Abstract:

Aim: Hemibagrus guttatus has historically been known as one of the “four famously economic fish in the Pearl River”. However, due to cascade development, water pollution, and overfishing, wild populations of H. guttatus have drastically declined. In February 2021, H. guttatus was listed as a national category II key protected wild animal species. The study is to investigate the population genetic structure and evolutionary history of H. guttatus to identify actions that can improve scientific management and protection of wild H. guttatus populations.

Methods: A total of H. guttatus samples were collected from 19 locations in the Pearl River and the Hanjiang River. We used multiple approaches, including phylogeny, divergence time estimation, and population genetics, to explore genetic diversity, genetic structure and population historical demography based on mitochondrial genomes.

Results: Genetic diversity analyses revealed nucleotide diversity in the H. guttatus populations of the Pearl River and Hanjiang River exhibit extremely low nucleotide diversity, indicating an urgent protection of H. guttatus populations is necessary. Phylogenetic trees and haplotype network indicated that H. guttatus populations in the Pearl River and the Hanjiang River formed independent lineages, with two sub-lineages present in the Pearl River. Divergence time estimation analysis suggests that the Pearl River populations and the Hanjiang River populations split between 0.284 and 0.401 million years ago (Ma), while the two sub-lineages in the Pearl River diverged between 0.092 to 0.132 Ma. Bayesian skyline plots suggested that overall H. guttatus populations experienced significant population contraction and expansion between 0.072 and 0.101 Ma and 0.024 and 0.033 Ma, respectively. This analysis also suggested that the Pearl River populations underwent significant population expansion between 0.024 and 0.032 Ma.

Conclusions: Results from this study suggest Pleistocene climate change in South China may be an important driving factor that triggered H. guttatuslineage divergence. Further, sea level fluctuations induced by the late Pleistocene glacial cycles and the Last Glacial Maximum may have influenced the distribution and effective population size of H. guttatus populations. Based on the results of this study, we recommend the following: (1) strengthen supervision of fisheries administration, (2) establish protected areas to maintain H. guttatushabitat, and (3) increase monitoring of Hanjiang River populations. Moreover, the maternal lineage of sampled fish should be determined (by mitochondrial sequencing) before reintroduction to avoid blind release of non-local parents or offsprings into local rivers. Implementation of these practices will help preserve, and even improve, the genetic diversity of H. guttatus, which will allow them to remain an important economic fish for years to come.

Key words: national category II key protected wild animal, Hemibagrus guttatus, mitochondrial genome, genetic structure, population demography