There’s a new king on the Susquehanna River in Pennsylvania – and it’s not smallmouth bass. Many anglers have probably noticed it too, especially if you’re a catfish angler.
The rise in invasive flathead catfish catches and sightings have been so pronounced that a team of researchers from Penn State, the U.S. Geological Survey, and the Pennsylvania Fish and Boat Commission set out to see how flatheads are affecting the food web in the Susquehanna River. They published their findings in Ecology in September 2025.
“Flatheads grow fast in this river system, attain large body sizes and can eat a variety of prey,” said study author Olivia Hodgson, a master’s degree student at Penn State University. “Because adult flatheads have few natural predators, flathead catfish can exert strong control over the ecosystem.”
Hierarchy Shakeup
Flatheads were first detected in the Susquehanna in the 1990s. Since then, its numbers have grown at an unmistakable pace. And this study puts them at the top “trophic position” — the level an organism occupies in a food web, based on its feeding relationships. That pecking order is surprising and potentially serious for the river’s future.
Flatheads are higher up than native predators such as smallmouth bass and channel catfish. Those two species now eat lower on the food chain, likely because they are being outcompeted by flatheads or avoiding them, the researchers explained. Prey species such as crawfish, panfish and baitfish are also affected.
“This suggests that resident species are changing what they eat to avoid competing with or being eaten by the invader,” Hodgson said. “These findings support the ‘trophic disruption hypothesis,’ that says when a new predator enters an ecosystem, it forces existing species to alter their behavior, diets and roles in the food web.
“This can destabilize ecosystems over time. Our study highlights how an invasive species can do more than just reduce native populations — it can reshape entire food webs and change how energy moves through ecosystems.”
What to Do About Flathead Catfish?
Catfish species are known for their opportunistic feeding and tolerance to thrive in a wide range of environmental conditions. This is especially true for flathead catfish (Pylodictis olivaris) that are found in or near swamps, brackish estuaries, moving rivers, and even manmade structures near cities. They aren’t particularly selective about what they feed on, live long lives, and can grow to 100 pounds.
Flathead catfish are native to western Pennsylvania’s Ohio River drainage, but invasive in the Susquehanna and Delaware rivers. The apex predator leads a trail of destruction wherever it invades, often with the help of anglers illegally releasing the species in new waterways. In the Altamaha River in Georgia, the flathead catfish eliminated bullhead catfish and caused an 80 percent reduction in redbreast sunfish numbers, according to Pennsylvania Sea Grant. In coastal North Carolina rivers, the flathead catfish has eliminated native catfish populations too.
Pennsylvania currently asks fishermen to help catch and take flatheads out of waters where they’re not native. Anglers who catch flatheads in the Delaware and Susquehanna watersheds are encouraged not to release them, regardless of size.
Make sure you can identify your catfish properly; flatheads have a unique broad, flat head and lower jaw which sticks out beyond the upper jaw. The flathead catfish also has a distinctive caudal fin that’s not forked like a blue catfish or channel catfish; instead it’s square or slightly notched.
