Experimental Analysis on Allometric Growth in Spualiobarbus curriculus Larvae and Juveniles in Zhaoqing Reach of the Pearl River

Ecological experiment was conducted in this paper to study the allometric growth in Squaliobarbus curriculus larvae and juveniles from Zhaoqing Reach of the Pearl River. The results showed that after first feeding, the organs associated to swimming, feeling and feeding of larvae differentiated rapidly, and exhibited allometric growth. The head length, tail length and head height exhibited positive allometric growth, while trunk length exhibited negative allometric growth before reaching the growth inflexion point 20 d after first feeding, and positive allometric growth after the inflection point. Body height exhibited positive allometric growth both before and after the growth inflexion point at 18 d after first feeding. The inflexion points of snout length, eye diameter and post-eye head length occurred 23, 19 and 16 d after first feeding. For swimming organs, the dorsal fin, pelvic fins and anal fin exhibited positive allometric growth both before and after the inflexion point at 18, 19 and 17 d after first feeding; but the tail fin exhibited positive allometric growth before the inflexion point at 14 d after first feeding, and negative allometric growth after the inflexion point. S. curriculus larvae can possess various abilities soon after first feeding to survive at early stage due to the rapid development of swimming, feeling, feeding and other organs, which has important ecological significance to adapt to the complex external environment.

Whole-genome resequencing reveals recent signatures of selection in five populations of largemouth bass(Micropterus salmoides)

Largemouth bass(Micropterus salmoides) is an economically important fish species in North America, Europe, and China. Various genetic improvement programs and domestication processes have modified its genome sequence through selective pressure, leaving nucleotide signals that can be detected at the genomic level. In this study,we sequenced 149 largemouth bass fish, including protospecies(imported from the US) and improved breeds(four domestic breeding populations from China). We detected genomic regions harboring certain genes associated with improved traits, which may be useful molecular markers for practical domestication, breeding, and selection. Subsequent analyses of genetic diversity and population structure revealed that the improved breeds have undergone more rigorous genetic changes. Through selective signal analysis, we identified hundreds of putative selective sweep regions in each largemouth bass line. Interestingly, we predicted 103 putative candidate genes potentially subjected to selection,including several associated with growth(psst1 and grb10), early development(klf9, sp4, and sp8), and immune traits(pkn2, sept2, bcl6, and ripk2). These candidate genes represent potential genomic landmarks that could be used to improve important traits of biological and commercial interest. In summary, this study provides a genome-wide map of genetic variations and selection footprints in largemouth bass, which may benefit genetic studies and accelerate genetic improvement of this economically important fish.

Development of microsatellite markers and their utilization in genetic diversity analysis of cultivated and wild populations of the mud carp (Cirrhina molitorella)

Microsatellite markers have been increasingly used in genetic studies on fishery species because of their high applicability in selective breeding programs. Here we reported the development of microsatellite markers and their utilization in mud carp （Cirrhina molitorella）. An （CA）15 enriched library has been constructed for mud carp, using the magnetic beads enrichment procedure. Sequence analysis of 60 randomly picked positive colonies indicate that 56 （93.3%） of the colonies contain microsatellites. Microsatellite polymorphism was assessed using 10 mud carp individuals, and 12 microsatellite loci turned out to be polymorphic. We utilized these loci to study the genetic diversity of a wild population （WM） and a cultured population （CM） of the mud carp. A total of 109 alleles were detected with an average of 9.08 alleles per locus. The mean value of the observed heterozygosity of WM and CM was 0.6361 and 0.6417, respectively, and significant decrease of genetic diversity in CM was not observed. The genetic distance between the two populations was 0.1546 and the value of Gsr was 0.0473. This showed that there existed a slight genetic differentiation between WM and CM.

Molecular cloning and expression of a heat-shock cognate 70 (hsc70) gene from swordtail fish (Xiphophorus helleri)

