Abstract:A comprehensive survey on the community structure of protozoa was conducted in Mingzhu Lake of Chongming Island in each month of 2008.The protozoa was collected and identified using freshwater plankton survey methodology,and the type of protozoa distribution,community structure,species composition,dominant species and species diversity were analyzed.The results showed that there were 60 species of protozoas in Mingzhu Lake,belonging to 3 classes,26 genera.The dominant species were Peridinium bipes,Euglena caudate,E.geniculata,Strombidium viride,Gymnodinium aeruginosum,Tintinnidium evtzii,Euplotes sp.The average annual density of protozoa was(42 075±21 594)ind/L and the average annual biomass was(1.531±1.384)mg/L.The Shannon-Wiener diversity,evenness index and richness index of the protozoa community in the Lake were relatively low.The relationship between species diversity index and the quality of water was closely correlated.In the functional nutrition taxa of protozoa,the proportion of algivores and bactivores-detritivores were higher than the photosnthetic qutotrophs and raptors.The significant factor affecting protozoa distribution was temperature,Chl.a content,TN and TP which suggested that the Mingzhu Lake was moderately polluted.

Abstract:The complete cDNA sequence of folliclestimulating hormone receptor(FSHR)gene was cloned by degenerate primer PCR amplification and RACE cDNA amplification for the first time.The length of the cDNA is 3105 bp,and it encodes a protein of about 704 amino acids,which contains the conserved seven transmembrane helix domains(TM-helix),and it belongs to glycoprotein hormone receptor(GHR)family.Phosphorylation site predictions identified 19 Ser,4 Thr and 5 Tyr potential phosphorylation sites in tongue sole,and only one protein kinase C phosphorylation site(⁴⁴¹T)was predicted.The Clustal X alignment also revealed the presence of specific signature sequences(e.g.⁸²CCAF,⁴⁸¹ERW,⁵⁹⁴FTD and ⁶⁶⁷NPFLY),which are highly conserved in GpHRs.And comparison with the halibut FSH-R also allowed the identification of 10 imperfect LRRs in the FSHR of Cynoglossus semilaevis.Tissue expression analysis showed that FSHR mRNA is expressed widely in C. semilaevis. Except the high levels in gonads,strong amplification signals were also detected in extragonadal tissues including the spleen,kidney and head kidney.Plasma 17β-Estradiol(E₂)seasonal changes are detected by radio immunoassay(RIA).The result shows that the lowest level appears in April and the highest peak of a year is in October.And we analyzed the relative expression level of FSHR in reproductive cycle of female.There is the highest level in October and the lowest level in January.

Abstract:Along with the oil spill accidents’ frequent occurrence,the natural fishery resources inevitably suffered large damage while marine environment was polluted.Concerns have been raised over how to correctly and reasonably assess the loss of natural resource from an oil spill.The index system of damage assessment of the natural fishery resources from oil spill has been approached combined with a real accident called “HYUNDAI INDEPENDENCE” which occurred in the coastal fishing ground of Zhoushan in April of 2006.The polluted index subsystem and assessing subsystem on natural fishery resource formed the whole assessing system,the former includes spilling oil property,spatial and dynamic distribution of spilling oil,the environmental character of influence scope and protection measures while the latter comprises lethal ratio,loss of different fishery resources,density and composition of fishery resources pre- and post-impact and the recovery costs of natural fishery resources.The procedure of damage assessment of oil spill accident for the natural fishery resources and methods for optimal parameter selection under different situations have been given.Case study showed that the influence area was beyond 100 km² and oil concentration in water was over 5 mg/L.The global losses of eggs and larvae of fish,juvenile of fish,crab and shrimp,and benthos were 6 700×10⁴,117 000×10⁴,3 681×10⁴,17 045×10⁴,406×10⁴ and 8 162×10⁴ ind respectively.The directly costs for recovering the natural fishery resources reached to ￥1 822×10⁴.Study result showed the established index system had strong operability with special reference for natural fishery resource claims.

