Mitogenomic phylogeny,biogeography,and cryptic divergence of the genus Silurus(Siluriformes:Siluridae)

The genus Silurus,an important group of catfish,exhibits heterogeneous distribution in Eurasian freshwater systems.This group includes economically important and endangered species,thereby attracting considerable scientific interest.Despite this interest,the lack of a comprehensive phylogenetic framework impedes our understanding of the mechanisms underlying the extensive diversity found within this genus.Herein,we analyzed 89 newly sequenced and 20 previously published mitochondrial genomes(mitogenomes)from 13 morphological species to reconstruct the phylogenetic relationships,biogeographic history,and species diversity of Silurus.Our phylogenetic reconstructions identified eight clades,supported by both maximum-likelihood and Bayesian inference.Sequence-based species delimitation analyses yielded multiple molecular operational taxonomic units(MOTUs)in several taxa,including the Silurus asotus complex(four MOTUs)and Silurus microdorsalis(two MOTUs),suggesting that species diversity is underestimated in the genus.A reconstructed time-calibrated tree of Silurus species provided an age estimate of the most recent common ancestor of approximately 37.61 million years ago(Ma),with divergences among clades within the genus occurring between 11.56 Ma and 29.44 Ma,and divergences among MOTUs within species occurring between 3.71 Ma and 11.56 Ma.Biogeographic reconstructions suggested that the ancestral area for the genus likely encompassed China and the Korean Peninsula,with multiple inferred dispersal events to Europe and Central and Western Asia between 21.78 Ma and 26.67 Ma and to Japan between 2.51 Ma and 18.42 Ma.Key factors such as the Eocene-Oligocene extinction event,onset and intensification of the monsoon system,and glacial cycles associated with sea-level fluctuations have likely played significant roles in shaping the evolutionary history of the genus Silurus.

Microsatellite analysis of genetic diversity and population structure of Chinese mitten crab (Eriocheir sinensis)

Chinese mitten crab （Eriocheir sinensis） has higher commercial value as food source than any other species of Eriocheir in China. To evaluate the germplasm resources and characterize the genetic diversity and population structure of the crabs in different water systems, two stocks and two farming populations were assessed with 25 polymorphic microsallite loci available in public GenBank. Basic statistics showed that the average observed heterozygosity （Ho） amongst populations ranged from 0.5789 to 0.6824. However, a remarkable presence of inbreeding and heterozygote deficiencies were observed. To analyze population structure, pairwise FST coefficients explained only -10.3% variability from the subdivision of mitten crab populations, the remaining variability stems from the subdivision within subpopulations. Although the four populations had slight differentiation, different allelic frequencies resulted in distinct population structures. Two stocks and one farming population were clustered together to the phylogenetic branch of Yangtze crab, with an approximate membership of 95%. Whereas, another farming population was clustered singly to the phylogenetic branch of the Liaohe crab, with a membership of 97.1%. The tests for individual admixture showed that Yangtze crab had probably been contaminated with individuals from other water systems. Genetic relationships between populations also supported the conclusion that Yangtze crab and Liaohe crab had different gene pools in spite of the origins of the same species.

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.

Comparative study of the nutritional composition and toxic elements of farmed and wild Chanodichthys mongolicus

