Stable isotopes and diet metabarcoding reveal trophic overlap between native and invasive Banded Killifish (Fundulus diaphanus) subspecies

Researchers, managers, and policymakers have historically neglected non-game fishes relative to game fishes, and this oversight has extended to invasive non-game fishes in the United States. One such fish—the Eastern Banded Killifish (Fundulus diaphanus diaphanus Lesueur 1817)—has established and rapidly spread in Lake Michigan and connected waters since 2000. Here, we assess potential drivers of the successful invasion of Eastern Banded Killifish, as well as their potential to disrupt native communities and food webs. Specifically, we compare the trophic niche breadth and diet composition between Eastern Banded Killifish and a native subspecies, Western Banded Killifish (Fundulus diaphanus menona Jordan and Copeland 1877), using stable isotope and gut content metabarcoding analyses. Stable isotope analysis showed that Eastern Banded Killifish had a higher variance in littoral dependence and trophic position than Western Banded Killifish, but both stable isotope and gut content metabarcoding analyses revealed an overlap in the diet composition and trophic position between the subspecies. Eastern Banded Killifish may successfully establish outside its native range due to higher feeding variability than Western Banded Killifish, including in habitats historically unused by the native subspecies, but the trophic niche between these two subspecies was similar overall. This study provides insights into the successful invasion of a potentially overlooked non-game fish—Eastern Banded Killifish—while also comparing stable isotope and gut content metabarcoding analyses for an invasive freshwater fish for the first time.