Flathead Catfish

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 Biological Synopsis:
  • Flathead catfish are a large, freshwater catfish that range in color from a mottled brown to olive green with a white or light-colored underside. They have a square-shaped caudal fin and flattened head with a protruding lower jaw.
  • Diets of flathead catfish include American eels, American shad and river herring, and sunfishes, as well as other fishes, crustaceans, and mollusks.
  • Flathead catfish have a wide native range that includes the Missouri, Mississippi, Ohio, and Rio Grande river basins. The species was introduced to Virginia waters in the 1960s through 1980s, and into the Susquehanna River in the 2000s.
  • Flathead catfish are the second largest catfish species in North America, and can reach over 60 inches in length and over 120 lbs in weight.
  • Notable specimens are 34 inches or longer and are eligible for a FishMaryland Invasive Species Award.

Fact Sheet




Environmental Concern:  
  • Flathead catfish are known to impact native catfish populations where introduced, and often reduce the abundance of native species. They have been associated with reductions of sunfish and largemouth bass populations in some introduced areas, and may prey heavily on shads and herring.
  • The species has quickly expanded its range and increased in abundance in regions of the bay watershed, particularly the Susquehanna River in the upper Chesapeake Bay, and the non-tidal Potomac River.
  • Flathead catfish quickly reach large sizes and have few predators aside from other flathead catfish and humans.​


  • Flathead catfish were introduced to rivers of Virginia during the 1970s and 1980s, and the Susquehanna River of Pennsylvania in the 2000s. The fish are now common in the non-tidal Potomac River, with small populations occurring in tributaries of the tidal Potomac River. The fish is regularly caught in Conowingo Reservoir of Maryland, as well as below Conowingo dam.
  • They inhabit deep, rocky pools in clear and eutrophic waters.


  • Research managers, concerned about flathead catfish and their impact on the Chesapeake Bay watershed, adopted an Invasive Catfish Policy in 2012 and in 2014, formed the Invasive Catfish Workgroup. The group brings in numerous stakeholder groups to coordinate research and evaluate the impacts of invasive catfishes in Chesapeake Bay.
  • Maryland adopted the Fishery Management Plan for Tidewater Catfish and the Aquatic Nuisance Species Plan to mitigate economical and ecological damage of flathead catfish.
  • Biologists and researchers from the department are collaborating with PA Game and Fish Commission, and other partners to research the impacts of flathead catfish in the Susquehanna River and upper Chesapeake Bay.
  • Maryland DNR biologists have begun researching life histories of flathead catfish in the non-tidal Potomac River and upper Chesapeake Bay and Susquehanna River.
Fishery Management Plan for Tidewater Catfish​​​

What can you do? 

  • The department asks anglers to remove and kill any blue and flathead catfish they catch.
  • Catch and release of these fish is discouraged, as they are invasive top predators and pose a serious long-term threat to our native species.
  • In Maryland, it is illegal to transport live blue and flathead catfish into another body of water, anyone in violation of this can be fined up to $2,500.
  • To report illegal transport or unauthorized introductions of invasive species please contact the Natural Resources Police at 800-628-9944.

Report Catching a Blue Catfish or a Flathead Catfish using Maryland's Invasive Species Tracker​