Information of the difference in quality between farmed and wild fish is central to better ensuring fish products produced in aquaculture meet regulatory and consumer requirements.Proximate composition,amino acid and fatty acid profiles,and toxic elements contents of farmed and wild Chanodichthys mongolicus were established and compared.Significantly higher crude protein content while lower moisture content in farmed fish compared to wild fish were observed(P<0.05).The percentages of total amino acids(TAA),total essential amino acids(TEAA),total non-essential amino acids(TNEAA)and total delicious amino acids(TDAA) in farmed fish were all significantly higher than those in the wild equivalent(PO.05).Compared to the FAO/WHO recommended reference values,the ratios of TEAA/TAA(39.84%-40.33%) were comparable to 40%and TEAA/TNEAA(66.22%-67.60%) were above 60%.Fatty acid profiles in both fanned and wild C.mongolicus were dominated by monounsaturated fatty acid(MUFA),with farmed fish contained much more MUFA content compared to wild counterpart(P<0.05).Notably,wild fish exhibited significantly higher levels of total polyunsaturated fatty acid(PUFA) including eicosapentaenoic acid(EPA) and docosahexaenoic acid(DHA) than farmed fish(P<0.05).The EPA(C_(20:5n3))and linoleic acid(C_(18:2n6)) were the predominant PUFA in wild and fanned C.mongolicus,respectively.Moreover,farmed fish displayed an overall lower toxic element levels(As,Cd,Pb and Hg) in comparison with wild fish,and both were far lower than the established limit standard.In conclusion,our results suggest that the nutritional quality of farmed C.mongolicus was inferior to their wild counterpart with respect to fatty acids nutrition,and therefore further studies should focus on the improving C.mongolicus diet in order to enhance the overall nutritional composition.

Analysis on Nutrient Compositions and Nutritional Quality of Lota lota( Linnaeus) Muscle

In order to evaluate the nutritional quality of Lota lota(Linnaeus) muscle,the common nutrient components,amino acid composition and fatty acid composition in muscle of wild Lota lota(captured in Hailang reaches of Mudan River) were determined by routine methods. The results showed that the contents of moisture,crude protein,crude fat and ash were 81. 82%,15. 93%,0. 44% and 1. 06% in fresh muscle of Lota lota,respectively. Totally 17 amino acids,including seven kinds of essential amino acids(EAA),were detected in dry muscle of Lota lota(Linnaeus),accounting for 72. 43% of total dry muscle. The content of EAA was 29. 82%,accounting for 41. 17% of TAA,meeting the amino acid composition of high-quality protein standard required by Food and Agriculture Organization /Word Health Organization(FAO /WHO). There were four delicious amino acids(DAA) in dry muscle,accounting for 28. 34% of total dry weight.The percentage of DAA to TAA was 39. 13% in dry muscle. The contents of C20:5n- 3(EPA) and C22:6n- 3(DHA) in dry muscle were 8. 65% and 20. 32%respectively,which were significantly higher than that of the artificially cultured fish species,such as Oxyeleotris marmorata(EPA:2. 24%,DHA:4. 74%),Spinibarbus sinensis(EPA:0. 87%,DHA:3. 08%) and Glossogobius giuris(EPA: 3. 94%,DHA: 8. 10%). Based on the amino acids score(AAS) and chemical score(CS),the first limited amino acid in Lota lota(Linnaeus) was sulfur-containing amino acid(methionine + cysteine). The essential amino acids index(EAAI) of Lota lota(Linnaeus) was 62.58. It is concluded that Lota lota(Linnaeus) is abundant in amino acids and high-unsaturated fatty acids,and rational in composition of amino acids. Thus,Lota lota(Linnaeus) is a high quality freshwater fish with high nutritional value and health value,possessing good exploitation and utilization prospects.

Genetic mapping and QTL analysis for body weight in Jian carp (Cyprinus carpio var.Jian) compared with mirror carp (Cyprinus carpio L.)

We report the genetic linkage map of Jian carp(C yprinus carpio var. Jian). An F1 population comprising 94 Jian carp individuals was mapped using 254 microsatellite markers. The genetic map spanned 1 381.592 c M and comprised 44 linkage groups,with an average marker distance of 6.58 c M. We identified eight quantitative trait loci(QTLs) for body weight(BW) in seven linkage groups,explaining 12.6% to 17.3% of the phenotypic variance. Comparative mapping was performed between Jian carp and mirror carp( Cyprinus carpio L.),which both have 50 chromosomes. One hundred and ninety-eight Jian carp marker loci were found in common with the mirror carp map,with 186(93.94%) showing synteny. All 44 Jian carp linkage groups could be one-to-one aligned to the 44 mirror carp linkage groups,mostly sharing two or more common loci. Three QTLs for BW in Jian carp were conserved in mirror carp. QTL comparison suggested that the QTL confidence interval in mirror carp was more precise than the homologous interval in Jian carp,which was contained within the QTL interval in Jian carp. The syntenic relationship and consensus QTLs between the two varieties provide a foundation for genomic research and genetic breeding in common carp.

