Objective Global climate change significantly affects all groups of organisms, among which freshwater aquatic organisms are considered to be one of the more serious groups. Studying how fish respond to climate change is important for biodiversity conservation. In this study, we studied the relationship between environmental changes and changes in the geometric morphology and genetic information of two stream-type fishes, Opsariichthys bidens and Zacco platypus, from the Beijiang River, a first-class tributary of the Pearl River system.

Method The morphological data of the specimens of O. bidens from 1960 to 2019 and Z. platypus from 1982 to 2013 were analyzed by geometric morphology. At the same time, the genetic diversity of O. bidens and Z. platypus was analyzed based on mitochondrial D-loop sequences in three decades from 2001 to 2019.

Result The results of geometric morphological analysis showed that in the past 60 years, there were significant changes in the six morphological characteristics of Z. platypus fish, including body length, head length, eye diameter, snout length, mouth cleft, and the ratio of snout length to head length. Body length, head length, and eye diameter were significantly correlated with climatic factors such as temperature and precipitation. The body height/body length of the Z. platypus was decreasing, and the head morphological characteristics such as snout length and eye diameter increased from 2006 to 2013. The results of genetic diversity based on mitochondrial D-loop showed that the nucleotide diversity of the two species decreased in the past 10 years, and the nucleotide diversity of O. bidens decreased from 0.05028 to 0.03007, and the nucleotide diversity of Z. platypus decreased from 0.02834 to 0.01108. After correlating with environmental factors, it was found that nucleotide diversity was significantly correlated with pH. The nucleotide diversity of the Z. platypus showed a decreasing trend in the past 20 years, but the population still showed high genetic diversity, and the change of genetic diversity was positively correlated with precipitation.

Conclusion Based on the results of this study, we conclude that there are obvious response characteristics of morphological and genetic diversity of freshwater fishes, especially stream fishes, to global climate change, and the specific mechanism of this study still needs to be further studied. The results of this study are helpful to discover the response of stream fish to environmental change, which can evaluate the impact of global climate change on aquatic organisms, enrich the research on the mechanism of freshwater fish response to climate change, and provide a theoretical basis for the management and protection of fish resources in the Beijiang River.