Abstract:In order to establish the method for primary isolation, culture and identification of grass carp (Ctenopharyngodon idella) intestinal macrophages, in the study, the intestinal mucosal lamina propria mononuclear cells (LPMC) were firstly prepared by curettage combined with collagenase IV digestion. Then, the intestinal macrophages were isolated from LPMC suspension using fish organ mononuclear cell isolation kit and purified by differential adherence method. The intestinal macrophages after purification were cultured primarily with RPMI 1640 complete medium supplemented with 10% FBS and 5% serum of C. idella at 28 ℃ in a 5% CO₂ incubator, and these cells were identified by morphological examination, molecular marker detection and function validation test. The results showed that the yield of intestinal macrophages was about 3×10⁷ cells per fish (about 250 g in weight), with a survival rate of 99.6% and a purity of more than 95%, respectively. The adherent cells in primary culture for 4–5 days were round or polygonal, the cell volume increased obviously, and the confluence degree of cell layer reached 95% observed under inverted microscope. After staining, the adherent cells had the morphological and structural characteristics of macrophages observed under light and electron microscopes, respectively. The expression of macrophage-specific marker molecule (macrophage colony stimulating factor receptor of C. idella) was detected by RT-PCR. It was also confirmed that the adherent cells in primary culture had phagocytosis, and LPS could significantly improve their respiratory burst activity. The above results indicated that the method for isolation, primary culture and identification of C. idella intestinal macrophages was successfully established for the first time, which might provide a cell model for research on the intestinal mucosal immune response of C. idella induced with oral vaccine.

Abstract:The crayfish Procambarus clarkii was introduced into China in the last century and has become a commercially important cultured species. Most of previous research of P. clarkii focus on physiology, ecology and reproductive biology. Little is known about its genetic basis. Chromosomes are carriers of genetic material. The study of chromosome in P. clarkii can provide indispensable basic data for genetic improvement and breeding of new varieties. In this paper, the chromosome and karyotype of the crayfish P. clarkii were studied by preparing metaphase spreads from the tissue of immature testis using the conventional method of hypotension and air-dry. Well-spreads in meiotic metaphase of spermatocyte and mitotic metaphase of spermatogonium were obtained after DAPI and Giemsa staining. Most of chromosomes in mitotic metaphase were X-shaped, which are regarded as metacentric chromosomes. The bivalents in meiotic metaphase were short rod with heterochromatin located at the end. The number of chromosomes in mitotic metaphase and bivalents in meiotic metaphase was statistically calculated based on 50 spermatocytes and 26 spermatogonia division phases, respectively. The number of bivalents which was N=94 appeared 28 times, accounting for 56% of spermatocyte. The number of chromosomes with 2N=188 appeared 20 times, accounting for 77% of the number of mitotic spermatogonia. Thus we concluded that the number of diploid and haploid chromosomes of P. clarkii was 2N=188 and N=94, respectively. Since the mitotic chromosome is too small to perform karyotype analysis, we conducted a preliminary meiotic karyotype analysis based on bivalent length and position of the centromere. The karyotype formula is N=55M+22(SM, ST)+17T, including 55 metacentric bivalents, 22 sub-metacentric or acrocentric bivalents, and 17 telocentric bivalents. No sex chromosome was identified.