Genome evolution trend of common carp (Cyprinus carpio L.) as revealed by the analysis of microsatellite loci in a gynogentic family

Genome evolution arises from two main ways of duplication and reduction. Fish specific genome duplication （FSGD） may have occurred before the radiation of the teleosts. Common carp （Cyprinus carpio L.） has been considered to be a tetraploid species, because of its chromosome numbers （2n=100） and its high DNA content. Using 69 microsatellite primer pairs, the variations were studied to better understand the genome evolution （genome duplication and diploidization） of common carp from a gynogenetic family. About 48% of primer pairs were estimated to amplify duplicates based on the number of PCR amplification per individual. Segregation patterns in the family suggested a partially duplicated genome structure and disomic inheritance. This indicates that the common carp is tetraploid and polyploidy occurred by allotetraploidy. Two primer pairs （HLJ021 and HLJ332） were estimated to amplify reduction based on the number of PCR amplification per individual. One allele in HLJ002 locus and HLJ332 locus was clearly lost in the gynogenetic family and the same as in six wild populations. Segregation patterns in the family suggested a partially diplodization genome structure. A hypothesis transition （dynamic） and equilibrium （static） were proposed to explain the common carp genome evolution between genome duplication and diploidization.

Effect of Dietary Alanyl-glutamine Supplementation on Growth Performance, Development of Intestinal Tract, Antioxidant Status and Plasma Non-specific Immunity of Young Mirror Carp(Cyprinus carpio L.)

Exogenous alanyl-glutamine（Aln-Gln） was evaluated for its effects on growth performance, intestinal structure and function, antioxidant status and non-specific immunity of young carp（Cyprinus carpio L.）. Six diets supplemented with 0, 2.5, 5.0, 7.5, 10.0, or 15.0 g · kg-1 of Aln-Gln were fed to fish for 12 weeks. Supplementation with 7.5, 10.0, or 15.0 g · kg-1 of Aln-Gln significantly increased weight gain rate（WGR）, protein efficiency ratio（PER）, but feed conservation rate（FCR） and survival were not affected（P〉0.05）. The intestinal fold height and number, digestive enzyme, Na＋, K＋-ATPase activities was found to be significantly high（P〈0.05） with increasing dietary Aln-Gln supplementation up to 7.5 g · kg-1, but there were no significant differences for Aln-Gln supplementation from 7.5 to 15.0 g · kg-1. The glutathione peroxidase（GPX） activity, glutathione（GSH）, superoxide dismutase（SOD） activity increased and malondialdehyde（MDA） levels decreased significantly（P〈0.05） in the intestine, hepatopancreas, plasma and muscles. The plasma complement-3（C3） and complement-4（C4） levels were significantly（P〈0.05） improved at 5.0 g · kg-1 level and decreased when over 7.5 g · kg-1. The plasma lysozyme（LSZ） activity increased significantly（P〈0.05） at 7.5, 10.0, or 15.0 g · kg-1 level. In summary, the results showed that Aln-Gln improved growth performance, development and function of the intestine, the activity of the antioxidant defense system and the plasma non-specific immunity of the carps. The optimal Aln-Gln level was 8.24 g · kg-1 diet for WGR based on broken-line regression model analysis.

Identification and Genetic Diversity Analysis of Chinese Mitten Crab(Eriocheir sinensis) in the Liao River Area

Chinese mitten crab （Eriocheir sinensis） is an indigenous and ecologically and economically important species in the Liao River area, but its identification and genetic diversity remain poorly understood. To evaluate the germplasm resources of this species, samples were collected from these locations： four sub-populations from the Liao River area and one population from the Yangtze River area; one primer was used to distinguish between the Liao River and the Yangtze River crabs. Thirteen loci were used for crab genetic diversity analysis, and basic statistics showed that the collecting samples were purebred in the Liao River area. The average observed heterozygosity （H0） of the Liao River population was 0.5931, and the expected heterozygosity （He） was 0.8064. The polymorphism information content （PIC） was 0.7753, which showed that the Liao River population had high genetic diversity. The genetic differentiation index （FST） averaged 0.0342, meaning a low degree of differentiation; cluster analysis indicated that Hujia （HJ）, Xinli （XL） and Chenjia （CJ） sub-populations were allocated to the same cluster, while Baqiangzi （BQZ） sub-population was isolated. In summary, these data demonstrated that the crabs in the Liao River had high genetic diversity, but low genetic differentiation. Thus, the Liao River population had the potential for breeding selection. Furthermore, this study also provided valuable genetic information for the conservation of Chinese mitten crab.

