Abstract:

Between June and September in 2012, we investigated fish resources from the Yellow River, Jialing rivers and Hexi inland rivers in Gansu Province, China. Three thousand specimens were collected, belonging to 64 species, 38 genera, 10 families and 5 orders. Cyprinidae was the predominant species, accounting for 45% of the total species. Diversity analysis showed that fish diversity in the Jialing River basin was the highest (H = 2.15-3.27), followed by the inland rivers (H = 2.01-2.83). Two tributaries of the Yellow River, the Xiahe River and the Zhuanglang River had relatively lower diversity levels with the H values of 1.38 and 1.09, respectively. The Pielou index of Shule River was the highest with a value of 1.10, while that of the Heihe River was the lowest with a value of 0.68. The Simpson index of the Zhuanglang River was 0.34, the highest of the investigated rivers, while the trunk streams of Jialing River was the lowest. A total of 662 specimens of 49 species were randomly selected for DNA barcoding analysis using a partial sequence of the COI gene. The results indicated that most species formed monophyletic groups in the neighbor-joining tree. The average K2P genetic divergence was 0.88% within species and 9.99% among species. A significant barcode gap was found between intraspecific genetic distance and interspecific genetic distance. A nucleotide diagnostic method was needed for further identification because the K2P genetic distance of three species pairs (between Triplophysa stoliczkae and T. dalaica, T. robusta and T. siluroides, Schizopygopsis kialingensis and S. pylzovi) was less than 2%. Cryptic species may exist within Triplophysa stoliczkae and Phoxinus lagowskii. Triplophysa robusta and T. siluroides cannot be distinguished through COI gene sequences. The results showed that molecular methods, morphological characteristic and geographical distribution of species should be combined in order to comprehensively and accurately identify closely related species and geographic populations.

Key words: freshwater fish, species diversity, DNA barcoding, COI, species identification, cryptic species