Environmental DNA technique for estimating fish biomass: Testing with fish catchment by pond draining

Background/Question/Methods

To estimate fish biomass in aquatic habitats, we traditionally used direct catchment of fish by nets and angling. Recently, environmental DNA (eDNA) analysis has been developed to estimate the fish presence and absence by detecting DNA in the water sample with quantitative real-time PCR. Some studies found that the strong relationship between fish biomass and the eDNA concentration in ponds and tank experiments (Takahara et al. 2012, Thomsen et al. 2012, Doi et al. 2015). From the experiments, fish biomass can be quantified by the number of target DNA copies. However, the field testing for the eDNA method would be difficult, because we cannot correctly estimate fish biomass in aquatic habitats. In Japan, many ponds have traditionally been drained and dried up once a year to maintain the pond structure. At the time, we can catch almost all of fish and estimate the fish biomass more correctly. Here, using eight ponds drained and dried, we evaluated the relationships between fish biomass and the eDNA concentrations for two fish species, the invasive bluegill sunfish, Lepomis macrochirus, and the common carp, Cyprinus carpio.

Results/Conclusions

We found the relationships between fish biomass and the eDNA concentrations for two fish species. The relationship for the common carp was stronger than that for bluegill sunfish. Also, we detected the eDNA from all the ponds, which we caught the fish species. In this study, we collected the eDNA samples from 3 pelagic and 3 shore sites in each study pond, but the eDNA concentrations of the fish species varied among the sampling sites. From the results, we can apply eDNA method to estimate fish biomass in aquatic habitats with carefully considering the sampling strategy.