Heat shock proteins are a family of molecular chaperones that are involved in many aspects of protein homeostasis. In the present study, a full-length cDNA, encoding the constitutively expressed 70-kDa heat shock cognate protein (Hsc70), was isolated from swordtail fish (Xiphophorus helleri) and designated as XheHsc70. The Xhehsc70 cDNA was 2104 bp long with an open reading frame of 1941 bp, and it encoded a protein of 646 amino acids with a theoretical molecular weight of 70.77 kDa and an isoelectric point of 5.04. The deduced amino acid sequence shared 94.1%-98.6% identities with the Hsc70s from a number of other fish species. Tissue distribution results show that the Xhehsc70 mRNA was expressed in brain, heart, head kidney, kidney, spleen, liver, muscle, gill, and peripheral blood. After immunization with formalin-killed Vibrio alginolyticus cells there was a significant increase in the Xhehsc70 mRNA transcriptional level in the head kidney of the vaccinated fish compared with in the control at 6, 12, 24, and 48 h as shown by quantitative real time RT-PCR. Based on an analysis of the amino acid sequence of XheHsc70, its phylogeny, and Xhehsc70 mRNA expression, XheHsc70 was identified as a member of the cytoplasmic Hsc70 (constitutive) subfamily of the Hsp70 family of heat shock proteins, suggesting that it may play a role in the immune response. The Xhehsc70 cDNA sequence reported in this study was submitted to GenBank under the accession number JF739182.

Phenotypic and genetic variation between two populations of the Chinese yellow pond turtle, Mauremys mutica (Cantor, 1842)

Mauremys mutica(Cantor,1842)is an endangered species in China.Main phenotypic variations inbody color,body weight,body shape,clutch size,egg size,and hatchling size were revealed betweenthe southern and northern populations.Both populations have the phenomenon of'larger male'sexualsize dimorphism(SSD),especially in the southern population.Furthermore,genetic variations betweenthe two populations were analyzed by RAPD band patterns of 30 random individuals in each population.The average genetic distance was 0.299±0.108 among the samples of two populations.The average ge-netic distance between southern and northern populations was 0.305±0.046.Cluster analysis indicatedthat all the individuals from the southern and northern populations were clustered among themselves toform two distinct clades.A total of 20 population-specific RAPD fragments were scored from 16 primers,and could be used as RAPD markers for distinguishing the southern and the northern population.Basedon the nucleotide sequences of two RAPD markers,two pairs of SCAR primers(SC1-S and SC2-S)weredesigned,which could be used as SCAR markers for the southern population.According to the significantphenotypic and genetic variations,we suggested that the northern population and southern populationmight be considered as two separate taxa,the'northern taxon'and the'southern taxon',and the con-servation should be respectively conducted on the two taxa.

Cloning,tissue distribution and effects of fasting on pituitary adenylate cyclase-activating polypeptide in largemouth bass

Pituitary adenylate cyclase activating polypeptide(PACAP) has a wide range of biological functions. We cloned the full-length c DNAs encoding PACAP and PACAP-related peptide(PRP) from the brain of largemouth bass(Micropterus salmoides) and used real-time quantitative PCR to detect PRP- PACAP m RNA expression. The PRP- PACAP cDNA has two variants expressed via alternative splicing: a long form,which encodes both PRP and PACAP,and a short form,which encodes only PACAP. Sequence analysis results are consistent with a higher conservation of PACAP than PRP peptide sequences. The expression of P ACAP-long and PACAP- short transcripts was highest in the forebrain,followed by the medulla,midbrain,pituitary,stomach,cerebellum,intestine,and kidney; however,these transcripts were either absent or were weakly expressed in the muscle,spleen,gill,heart,fatty tissue,and liver. The level of PACAP-short transcript expression was significantly higher than expression of the long transcript in the forebrain,cerebella,pituitary and intestine,but lower than that of the long transcript in the stomach. P ACAP-long and PACAP-short transcripts were first detected at the blastula stage of embryogenesis,and the level of expression increased markedly between the muscular contraction stage and 3 d post hatch(dph). The expression of PACAP- long and PACAP- short transcripts decreased significantly in the brain following 4 d fasting compared with the control diet group. The down-regulation effect was enhanced as fasting continued. Conversely,expression levels increased significantly after 3d of re-feeding. Our results suggest that PRP- PACAP acts as an important factor in appetite regulation in largemouth bass.

