Primary Studies On Fish Resources And Feeding Ecology After Impoundment Of Three Gorges Reservoir

As the most important one of the tributaries of Yangtze River,Da Ning River was rich in fish resources,and it was a representative area of the fishery resources in the upper Yangtze river,which had73species of fish,including13endemic. In order to evaluate how the tributary hydrological environment change effects fish community composition after the impoundment of the three gorges reservoir, the author investigated Da Ning River’s fish resources and their community structure in2010-2012,then analyzed the tributary fish resources situation and species diversity,with the purpose of providing some basic data for fish resources protection, fish reproduction and fish community structure optimization of ecological restoration. From studying about food content and feeding competition of the major fish, it could probe into feeding competition and relationship between dynamics population and alternating dominant species, and also provided basic data for studying food webs in the DaNing river. The results were summarized as follows:1) There were68kinds of fishes in the Daning river,and they belonged5orders13families,71genera.Among these fish,Cypriniformes which contained51species was the most dominant order,accounting for75%of the total species in Daning river, followed by Siluriformes,which contained10species accounted for14,7%; Perciformes contained4(6.0%); Salmoniformes Contained2(3.0%); Synbgranchiformes contained only1(1.5%). Cyprinidae was the dominant family with41species in the Cypriniformes, accounting for60.3%of total fish species; followed by Cobitidae, which contained8,acounting for11.8%; Bagridae contained5species in the Siluriformes, accounting for7.4%.2)The catches were42species in Wushan,35species in Dachang,35species in Wuxi.The similarity index of Dachang and Wuxi was0.638, The similarity index of Wushang and Dachang was0.228, The similarity index of Wushang and Wuxi was0.203, Wushan and Dachang had the higher similarity index, while Wushan and Wuxi, Dachang and Wuxi had the lower similarity index.3)The main dominant species, were Ctenopharyngodon idella, Aristichthys nobilis, Hypophthalmichthys molitrix, Pseudobagrus vachellii, Tachysurus nitidus, Silurus asotus, Schizothorax prenanti, Zacco platypus.4) Biological diversity of three sample sites were all the same. but thier degree of change is significantly different.5) The daily catch of Wushan and Dachang was basicly little difference, however there is significant difference in Wuxi. The average daily catch of Wushan and Dachang reached maximum.It may be the reason of fish enhancement and release increasing the types and number of fish.6) During the investigation, the feeding rate of fishes was over50%, and totally keep high level excepting for some special fishes. Result showed that there were abundant biological resources in this river. The feeding intensity varied significantly among seasons.The feeding activity was the higher in autumn and the lower in spring.7) Weight percentage, quantity percentage, occurrence rate of stomach contains were analyzed. It turned out that Hypophthahnichthysmolitrix and Aristichthysnobilis mainly fed on phytoplankton, such as Cyanophyta and Bacillariophyta, and partly fed on zooplankton, namely Cladocera, while the carnivorous fish (Siniperca kneri, Silurus asotus and Pseudobagrus vachellii) mainly fed on fishes and shrimps. Ctenopharyngodon idellus mainly fed on Plant detritus and Algae. Schizothorax prenanti mainly fed on Algae, and partly fed on Protozoa and Aquatics insect.8) The formula proposed by Pianka (1973) was used to calculate the dietary overlap coefficient between the major fish. Beacasue they had the same feeding diet,the dietary overlap between Siniperca kneri and Silurus asotus is much higher,...