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Length–weight (LWR) and length–length (LLR) relationships were estimated for 20 species of fish from the upper Yangtze River, southwest China. Samples were collected using multiple types of gear (2–6 cm mesh trammel nets, 2 cm mesh trap nets, and baited hooks) in Jiangjin and Yibin sections from 2007 to 2009. New maximum lengths for 16 species were recorded for FishBase. LWRs were significant for all species. Standard length–total length equations for converting size measurements for these 20 species are also presented. The results provide primary data for future fish research and conservation.

Summary The aim of this study was to quantify the fish fauna in the Three Gorges Dam (TGD) and assess the tendency for change as well as for any spatial and temporal distribution. Two types of echo-sounder equipment (HTI Model 241 and Simrad EY60) were used to detect the fish density and fish spatio-temporal distribution. Eight surveys were conducted between 2006 and 2010, with the results showing that fish abundance in the Three Gorges Reservoir (TGR) increased yearly from 15.5 to 123 ind./1000 m3, a change apparently correlated with the corresponding increase in the reservoir water level. Horizontally, fish density increased from the lower reaches to the upper reaches. Fish preferred inhabiting the area around the Zhongxian section during winter and the Chongqing section in spring. Vertically, fish density was highest in the lower layer, followed by the middle layer. The difference in fish density in different water layers observed in spring was not as evident as in the winter. Fish target strength throughout the eight investigations showed a skewed distribution with respect to fish size. The overall increasing tendency of fish density and the spatio-temporal distribution of fish species were closely related to the water level of the TGR during the impounding period. Other influencing factors included water flow rate, water depth, reservoir shape, habitat type, and protection policy.

The bronze gudgeon, Coreius heterodon (Bleeker), is an economically important species, which only inhabits the Yangtze River. The stock declined drastically in recent years due to dam construction, over-fishing, and pollution. Little is known about its population genetic structure. In this study, the sequences of the mitochondrial DNA (mtDNA) control regions of natural bronze gudgeon was determined for fish collected from four sites in the Yangtze River (n = 102). The molecular data were used to estimate the genetic diversity and differentiation of the bronze gudgeon. The results showed that 28 haplotypes and 22 variable sites were found, and the haplotype diversity (π) and nucleotide diversity (h) were 0.849 and 0.00257, respectively. A low level of genetic diversity exists in the bronze gudgeon. Analysis of molecular variance (AMOVA) suggests that 98.8% of the genetic variability occurred within the populations; the site of collection had little influence on diversity. Future research should focus on investigating the genetic divergence of populations in different tributaries and using additional polymorphic markers, such as microsatellite DNA, to verify the results and improve interpretation.