Species diversity and distribution patterns of fish in the western headwaters of Xiangjiang River

To systematically evaluate the structural characteristics of fish communities in the western headwaters of the Xiangjiang River, we conducted fish surveys at nine sampling sites (divided into two river sections: the Xiangjiang River and the Guanjing River) during the flood season, normal season, and dry season in 2024. We quantified fish diversity and distribution patterns using the index of relative importance, species diversity indices, and multivariate statistical methods. A total of 70 fish species were recorded, belonging to 6 orders, 17 families, and 51 genera, with Cypriniformes, particularly Cyprinidae, dominating the community. In terms of ecological types, resident, demersal, and omnivorous fishes were predominant. Zacco platypus, Acrossocheilus hemispinus, and Odontobutis sinensis were identified as dominant species throughout the year. The mean values of the Shannon diversity index, Margalef richness index, and Pielou evenness index were 2.48, 2.18, and 0.72, respectively. Among these, only the Margalef richness index in the dry season was significantly higher than that in the flood season, and there were no significant differences among other hydrological periods or between river sections. We estimated β diversity based on the nine sampling sites, using the Cody and Routledge indices. We found that site S1 exhibited higher habitat heterogeneity and species turnover compared to the other sites, whereas differences among the remaining sites were relatively small. Non-metric multidimensional scaling combined with permutational multivariate analysis of variance (Permanova) indicated that fish community structure differed significantly between two river sections, but not among hydrological periods. Similarity percentage analysis showed that overall community similarity was at a moderate level (0.29-0.64), with higher similarity within the same river section than between different sections, suggesting that spatial heterogeneity was the primary driver of community variation. Abundance-biomass comparison (ABC) curves indicated that fish communities in the study area were subject to disturbance. This study provides baseline data on fish resources in the western headwaters of the Xiangjiang River and offers a scientific reference for regional fish conservation and fisheries management.