Abstract:Turbot,a flatfish of deep water species,is a highnutrition and economic valued species and currently cultured widely in China.In recent years,however,serious germ plasm degeneration has come into being due to the lack of the long-term and effective broodstock management programmes,production of farmed turbot became highly unstable and total output declined gradually.Therefore,the genetic improvement of turbot will be necessary to sustain the industry development.Within a breeding program in aquaculture,growth rate which determines the total harvest yield is a highly desirable economic trait.However,the growth rate at different development is variational because genes are expressed selectively at different growth stages following a certain sequence of time and place.It is necessary,obviously,to determine a good selection time during selective breeding for obtaining maximal genetic gain.In present study,according to Box-Jenkins theory and ARIMA(p,d,q)model,the time series of growth rate of body weight of five selected families of turbot selective breeding F₁ were identified,simulated and predicted.SPSS 15.0 software was used to construct the ARIMA model.Raw data for model establishment and validation were from 3 to 27 months.The results showed that family E♂1×E♀2,F♂4×N♀3,F♂2×E♀4,E♂2×F♀1 and F♂1×F♀4 adapt to ARIMA(2,0,0),ARIMA(1,0,0),ARIMA(2,0,0),ARIMA(1,0,0)and ARIMA(1,0,0)model,respectively(Constants were not included in all five models).The residual errors of five models were all the white noise series(P>0.05).Relative precisions of the forecasting for growth rate of body weight of five families during months 27-27.5,27.5-28 were comparatively high,which indicated those ARIMA models are able to well-describe the temporal and spatial changes in growth rate of body weight of turbot.The development changes of growth rate of body weight would be analysed through past observed values and forecast values,which can provide theoretic basis for determining optimal selection time during selective breeding of turbot.

Abstract:An experiment was conducted to investigate the effects of dietary zinc on growth performance,body composition,tissue zinc accumulation and antioxidation of juvenile starry flounder(Platichthys stellatus)with zinc sulfate(ZnSO₄·7H₂O)as zinc source,by using a purified diet based on caseingelatin as the protein sources.The basal diet was supplemented with 0,50,100,150,200 and 400 mg zinc per kg diet respectively and juvenile starry flounder［initial weight(62.89±0.51)g］were fed 6 purified diets containing graded levels of zinc(19.95,71.06,118.50,174.00,226.10 and 411.20 mg/kg)respectively for 66day experimental period.The results showed that weight gain rate(WGR)increased significantly with increasing dietary zinc level(P<0.05),but no significant differences were observed among the juveniles fed the diets with equal to or higher than 174.00 mg/kg of dietary zinc(P>0.05),special growth rate(SGR)and WGR followed the same trend.The fish got the highest WGR,SGR and the lowest feed conversion rate(FCR)in the treatment with 174.00 mg/kg of dietary zinc.No significant differences were observed in whole body composition among dietary treatments(P>0.05),the fat deposition in muscle of zinc supplementation of 0 mg/kg group was significantly higher than those in the other groups(P<0.05).When the juveniles were fed the diet with 411.20 mg/kg of dietary zinc,the zinc accumulation contents in the whole body,vertebrae and muscle were significantly higher than those in the other groups(P<0.05).When the juveniles were fed 118.50-411.20 mg/kg of dietary zinc,the zinc accumulation contents in whole body,vertebrae and serum were significantly higher than 19.95 mg/kg group and 71.06 mg/kg group(P<0.05),however,the liver zinc contents remained comparatively stable among all groups(P>0.05).Serum total antioxidant capacity and superoxide dismutase(SOD)activity increased significantly with increasing dietary zinc level(P<0.05),and then leveled off when the juveniles were fed the diets with equal to or higher than 174.00 mg/kg of dietary zinc.In conclusion,it could improve growth performance and tissue zinc accumulation,and enhance antioxidation function by adding proper dose of zinc in basic diet of juvenile starry flounder.Brokenline regression analysis showed that the optimum dietary zinc requirement for juvenile starry flounder,using WGR as response criteria,was 167.88 mg/kg of dietary zinc.