Denitrification potential evaluation of a newly indigenous aerobic denitrifier isolated from largemouth bass Micropterus salmoides culture pond

This work evaluates the application potential of a new indigenous aerobic denitrifi er, strain Pseudomonas CW-2, isolated from a largemouth bass culture pond. The rate of ammonium-N removal by strain CW-2 was approximately 97% at a DO concentration of 5.2 mg/L. Furthermore, when nitrate and ammonia coexisted, the strain gave priority to assimilating ammonia, and thereafter to denitrifi cation. Under optimal cultivation conditions, citrate and acetate were the carbon resources, C/N was 8, dissolved oxygen was 5.2 mg/L, and pH was 7; the removal rate of ammonium reached nearly 90%. The changing patterns of different bacteria in strain CW-2-treated and the control pond water were also compared. Lower levels of ammonia, nitrite, and phosphates were observed in the treated water as compared with the controls. Meanwhile, phylum-level distributions of the bacterial OTUs revealed that P roteobacteria, Bacteroidetes, Planctomycetes, and N itrospirae continuously changed their relative abundances in relation to carbon and the addition of strain CW-2; this finding implies that the conventional denitrifi cation process was weakened under the ef fects of carbon or the presence of strain CW-2. We propose that strain CW-2 is a promising organism for the removal of ammonium in intensive fish culture systems, according to our evaluations of its denitrifi cation performance.

SNP Detection of High Density Lipoprotein Binding Protein Gene (HBP) and Its Correlations with Growth Traits in Largemouth Bass(Micropterus salmoides)

High density lipoprotein binding protein （HBP） plays an important role in lipid metabolism of animals. Lipids are indispensable energy materials for fi- shes, especially for carnivorous fishes with low utilization efficiency of carbohydrates. The single nucleotide polymorphism （SNP） of HBP gene may affect the fat metabolism, thereby exerting an effect on the growth traits of largemouth bass （Micropterus salmoides）. Investigating the correlations between SNP and growth traits can provide candidate markers for molecular marker-assisted selection. In this study, partial genomic fraganents of HBP gene （ GenBank accession number： KF652241 ） were amplified based on the sequences of an available contig in the EST-SNP database of largemouth bass. Three SNP mutation loci were identified in the 3＇ non-ceding region of HBP gene by direct sequencing, including H1 （G ＋ 2782T）, 142 （T ＋ 2817C） and H3 （G ＋ 2857A）. Three SNP loci of 165 randomly selected largemouth bass individuals were detected and genotyped by SnaPshot assay. Genetic structure was analyzed by POPGENE32 software. By using spssl7.0 software, a general linear model （GLM） was established for correlation analysis between different genotypes at SNP loci of HBP gene and various growth traits. The results showed that three SNP loci were in Hardy-Weinberg equilibrium state. To be specific, loci H1 and H2 formed two haplotypes （ A and B）, and three geno- types （AA, AB, and BB） were observed; loci H1, H2 and H3 formed six diplotypes （DI, I）2, D3, D4, D5 and D6）. According to the correlations between dif- ferent genotypes and various growth traits, the body weight and total length of largemouth bass individuals with genotype BB were significantly higher than those of individuals with genotype AB （ P 〈 0.05 ） ; the body weight and total length of largemouth bass individuals with diplotype D6 were significantly higher than those of individuals with diplotype D4 （P 〈0.05）. In this study, SNP markers correlated with growth traits were obtained in the 3＇ non-coding region ofHBP gene in large-mouth bass, which could be used as candidate genetic markers for subsequent molecular marker-assisted selection breeding of largemouth bass.

Molecular Characterization and Expression Analysis of Matrix Metalloproteinase 3 in the Asian Yellow Pond Turtle Mauremys mutica

Matrix metallopeptidase 3 is a zinc-containing proteinase that participates in tissue remodeling and immune responses. In this study, a cDNA encoding matrix metallopeptidase 3 was isolated and characterized from the Asian yellow pond turtle Mauremys mutica（designated as MaMMP3）. The MaMMP3 cDNA is 1805 bp and consists of a 5＇-untranslated region（UTR） of 56 bp, a 3＇-UTR of 243 bp, and an open reading frame（ORF） of 1506 bp encoding 481 amino acids. Homology analysis of MaMMP3 revealed that the MaMMP3 shared 25%–63% similarity to other known MMP3 sequences. The genomic sequence covers 6007 bp. Comparative analysis of the cDNA sequence revealed that the Asian yellow pond turtle MMP3 has eight exons and seven introns. The phylogenetic tree showed that the MaMMP3 is closely related to Gallus gallus MMP3 and Taeniopygia guttata MMP3. The mRNA expression of the MaMMP3 in normal group without any bacterial challenge could be detected in all studied tissues including kidney, heart, live and spleen, with the highest level in the spleen. The results of immune challenge showed that the expression level of MaMMP3 was up-regulated in the spleen and liver. These results provided an important information for studying the roles of Asian yellow pond turtle MMP3 in immunity further.

