end of the experiments.However,PK activity in muscles showed a different change:no significant change was found in seawater shrimps,which was different from that in freshwater shrimps.(3)No significant effects of nonionic ammonia in lower concentration on LDH activity in gills and muscles of freshwater and seawater shrimps were observed.In contrast,nonionic ammonia in higher concentration imposed a significant effect on LDH activity in gills and muscles of freshwater shrimps.(4)SDH activity was significantly lower in both seawater and freshwater after nonionic ammonia stress.We conclude that nonionic ammonia stress has a significant effect on respiratory metabolic enzyme activities of L.vannamei,and aerobic metabolism decreased drastically after nonionic ammonia stress,while anaerobic metabolism increased slightly in the initial period prior to decreasing.It was suggested that nonionic ammonia probably led to a change in main energetic materials in shrimps.

Abstract:Streptococcus agalactiae was isolated and identified as the pathogen from diseased Nile tilapia(Oreochromis niloticus)populations in China.The pathogen was gram stained through a standard protocol,negative stained and then photoed under electron microscopy.Tissue samples from infected fish were collected and examined for pathological changes under optical and transmission electron microscopes to elucidate the mechanism of infection of Streptococcus agalactiae in tilapia.The result showed that the pathogen was gram positive.And sphere-shaped bacteria were alone or arranged in chains.The most marked pathology observed was severe congestion in the liver,spleen and kidney.Edema,degeneration and acute multifocal necrosis were commonly observed in many organs.There was also evidence of an infiltration of numerous inflammatory cells.Ultrastructural pathology examination indicated that S.agalactiae were widely distributed in many internal organs,especially in the spleen.Moreover,a series of pathological changes were found in the target tissue cells.The boundaries between the cellular compartments were less defined,resulting in the loss of a normal cytoplasmic compartmentalization.There were numerous cases in which cells containing aberrant nuclei appeared singly or in clusters.The cytoplasm often contained degenerated mitochondria,which swelled with disintegration and lyses of the cristaes.Degranulation of the rough endoplasmic reticulum as well as dilatation of the reticulum cisternae was also prevalent.Cells containing such features were frequently accompanied by vacuolar degeneration in cytoplasm.Cardiac and dorsal muscle fibers were fractured and disordered.Sarcomere length of dorsal fiber bundles differed.Microvillus arranged disorderly and in different length.Fibrin precipitated in necrotic foci of the eye.These observations indicated that S.agalactiae can cause simultaneous development of multiple-organ lesions with an acute systemic inflammation in the host,especially in the liver,spleen,kidney and brain,which leads to the death of the fish.

Abstract:To investigate the expression pattern and function of genes expressed in the development and organogenesis of nile tilapia embryos,whole mount in situ hybridization(WISH)of nile tilapia embryo was established based on the commonly used protocols in zebrafish(Danio rerio)and striped bass(Morone saxatilis).However,the WISH protocols of zebrafish and striped bass are not completely viable for nile tilapia embryos because of their huge,opaque yolk with early pigment formation.Thus we optimized the protocol for its application in nile tilapia.Specifically,we improved the methods of removing the pigments by H₂O₂ and KOH,and enhanced tissue permeabilization in tilapia embryos using cold acetone instead of proteinase K,reduced the times of washing embryos after being incubated in probes or antibodies,and optimized the system of image collection and the storage of embryos post-WISH.Using the recombination activating gene 1(Rag1)of nile tilapia as the probe gene,the result of WISH in nile tilapia embryos showed that its expression pattern was highly conserved compared with zebrafish Rag1 and medaka(Oryzias latipes)Rag1.The embryos post-WISH were unbroken and the gene expression position was distinct.The results indicated that the protocol of WISH in nile tilapia was effective and entirely feasible.

