The release rate of environmental DNA from juvenile and adult fish

Abstract

The environmental DNA (eDNA) technique is expected to become a powerful, non-invasive tool for estimating the distribution and biomass of organisms. This technique was recently shown to be applicable to aquatic vertebrates by collecting extraorganismal DNA floating in the water or absorbed onto suspended particles. However, basic information on eDNA release rate is lacking, despite it being essential for practical applications. In this series of experiments with bluegill sunfish (Lepomis macrochirus), we examined the effect of fish developmental stage on eDNA release rate. eDNA concentration reached equilibrium 3 days after the individual fish were introduced into the separate containers, enabling calculation of the eDNA release rate (copies h-1) from individual fish on the assumption that the number of eDNA released from the fish per unit time equals total degradation in the container (copies h-1). The eDNA release rate was 3-4 times higher in the adult (body weight: 30-75 g) than in the juvenile group (0.5-2.0 g). Such positive relationship between fish size and eDNA release rate support the possibility of biomass rather than density estimation using eDNA techniques. However, the eDNA release rate per fish body weight (copies h-1 g-1) was slightly higher in the juvenile than the adult group, which is likely because of the ontogenetic reduction in metabolic activity. Therefore, quantitative eDNA data should be carefully interpreted to avoid overestimating biomass when the population is dominated by juveniles, because the age structure of the focal population is often variable and unseen in the field. eDNA degradation rates (copies l-1 h-1), calculated by curve fitting of time-dependent changes in eDNA concentrations after fish removal, were 5.1-15.9% per hour (half-life: 6.3 h). This suggests that quantitative eDNA data should be corrected using a degradation curve attained in the target field.

Figure 1. Time-dependent changes in the eDNA concentration after fish removal.

Regression curves of the non-linear models are shown. Each color indicates one of five individuals (black and aqua: adult, others: juvenile).

Figure 2. Time-dependent changes in the eDNA concentration after fish introduction.

Plots and error bars indicate means and standard deviations of five individuals, respectively.

Figure 3. Box plots of the eDNA release compared between juvenile and adult groups.

a) Stabilized concentration, b) release rate per individual fish, and c) per fish body weight. Body wet weight was 0.5–2.0 g (n = 10) and 30–75 g (n = 9), respectively.