Abstract:The partial cDNA of peroxisome proliferator activated receptorgamma coactivator1 alpha(PGC-1α)was cloned(GenBank accession number HM015283),and the homologous alignment was analyzed.The expression in different organs of PGC-1α was detected in grass carp with the methods of qRT-PCR.The influence of dietary highly unsaturated fatty acids(HUFAs)on the temporal expression of PGC-1α in hepatopancreas of grass carp was also studied.The results showed that the obtained cDNA sequence was 612 bp in length,and its homology with human,cow,mice,zebra fish and other species is 75%-97%; and it is revealed that PGC-1α is widely expressed in hepatopancreas,kidney,muscle,heart,gill,and so on,with the highest expression level observed in kidney and heart,lowest in spermary and spleen.After six days feeding with HUFAs contained diet,the expression level of PGC-1α was significantly increased,then descended quickly in the following days.Our results indicate that PGC-1α is mainly express in high energy generating tissues and its expression level described as could be regulated by HUFAs.The expression pattern of PGC-1α induced by dietary HUFAs could be rising at first then going down back to the normal level.

Abstract:A 62-day growth trial was undertaken to estimate effects of crystalline amino acid(CAA)supplementation of diets with different protein levels on growth performance and feed utilization in juvenile tilapia(Oreochromis niloticus).8 plantbased diets were prepared,and they were formulated to contain 4 graded protein levels(crude protein:34%,32%,30% and 28%)with(expressed as 34AA,32AA,30AA and 28AA,respectively)or without(expressed as 34CP,32CP,30CP and 28CP,respectively)CAA supplementation,respectively.In the supplementary group,lysine,methionine and threonine were added to ensure the amino acid requirement of Nile tilapia.With CAA supplementation,higher weight gain improvement was observed at 30% and 28% protein level,which is 48.4%,and 55.6%.Feed efficiency,protein efficiency,protein retention ratio and energy retention ratio were significantly lower in 28CP and 30CP groups,while increased by adding CAA,which were similar to that in another two protein levels.Regardless of diet protein level,CAA supplementation had no effects on the apparent digestibility coefficients(ADC)of dry matter,crude protein and gross energy of the diets,except for reducing the ADC of phosphorous.VSI,HSI and IPR decreased to some extent with CAA supplementation,yet body composition was not affected.The results indicated that supplementing CAA to the plantbased diets with different protein levels can improve the growth performance and feed utilization of juvenile tilapia,and it had no adverse effects when diet protein level reduced from 34% to 28%.

Abstract:DNA methylation is related to a number of epigenetic phenomena and plays an important role in gene expression.In this study,the technique of methylationsensitive amplified polymorphism(MSAP)was used for the first time to analyze the DNA cytosine methylation of Chlamys farreri,Patinopecten yessoensis,F₁ and F₂,and we made a concrete analysis between the methylation ratio and phenotypic traits,assessed the extent and pattern of cytosine methylation between the parents and the offspring,and emphasized the discussion on the molecular basis of heterosis in terms of the DNA methylation.The results showed that,(1) DNA-methylation was negatively related to the shell length,shell height,soft body weight and adductor muscle weight,but positively related to the shell wideness and gross weight,and there was great correlativity between the DNA methylation and the adductor muscle weight(P<0.01);(2) there was a significant difference between the parents and the offspring:the methylation ratio of 5′-CCGG sites was 32.79% in P.yessoensis,24.13% in C.farreri,19.98% in F₁,and 20.18% in F₂ respectively,the methylation ratio of F₁ was less than the parents and there was no significant difference between F₁ and F₂,the alteration of the DNA methylation was the result of the cross of the parents; four classes of MSAP patterns,A,B,C and D,among hybrids and their parents were detected:pattern A,methylation levels were not changed in both parents and F₁; pattern B,demethylation,both or one of the parent was methylated,but there was no methylation in the same site in F_l; pattern C,hypermethylation,the methylation level in F₁ was higher than those in both parents; pattern D,hypomethylation,methylation ratio in F₁ was lower than those in both parents.The patterns of the F₁ DNA methylation experienced change and adjustments in order to coordinate the expression of the gene from the parents,and the DNA methylation has something to do with the expression of heterosis.

