3.3 The diversity relationships between eDNA and electrofishing sampling
The linear regression results showed that the relationships between the alpha diversity calculated by eDNA OTU richness and fish individual number exhibited significant (P < 0.05) positive correlations (Fig. 4A). The regression equation is fitted as Y = 0.9572∙X + 0.5425 (R ² = 0.8218), where Y is the number-based diversity, X is the eDNA-based diversity, andR -squared (R 2) measures how close the data points are to the fitted line. The linear regression between the fish diversity calculated by eDNA OTU richness and by fish biomass (i.e., wet weight) exhibited significant (P < 0.05) positive correlations. The regression equation is fitted as Y = 0.4339∙X + 2.3043 (R ² = 0.4558), where Y is the biomass-based diversity and X is the eDNA-based diversity (Fig. 4B). These results indicated that the eDNA metabarcoding protocol could reflect the alpha diversity of local fish communities as well as the diversity determined by traditional biological counting, and the eDNA-based diversity had a higher matching degree with number-based diversity than with biomass-based diversity. In addition,R 2 showed significant (P < 0.05) intergroup differences between the spatial zones (Fig. 4C). The highest R 2 values were observed in zones I − II and VII – VIII, which were significantly higher than those in zones IV − V. This result indicated that the eDNA-based diversity had higher linear regression with number-based diversity in headwater and the estuarial zones.