Genetic diversity and differentiation of masu salmon(Oncorhynchus masou masou) between and within cultured populations inferred from microsatellite DNA analysis

Masu salmon,Oncorhynchus masou masou,is one of the most valuable fishery species that has been introduced to China,though to date no studies on the genetic diversity and genetic relationship among hatchery populations has been performed with molecular markers.We undertook such a study and sampled 120 individuals from three hatchery stocks and analyzed 20 microsatellite loci.All loci were polymorphic and a total of 91 alleles were detected.A relatively low level of genetic diversity was revealed with effective number of allele of 3.1094,3.3299 and 3.1894 and expected heterozygosity of 0.6600,0.6648 and 0.6638 in the three stocks,respectively.Deviations from Hardy-Weinberg equilibrium were found due to heterozygote deficit.Accordingly,evidence of genetic bottlenecks were found in the three stocks.An individual assignment test demonstrated that 85% of individuals were correctly assigned into their original stocks.Pairwise Fst revealed that significant differentiation occurred between these three stocks.The results of the study indicated that disequilibrium of genetic structure and differentiation has occurred in all three stocks.This information collectively provides a basis for measures to avoid of loss of genetic diversity and introgression in Chinese aquaculture.

Determining oxygen consumption rate and asphyxiation point in Chanodichthys mongolicus using an improved respirometer chamber

Knowledge of oxygen consumption rates and asphyxiation points in fish is important to determine appropriate stocking and water quality management in aquaculture.The oxygen consumption rate and asphyxiation point in Chanodichthys mongolicus were detected under laboratory conditions using an improved respirometer chamber.The results revealed that more accurate estimates can be obtained by adjusting the volume of the respirometer chamber,which may avoid system errors caused by either repeatedly adjusting fish density or selecting different equipment specifications.The oxygen consumption rate and asphyxiation point of C.mongolicus increased with increasing water temperature and decreasing fish size.Changes in the C.mongolicus oxygen consumption rate were divided into three stages at water temperatures of 11-33℃:(1) a low temperature oxygen consumption rate stage when water temperature was 11-19℃,(2) the optimum temperature oxygen consumption rate stage when water temperature was19-23℃,and(3) a high temperature oxygen consumption rate stage when water temperature was >27℃.The temperature quotients(Q_(10)) obtained suggested that C.mongolicus preferred a temperature range of19-23℃.At 19℃,C.mongolicus exhibited higher oxygen consumption rates during the day when the maximum values were observed at 10:00 and 14:00 than at night when the minimum occurred at 02:00.

Growth and energy budget of juvenile lenok Brachymystax lenok in relation to ration level

We evaluated the effect of ration level(RL) on the growth and energy budget of lenok Brachymystax lenok. Juvenile lenok(initial mean body weight 3.06±0.13 g) were fed for 21 d at five different ration levels: starvation,2%,3%,4% bwd(body weight per day,based on initial mean values),and apparent satiation. Feed consumption,apparent digestibility,and growth were directly measured. Specific growth rates in terms of wet weight,dry weight,protein,and energy increased logarithmically with an increase in ration levels. The relationship between specific growth rate in terms of wet weight(SGRw,%/d) and RL(%) was characterized by a decelerating curve: SGRw=-1.417+3.166ln(RL+1). The apparent digestibility coefficients of energy exhibited a decreasing pattern with increasing ration level,and there was a significant difference among different RLs. Body composition was significantly affected by ration size. The relationship between feed efficiency rate in terms of energy(FERe) and RL was: FERe=-14.167+23.793RL–3.367(RL)2,and the maximum FERe was observed at a 3.53% ration. The maintenance requirement for energy of juvenile lenok was 105.39 k J BW(kg)-0.80/d,the utilization efficiency of DE for growth was 0.496. The energy budget equation at satiation was: 100IE=29.03FE+5.78(ZE+UE)+39.56 HE+25.63 RE,where IE is feed energy,FE is fecal energy,ZE+UE is excretory energy,HE is heat production,and RE is recovered energy. Our results suggest that the most suitable feeding rate for juvenile lenok aquaculture for wet weight growth is 2.89% bwd,whereas for energy growth,the suggested rate is 3.53% bwd at this growth stage.

