Variation of Japanese eel eDNA in sequentially changing conditions and in different sample volumes

Area of Science:

• Aquatic Ecology
• Molecular Ecology
• Fisheries Science

Background:

• Environmental DNA (eDNA) is a valuable tool for assessing aquatic species distribution and abundance.
• Factors influencing eDNA concentrations, such as biological and environmental variables, require further investigation for accurate ecological assessments.
• Understanding eDNA dynamics is crucial for effective conservation and management of Japanese eel populations.

Purpose of the Study:

• To investigate the impact of feeding and temperature on Japanese eel environmental DNA (eDNA) concentrations.
• To determine if water sample volume affects eDNA detection rates in controlled experimental settings.

Main Methods:

• Controlled aquarium experiment simulating feeding/nonfeeding and low/high temperature conditions for Japanese eels.
• Collection of water samples in three replicate volumes (50, 100, 200 ml) under varied experimental conditions.
• Quantification of Japanese eel eDNA concentrations from collected water samples.

Main Results:

• Japanese eel eDNA concentrations showed a slight increase at higher temperatures (22-23°C) during nonfeeding periods.
• The highest eDNA concentrations were observed immediately upon the initiation of feeding, even under lower temperatures (16-17°C).
• Water sample volume (50, 100, or 200 ml) did not significantly affect the measured eDNA concentrations.

Conclusions:

• Feeding status is a primary driver of Japanese eel eDNA shedding into the aquatic environment.
• Temperature has a secondary effect on eDNA concentrations, with higher temperatures potentially increasing levels when eels are not feeding.
• Standardized sampling protocols for eDNA surveys should consider the influence of fish activity, particularly feeding, and may not require large sample volumes.