Abstract:The objective of this study was to determine the impact of dietary lipid sources on growth,body composition and apparent digestibility of Carassius auratus gibelio［initial weight:(6.04±0.05) g］.5 experimental diets were formulated to contain 4% lipid originated from fish oil,soybean oil,lard,peanut oil and mixed oil(fish oil∶soybean oil∶lard,3∶4∶3),respectively.The feeding trial lasted for 60 days.Weight gain and protein efficiency ratio(PER)of fish fed mixed oil was significantly(P<0.05) higher than that of fish fed fish oil and lard,but not different from that of other groups.No significant difference was found among all treatments in specific growth rate(SGR)and feed conversion ratio(FCR).Mesenteric length/length of fish fed soybean oil was significantly(P<0.05) higher than that of fish fed fish oil and lard.Hepatosomatic index(HSI)of fish fed lard was significantly(P<0.05) higher than that of fish fed fish oil.However,visceralsomatic index(VSI)of fish fed lard was significantly(P<0.05)higher than that of fish fed mixed oil.However,no significant difference was observed among all treatments in muscle moisture,protein,lipid,ash and phosphorus content.Liver lipid content of fish fed lard was significantly(P<0.05)higher than that of fish fed fish oil and peanut oil,and liver protein content of fish fed fish oil and soybean oil were significantly(P<0.05)higher than that of fish fed lard and peanut oil.Apparent protein and lipid digestibility of fish fed lard were significantly(P<0.05) lower than that of other groups.The results of this study there was no significant difference on growth performance and body composition of C. auratus gibelio when soybean oil,peanut oil and fish oil were used solely.It also suggested that fish oil,soybean oil and lard could be mixed together as a better oil source for C. auratus gibelio,which not only reduced feed costs but also enhanced fish growth.

Abstract:Abstract: Based on the conserved amino acid sequences (TMFWALF and HHDIGTH) of ω3 fatty acid desaturase from Chlamydomonas reinhardtii and Chlorella vulgaris (GenBank accession Nos. ABL09485 and BAB78717, respectively), a degenerated pair of primers was designed. A gene was cloned from Myrmecia incisa Reisigl H4301 with these primers using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). Its homology with C. reinhardtii ω3 fatty acid desaturase reached 69% in amino acid sequence. The full-length cDNA sequence (GenBank accession No. EU658930) was composed of 2330 bp. It comprised a 107-bp 5′-untranslated region (UTR), a 912-bp 3′-UTR with a typical poly A tail, and a 1311-bp open reading frame (ORF) encoding a 436-amino-acid protein with a putative molecular weight of 49.06 kDa and pI at 7.85. The deduced amino acid sequence was characterized by a membrane-bound desaturase with two hydrophobic regions and three conserved histidine-rich motifs. Compared to the DNA sequence of this gene, its coding region was found to be interrupted by 6 introns with splicing sites well matching the GT-AG rule. Quantitative real-time PCR result showed that during the stress course of nitrogen starvation, the relative transcription of ω3 fatty acid desaturase gene increased (P<0.05) at 4 h possibly due to shock, subsequently declined and did significantly from 12 h on (P<0.05). The transcript level of this gene dropped to minimum at 20 h, where it accounted for 11.6% of that at 0 h, thereafter fluctuated at a low level only 23.2% of that at 0 h (P<0.01). Composition of fatty acid analysis illustrated that arachidonic acid percentage of total fatty acids in M. incisa increased gradually during this stress course. On the contrary, the percentages of ω3 pathway products, such as α-linolenic acid and 16:3ω3, descended significantly (P<0.05) from 40 h or 96 h on. These results suggested that the lower relative transcription of ω3 fatty acid desaturase gene was responsible for the decreased percentages of ω3 pathway products, ensuring the biosynthesis and accumulation of arachidonic acid along the ω6 pathway in M. incisa grown under the condition of nitrogen starvation. In addition, 16:2ω6, linoleic acid and arachidonic acid were possibly the substrate of this enzyme encoded by this cloned gene in this microalga.