Abstract:This investigation was designed to find out the best polyculture mode of giant freshwater prawn(Macrobrachium rosenbergii,GFP)pond.The culture output,feed coefficient(FC),growth rate,use efficiency of total nitrogen and total phosphorus,and integrated farming effect in land-based enclosures,with different culturing combinations of M.rosenbergii, triangle sail mussel(Hyriopsis cumingii),silver carp(Hypophthalmichthys molitrix)and bighead carp(Aristichthys nobilis)were studied.There were six treatments,i.e.,GFP monoculture enclosure(G),GFP polyculture enclosure with silver carp and bighead carp(GSB); GFP polyculutre enclosure with triangle sail mussel(GH2); and three other GFP polyculture treatments with different proportion of stock density of giant freshwater prawn,silver carp,bighead carp treatment and triangle sail mussel(GSBH1,GSBH2 and GSBH3).Four replicates of enclosure were applied for each treatment.The results indicated that the culture output of giant freshwater prawn ranged from(14.71±0.33)kg/32 m² to(12.44±0.60)kg/32 m² with the highest yield for treatment GSBH1,which was significantly higher than that for treatment G(P<0.01).Growth rate ranged from(3.80%±0.23%)to(4.66%±0.12%),with the highest growth rate for treatment GSBH1 and the lowest growth rate for treatment G.The mean use efficiency of total nitrogen ranged from(0.92±0.09)to(0.09±1.60),with the highest for treatment GSB and the lowest for treatment G.The synthetic efficiency index used for assessing integrated farming effect ranged from(0.91±0.02)to(1.25±0.05),with the lowest for treatment G and the highest for treatment GSB,and with significant difference between treatment G and treatment GH2.In summary,the polyculture treatments obviously improve economic profits and ecological benefits of culture of the giant freshwater prawn compared with monoculture treament.

Abstract:To study the change of reproductive system in morphology and tissue structure of imposex of H.tuba and the possible adverse effects on the populations of Hemifusus tuba,this experiment studied the reproductive system structure of immature and mature,normal and imposex of H.tuba collected from Zhanjiang,Beihai,Qinzhou,Fangchenggang in China and Ho Chi Minh City in Vietnam along the coastal waters of Beibu Gulf by the methods of anatomy,histology and SEM.In this paper,we described anatomical and histological structures of imposex genital system of H.tuba for the first time.The results showed that the imposexed females exhibited a penis and/or vas deferens in addition to the normal female genital organs.Moreover,the penis location,shape and tissue structure of vas deferens in the imposexed females are similar to the normal males.We found that the imposex phenomenon only occurred in mature H.tuba,and the gonadogenesis was blocked in high degree's imposexed females.All the results indicate that the imposex order of severity in H.tuba from IOI is Beihai 1>Beihai 2>Zhanjiang>Qinzhou 1>Fangchenggang offshore>Ho Chi Minh City,Qinzhou 2 and Fangchenggang White Dragon Pearl Bay.Especially,the imposex is the most serious in Beihai populations,the imposex rate is 90% on average,and it is also higher than the other populations in VDSI.What is more,the sex ratio index of H.tuba in Beibu Gulf is almost all less than 1,and presents a decreasing trend in general.Therefore,imposex induced by TBT may result in population decline of H.tuba in Beibu Gulf by disrupting the female reproductive mechanism.

Abstract:We evaluated the effects of dietary lipid levels on body index,lipid deposition,blood biochemistry indices and lipid metabolic enzyme activities of Sebastes schlegeli.Juvenile fish[average initial body weight:(7.13±0.03)g]were randomly divided into 5 groups and fed diets containing different lipid levels(3.7%,6.8%,9.6%,13.1% and 15.6%)using fish oil as the lipid source for 60 d.The results showed that the hepatosomatic index(HSI)and viscerosomatic index(VSI)of S.schlegeli increased with increasing dietary lipid levels(P<0.05),while the condition factor(CF)had no significant differences among groups(P<0.05).The crude lipid content of whole body,muscle and liver of S.schlegeli increased with increasing dietary lipid levels(P<0.05).The crude lipid contents of whole body,muscle and liver in the group fed 15.6% lipid were significantly higher than those of the groups fed 3.7% and 6.8% lipid(P<0.05).Dietary lipid had a significant effect on lipid metabolic enzymes(P<0.05).The activities of hepatic glucose-6-phosphate dehydrogenase(G6PDH)and malic dehydrogenase(MDA)decreased with increasing lipid level,but the activities of lipoprotein lipase(HPL)and hepaticlipase(HL)increased(P<0.05).The activities of G6PDH and MDA were significantly lower in the groups fed 15.6% and 13.1% lipid than those of the groups fed 3.7% and 6.8% lipid(P<0.05),but the activities of HPL and HL were significantly higher(P<0.05).The contents of blood triglyceride(TG)and cholesterol(CHO)decreased with increasing dietary lipid levels,but the contents of blood high density lipoprotein cholesterol(HDL-C),glutamic oxaloacetic transaminase(AST)and glutamic pyruvic transaminase(ALT)increased(P<0.05).The contents of blood TG and CHO in the group fed 15.6% lipid were significantly lower than those of the groups fed 3.7% and 6.8% lipid(P<0.05),but the contents of blood HDL-C,AST and ALT were highest.The contents of blood low density lipoprotein cholesterol(LDL-C)initially increased with increasing lipid levels,but then decreased(P<0.05).Results of the above show that dietary lipid level had significant effects on body index,lipid deposition,blood biochemistry indices and lipid metabolic enzyme activities of S.schlegeli,but when dietary lipid level exceeds 9.6%,the lipid deposition in liver would increase,which is bad for health and growth of S.schlegeli.

