Studies on fish resources and species diversity in the middle reaches of the Yangtze River from Yichang to Chenglingji section

From 2010 to 2011,we collected the fish resources in the middle reaches of the Yangtze River in Yichang,Jingzhou and Chenglingji section.Totally,58 species which belonged to 7 orders and 14 families were collected.In these samples,36 kinds of fish belonged to Cyprinidae family,which occupied 62.07% of the total number of the species.Hypophthalmichthys molitrix,Cyprinus carpio,Ctenopharyngodon idellus and Silurus meridionalis as the dominant species in the middle reaches of the Yangtze River occupied the top 4 of the total catches in order.But as the economic fish,the the proportion of the number of H.molitrix,Mylopharyngodon piceus,Aristichthys nobilis,C.idellus was lower than Hemiculter leucisclus which is a kind of wild fish.From Yichang to Jingzhou and then to Chenglingji section,both Shannon-Weaver diversity index and Margalef richness index declined in turn,while the Simpson index of each section in the middle reaches of the Yangtze River were different.Fish biological statistics indicated that the mean body length and mean body weight of some fish in Chenglingji section decreased,Ctenopharyngodon idellus decreased 60% and 95% and H.molitrix decreased 50% and 80%,respectively.Fishery catches analysis results showed that the fish resources of the middle Yangtze River presented a trend of younger age and miniaturization.The most obvious change appeared in Coreius heterodon,the situation of its recession is very serious.