Effect of Bioactive Peptides(BPs) on the Development of Pacific White Shrimp(Litopenaeus vannamei Boone, 1931)

The present study was conducted to evaluate the feasibility of replacing fish meal(FM) with bioactive peptides(BPs) in diet of white shrimp(Litopenaeus vannamei). The changes in growth performance, body composition, non-specific immunity, and water quality were examined after the shrimp were fed four diets, in which 0%(control), 33.3%, 66.7% and 100% of FM was replaced by BPs, respectively. The groups were designated as Con, 1/3BPs, 2/3BPs, and 3/3BPs. A total of 720 shrimp with an initial body weight of 1.46 ± 0.78 g were fed the experimental diets for 56 days. The results revealed that: 1) the weight gain rate(WGR) in 1/3BPs, 2/3BPs, and 3/3BPs was significantly higher than that in Con(P < 0.05), while no significant difference was found on survival rate and feed conversion ratio(FCR); 2) the whole-body crude protein(CP) and crude lipids(CL) were significantly different among groups, while there was no significant difference between crude ash and phosphorus contents; 3) the levels of acid phosphatase(ACP), lysozyme(LZM), superoxide dismutase(SOD), phenol oxidase(PO) and bactericidal activity increased significantly with the inclusion of BPs; 4) in terms of water quality, no significant difference was found in p H and dissolved oxygen among diets during the whole experimental period. Moreover, even though nitrite and ammonium levels tended to increase with time, there was no significant difference among groups. The results indicated that BPs is an applicable alternative of protein source, which can substitute FM in the diets of L. vannamei; it is able to effectively promote growth performance and improve immunity. Moreover, BPs in the diets had no negative impact on water quality.

An outbreak of granulomatous inflammation associated with Francisella noatunensis subsp, orientalis in farmed tilapia (Oreochromis niloticus × O. aureus) in China

In 2013,a novel disease was detected in tilapia( Oreochromis niloticus × O.aureus) in Guangzhou,South China.To identify the causative pathogen,we conducted histological examination,bacteria isolation,and purification,and sequenced the 16 S rRNA gene of isolates.Infected fish had a large number of white granulomas in the kidney,liver,heart,and spleen.The head kidney and spleen were markedly swollen.A bacterium strain designated as gz201301 was recovered from the spleen of infected tilapia.The 16 S rRNA sequence of gz201301 revealed that it was highly similar to F.noatunensis subsp.orientalis.This is the first report of a Francisella-like infection in farmed tilapia in China.

Comparative Analysis of Microsatellite DNA Polymorphism in Gold Grass Carp and Four Grass Carp Populations from China

[ Objectives ] To analyze the genetic structure and genetic diversity of gold grass carp population. [ Methods ] A total of 15 microsatellite markers were used to examine gold grass carp population and four grass carp populations[ Yuanjiang （YJ）, Ningxiang （NX） , Honghu （HH） and Xijiang （XJ） ] from the Yangtze River and the Pearl River of China. [ Results] All the 15 microsatellite loei were highly polymorphic, with polymorphism information content （PIC） of 0.763 -0.939. The expected heterozygosity （HE ） of gold grass carp population was 0. 662, lower than those of the four Chinese grass carp populations （HE = 0.85 - 0. 885 ）. The genetic differentiation index （ FST ） between gold grass carp population and YJ, NX, HH, XJ populations were 0. 157 2, 0. 129 5, 0. 147 5 and 0. 114 4, respectively. This suggests that gold grass carp population is highly differentiated from YJ grass carp population （0.15 〈 FST 〈0.25）, while moderately differentiated from other three grass carp populations （0.05 〈 FST 〈 0.15 ）. Gold grass carp population had the closest genetic relationship with XJ population （DA = 0.476 3）, and it showed the farthest genetic relationship with YJ grass carp population （DA = 0. 810 7）. The NJ phylogenetic tree based on genetic distance indicated that four Chinese grass carp populations clustered together as one branch, while gold grass carp population as another. [ Conclusions] Genetic di- versity of gold grass carp population is lower than that of Chinese grass carp population, with relative distant genetic relationship.