The Post-Embryonic Development of Digestive System and the Demand of Energy of Hucho taimen

With the technology of morphology, histology and nutrition, the characteristics of organ development and the source and demand of nutritional at different stages in post-embryonic （water temperature 3-14℃） of Hucho taimen were discussed. The results showed that the membrane of H. taimen fertilized ovum was ruptured in 30 d, the prototype of U-type stomach was formed, the mouth could open and close freely, and nutrition was supplied from its yolk sac. The membrane ruptured after 8 d, teeth formed, and anus communicated with outsiders. The oropharyngeal cavity, esophagus, U-type stomach, intestine, and anus initially formed in the digestive tube, which nutrition was supplied from the huge yolk sac. The membrane ruptured after 16 d, pancreas and pyloric caeca appeared, larvae could intake and digest exogenous food, fish mixed nutrition, which was from yolk sac and outsiders, mainly depended on endogenous. The membrane ruptured after 24 d, the fish began floating and intaking actively, the fish mixed nutrition which mainly depended on exogenous. The membrane ruptured after 30 d, the yolk sac was completely absorbed, the function and structure of each digestive organs developed consummately, fish was from mixed nutrition into the stage of exogenous nutrition, the nutritional need of juveniles was below 10% fat, level of the optimal protein was 50%.

Effects of Dietary Protein and Temperature on Growth and Flesh Quality of Songpu Mirror Carp

The study was conducted to demonstrate the effects of dietary protein and water temperature on growth and flesh quality of Songpu mirror carp （Cyprinus carpio） at an initial weight （165.24±5.08） g. Practical diets were formulated to contain five protein levels （29.12%, 31.46%, 34.49%, 38.17%, and 40.13%）, and each diet was randomly assigned triplicate groups of 15 fishes at three temperatures （18℃, 22℃, and 26℃） in the recirculation system. Fishes were fed twice daily to apparent satiation for 56 days. Results indicated that fishes had higher weight gain rate at 22℃ and 26℃ than that at 18℃ （P〈0.05）, but there were no significant differences between 22℃ and 26℃ （P〉0.05）. Based on the weight gain rate, dietary protein level 29.12% could meet the requirement of the body at 18℃, 22℃, or 26℃. Crude protein, crude lipid, moisture and ash of muscle had no significant differences among those treatments （P〉0.05）. pH （after 24 h） of muscle was the highest at 18℃ and the lowest at 22℃ （P〈0.05）, but no differences were observed among different protein level groups at each temperature （P〉0.05）. No significant differences on shear force, water holding capacity, collagen, glycogen and lactate among all the treatments were found （P〉0.05）. It was concluded that when C. carpio fed to apparent satiation, the growth mainly depended upon temperature. Dietary protein could not significantly affect flesh quality, but temperature significantly affected pH of muscles. A dietary protein level 29.12% could meet the requirement of the body at 18℃, 22℃, or 26℃.

