The effect of artificial light at night on wild fish community: manipulative field experiment and species composition analysis using environmental DNA

The use of artificial light at night (ALAN) has been increasing globally and has been reported to affect a wide range of organisms. However, the effects of ALAN on wild fish communities remain unknown. In this study, we investigated the effects of ALAN on the species distribution and composition of a fish community in a canal. We hypothesized that the fish species composition in areas subjected to ALAN would differ from that in the control area. To test this hypothesis, we conducted a three-week manipulative field experiment in which real-world ALAN conditions were simulated by illuminating the water surface at night using LED lights for two weeks. During the experiment, water samples were collected from ALAN and control conditions four times a week, from which environmental DNA (eDNA) were extracted. Additionally, the number of arthropods in the ALAN and control environments was recorded daily to investigate whether ALAN impacts distribution patterns of fish prey, which may have indirect effect on fish through changed prey-predator relationships. Collected water samples were analyzed using eDNA metabarcoding with MiFish primers and real-time PCR targeting six fish species to obtain qualitative and quantitative data on fish species composition. We compared the fish species composition data between the ALAN and control environments. Our results suggest that ALAN did not significantly influence the overall fish species composition and that the sampling location had a more significant impact. Our findings also point to the possibility that the effect of ALAN on habitat selection may vary depending on the diet of the individual fish. Overall, the effect of ALAN on fish was less significant than expected. By combining eDNA methods with manipulative field experiment, this study shows the applicability of eDNA methods in investigating the effect of pollutants and offers a promising area for future investigation