Abstract:The study aims to evaluate the effects of dietary emodin,high-dose vitamin C(Vc)and their combination on growth,non-specific immunity and resistance to pathogens of Wuchang bream, Megalobrama amblycephala.1200 healthy fish with initial body weight(133.44±2.11)g were selected and randomly divided into four groups:one control and three tested.The control group was fed with basal diet(Vc content 50.3 mg/kg,with L-ascorbyl-2-ployphosphate as source).The three tested groups were fed with basal diets supplemented with 60 mg/kg emodin,700 mg/kg Vc,and 60 mg/kg emodin+Vc 700 mg/kg,respectively.Fish were fed twice daily(8:30 and 16:30)at a feeding rate of 2%-4% body weight.After 60 days feeding,the growth performance,muscle composition,biochemical parameters of serum and liver,the mRNA levels of two heat shock protein 70s(HSP70s),and survival rates after being infected with Aeromonas hydrophila were investigated.The results showed that compared with the control,the weight gain and specific growth rates,the levels of total protein(TP),lysozyme(LSZ)and the alkaline phosphatase(AKP)in serum,the activity of superoxide dismutase(SOD)and basal expression level of inducible HSP70 mRNA in liver were significantly improved(P<0.05),while feed coefficient,mortality,the contents of serum cortisol(COR)and triglycerides(TG),and liver malondialdehyde(MDA)were reduced(P<0.05)in emodin and Vc groups.Although the serum TP,LSZ levels,and the mRNA level of liver HSP70 increased significantly(P<0.05),and the liver MDA content also significantly decreased(P<0.05)in combination group,the synergism didn’t appear,and other indices were not significantly different(P>0.05)from the control.In addition,the liver catalase(CAT)activity was also significantly improved in emodin group compared with the control(P<0.05),while the CAT activities in Vc and combination groups were not significantly different from the control(P>0.05).Other indices,such as serum glucose(GLU),glutamicpyruvic transaminase(GPT),glutamicoxaloacetic transaminase(GOT),cholesterol(CHOL),the mRNA level of liver constitutive HSC70,the fish body indices,and muscle composition were not significantly different between groups(P>0.05).The challenge experiment with A.hydrophila showed that compared with the control the survival rates in emodin and Vc groups significantly increased(P<0.05)whereas the survival rate in combination group had no significant difference(P>0.05).These results indicate that the basal diets supplemented with emodin 60 mg/kg or Vc 700 mg/kg could promote the growth of fish,improve the nonspecific immunity,antioxidation capacity,and the basal expression level of HSP70 mRNA,and enhance disease resistance.However,the combination of emodin and highdose Vc showed no better effect,and the mechanism of their interaction remains to be further studied.

Abstract:Porphyra haitanensis is an important economic marine crop in south China.The development of the P.haitanensis cultivation is highly desirable to select or breed new lines of P.haitanensis with strong economic traits and use them for cultivation.Molecular markers and molecular genetic maps are pre-requisites for molecular breeding in any plant species.A comprehensive genetic linkage map for cultivated P.haitanensis has not yet been constructed.In this study,157 double haploid(DH)lines［derived from a YSⅢ(wildtype)×RTPM(redtype artificial pigmentation mutant)cross］were used as a mapping population in P.haitanensis.A total of 100 pairs of sequencerelated amplified polymorphism(SRAP)primers and 39 pairs of simple sequence repeat(SSR)primers were used to detect polymorphisms between the two parents and 5 DH lines.Twentyfour SRAP and 16 SSR polymorphic primer pairs were selected to analyze the DH population.A linkage genetic map comprising 104 SRAP markers and 20 SSR markers in five linkage groups,witha total length of 879.2 cM and an average of 7.09 cM between markers was constructed.The linkage groups comprised 18-31 markers ranging in length from 134.2 to 213.6 cM.The estimated genome length of P.haitanensis was 955.3 cM,with a coverage of 92.0% coverage.This is the first report of a comprehensive genetic map in P.haitanensis.The map presented here will provide a basis for the development of high-density genetic linkage maps,which will facilitate QTL mapping of desirable traits,and provide markers for MAS,map-based cloning of genes,and the introgression of beneficial genes from wild species into modern cultivars in P.haitanensis.