Effects of the Chinese Medicinal Herb Com plex Additives on Non-specific Immunity of Amursturgeon( Acipenser schrencki Brandt)

This study was to investigate the effects of aqueous decotion from three Chinese medicinal herb additives （ Cyrtomium fortunei, prescription I and prescription II） on non-specific immunity of 1 ＋ age old Amur sturgeon （Acipenser schrencki Brandt） by oral perfusion. Cyrtomiumfortunei, prescription I and prescription II were orally given to 15 fishes for each experimental group once a day, with the concentration of 9,175 and 36 g/S0 kg body weight, respectively. The administration was lasted for 14 days. Meanwhile, distilled water was orally given as the control. After the experiment, some of the experimental fishes were stimulated with high temperature （30 ℃ ） for two hours. Sampling was performed from fishes treated at 22 ℃ and 30 ℃ for measuring the protein content in the serum, phagocytic activity of leucocytes and the activity of the lysozyme in six tissues. The results indicated that Cyrtomiumfortunei and prescription II could help to enhance the content of various proteins and the phagocytic activity of leucocytes. There was no significant change in the effects between these two additives at either the normal temperature or high temperature. Prescription I did not show an obvious effect on the immunity of fishes at the normal temperature, but it did in promo- ting high-efficiency response and improving immunoregulation of fish shocked by some stimuli.

Effects of Feeding Attractants on the Growth and Body Composition,Digestive Enzyme and Serum Indices of Hucho taimen

[ Objective] The aim was to study the effects of four feeding attractants（dimethyl-15-propiothetin, trimethylamine oxide, betaine, sodium- 5＇-inosinate） on feed intake, growth performance, body composition, digestive enzyme activities and serum indices of Hucho taimen with initial body weight 9.39 ±0.26 g. [ Method] The Hucho taimen was raised in water flow system. There was one control group and four process group. Each diet was randomly assigned to triplicates of 50 fish for 56 days. During the experiment, the water temperature fluctuated from 9.3℃ to 14.2℃ and the dissolved oxygen was above 8.0 mg/L. [ Result ] The weight gain rate and specific growth rate increased significantly by adding 0.2% dimethyl- 13-propiothetin, 0.2% trimethylamine oxide, 0.2% betaine, but there were no changes with 0.05% sodium-5＇-inosinate supplementation （ P 〉 0.05）. The body crude protein increased significantly by supplementing 0.2% dimethyl-15-propiothetin（ P 〈0.05）, and body crude lipid decreased signifi- cantly by adding 0.2% trimethylamine oxide and 0.2% betaine（ P 〈0.05）, but body composition had no changes by supplementing 0.05% sodium- 5＇-inosinate（ P 〉0.05）. The digestive enzyme activities increased significantly by adding 0.2% dimethyl-13-propiothetin and 0.2% trimethylamine oxide（ P 〈0.05）, and the lipase increased significantly by supplementing 0.2% betaine（ P 〈 0.05）, but digestive enzyme activities had no changes supplemented 0.05% sodium-5＇-inosinate（ P 〉 0.05）. The serum total protein, albumin and globulin increased significantly added 0.2% dimethyl-15- propiothetin（ P 〈0.05）, and the high density lipoprotein content increased while cholesterol, triglycedde and low density lipoprotein decreased sig- nificantly added 0.2% trimethylamine oxide and 0.2% betaine（ P 〈 0.05）, and serum complement 3 and complement 4 increased significantly sup- plemented 0.05% sodium-5＇-inosinate （ P 〈 0.05）. [ Conclusion] The food intake, growth performance, body composition and digestive ability of taimen were improved supplemented with 0.2% dimethyl-15-propiothetin, 0.2% trimethylamine oxide and 0.2% betaine, respectively（ P 〈 0.05）, but not 0.05% sodium-5＇-inosinate. The immunity of body was improved by adding 0.05% sodium-5＇-inosinate.

Evidence of return of chum salmon released from Tangwang River by strontium marking method

In order to assess the effect of enhancement release of chum salmon(Oncorhynchus keta),otolith strontium(Sr)marking method was used to tag chum salmon released in Tangwang River in 2016.The homing chum salmon were detected and the samples were collected in Tangwang River,Ussuri River and Suifen River in the autumn of2018.The samples were analyzed by examining Sr and calcium(Ca)fingerprints in the otolith using electron probe microanalysis.The results suggested that two samples collected in Tangwang River had the marking ring near the core of otolith where the Sr concentration and Sr/Ca ratio were significantly higher than comparative samples.Proving that the two fish belonged to the released population in Tangwang River in 2016.This article indicated the success of the enhancement release of chum salmon from the Tangwang River for the first time and also confirmed the validity of Sr marking in enhancement release of fishes.