Abstract:Inflammatory cytokines are often used as one of the indicators to detect host immune responses. The lack of cytokines antibodies for fish has hindered analysis of cytokines protein expression by ELISA. In this paper, the fragments of TNF-α, IL-1β, IL-6, IL-12, IL-10 and TGF-β genes of Cyprinus carpio, containing partial antigenic determinants were cloned by PCR. The target sections of cytokines were cloned into plasmid pET-32a/21a vectors which had restriction sites for BamH Ⅰ and Hind Ⅲ. The recombinant plasmids were transformed into E. coli BL21 (DE3). The fusion proteins were highly expressed in E. coli BL21 (DE3) after being induced with IPTG. The purified fusion proteins were used as antigen to immunize New Zealand Rabbits by ear margin veins injection combined with subcutaneous injection to obtain rabbit anti carp polyclonal antibodies of cytokines. Enzyme-Linked Immuno Sorbent Assay (ELISA) was used to evaluate the antibody titers, and the antibodies were used as a test tool to detect the expression of inflammatory cytokines in carp serum after infection with Aeromonas hydrophila. The results showed that the sizes of fusion proteins were about 31.8, 31.7, 35.3, 32.5, 18.0 and 33.6 ku, respectively. The titers of the antiserum were about 2.4×10⁶. The pro-inflammatory cytokines TNF-α, IL-1β, IL-6, IL-12 and anti-inflammatory cytokines IL-10 and TGF-β showed different expression patterns at different stages after A. hydrophila infection. The results indicated that the prepared antibodies performed high titer, affinity and specificity and could be applied to study the expression of cytokines in C. carpio. The availability of these polyclonal antibodies laid the foundation for the systematic study of immune response and cytokines expression in C. carpio. Meanwhile, these polyclonal antibodies could also be used to exploratively study the cytokines protein expression of TNF-α, IL-1β, IL-6, IL-12, IL-10 and TGF-β in other fishes.

Abstract:In order to analyze the role of Caspase recruitment domain (CARD) of abalone in development and under stress, the full length cDNA of a coding CARD gene was cloned by RACE according to its partial sequence in transcritpome of Haliotis diversicolor. Its expression profile of development and stress was obtained by real time quantitative PCR. The cDNA sequence was named HdCARD and was 1371 bp, with a 735 bp open reading frame encoding a protein of 244 aa (HdCARD) and containing a conserved CARD domain. Quantitative real-time PCR results indicated that HdCARD could be detected in all examined tissues, with the highest expression level in mucus gland. There was also expression of HdCARD in different developmental stages, with highest expression level during late veliger stage. There was a significant difference of HdCARD in hemocytes after a bacterial challenge/thermal/hypoxia stress. The RNAi of HdCARD could increase larval malformation rate in trochophore stage. Moreover, larval caspase-8 and DAD1 significantly rose, but larval caspase-3 significantly reduced. The results suggested that HdCARD might play a role in larval development, immunity, and under thermal stress and hypoxia stress.

Abstract:There are only a few cell lines of Siniperca chuatsi (mandarin fish) that could be widely used in scientific research. For mandarin fish, cell culture technique is an important aspect of the quality control program for the National Wild Fish Health Survey. Healthy, sensitive and mycoplasma-free cells are essential for detection of fish viruses in free-ranging fish populations. S. chuatsi is native to China and an important commercial species. In addition, the transfection efficiency is quite low in most fish cell lines. That is an obstacle in the basic research on fishes. In this study, a continuous cell (MFE) culture derived from the mandarin fish embryo was developed and has been subcultured over 20 passages in DMEM cell culture medium. MFE consists predominantly of epithelial-like cells and grows well in DMEM supplemented with 20% fetal bovine serum. Cell proliferation was assessed by MTT assay. The absorbance of the sample was read directly in the wells at an optimal wavelength of 570 nm. The results showed that MFE cell experienced proliferation, decrease and stable phases during 96 h. Meanwhile, we used GFP-expressing retrovirus produced by HEK293T cells to test the transfection efficiency in MFE cell line. The result showed that the transfection efficiency reached 20%±5% without affecting the growth of these cells. Subsequently, the expression of three genes of Irf1, Irf2 and Irf7 was examined in MFE cell line by qRT-PCR. The results indicated that Irf1 is the highest one, and all increased to 3.5, 2.3 and 2.1 folds after poly I:C stimulation. The results of this study showed that MFE is the first cell line originated from embryo of mandarin fish. It could be used as a tool for gene function research and genetic modification.