Abstract:From January to April of the year 2006,in cultured Apostichopus japonicus broke out skin ulcer syndrome in several areas nearby Qingdao,whose typical clinical signs were mouth swelling,eviscerating bowels,skin ulcer,body disjointing and then the infected sea cucumber died.Bacterium 060330B was isolated from focus tissue of Apostichopus japonicus,whose predominance degree reached 90% and was verified to be the pathogen causing skin ulcer syndrome based on artificial infection test.Morphological observation,semiautomatic identification through API system as well as traditional physiological and biochemical methods were applied in the bacterial classification.The results showed that 060330B had same character as Pseudomonas genus bacteria,its characteristics were similar with Pseudomonas putida,having short rods with several polar flagella,forming green colony on TCBS agar.Further results from 16S rRNA sequence analysis turned out that the sequence of 060330B was highly identical to Pseudomonas putida,with 99.5% identity.Thus bacterium 060330B was identified as Pseudomonas putida,and regarded as one of the pathogens causing skin ulcer syndrome of cultured Apostichopus japonicus.In addition,epidemiology investigation and detection of several samples from different areas revealed that the ponds whose culturing history reached two years or more and having thick black bottom mud with fishy smell were likely to result in the outbreak of skin ulcer syndrome in cultured Apostichopus japonicus at that time.

Abstract:From the regenerated blades of single somatic cells isolated enzymatically from a blade collected from the cultivation ground of Porphyra haitanensis Chang et Zheng,the fastest growing blade was selected for isolating somatic cells,and was cultured for getting regeneration blades again.From its regenerated blades,the fastest growing blade was isolated.After 3 times of selections continuously in this way,we got an improved strain named XS-1,characterized by faster growing,later maturation and higher contents of phycobiliprotein as compared with the wild type(wt)strain.After 80 days in culture,the mean length of F₁ gametophytic blades of XS-1 grew up to 128.8 cm,which was 10.5 times faster than those of the wt.The maturation peak of F₁ blades of the XS-1 delayed about 20 days later than the wt.In the wavelength of 350-750 nm, in vivo absorption spectra of the F₁ blade of the XS-1 was similar to the wt, showing five absorption peaks but having higher absorption value in every peak than the wt.The contents of phycobiliprotein(PE+PC)and Chl. a in XS-1 were 80.4 mg/g and 8.9 mg/g,increasing by 188.8% and 32.5% compared with the wt, respectively.Mean thickness of the F₁ gametophytic blades of XS-1 was 32.2 μm,decreasing 15% compared with the wt.In short,the XS-1 is a fast growing strain that may offer broad applications for the nori industry.

Abstract:Branched and sac-like Ulva linza is first reported in this paper.Branched U.linza collected from Jiangsu, Shandong and other places,was researched.The results showed that there are two kinds of branches,one is real and the other is false.Life history of branched U.linza was also studied.Its life history is typically an isomorphic alternation of generations,in which the unisexual haploid gametophytes and diploid sporophytes alternate mutually.The thalli of U.linza collected from green tide outbreak in 2008 were branched and had sac-like structure which contributed to floating and growing on the sea.Free floating green tide algae became the substrate which the spores were attached to.A great quantity of spores attached to the sac-like thalli to grow.This could be one of the causes that the free floating seaweeds bloomed in Huanghai Sea area.

Abstract:This study investigated morphological structure and growth characteristics of juvenile Asian arowana,Scleropages formosus listed in CITES as a highly endangered fish species,which is an ancient member of the Osteoglossidae family inhabiting Southeast Asia.The result showed(1) body compressed and elongated,with pelvic scutes,snout pointed sharply,mouth superior and slit slanted,chin barbells 1 pairs,cycloid scales very large on body,scale formula 23-25;dorsal fin 18-19,pelvic fin 1+4,anal fin 25-26,pectoral fin1+6,caudal fin 15.End of the tongue roundness,dissociation,with cartilage;5 gill archs,15-17 gill rakers; stomach with “U”shape winding is big and thick wall,2 pyloric caecum;left liver bigger than right liver;1 swim bladder,almost as long as abdominal cavity;1 gonad,mature females have about 30-60 mature eggs,egg diameter up to 12-15 mm.(2) The general correlation equation of body length(AL)and body weight(W)was W=0.023 5L^{2.876 3}(R²=0.986 7)under artificial farming conditions,which indicated the growth trend of body length and body weight was almost synchrony.(3) Body length of juvenile Asian arowana grew relatively slowly before five-month-old but subsequently accelerated growth.The relation with body length and monthold presented linear,namely AL=-0.007 7m³+0.161 5m²+1.363 3m+6.688 3(R²=0.998 7).Then the linear correlation equations between body weight that rapidly put on weight at juvenile stage and month-old was W=-0.133 6m³+5.554 5m²-6.915m+9.911 6(R²=0.997 2).The value for daily weight gain varied with different periods of growth,and the growth maximum of daily weight gain was 3.06 g/d at twelve-month-old.(4) And fatness of juvenile Asian arowana usually varied with the month age.

