Flathead catfish, originally from the Mississippi River basin, were first identified in the Susquehanna River of Pennsylvania in 2002, as stated by the U.S. Geological Survey. Over the last 20 years, these invasive fish have expanded throughout the river system. The effect of this large predator on the existing food webs and ecology of the Susquehanna River was previously unclear. However, a research team is now gaining insights into the diet of the flathead catfish in the area and its implications for native aquatic species.
Originally from the Mississippi River basin, flathead catfish were first spotted in Pennsylvania’s Susquehanna River in 2002, according to the U.S. Geological Survey. Since then, this invasive species has spread across the river basin over the past two decades. The influence of this large predator on the river’s food webs and ecology remained largely unknown until a research team began examining what flathead catfish consume and how they are impacting the river’s native species.
The study’s outcomes, valuable for state fisheries managers to enhance river management, were recently reported in Transactions of the American Fisheries Society. The collaborative research effort involved scientists from Penn State, the Pennsylvania Fish and Boat Commission, the U.S. Fish and Wildlife Service, and the U.S. Geological Survey. Researchers found that flathead catfish are opportunistic feeders, preying on a variety of aquatic species. These fish are aggressive predators and have established themselves as the top predators in the river; some can exceed 4 feet in length and weigh nearly 70 pounds in Pennsylvania’s waters. This poses a significant threat to the populations of local fish species, as noted by the researchers.
“This study on flathead catfish diets in a mid-Atlantic river was essential because we previously lacked information on how this invasive species affects food webs and which native species are most at risk,” said Megan Schall, a co-author and associate biology professor at Penn State Hazleton. “The flathead catfish can be a danger to native aquatic communities in non-native waters.”
To analyze the diet of the flathead catfish, the research team collected 576 specimens over two years using methods like electrofishing and hoop nets, as well as from the Conowingo Dam fish lift. Of these, 241 fish had storable stomach contents. The team utilized a molecular genetics technique known as DNA barcoding to extract and identify the prey from these contents. They performed genetic sequencing of selected samples at Penn State’s Huck Institutes of the Life Sciences Genomics Core Facility.
In total, researchers identified 47 distinct prey species. Among these, 34 species were found at low frequencies, appearing in less than 2% of the sampled fish. The most frequently consumed prey included rusty crayfish, margined madtoms (a small catfish species of conservation concern), and various shiners, which are small silvery minnows. The types of prey varied with the size of the flathead catfish; notably, rusty crayfish were present in nearly half of the sampled fish.
Other identified prey species included blueback herring, gizzard shad, northern hog sucker, shorthead redhorse, goldfish, river chub, bluntnose minnow, longnose dace, white catfish, brown bullhead, channel catfish, flathead catfish, banded killifish, rock bass, green sunfish, bluegill, smallmouth bass, white crappie, black crappie, white perch, greenside darter, yellow shield darter, and walleye.
As expected, the research indicated that larger flathead catfish tend to consume bigger prey. Specifically, fish exceeding 24 inches mainly ate other fish, while smaller ones under 24 inches had a more diverse diet, including both invertebrates and fish.
Learning that these flathead catfish in the Susquehanna River basin feed on a wide variety of prey, including important recreational fish like smallmouth bass, rock bass, channel catfish, and walleye, as well as conservation concern species such as blueback herring and margined madtom, is essential for fisheries managers overseeing the river’s ecosystem, Schall commented.
“Understanding the diet of this invasive predator is a crucial first step in assessing its potential impact on local aquatic communities,” Schall explained. “This knowledge is key for developing possible management strategies against this new invasive threat.”
Interestingly, it was discovered that flathead catfish in the Susquehanna River consume a sizable amount of rusty crayfish, another invasive species that has been replacing native crayfish in the Northeast U.S. Julian Avery, an assistant research professor of wildlife ecology and conservation who led the study, noted the significance of this finding.
“These invasive species likely arrived in the Susquehanna River through human activities, such as anglers relocating them. The extent of disruption that can occur in ecosystems due to such actions is striking,” he stated. “We are just beginning to understand the impacts that these aquatic invaders have on river ecosystems.”
The research also included contributions from Geoffrey Smith, Pennsylvania Fish and Boat Commission, Division of Fisheries Management; Sam Maloy and Jason Coombs from the U.S. Fish and Wildlife Service, Northeast Fishery Center, Lamar, Pennsylvania; and Tyler Wagner from the U.S. Geological Survey, Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State.
This study received funding support from the Pennsylvania Sea Grant, the Penn State Commonwealth Research and Development Program, and the Mid-Atlantic Panel on Aquatic Invasive Species.