Abstract:The stressful effect of Cu²⁺ with exposure duration for 96 hours on physiology metabolism, histopathological structure and enzyme activity of ark shell Scapharca broughtonii was studied by the methods of biological toxicity test. The incubating concentrations of Cu²⁺ were set at (0.01, 0.05, 0.10, 0.50, 1.00) mg/L and a control group was set with no Cu²⁺ stress (normal seawater). Results showed that incubating concentration and exposure duration both had significant influence on physiological indices of S. broughtonii, including oxygen consumption rates (OR), ammonia excretion rates (NR) and ratios of O to N (O∶N). The OR, NR and O∶N all decreased sharply after initial exposure to the Cu²⁺ stress. The minimum values for OR, NR and O∶N were found to be (0.005±0.001) mg/(g·h), (0.5±0.05) μmol/(g·h), 0.7±0.1 with the 1.00 mg/L treatment at the end of the experiment, which equaled 1%, 29%, 3% of control groups, respectively. Generally, apparently reduced metabolic rate of S. broughtonii individuals exposed to Cu²⁺ stress was observed within 72 h. After 72 h, each group with different Cu²⁺ concentration behaves differently. After being incubated at 0.01 mg/L for 96 h, the S. broughtonii seemed to be acclimated to Cu²⁺ stress. Metabolic rates of the animals were restored to the control level, while O∶N was not different from the control groups and no detectable histopathologic damage was found. The physiological metabolism and histopathological structure of individuals under concentrations that higher than 0.05 mg/L Cu²⁺ were significantly affected after 96 h, while most of the O∶N in all the experimental groups were below 9 and histopathologic damage such as gills damage and tissues messy structure were found. The ACP and ALP activities of individuals exposed to 0.10 mg/L Cu²⁺ increased in gill and decreased in hepatopancreas, while GPX and GST increased in both tissues. Our results demonstrated that incubating concentration (≥0.05 mg/L) after 96 h exposure significantly affect physiological metabolism and histopathological structure of the ark shell. ACP, ALP, GPX and GST activities of individuals incubated at 0.10 mg/L were significantly affected. Our results provide the basic data for studying the response mechanism of S. broughtonii and other coastal shellfishes to Cu²⁺ stress, and referential data for the prevention and biological reparation of potential heavy metal pollution risk in coast area.

Abstract:In order to study the correlation between microbial composition of intestinal tract and aquaculture environment of Oreochromis niloticus and streptococcicosis, 16S rDNA high-throughput sequencing method was used to analyze the microflora structure of intestinal tract of healthy and diseased O. niloticus and that of their pond water and sediment. The results showed that the microbial diversity of sediment was higher than that of pond water and O. niloticus intestinal tract. The microbial composition of O. niloticus intestinal tract was more similar to pond water than to sediment. The microbial diversity of O. niloticus intestinal tract and sediment in the disease group was lower than that in the healthy group, while the microbial diversity of pond water in the disease group was higher compared with the healthy group. The OTU cluster analysis revealed that significant difference only existed in intestinal microorganism between the disease group and the health group. The majority of healthy intestinal samples were clustered together. The microflora structure analysis showed that the dominant bacteria of pond water and sediment in the healthy group and the disease group were similar. The abundance of proteobacteria and fusobacteria was far higher in the disease group of pond water, while the abundance of verrucomicrobia and planctomycetes was obviously lower compared with the healthy group of pond water. The abundance of flora with the function of organic degradation and ecologic restoration (such as Anaeromyxobacter, Methanosaeta and Virgibacillus) was far lower in the sediment of disease group, while the abundance of pathogenic bacteria (such as Mannheimia) was higher compared with the sediment of healthy group. The abundance of pathogenic bacteria (such as Streptococcus, Mycobacterium and Mannheimia) in intestinal tract of disease group was higher, while the abundance of probiotics (such as Lactococcus, Cetobacterium and Rhodococcus) was lower compared with intestinal tract of healthy group. Streptococcus agalactiae was detected not only in aquaculture environment and intestinal tract of the disease group but also in those of the healthy group. The abundance of S. agalactiae in intestinal tract of the disease group was significantly higher than that in the healthy group, while there was no significant difference between the disease group and the health group either for pond water or sediment. In conclusion, the variation of the abundance of pathogenic bacteria and probiotics in pond water and sediment revealed that the aquaculture environment of the diseased pond was deteriorated. The outbreak of streptococcicosis was closely related to the rapidly increased abundance of S. agalactiae in the intestinal tract of O. niloticus after its microecological balance had been destroyed. The increased abundance of S. agalactiae in the intestinal tract of infected O. niloticus had no direct link with its abundance in pond water or sediment.

