Environmental DNA integrity index is sensitive for species biomass estimation in freshwater

Environmental DNA (eDNA) derived from aquatic vertebrates has recently been employed to estimate species presence. However, the accuracy of these estimations is contingent upon the degradation rate of eDNA. In this study, we introduced the eDNA Integrity Index (eDI) to adjust eDNA concentration for the purpose of estimating carp biomass. The adjusted eDNA concentration is designated as the Biomass Index (BI). We investigated the degradation rate of eDNA through a series of simulation experiments, followed by experiments conducted in tanks and ponds. In all experimental setups, eDNA concentration exhibited a gradual decline, while eDI demonstrated rapid fluctuations following the removal of fish species. Notably, the eDI decreased to nearly zero within two days, whereas eDNA remained detectable for over a month. In experiments involving multiple species raised in conjunction, we observed no significant mutual interference among different species concerning eDI. Furthermore, temperature was determined to have a minimal impact on eDI. Although both eDNA concentration and BI were positively correlated with carp biomass across all experiments, BI exhibited a stronger correlation (R² > 0.95), was more sensitive to variations in biomass, and provided a more accurate estimate of carp biomass. We successfully applied this methodology to estimate the biomass of carp in a fishpond, demonstrating that precise biomass data can reflect the potential distribution of common carp in natural environments. We present a non-invasive, straightforward, rapid, and accurate method for biomass estimation. SYNOPSIS: We developed an environmental DNA integrity-based method which can estimate species biomass sensitively for species distribution and resource investigations.