Abstract:Since fish population is a basic unit of study and management of fishery resources,analysis of fish population is a foundation for biological and ecological study on fish reproduction,distribution and migration.Using molecular biology method,the paper analyzed population of Saurida tumbil,an important commercial species from northern continental shelf waters of South China Sea. A total of 78 samples of Saurida tumbil were collected from Beihai,Zhanjiang,Maoming,Dongguan,and Shanwei of northern South China Sea.We found there are 48 haplotypes and 39 variation sites in 568 bp gene fragments of 78 sequences obtained by sequencing the mitochondrial D-loop of the samples.Analysis of molecular variance(AMOVA)indicates that the genetic variability within groups is 98.82% and that among groups is only 1.18%.The genetic differential index(Fst)and the genetic distance between every two groups are 0.000 24-0.030 08 and 0-0.025,respectively.Molecular tree constructed by NJ method and the network constructed by TCS1.21 show that the individuals of different groups are not clustered as one independent group and intermixed together,which indicates that there clearly exists a great gene flow among groups,and the genetic diversities among groups are at quite lower levels.According to the criteria distinguishing different populations,species and genera given by scholars Theorpe and Shaklle,the five groups should be merged to the same population.However,Saurida tumbil population built its geological groups by means of continuously rapid growth in small ones after undergoing fast expansion,differentiation and bottleneck phase,which not only accords with the traditional viewpoint of basic characteristics of fishery resources of South China Sea to a certain extent—“The populations of most species belong to local population without a longdistance migration”,but also is regarded as an evidence of molecular biology.

Abstract:To study ecological characteristics of the fish density,this paper compared the spatialtemporal distribution of fish density between the Minjiang Estuary and Xinghua Bay,involved in some impact factors such as dominant species,background of topography and geomorphy,as well as hydrological features,based on the data from four oceanographic censuses in the two kinds of waters during April(spring)and September(summer)2008.Results showed that weight density(165.31 kg/km²)and individual density(15.89×10³ ind/km²)at the Minjiang Estuary,were higher than those(638.4 kg/km² and 19.73×103 ind/km²)at the Xinghua Bay during spring,contrarily in summer,weight density(1 728.83 kg/km²)and individual density(158.81×10³ind/km²)at the Minjiang Estuary,were far higher than those(1 378.20 kg/km² and 58.15×10³ ind/km²)at the Xinghua Bay,which are related to fish resources of the two waters.In the Xinghua Bay,the most dominant species were endemic species with low dominance and contribution to total density except Polynemus sextarius.But in the Minjiang Estuary,the most dominant species were economic migratory species among which Coilia mystus contribute the largest percentage both in weight and in individual densities.The weight density in the Minjiang Estuary was lower than that in the Xinghua Bay in spring because migratory fishes did not arrive at the Minjiang Estuary waters to spawn,but the case was opposite with the migratory fishes arriving at Minjiang Estuary in summer.High density located in southern waters of the Minjiang Estuary where a lot of migratory fishes such as Mugil ophuyseni,Coilia mystus,Harpodon nehereus,Chelidonichthys spinosus and Mugil soiuy while aggregation of migratory fishes(such as Polynemus sextarius and Trachurus japonicus)together with endemic fishes(such as Dasyatis zugei and Johnius belengerii)formed the higher density in head waters than other waters in the Xinghua Bay.