Molecular Typing of Aeromonas hydrophila Isolated from Common Carp in Northeast China

A total of 59 isolates of Aeromonas hydrophila were collected from common carp suffering from freshwater fish hemorrhage disease in 13 fishing grounds in the northeast China, and their phenotypic and genetic characteristics were investigated. All of the isolates were identified as A. hydrophila by traditional biochemical method and yielded a 686-bp DNA fragment of the 16S rDNA gene in the PCR experiments. Collected strains were also evaluated for their susceptibility to 17 different antibiotics. The isolates showed an even trend of the resistance and sensitivity to drugs, highly sensitive to antibiotics, such as Levofloxacin, PolymyxinB, Ofloxacin and resistant to antibiotics, such as Bristopen, Lincomycin, Ampicillin, Teicoplanin. Evaluation of genetic diversity was performed on all isolates by molecular typing with enterobacterial repetitive intergenic consensus （ERIC-PCR） method. The results showed that three different types, i.e. type I, ]I, and type ~I, were found in 59 isolates and type III accounted for a large proportion of 54.84%. There was no dominant difference between the tendency of the isolates of Heilongjiang Province and Jilin Province in these three types, which showed DI 〉 I 〉 I, while the isolates of Liaoning Province showed III 〉 II 〉 I. The percentage of different types in different provinces varied in each other; however, they didn＇t show any obvious regional or cluster-specific branches. In conclusion, the ability to distinguish Aeromonas hydrophila strains from diseased common carp with ERIC-PCR would be useful for epidemiological investigation and population genetic analysis of this pathogen in China.

The Artificial Propagation and Fry Rearing of Lenok (Brachymystax lenok)

[ Objective] This paper aimed to summarize the results of the lenok reproduction in a hatchery, including growth of the artificially bred lenok, artificial propagation and fry rearing. [ Method ] Lenok （ Brachymystax lenok） collected at wild were fed with pelleted feed and cultured to ma- turity in a flowing -water pond. The broodstocks were hormonally induced to spawn, and fry were reared from 2003 to 2010 in order to obtain a suit- able and reliable method for the mass production of lenok juveniles. The embryos were hatched at accumulative temperature of up to 180 -213 day degree at water temperature of 8 -10 ~C. [Result]The results showed that 68% -85% of success rate was obtained with the eyed rate （fertilizing rate） of 32.8% -83%, hatching rate of 56.5% -87%, and emerging rate of 59.9% -90%. The fry developed into swim-up stage 10-12 days post - hatching. There were no significant differences in growth rate, fecundity and the eyed rate in the cultured lenok from those of the wild lenok. [ Conclusion] Mass fry production of lenok could be achieved by hormonally induction.

Genetic diversity and differentiation of masu salmon(Oncorhynchus masou masou)between and within cultured populations inferred from microsatellite DNA analysis

Masu salmon,Oncorhynchus masou masou,is one of the most valuable fishery species that has been introduced to China,though to date no studies on the genetic diversity and genetic relationship among hatchery populations has been performed with molecular markers.We undertook such a study and sampled 120 individuals from three hatchery stocks and analyzed 20 microsatellite loci.All loci were polymorphic and a total of 91 alleles were detected.A relatively low level of genetic diversity was revealed with effective number of allele of 3.1094,3.3299 and 3.1894 and expected heterozygosity of 0.6600,0.6648 and 0.6638 in the three stocks,respectively.Deviations from Hardy-Weinberg equilibrium were found due to heterozygote deficit.Accordingly,evidence of genetic bottlenecks were found in the three stocks.An individual assignment test demonstrated that 85%of individuals were correctly assigned into their original stocks.Pairwise Fst revealed that significant differentiation occurred between these three stocks.The results of the study indicated that disequilibrium of genetic structure and differentiation has occurred in all three stocks.This information collectively provides a basis for measures to avoid of loss of genetic diversity and introgression in Chinese aquaculture.