Study On Fish Community Composition And Biodiversity In Lower Reaches Of Changjiang River

Base on the data of set net surveys in the lower reach of Changjiang River from March2003to March2010, this paper described the dynamic state of fish community, and analysed the variation of fish community structure with multivariate analysis firstly, then discussed the fish community succession of the research area.Main results of this study are followed:There were67species collected from all surveys from March2003to March2010, which belong to50genera,22families and12orders. There were50species which belong to34genera,11families and6orders in Anqing Section, while52species which belong to44genera,21families and12orders in Changshu Section. The species of Cypriniformes occupy a dominant position in both Anqing and Changshu section. The euryhaline fishes account for3.56%of the quantity abundance and2.31%of the biomass abundance of the total catch in Anqing Section, while16.62%for quantity abundance and14.57%for biomass abundance of total catch in Changshu section.In Anqing section, several species with average weight less than100g occupy68.00%of total species, their quantity abundance and biomass abundance account for87.81%and46.30%of the total catch, respectively; several species with average weight above500g occupy only8.00%of total species, their quantity abundance and biomass abundance account for0.44%and6.01%of the total catch, respectively.In Changshu section, several species with average weight less than100g occupy63.46%of total species, their quantity abundance and biomass abundance account for87.26%and35.95%of the total catch, respectively; several species with average weight above500g occupy only7.69%of total species, their quantity abundance and biomass abundance account for3.97%and45.31%of the total catch, respectively.Based on research sets by year, there were9dominant species in seven years in Anqing section, Carassius auratus auratus and Pelteobagrus vachellii occurred5times, they were most frequently dominant species, while Hemiculter leucisculus, Xenocypris davidi and Siniperca chuatsi only occurred1time, respectively; there were11dominant species in seven years in Changshu section, Parabramis pekinensis, Hypophthalmichthys molitrix and Carassius auratus auratus occurred every year, Coreius heterodon, Cyprinus carpio carpio and Hemiculter bleekeri only occurred1time, respectively. All biodiversity indices haven’t significant difference trend in the7years in Anqing section. In Changshu section, Shannon-wiener index, Pielou index and Simpson index also haven’t significantl difference trend, but Wilhm have a downward trend and Margalef index have an upward trend.Based on research sets by season, there were18dominant species in seven years in Anqing section, and9dominant species in spring,13in summer,10in autumn,12in winter. There were23dominant species in Changshu section and16dominat species in spring,11in summer,12in autumn,12in winter. The widest rangeability of Wilhm index, Shannon-Wiener index, Pielou index and Simpson all turn up in Summer, while widest rangeability of Margalef index appear in winter. The diversity in winter was not as good as in spring, or in summer, also in autumn.The average similarity of the fish community composition was53.05%in Anqing section from March2003to March2007, while68.81%in Changshu section. The average dissimilaritiy of the fish community constitution was77.33%between Anqing and Changshu section, The ANOSIM shows that the fish community annual compositions of Anqing section and Changshu section have highly significant difference. The fish community compositions have highly significant difference between winter and summer, also winter and spring in Anqing section, and highly significant difference between winter and summer, winter and spring, also summer and autumn in Changshu section. There’s significant difference of the fish community seasonal structure between Anqing and Changshu section. There’s regularly variation of fish community seasonal composition, and the fish community may do the cycle succession in Anqing section. The fish community compositon have unconspicuous develop direction in autumn from second year to fifth year, which may do the progressive succession in the overall view.