Identification of drifting fish eggs in Guiping section of Xunjiang River based on DNA barcoding technology

【Objective】DNA barcoding technology was used to identify drifting fish eggs in the Guiping section of Xunjiang River， and reveal the early resource status of fish， which could provide data support for the investigation of fish spawning grounds and fish resource conservation in Xunjiang River.【Method】Fish eggs were collected from May to August of 2024 in Jiangkou Town section of Guiping City， located 25-50 km downstream of the Datengxia spawning ground， Qianjin spawning ground， and Dongta spawning ground. The samples were transported to the laboratory for DNA extraction. DNA barcoding technology was used to identify the fish egg samples.【Result】A total of 565 valid sequences were obtained from the 646 collected fish eggs in Jiangkou Town section， of which 93.98% of the samples could be identified to the species level， and 6.02% could be identified to the genus level. A total of 18 species were identified， belonging to 1 order， 3 families， 8 subfamilies， and 16 genera. Among them， there were 15 species of Cyprinidae， corresponding to 557 valid sequences， accounting for 98.58% of the total valid sequences； there were 2 species of Cobitidae， corresponding to 2 valid sequences， accounting for 0.35% of the total valid sequences； and there was 1 species of Gastromyzontidae， corresponding to 6 sequences， accounting for 1.06% of the total sequences. Among the 565 valid sequences， Xenocypris davidi had the highest number of sequences （183 sequences， accounting for 32.39%）， followed by Squalibbarbus curriculus （135 sequences， accounting for 23.89%）. Relatively high numbers of sequences were also obtained for Squalidus argentatus （113 sequences， accounting for 20.00%）， Xenocypris argentea （29 sequences， accounting for 5.13%）， Cirrhinus molitorella （21 sequences， accounting for 3.72%）， and Pseudohemiculter dispar （18 sequences， accounting for 3.19%）. Among the 18 species identified to multiple species level， 15 were typical drifting egg spawners. Analysis of intraspecific and interspecific genetic distances revealed that the average interspecific genetic distance was as 28.74 times as that of the average intraspecific genetic distance. The phylogenetic tree showed that the identified fish egg samples clustered into 19 independent clusters， and multiple species in the same genus clustered into the same branch.【Conclusion】The species composition of drifting fish eggs in the Guiping section post-impoundment remain consistent with pre-impoundment conditions of Dateng Water Control Hub. However， there is a noticeable decline in the proportion of medium and large fish （such as Ctenopharyngodon idella， Aristichthys nobilis， Hypophthalmichthys molitrix， Mylopharyngodon piceus）， while small-sized fishes have gradually become dominant. The operation of water conservancy projects may lead to a trend of miniaturization in fish community structure. Therefore， it is imperative to strengthen habitat protection and implement ecological regulation during the critical reproductive periods of fish.