崇明岛内河夏季鱼类群落组成及分布特征

崇明岛为世界最大的河口冲积沙岛，岛内河网水系发达。2018年6月，选择崇明岛内主要代表性河道包括北横引河、南横引河和竖河（庙港、堡镇港、八滧港），设置16个固定站点，对内河鱼类开展了拖网调查，分析了崇明岛内河夏季鱼类群落组成及分布特征。调查期间共采集到鱼类4417尾，分属6目9科30种，主要为鲤形目鲤科鱼类；其中，淡水鱼类27种，洄游鱼类2种，近海鱼类1种。从空间分布来看，北横引河记录鱼类20种，南横引河记录鱼类17种，竖河记录鱼类18种，不同河道鱼类种类组成及优势种特征存在明显差异，其共有优势种为鲫Carassius auratus、似鳊Pseudobrama simoni和翘嘴红鲌Erythroculter ilishaeformis，部分种类只在特定的河段有记录。北横引河各站点平均物种数、丰度和生物量均高于南横引河和竖河，但3类河道间不存在显著差异（P>0.05）；主要优势种鲫、翘嘴红鲌和似鳊平均体长均以北横引河为最大，且在南横引河与北横引河中的个体体长均存在极显著差异（P<0.01）。聚类和排序分析结果表明，北横引河和南横引河鱼类组成差异较大，而竖河介于两者之间。相似性分析的结果也表明，南、北横引河鱼类群落结构差异极显著（R=0.524，P=0.008），且这两组间鱼类种类组成的平均相异性最高，为43.92%，造成两组间差异的主要物种有10种（贡献率均大于5%）。综合来看，崇明岛内河鱼类群落组成与分布特征不同于一般的内陆河流，而具有河口型岛屿的特点。未来需要在长期监测基础上，综合多种因素，对崇明岛内河鱼类组成、分布、变化趋势及内在机理开展系统研究。

Community composition and distribution characteristics of the fish assemblages in the rivers of Chongming Island in summer

Chongming Island is the largest estuarine alluvial island in the world. It has a well-developed river network. In June 2018, trawl surveys on the fish were carried out in 16 fixed sampling sites in the representative rivers of Chongming Island, including the Nanheng Canal, Beiheng Canal and also the vertical canals Miaogang, Baozhengang, and Bayaogang. The composition and distribution characteristics of the fish communities in summer were analyzed based on these surveys. A total of 4417 specimens belonging to 6 orders, 9 families and 30 species of the fishes were collected in the surveys. Among them, 27 species were freshwater fish, 2 species were migratory fish and 1 species was coastal marine fish. And 20, 17 and 18 fish species were recorded in the Beiheng Canal, Nanheng Canal, and the vertical canals respectively. The characteristics of the fish assemblages, including the dominant species, varied among the rivers. The common dominant species of all the rivers were Carassius auratus, Pseudogramma simoni and Erythroculter ilishaeformis. Some species were only recorded in some specific reaches. The average species number, abundance and biomass of the fish in the Beiheng Canal were much higher than those in the Nanheng Canal and also the vertical canals, but there was no significant difference among the rivers (P>0.05). The average body length of major dominant species, Carassius auratus, Pseudogramma simoni and Erythroculter ilishaeformis in the Beiheng Canal were also the largest, and there was a very significant difference in individual body length between the Nanheng Canal and the Beiheng Canal (P<0.01). Cluster and nMDS analysis showed the greater difference between the fish assemblages in the Beiheng Canal and the Nanheng Canal, while those in the vertical canals were between these two. The results of ANOSIM also showed that the difference of the fish community structure between the Beiheng Canal and the Nanheng Canal was extremely significant (R=0.524, P=0.008), the average dissimilarity between these two groups appeared to be the highest at 43.92%, and there were 10 main species causing such difference (contribution rate was greater than 5%).In general, we found out that the community composition and distribution characteristics of the fish assemblages in the rivers of Chongming Island were different from those of general inland rivers, while had some characteristics of the estuarine islands. In the future, comprehensive studies on the community composition, distribution characteristics, developing trends and the corresponding mechanisms of the fishes in the rivers of Chongming Island should be carried out based on the long term monitoring.