Abstract:Recently, krill fishery has concentrated increasingly in the Bransfield Strait, and krill abundance and ecological characteristics have received much attention. Antarctic krill (Euphausia superba) presents significant diel vertical migration (DVM) pattern, such studies were conducted to provide the basic data for exploring the formation mechanism of fishing ground and the reference for feedback management of krill fishery. Scientific acoustic device mounted in fishing vessels can reflect directly the distribution and vertical movement of krill in the water column. Based on the acoustic data recorded by Simrad EK 80 used in krill fishing vessel, krill swarms were identified using Echoview software.The present study analyzed DVM of krill in the Bransfield Strait during the austral autumn 2016 and the factors that impact DVM of krill were further explored. The results indicate that the depth of krill swarm maintained to above 250 m, the highest frequency of average deepest (shallowest) krill swarm occurs at sunrise (at night). The largest thickness of krill swarm presents at sunrise. Krill swarms are distributed in the deeper water column in the daytime, but move to the shallower depth at night. Compared to March, the average depth of krill swarms increased in April. Brightness and bottom depth are the main factors that impacted depth change of krill swarms.

Abstract:In the experiment, the preparation technology of the high Fischer ratio oligo-peptide (HFP) from Trichiurus japonicus (HFP-T) was studied, and the parameters on two-step sequential enzymolysis and removing aromatic amino acids (AAA) using activated carbon were optimized. The F value of the HFP was confirmed by determination of amino acid components. Taking hydrolysis degree and protein conversion ratio as criterions, binary-enzymes hydrolysis process was optimized and the results were as follows: pepsin was selected as the first enzyme, and its optimal parameters were ratio of enzyme to substrate 3%, ratio of meat to water 1∶5 (g/mL), temperature 35 ℃, pH 2.0 and enzymolysis time 3 h; flavourzyme was selected as the second enzyme, and its optimal parameters were ratio of enzyme to substrate 3%, pH 7.0, temperature 50 ℃ and enzymolysis time 3h. The highest hydrolysis degree and F value (OD₂₂₀/OD₂₈₀) of hydrolysate prepared under the optimal parameters were 40.51%±3.18% and 5.75, respectively. In order to raise the F value of the sample by removal of AAA, five kinds of activated carbons including one powdered and four granular activated carbons were chosen to evaluate their removing AAA effects, and the results indicated that No.4 activated carbon (200 mesh) have the best removing AAA effects under the parameters of solid-liquid ratio 1∶20 (g/mL) and pH 6.0 for 4 h at room temperature, and the F value (OD₂₂₀/OD₂₈₀) of hydrolysate reached 30.72 from 5.75. The F value (BCAA/AAA) of hydrolysates (removing AAA) measured on Automatic Amino Acid Analyzer was calculated to be 28.06, and the content of Lysine was 22.403 μmol/L. The results of activity tests showed that HFP-T can significantly prolong time of the loss of righting reflex and shorten time to sober up, increase liver and muscle glucogen contents and lower blood urea nitrogen and blood lactate levels after mice have exercised. HFP-T also enhanced the activity of lactic dehydrogenase to scavenge excessive LA for slowing the development of fatigue. In addition, HFP-T increased the activities of superoxide dismutase, catalase and glutathione peroxidase to reduce the reactive oxygen species (ROS) damage in mice. In conclusion, HFP-T possessed good anti-fatigue capacities in mice by inhibiting the oxidative reactions and provided an important basis for developing the swim bladder peptide functional food.

