Abstract:

Aims: To investigate the gut bacterial community structure and diversity of six economically important cyprinid species (Hypophthalmichthys molitrix, Parabramis pekinensis, Aristichthys nobilis, Culter alburnus, Carassius auratus, Megalobrama amlycephala) in the Nanhai Wetland of Baotou. Specifically, this study aimed to explore correlations between gut bacteria and host growth performance, antioxidant capacity, and dietary niche to provide a theoretical basis for healthy aquaculture and disease prevention. 

Methods: High-throughput sequencing technology was employed to systematically analyze the gut bacteria across six cyprinid fish species. Additionally, we investigated their correlations with host growth performance, antioxidant capacity, and dietary niche. Key methods included: alpha diversity analysis, beta diversity analysis, and community composition analysis. Linear discriminant analysis effect size (LEfSe) was employed to identify significantly differential microbes across groups. Correlation analysis was conducted using redundancy analysis (RDA) and Spearman correlation heatmaps. 

Results: A total of 1,051,137 valid sequences were obtained, which were divided into 11,164 OTUs (Operational Taxonomic Units). Based on the minimum number of reads (45813) of all samples, 11108 OTUs were retained for subsequent statistical analysis, among which these OTUs belonged to 37 phyla and 1,005 genera. Microbial community composition analysis revealed that all six Cyprinidae fish species shared a core gut microbiota, with Pseudomonadota, Fusobacteriota, and Actinomycetota identified as the dominant phyla, while Cetobacterium and Rothia emerged as the dominant genera. The results suggest that Cyprinidae fish share a core gut microbiota, which is likely functionally conserved in processes such as short-chain fatty acid production, vitamin synthesis, and energy metabolism. Nevertheless, significant interspecific divergence was detected. There were significant differences among the gut bacterial structure of the six cyprinid fish species using the methods of principal coordinates analysis (PCoA) and permutational multivariate analysis of variance (PERMANOVA), indicating species-specific characteristics, meaning that the gut bacterial communities of different fish species possess unique compositional features. At the phylum level, LEfSe analysis identified significant enrichment of Cyanobacteriota in Hypophthalmichthys molitrix, consistent with its filter-feeding ecological habit in the upper water layer, reflecting host adaptation to specific food sources. At the genus level, 20 significantly differential bacterial genera were identified, such as Methylobacterium_Methylorubrum, Synechocystis sp. PCC 6803, and Cyanobium sp. PCC 6307 in Hypophthalmichthys molitrix; Plesiomonas in Aristichthys nobilis; and Candidatus_Competibacter in Carassius auratus, all of which are closely associated with host ecological habits. Moreover, the gut bacterial community structure was significantly correlated with host growth performance, antioxidant indicators, and dietary niche using correlation analysis. Specifically, growth-related parameters including condition factor (R^²=0.731, p=0.001), sex (R^²=0.595, p=0.002), age (R^²=0.530, p=0.003), and viscerosomatic index (R^²=0.453, p=0.013) sequentially exerted significant effects on gut bacterial structure, with four key bacterial genera (e.g., Sphingomonas, Algoriphagus, and Acinetobacter) identified as critical correlates. In terms of antioxidant capacity, DPPH radical scavenging activity (R^²=0.700, p=0.001) and H₂O₂ content (R^²=0.690, p=0.001) were the primary determinants of microbial community composition, linked to ten functional genera, including Vibrio, Aeromonas, and Plesiomonas. Meanwhile, six bacterial genera were identified as significantly associated with distinct feeding niches, including  Marivivens, Acinetobacter, and Candidatus_Competibacter, were also identified. 

Conclusion: The results demonstrated that Cyprinidae fish shared a core gut microbiota, which exhibited functional conservation in fundamental metabolic processes, while species-specific bacteria synergistically regulated host nutrient metabolism, oxidative stress responses, and growth-related physiological processes to enhance their adaptation to specific environmental conditions. These findings provide a scientific experimental basis for wetland fish resource management and precision fish farming.

Key words: Cyprinidae, gut microbiota, growth performance, antioxidant capacity, dietary niche