Acute Toxicity and Bactericidal Property of Tetrakis Hydroxymethyl Phosphonium Sulfate in Japanese Eel

[ Objective] To understand the toxicity and sterilization effects of the tetrakis hydroxmethyl phosphonium sulfate （THPS） as a novel quatemary phosphonium biocide. [ Method] Under hydrostatic conditions, the acute toxicity and bactericidal property of THPS on the Fiexibacter coiumnaris （ F. columnaris） were observed in Japanese eel. The semi-lethal concentration （LCso）, safe concentration （Sc）, minimum inhibitory concentration （MIC）, minimum bactericidal concentration （MBC） and the sterilization rate of THPS were calculated, respectively. [ Result ] The LCso of THPS at 24, 48 and 96 h were 11.9, 9.9 and 9.1 mg/L, respectively. The Sc of THPS at 24 h was 2.1 mg/L; the MIC and MBC of THPS to the F. columnaris were 0.36 and 0.72 mg/L; and the sterilization rate was 100% at a concentration of 0.7 mg/L at 12 h. The sterilization rate of THPS had no great change with pH values varying from 5.5 to 9.5. [ Condusion] The THPS is a novel, safe and effective biocide for prevention and treatment of bacterial diseases of Japanese eel.

Growth and Morphological Differences between the Sexes and Female Fecundity of Ocadia sinensis

In this study, artificially hatched Ocadia sinensis individuals were cultured for 60 months, to record the growth and development process and investigate the morphological characteristics between the sexes and individual fecundity of O. sinensis. Results showed that the main morphological differences between male and female individuals are concentrated in secondary sexual characteristics ： female turtle individuals have flat or slightly prominent sternites, short tails, short length from anal pore to sternite trailing edge; male turtle individuals have concave sternites, relatively stout tails, large length from anal pore to sternite trailing edge. There were significant differences in the growth of male and female individuals, in the first 12 months, female individuals grew faster than male individuals, with greater carapace length, carapace width and weight, but the differences between male and female individuals were not significant; in the late stage, the growth rate of female individuals was much higher than that of male individuals; by the end of the experiment, the average weight of female individuals was 3.86 times of that of male individuals. Regression analysis of female fecundity showed that the clutch size of O. sinensis had significant regression relationship with carapace length and weight, the fertility of female individuals was improved with the increasing size （ carapace length and weight）.

Preliminary Screening and Characterization of Microsatellite Markers in RAD-seq Data of Datnioides pulcher

[Objective]The paper was to develop the microsatellite markers of Datnioides pulcher,and to screen polymorphic SSR primers.[Method]D.pulcher was performed reduced-representation genome sequencing using RAD-seq(Restriction-site associated DNA sequencing).[Result]A total of 13308806 high-quality clean reads(HQ clean reads)lengths were obtained and 26359 simple sequence repeats(SSR)loci were detected in the obtained sequence by SSR search software,which consisted of 496 repeat motifs.The most common types of repeat were A/T in single base repeat sequence,and AC/GT and A G/GT repeat units in di-base repeat sequence.AGG/CCT,AGC/CTG and AGG/CCT were the dominant types in tri-base repeat sequence.In quantity,the di-base repeat type SSR loci were the largest(19492),accounting for 73.95%of the total SSR loci.Except for mono-nucleotide type,the repetition frequency of SSR loci was mainly ranged from 4 to 9,and the number of polymorphic SSR loci was 2783.About 20066 pairs of SSR primers were successfully designed with Primer 5.0.The success rate of primer design was 76.13%.According to the repetition type and repetition number in the sequencing data,100 di-to penta-base repetition type SSRs were randomly selected and validated by PCR and polyacrylamide gel in six D.pulcher samples.A total of 73 pairs of primers were amplified by electrophoresis,and 20 of them were polymorphic.[Conclusion]The developed SSR sequences can be used for genetic analysis,genetic map construction and molecular marker assisted breeding of D.pulcher and its related species.

Species identification of Chinese sturgeon using acoustic descriptors and ascertaining their spatial distribution in the spawning ground of Gezhouba Dam

This study has developed an improved subjective approach of classification in conjunction with Stepwise DFA analysis to discriminate Chinese sturgeon signals from other targets. The results showed that all together 25 Chinese sturgeon echo-signals were detected in the spawning ground of Gezhouba Dam during the last 3 years, and the identification accuracy reached 90.9%. In Stepwise DFA, 24 out of 67 variables were applied in discrimination and identification. PCA combined with DFA was then used to ensure the significance of the 24 variables and detailed the identification pattern. The results indicated that we can discriminate Chinese sturgeon from other fish species and noise using certain descriptors such as the behaviour variables, echo characteristics and acoustic cross-section characteristics. However, identification of Chinese sturgeon from sediments is more difficult and needs a total of 24 variables. This is due to the limited knowledge about the acoustic-scattering properties of the substrate regions. Based on identified Chinese sturgeon individuals, 18 individuals were distributed in the region between the site of Gezhouba Dam and Miaozui reach, with a surface area of about 3.4 km2. Seven individuals were distributed in the region between Miaozui and Yanshouba reach, with a surface area of about 13 km2.

