| Yellow River plays an important role in the inland River of our country. She gestates rich fish resources which occupies important position in aquatic ecosystems.For a long time, many effective investigation and research about Yellow River have been made by many scholars. But there are some differences in these researches in different reach. It exists some vacancies in some respects, especially in upstream. So the author studied the fish and the aquatic environment of reach in Ningxia to Inner Mongolia from the fish community to improve and enrich the basic information of this reach.2 field surveys which continued 4 months have been conducted during April to June and August to September in 2009. The survey objects are the fish community diversity and the age and growth of major large-scale fish in Ningxia to Inner Mongolia in the main stream of Yellow River. The main purposes are solve these problems:(1)the species composition and community diversity of fishes; (2) the growth characteristics of the large-scale fish; (3) the relation between the component and biomass of feed resources with community diversity of fishes.The content ofis the standard in the surveys. Ten sampling points were set up.1886 fish were catches. The study were in accordance with the corresponding concrete operation method. The results shows:1. After identification, there are a total of 24 species fishes in reach in Ningxia to Inner Mongolia, belonging to 4 orders,9 families,22 genera. Among them, cyprinidae is dominant species (a total of 17 species), accounting for 70.83% of total fish in this reach. In the aspect of the type of figure, the small-scale fish is main part (16 species, a total of 1275), accounting for two-thirds while the large-scale fish is a small part of total(16 species, a total of 611). Fish fauna composition in this stream is complicated. There are 5 fish fauna composition in this stream:China department of complex river plain, Late Tertiary fish fauna of early complex, Northern Plains Flora complex, Southern Plains Flora Complex, Arctic freshwater fauna complex. Among them, Late Tertiary fish fauna of early complex is mainly(a total of 17, accounting for 54% of the total).2. After computing of fish community diversity parameters, and compared with the other rivers and lakes, the result is the fish community diversity of this stream is lower (the mean of richness index 1.3904, the mean of diversity index 1.1832)and stability is not high(equitability index 0.5577). We calculated Index of Relative Importance (IRI) of every species to determine which is dominant species. There are 5 dominant species, Carassins auratus,Parasilurus asotus,Leuciscus Cuvier,Carassins auratus,Abbotina rivularis. The common types, general types and rare types are a total of 7,7,5.3. We collected plankton in every sampling point. After qualitative and quantitative analysis, we got the density and the biomass of plankton which were analyzed with the community diversity parameters by Correlation Analysis. The result shows that there is a certain correlation between richness index and diversity index with the plankton, while equitability index has no correlation with the plankton.4. After identification of measurement and statistical analysis to the age, length, body weight of the large-scale fish, the result shows that the age of Cyprinus carpiois is mainly 1 to 3 years, and the age of other fishes are mainly 1 to 2 years. The length and the body weight are mainly in small individual. The body weight is proportional to the length of the cubic, which shows that these fishes are uniform growth.Through the above analysis, the major result of this study is that there is rich resource in reach of Ningxia to Inner Mongolia, but the tendency of the fish stocks is " younger in age and smaller in body" because of some unavoidable factors. So the job of protection and management to this reach and all of the Yellow river is of great urgency.
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