Abstract:The Chinese mitten crab,Eriocheir sinensis is an important freshwater aquaculture species in China.Molting death syndrome(MDS)is a common phenomena during the culture of E.sinensis,which maybe related to the deficiency and unbalance of lipid deposition in the body of E.sinensis.Therefore,this study was designed to investigate the dynamic changes of lipids in the hepatopancreas and muscle during the molting cycle of young E.sinensis by the biochemical analysis.Based on the changes of external morphology,the molting cycle of the crab was divided into four stages,premolt(D),molt(E),postmolt(AB),intermolt(C1 and C2).The results showed that there was significant difference on the total lipids of hepatopancreas among the different molting stages(P<0.05)and the trend of "high-low-high" was found for the total lipids in the hepatopancreas of E.sinensis.The opposite trend was found on the total lipids of muscle,and the trend was "low-high-low" with the highest total lipids in AB stage.The hepatopancreas had the high triacyglycerol(TG)levels while the muscle contained the high phospholipid(PL)percentages(% total lipids).The hepatopancreas TG decreased significantly from D to C1 stage,then increased significantly after that stage while the lowest TG level was found in the E stage of muscle.As for the fatty acid composition,the dominated fatty acids(≥4% total fatty acids)were C16:0,C18:1n9,C18:1n7,C18:2n6(LOA),C20:5n3(EPA)and C22:6n3(DHA)for both hepatopancreas and muscle.During the molting cycle,the saturated fatty acid(SFA)and polyunsaturated fatty acid(PUFA)remained relatively stable while the decreasing trends were found on monosaturated fatty acid(MUFA)and highly unsaturated fatty acids(HUFA)in hepatopancreas,and the highest DHA and EPA levels were found in D stage of hepatopancreas.For the muscle,the trend of "low- high-low" were found on SFA and MUFA while PUFA and HUFA had the opposite trends during the molting cycle of E.sinensis.In conclusion,the significant changes were found on the lipid classes and fatty acid composition for the hepatopancreas and muscle during the molting cycle,the hepatopancreas lipids may be one of the major energy source during the molting process of young E.sinensis.

Abstract:In this study,we qualitatively compared and analysed microbial community structure in stomach,pylorus,foregut,midgut,hindgut of wild and farmed silver pomfret(Pampus argenteus),isolated and identified produced protease,amylase,lipase,cellulase strains.The results showed very different structure of flora between each part of the digestive tract,and microflora populations of the entire digestive tract of the wild and farmed silver pomfret were quite different.The digestive tract flora of the wild silver pomfret mainly included Psychrobacter species,Bacillus species,and the digestive tract flora of the farmed silver pomfret mainly included Acinetobacter species,Pseudomonas species,Psychrobacter species.Psychrobacter piscatorii strain VSD503 was the only kind of bacteria,which not only existed in the digestive tract of the wild silver pomfret but also existed in the digestive tract of the breeding silver pomfret,but there are different parts.In the experiments of identification of enzyme-producing bacteria,culturable bacteria in the digestive tract of wild silver pomfret yielded protease by 44%,amylase by 56%,lipase by 11%,cellulase by 56%,of which more than three enzymes strains had 5 kinds,and rich enzyme production.Relative to the wild silver pomfret,culturable bacteria in the digestive trace of breeding silver pomfret mainly produced protease and amylase,producing protease by 70%,producing amylase by 21%,and only Bacillus thuringiensis strain VITGS producing cellulose,no bacteria could produce lipase,and only Bacillus thuringiensis strain VITGS can yield three kind of enzymes,but relatively few amount of enzyme production.Analysis shows that the structure of the digestive tract flora affected the species and the activity of digestive enzymes,so enzyme-producing bacteria in the digestive tract of wild silver pomfret can be used as feed additives for the aquaculture of silver pomfret,which can increase production of silver pomfret.