Abstract:Some traditional fishery resources in the East China Sea have showed an apparent decline trend over years and therefore, those subordinate economic species, such as Harpadon nehereus, have gradually became dominant species, which also has important economic value and plays a key role in local eco-system. During the period from November 2015 to August 2016, a total of 2611 samples of H. nehereus were collected in the Wentai fishing ground. Based on the length information recorded, an ELEFAN I technique was used to estimate growth and mortality parameters of H. nehereus, and an incomplete β function dynamic pool model was adopted to determine the catchable size and evaluate the exploitation conditions for H. nehereus resources. The results show that: the length-weight relationships of H. nehereus in the Wentai fishing ground was W=0.000 5L^3.87 (R²=0.906 7), and this relationship was insignificantly different between females and males. The parameters of Von Bertalanffy Growth function for H. nehereus were L_∞=32.13 cm, K=0.39 and t₀=–0.69, with the inflexion for body weight growth estimated at 2.78 years. The total mortality coefficient calculated with linear catch curve based on body length structure was 2.55, and the natural mortality coefficient estimated by Pauly’s empirical equation was 0.66. Meanwhile, the fishing mortality coefficient was found to be 1.89 and the exploitation rate was 0.74. The dynamic pool model indicated the age of capture and the first catchable size should be increased, and the first catchable age and the corresponding capture length should be set at 1.15 years, and 16.5 cm, respectively.

Abstract:Based on the macrobenthic samples collected from 9 mid-tidal sites (3 in sandy beaches and 6 in gravel beaches) in Sanya Bay, Dongmaozhou and Ximaozhou Island in March 2014, the influences of the sediment type on ecological functions of macrobenthos were studied. The results showed that ① low mobility, burrower and filter-feeder were more in sandy beaches, however, the none and high mobility, sessile, surface crawler/swimmer, herbivore and predator-feeder were more observed in gravel beaches; ② canonical analysis of principal coordinates (CAP) showed that different sediments had different trait patterns, and mobility, habitat and feeding mode were the main factors for the differences; ③ both Shannon-Wiener index and functional diversity were generally higher in gravel beaches than those in sandy beaches; ④ the functional redundancy was all high, however, it was higher in sandy beaches than in gravel beaches.

Abstract:Data-limited stock assessment with Data-Limited Methods (DLMs) is capable of evaluating and managing data-limited fisheries and widely used in the world. Fisheries in China are at high risk of overfishing but meanwhile subject to limited data, which makes DLMs the optimal scientific advisory tools to support management. However, DLMs are rarely studied and implemented in China. In order to examine the effectiveness of DLMs in China, the present study conducts management strategy evaluation (MSE) with four data-limited management procedures (MPs) on silvery pomfret (Pampus argenteus), small yellow croaker (Larimichthys polyactis), greenling (Hexagrammos otakii), and lizardfish (Saurida elongate) from Haizhou Bay. According to the results, MPs based on DLMs are proved to be sustainable fisheries management methods by effectively enhancing the spawning stock biomass of overfished stocks while maintaining a considerable level of yield. The length-based MPs (matlenlim and minlenLopt) outperformed the effort-based MPs (CurE and CurE75) with better trade-offs between yields and overfishing. The results also suggest that, with the implementation of DLMs, the overfished status of silvery pomfret and greenling can be improved, and the lizardfish stock can be better exploited. DLMs with the small yellow croaker stock are subject to fluctuation and uncertainty. In general, DLMs have broad application prospect in China.

