Flathead catfish -- native to the Mississippi River basin -- were first detected in the Susquehanna River in Pennsylvania in 2002, according to the U.S. Geological Survey. In the two decades since then, the invasive species has spread throughout the river basin. The impact of the large predator on the waterway's food webs and ecology was unknown, but now a research team is beginning to understand what Susquehanna flatheads are eating and how their presence is affecting native aquatic species in the river.