Analysis Of Fish Community Structure And Species Diversity In The Downstream Of Ganjiang River

Ganjiang River,the largest tributary of Poyang Lake,plays a crucial role in protecting and restoring the fish diversity and biological integrity of Poyang Lake and even the Yangtze River.Before the 1990 s,the study of Ganjiang fishery resources mainly centred on species composition.Over the past 20 years,the regional studies of fish in Ganjiang River have mainly concentrated in its middle and upper reaches,but few studies have been carried out on the fish diversity in its lower reaches,so that the connection between the fish diversity and the environment in its lower reaches has not been reported.By systematically investigating the fish in the lower reaches of Ganjiang River from March 2017 to February 2018,this paper analyzed the species compositio n and ecological types of fish,temporal and spatial dynamics of fish diversity,and the link between fish diversity and environmental factors in its lower reaches.The main conclusions are as below:(1)A total of 12,479 fishes were caught in the lower reaches of Ganjiang River in four seasons,and 84 species were identified and classified which belong to 54 genera,15 families and 7 orders,with 58 species as 2 families of Cyprinidae,12 species as 6 families of Perciformes,10 species as 3 families of Siluriforms,and Clupeifor mes,Beloniformes,Synbgranchiformes and Salmonifo as 1 family.(2)Based on the classification of ecological types,the fish of sedentary type is the most,constituting 48.81% of the total species.According to the classification of ecological niche,the proportion of epipelagic fish and demersal fish is relatively large,accounting for 36.90% and 35.71% of the total species respectively.According to feeding habits,omnivorous fish is the largest number of species,accounting for 58.33% of the total species.According to reproductive types,the fish with drifting egg is the largest number of species,making up 33.33% of the total species.(3)The dominant species in the lower reaches of Ganjiang River are C.carpio,P.simoni and X.macrolepis.There are differences in the spatial composition of dominant species with 6 species in Nanchang,5 species in Zhangshu,Gao'an,Yichun,Fengcheng and Qiaoshe,4 species in Chucha,3 species in Shanggao and Xinyu and 2 species in Nanxin as the minimum ones.There are also seasonal differences in dominant species.There are at most 6 dominant species in summer,and only 2 species in spring,autumn and winter.(4)The Margalef richness index(D)is 8.80,Shannon-wiener diversity index(H)is 1.30 and Pielou evenness index(J)is 0.30 in the lower reaches of Ganjiang River with Margalef richness index(D),Shannon-wiener diversity index,Pielou evenness index and species number as the maximum ones among sampling points spatially.Seasonally,Margalef richness index(D),Shannon-wiener diversity index(H)and Pielou evenness index(J)are at their highest in summer.Fish species richness is also highest in summer.(5)The ABC curve shows that the fish community in the lower reaches of Ganjiang River is in a moderate disturbance.Spatially,there are differences in the degree of disturbance among sampling points with Yichun,Nanxin and Chucha in serious disturbance,Fengcheng,Qiaoshe,Gao'an and Nanchang in moderate disturbance,and Shanggao,Xinyu and Zhangshu free from disturbance.Temporally,seasonal changes of fish community is taking a turn for the better.(6)The seasonal similarity of fish community structure in the lower reaches of Ganjiang River is quite different with better similarity in spring and winter.The best sampling point of similarity is Gao'an.Yichun,Zhangshu,Fengcheng and Nanchang bear a 67% overall similarity to other sampling points while Xinyu,Qiaoshe,Nanxin and Chucha bear only a 44% overall similarity to other sampling points.The fish communities in the river mouth are slightly similar to those in the upper reaches.There is no statistical significance of similarity among the three tributaries in the river mouth.(7)The results of NMDS suggests that there are notable spatial variations in the composition of fish communities in the lower reaches of Ganjiang River,and fishes mainly gather in Nanchang,Qiaoshe,Nanxin and Chucha,but the seasonal compositio n of fish communities differs little.(8)It is altitude the primary environmental factor that affects the fish community structure in Ganjiang River Basin.Individual weight has significantly negative correlation with transparency and altitude,and Pielou(J)evenness index has obviously positive correlation with altitude.