Androgen signaling regulates the transcription of anti-Müllerian hormone via synergy with SRY-related protein SOX9A

Anti-Müllerian hormone(amh) is one of the earliest functional genes expressed during testicular differentiation. It has been suggested that androgen signaling regulates critical genes for the differentiation and development of the testis. To elucidate the exact regulatory mechanisms involved in amh transcription mediated by androgen signaling, androgen signaling was manipulated in zebrafish by cytochrome P45017a1(cyp17a1) knockout and Flutamide treatment. In cyp17a1-deficient and Flutamide-treated testes,up-regulated sry-box9a(sox9a) and down-regulated amh were observed. Moreover, a physical association of the zebrafish androgen receptor(AR) and SOX9 A was found. The interaction between AR and SOX9 A was mediated via the DNA binding domain(DBD) of AR and the transactivation domain(TA) of SOX9 A,and was further enhanced by 5-alpha dihydrotestosterone(DHT), one of the most potent androgens.Intriguingly, together with SOX9 A, androgen signaling synergistically promoted amh transcription,mainly through the proximal 1 kb of the amh promoter region. Taken together, our data demonstrate a critical mechanism underlying the direct synergy of androgen signaling and SOX9 A in the regulation of amh transcription.

Sex determination mechanisms and sex control approaches in aquaculture animals

Aquaculture is one of the most efficient modes of animal protein production and plays an important role in global food security.Aquaculture animals exhibit extraordinarily diverse sexual phenotypes and underlying mechanisms,providing an ideal system to perform sex determination research,one of the important areas in life science.Moreover,sex is also one of the most valuable traits because sexual dimorphism in growth,size,and other economic characteristics commonly exist in aquaculture animals.Here,we synthesize current knowledge of sex determination mechanisms,sex chromosome evolution,reproduction strategies,and sexual dimorphism,and also review several approaches for sex control in aquaculture animals,including artificial gynogenesis,application of sex-specific or sex chromosome-linked markers,artificial sex reversal,as well as gene editing.We anticipate that better understanding of sex determination mechanisms and innovation of sex control approaches will facilitate sustainable development of aquaculture.

Effects of dietary probiotic supplementation on the growth,gut health and disease resistance of juvenile Nile tilapia(Oreochromis niloticus)

This study investigated the effects of the Streptococcus agalactiae antagonizing probiotics Bacillus cereu NY5 and Bacillus subtilis as feed additives for Nile tilapia in terms of growth performance,intestinz health and re sistance to S.agalactiae.A total of 720 apparently healthy juvenile Nile tilapia(0.20±0.05 g were randomly divided into 4 equal groups with 3 replicates for each group.Fish were fed a basal die(control check group,CK group)supplemented with B.subtilis(1 x 108 CFU/g feed,BS group),B.cereu NY5(1 x 10~8 CFU/g feed,BC group),and B.subtilis+B.cereus NY5(0.5 x 10~8 CFU/g feed of each probioti BS+BC group)for 6 wk,and the probiotic supplementation groups were then fed the basal diet for 1 w to investigate the gut microbial community.The results of this study showed that BS+BC and B treatments significantly increased weight gain(WG),feed conversion ratio(FCR)and S.agalactia resistance in Nile tilapia(P<0.05).Gut microvilli length and density and c-type lysozyme(lyzc)gen expression were significantly increased by probiotic supplementation(P<0.05).The results of high throughput sequencing showed that the B.cereus NY5 and B.subtilis+B.cereus NY5-supplementei feed resulted in a significant improvement in tilapia autochthonous gut bacterial communities ani had a stimulation effect on a variety of potential probiotics after 6 wk of feeding.After cessation c probiotic administration for 1 wk,the gut bacteria of the fish in the BS+BC and BC groups had mino changes and maintained a stable state.Consequently,it was inferred that,as a feed supplement,B.cereu NY5 and the mixture of B.subtilis and B.cereus NY5 at 1 x 10~8 CFU/g feed were able to promote growtl and disease resistance,which may be associated with the supplement’s effects on gut immune statu intestinal morphology,and intestinal microbial community composition.