Abstract:In the present study, a hybrid F₁ of Megalobrama terminalis (♀)×Culter alburnus (♂) (MT♀×CA♂) was obtained by intergeneric crossing, based on M. terminalis, from Dongjiang River, and C. alburnus, from Dianshan Lake. Growth performance and morphological characteristics of MT♀×CA♂ were compared and analysed further, with M. terminalis (MT), C. alburnus (CA), M. amblycephala (♀)×C. alburnus (♂) F₁ (MA♀×CA♂) and M. amblycephala (MA) as controls. The results are as follows: (1) at 1-year-old stage, both MT♀×CA♂ and MA♀×CA♂ grew significantly faster than CA, suggesting a remarkable growth advantage of over-male-parent. At 2-year-old stage, MT♀×CA♂ was similar to MA♀×CA♂ in growth rate, which grew faster than their parents. At 3-year-old stage, the hybrid MT♀×CA♂ had not only marked growth advantage of over-dual-parent, but also its body weight exceeded MA♀×CA♂ value. (2) Most numeric traits of MT♀×CA♂ presented to be medium. Among countable traits, the numbers of soft ray of anal fin and other traits are within the range of its parents, the average hybrid index is calculated to be 65.00, which shows that the countable traits approach the middle values between MT and CA, while slightly incline to its male parent CA. Of measurable traits, seven traits are significantly different from its parents, the average hybrid index is calculated to be 51.61, which indicates the measurable traits are also close to the middle values. (3) The results of cluster analysis revealed that MT♀×CA♂ and MA♀×CA♂ were much closer, the same to the MT and MA, joined CA again after the two groups clustered. Three principal components with accumulative variance percentage 56.02% were summarized in principal component analysis, reflecting the morphological variations of frame, head and caudal peduncle. Discriminant accuracy was 87.1%-100.0% by established discriminant function of the populations. In summary, the hybrid F₁ of MT♀×CA♂ showed advantageous characteristics such as fast growth and excellent morphology, and it is expected to further cultivate improved varieties.

Abstract:To test change of genetic gain for body weight, we designed selection schemes which included 10 levels of family number (100–1 000) and 11 levels of family size (100–5 000). By using computer simulation technology, breeding values and inbreeding coefficients of the nucleus breeding and multiplication populations from different simulation schemes were compared after performing between-family (percentage retained: 50%) and within-family selections (1 male and 2 females selected per family) of 19 generations. The mean and standard deviation for body weight were set at 18.41 g and 3.24 g, respectively. Three levels of heritability (0.1, 0.35, 0.6) were included in the simulation. This study will provide basic parameters to optimize the selective breeding program based on large-scale families. Compared with the control scheme with parameters including 100 families, 100 individuals tested per family, and heritability of 0.35, breeding values of body weight for the nucleus population increased by 48% (62.75–92.87 g) with the increase of family size (100 to 5 000) due to higher selection intensity, but increasing extent presented downward trend (100–2 500: 40.60%; 2 500–5 000: 7.40%); standard deviation of breeding values decreased by 2.90% (1.38–1.34 g) when family size increased. Breeding values of body weight for the nucleus breeding population increased by 1.88% (62.75–63.93 g) and the standard deviation of breeding value increased by 4.35% when increasing family number due to low selection intensity. Breeding values of harvest weight for the multiplication population had the same increase trend with those of the nucleus population, but increasing extent was more than that in the nucleus population on family level (63.63–65.48 g, 2.91%). Inbreeding coefficients of the nucleus breeding population decreased by 90.32% (0.093–0.009) with increase of family number, but decline rate presented downward trend (100–500: 79.57%; 500–1 000: 10.75%). It did not affect inbreeding level of the nucleus population when increasing family size. In summary, it will further improve the genetic gain for body weight of nucleus breeding population and multiplication population if there is increase of family size. The inbreeding level (inbreeding rate 0.25%) is below the safety threshold (<0.5%) when the breeding population consists of more than 200 families. Therefore, the main purpose of increasing the number of family is to reserve more genetic variation and establish multiple breeding lines for different traits.

