| Schizothorax kozlovi Nikolsky is one of Schizothoracinae (Cypriniformes, Cyprinidae) fish species, which is widely distributed in the upstream of the Yangtze River (upstream of Wujiang, Hengjiang and Chishui, master stream of Jinsha and Yalong). It is one of the endemic large-scale commercial fishes in the upper section of the Yangtze River. In recent decades, the population sinks rapidly because of heavy fishing and habitat destruction, attracted a lot of attentions of the community, conservation scientists and other conservative organizations in the world. In order to design effective conservation strategies, this paper have did comprehensively research its Characters, Age&Growth, Nutritional Components, Isoenzyme, Karyotype and D-Loop of mitochondrial DNA on S. kozlovi. Genetic polymorphism of this species is also analyzed in our work. The major results are as follows:1. The Characters and morphology of78S. kozlovi specimens collected from Zongji River (the upper reach of Wujiang River), Yangjie River (the upper reach of Hengjiang River), Yalong River and Jinsha River were been analyzed using conventional methods. The results indicate that the countable and measurable characters differ in four different populations to varying degrees (P<0.05). By comparing to31S. davidi colected from Qingyi River(the upper reach of Minjiang River). The results show that, intra-specific variations of S. davidi and S. kozlovi were striking divergence (P<0.01) in most parameters and thus merging of the two species is not supported. 2. By comparing with different age assessment materials (Buttocks scales, Opercular, Vertebra, Otolith), otolith is the most adequate for age assessment, because its annual rings was easy distinct and no accessory mark almost. This experiment usied computer technology and according to the principle of back-calculation. The growth performance of S. kozlov (50samples collected from upstream of Wujiang River) were been preliminary researched through mathematical statistical method.The relation equation between body length and scale radius is L=27.009676R+107.260658(r=0.959147, N=50) and the relation equation between body length and body weight is W=0.00002L29657(r=0.9719, N=50). Individuals below3years old grow quicker.3. In order to understand and compare the genetic characteristics, muscle nutritional components in5. graham (26samples) and S. kozlovi (25samples) were been measured through the gas chromatograph-mass spectrometer(GS-MS), automatic amino acid analyzer and conventional method. The content of protein, fat and ash is15.49%,1.03%and1.06%, respectively. Unsaturated fatty acid content takes up71.72%of total fatty acid. Total contents of18amino acids are75.20%(dry weight accounted for muscles) in which essential amino acids contents are31.95%, delicious amino acids contents are30.03%, each taking up42.51%and39.97%of total amino acids contents, respectively. No significant differences in muscle composition compare with S. grahami.4. Polyacrylamide gel electrophoresis is used to analyze five isozymes (lactic dehydrogenase-LDH, malic dehydrogenase-MDH, glutamic dehydrase-GDH, alcohol degydrase-ADH and esterase-EST) from nine tissues (eyeball, muscle, heart, gonad, liver, gill, kidney and brain). Isozymes loci and zymogram are also analyzed. The results indicate that five isozymes from nine tissues have apparent tissue specificity in S. kozlovi.5. Chromosome karyotype was preliminary researched on S. kozlovi through injected phytohemagglutinin (PHA) The chromosome number is2n=96and karyotype formula is2n=36m+16sm+10st+34t,NF=148. Heteromorphic sex chromosomes, satellite chromosome and secondary constriction were not been found. 7. This experiment adopted the PCR amplification and direct sequencing method. The genetic structure and phylogenetic relationship of four wild populations (population of the Wujiang River upstream, population of the Hengjiang River upstream, population of the Yalong River, population of the Jinsha River) were examined according to mitochondrial DNA (mtDNA) control region. After being aligned,834bp sequences of mtDNA control region were acquired and revealed84variable sites in92samples, accounting for10.07%of the total number of sites. Among these polymorphic sites,17were singleton variable sites and67were parismony-informative sites. On average, base composition of all samples was T=33.4%, C=19.7%, A=33.1%, and G=13.7%. The mtDNA control region was an A+T-rich region of the mitochondrial genome. A total of32haplotypes were identified based on nucleotide variability. The total nucleotide diversity (%) and haplotype diversity (h) were0.951and0.02244, respectively. Haplotype and nucleotide diversities varied across the four populations. The geographic populations showed different genetic structure due to the influence of geographical isolation. Based on the Kimura2-parameter model, the overall average genetic distance among individuals was0.023. The overall mean intra-population genetic distance of the Yalong River Population (0.030) was the largest in the four populations, and that of Yangjie River Population (0.004) was the smallest. The neighbour-joining tree and the median-joining network which were constructed based on all haplotypes showed that the haplotypes from the Yalong and Panzhihua populations were promiscuously distributed, the Yangjiehe and Zongjihe populations were distributed similar. The Yalong population had a relatively distant relationship with the Panzhihua populations. The AMOVA revealed that most molecular variance was observed to occur among populations (50.16%), whereas variance within populations (49.84%) was relatively small.7. Pairwise Fsts demonstrated significant divergence between any two populations except between the Yalong and Panzhihua populations. Significant divergence across all samples was also observed, indicating a high level of geographical population structure. Gene flow (Nm) estimates among populations showed there were very limited genetic exchanges between any two populations except for the Yalong and Panzhihua populations. It appears that the level of divergence among populations (excluding Yalong and Panzhihua) was very high, and isolation has occurred among them. For the Yalong and Panzhihua populations, they had a low genetic distance (0.027), high gene flow (28.72), and no significant Fst (P>0.05), indicating a low level of divergence between them. The mismatch distributions, Tajima’s D and Fu’s Fs statistics showed that as a whole, Schizothorax kozlovi had not passed through a bottleneck, however, the Yanjiehe population had suffered a strong genetic drift might be related to a bottleneck or founder effect. |
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