Abstract:The plankton in water under six cultural patterns of Macrobrachium rosenbergii was evaluated in an enclosure experiment. The cultural patterns included prawn monoculture group (MP), prawn with aquatic plant (Lemna minor, water-coverage 5%) group (PP), prawn with silver carp (Hypophthalmichthys molitrix) group (PF), prawn with mussel (Anodonta woodiana) and H. molitrix group (PMF), prawn with mussel and aquatic plant group (PMP), prawn with A. woodiana, L. minor and H. molitrix group (PMPF). Four replicates of each treatment were set up in this study. After 64 days of culturing, the phytoplankton and zooplankton (Rotifera, Cladocera and Copepods) in water of each cultural pattern were evaluated. The results showed that there were four common phytoplankton dominant species in all cultural patterns. However, the most dominant phytoplankton species was different. The most phytoplankton dominant species were Dinobryon in MP group, and Oscillatoria minima in culturing L. minor groups (PP and PMP), and Synedra sp. in H. molitrix polyculture groups (PF, PMF and PMPF). There were no common dominant species of zooplankton in six cultural patterns. The density of phytoplankton in the PF group was the highest, and it was higher than that of MP, PP and PMP by 78%, 53% and 61%, respectively. In contrast, the density of zooplankton was the highest in MP, and that of PF group was the lowest. The density of zooplankton in H. molitrix polyculture groups (PF, PMF and PMPF) was significantly lower than that of other three groups. The results showed that the stocking H. molitrix in M. rosenbergii pond can increase the density of phytoplankton and reduce the density of zooplankton. Both L. minor and H. molitrix could affect dominant species in pond.

Abstract:As an important freshwater aquaculture species in China, Carassius auratus culture is currently suffering from serious losses due to infectious diseases. The use of antibiotics in preventing and controlling the bacterial diseases has caused the evolution of resistant strains of aquatic pathogens. This is a serious constraint on aquaculture development. Therefore, some alternative measures need to be developed to improve the quality and sustainability of aquaculture production. Probiotics can be a substitute for antibiotics. Lactobacillus sp. from the host or the culture environment have shown to have ability to better adapt to the culture environment and colonize in the host gut, which help them exhibit their probiotic effects better. This study intends to screen probiotic candidates from C. auratus according to their in vitro probiotic properties, which include acid and bile tolerance ability, antimicrobial activity, cell surface hydrophobicity, aggregation ability, in vitro adhesive ability and pathogenicity in crucian carp. Based on biochemical tests and 16S rRNA gene sequence analysis, thirty-eight strains of Lactobacillus sp. were isolated from the gut of C. auratus, which belonged to Lactococcus, Leuconostos, Carnobacterium and Enterococcus faecium, respectively, and eight of them were selected to evaluate the in vitro probiotic properties. The results showed that all eight strains of Lactobacillus sp. bacteria could tolerate acid (pH 4.6) and bile (10% bile of C. auratus), and exhibit good antibacterial activities against four pathogens including Aeromonas hydrophila, A. caviae, Streptococcus agalactiae and Vibrio parahaemolyticus. Five of eight strains showed high cell surface properties, i.e. hydrophobicity (63%-89%) and autoaggregation (37%-45%), and their adhesive rates to C. auratus intestinal mucus were ranged from 4.5% to 7.9%. These five isolates differed in coaggregation ability, but exhibited good adhesion inhibition rates for the binding of A. hydrophila to C. auratus intestinal mucus, with the inhibition rates of 30% to 35%. Three L. lactis isolates 16-7, 16-19 and 16-24 with a higher adhesive ability showed no pathogenicity when administered by intraperitoneal injection to C. auratus. Based on our data, the three L. lactis isolates could be considered as potential probiotic candidates for C. auratus farming. Further in vivo evaluation needs to be performed in the future study.