What Do Flathead Catfish Eat? A Predator’s Diet

Flathead catfish are dedicated predators that eat primarily live fish and crayfish. Unlike their relatives the channel catfish and blue catfish, which readily scavenge dead or decaying food, flatheads have a strong preference for living prey and rank among the most committed piscivores in North American freshwater. Studies across multiple river systems consistently find that fish and crayfish account for the overwhelming majority of their diet by weight, and their physical design lets them swallow surprisingly large meals. The specifics of what ends up in a flathead’s stomach, though, depend on the fish’s size, the season, and what prey happens to be available.

Fish and Crayfish Dominate the Diet

In rivers where researchers have examined flathead catfish stomachs, the pattern is remarkably consistent: fish and crayfish together make up most of what flatheads eat. A study of introduced flathead catfish in two North Carolina coastal rivers found that fish or crayfish contributed more than half of stomach contents whether measured by how often they appeared, their numbers, or their total weight.¹ Work in the Susquehanna River basin found the same story, with a diverse list of fish species turning up as prey alongside crayfish, which were consumed by flatheads of every size.²

The specific fish species that show up in flathead stomachs reads like a roster of whatever lives nearby. In the Susquehanna, researchers recovered remains of smallmouth bass, rock bass, channel catfish, blueback herring, and margined madtom, among others.³ In Virginia’s James River, flatheads prey on at-risk species of river herring in the genus Alosa.⁴ They do not appear to be particularly choosy about species. Analysis using selectivity indices in those North Carolina rivers showed that flathead catfish feeding was generally random with respect to which fish species they ate, meaning they grabbed whatever prey they encountered in rough proportion to its availability rather than targeting certain species and ignoring others.¹

This indiscriminate approach is part of what makes flatheads such effective predators. They are not locked into hunting one type of prey. Sunfish, shad, suckers, other catfish species, and crayfish all end up on the menu depending on the river and the season. Invertebrates like insect larvae can appear in stomach contents too, particularly in smaller flatheads, but they are a minor dietary component in adults.

How Size Reshapes the Menu

A juvenile flathead catfish does not eat the same things as a 50-pound adult, and this size-dependent shift in diet is one of the most consistent findings across studies. Young flatheads eat more invertebrates, especially crayfish and aquatic insects, relative to their body size. As they grow, fish become an increasingly large share of the diet. Researchers in the Susquehanna basin documented this clearly: crayfish stayed important for all sizes, but the types of fish prey changed as flatheads got bigger.³

Small flatheads tend to eat small-bodied fish like minnows and young-of-the-year sunfish. Once a flathead reaches a foot or so in length, it begins regularly consuming larger prey fish, including species that anglers care about. By the time a flathead passes two feet, it is large enough to swallow adult game fish. This progression means that the ecological impact of a flathead catfish population depends partly on the size structure of that population. A river full of juvenile flatheads exerts different pressure on the food web than one harboring large adults.

A Mouth That Can Swallow Almost Anything

One reason flatheads can eat such a wide range of prey is their mouth. Flathead catfish have broad, flattened heads with a wide gape that scales predictably with body length. Researchers who measured gape dimensions across a range of flathead sizes found that no size of largemouth bass, bluegill, or gizzard shad would be too large for a flathead to eat, given a flathead of sufficient body length.⁵ That is a striking result. Many predatory fish are strongly limited by how wide they can open their mouths, which creates a size refuge for prey fish that grow large enough. Flatheads have very little of this limitation.

The study concluded that flathead catfish rank among the least gape-limited piscivores in freshwater.⁵ In practical terms, a large flathead can physically swallow fish that many other predators in the same river cannot. This gives flatheads access to prey that are effectively safe from bass, walleye, and other predatory fish sharing the same water. It also means that the usual strategy some prey fish rely on, growing fast enough to outpace predator gape size, does not work well against flatheads.

Hunting After Dark

Flathead catfish are overwhelmingly nocturnal feeders, and their daily movement patterns reflect this. A tracking study in two Missouri streams found that flatheads moved less than 100 meters during early afternoon and the first couple of hours after sunset, then undertook longer movements from around 9 p.m. through the night until about 5 a.m., ceasing activity at sunrise.⁶ During the day, flatheads tend to hold tight to cover. They tuck under log jams, in undercut banks, around submerged boulders, and in other structures. When darkness falls, they move out to hunt.

This nocturnal pattern ties into how catfish sense the world. Flatheads rely heavily on their lateral line system and chemoreception rather than vision to locate prey. Research on a related species, the European catfish, has shown that piscivorous catfish can accurately track the three-dimensional swim path of prey fish in complete darkness by following the water disturbances the prey leaves behind. In those experiments, wakes up to 10 seconds old were followed over long distances, and the catfish tended to attack from behind, making the approach harder for prey to detect.⁷ While that study examined European catfish rather than flatheads specifically, the sensory equipment is similar across large catfish species, and the strategy fits what biologists observe in flathead behavior: a sit-and-ambush predator that ventures from its daytime cover at night, locating and intercepting prey in low-visibility conditions.

This nocturnal hunting style has practical implications for anyone trying to catch flatheads. The fish are simply more active and more willing to feed after dark. Anglers who target flatheads know this well, and many of the biggest specimens are caught on night lines or during after-dark fishing sessions.

How Season Influences Feeding

Like most freshwater fish, flathead catfish are cold-blooded, and their metabolism and feeding intensity track water temperature. Feeding ramps up as water warms in spring, peaks during the summer months, and tapers off as temperatures drop in autumn. During winter, flatheads eat very little, often going extended periods without feeding at all as they hold in deep pools or log jams.

Beyond just how much flatheads eat, research shows that the types of prey they consume shift with the seasons. In the Susquehanna basin, both flathead body size and seasonality influenced which prey species showed up in their stomachs.⁸ This makes sense when you consider that prey availability changes over the year. Crayfish are more active and vulnerable in warmer months. Seasonal fish migrations, like runs of river herring, create temporary pulses of prey that flatheads exploit when available. Young-of-the-year fish from spring spawning become vulnerable as they grow through summer. The flathead’s generalist approach means it capitalizes on whatever prey is most abundant and accessible at a given time of year, rather than waiting for a single preferred food source.

Spring also brings the flathead’s own spawning season, typically occurring when water temperatures reach roughly 70 to 80 degrees Fahrenheit. Males guard nests during this period and may feed less actively, but the spawning window is relatively brief, and feeding intensity picks back up quickly once nesting duties are complete.

Sitting at the Top of the Food Chain

Flathead catfish are apex predators in many of the rivers they inhabit, and isotopic analysis has put hard numbers on their position in the food web. In the Susquehanna River, researchers used stable isotope techniques to measure the trophic position of flatheads relative to other species. Flatheads occupied the highest trophic position in the food web, with a mean trophic position of about 3.1, exceeding both smallmouth bass and channel catfish, the two resident predators that dominated the system before flatheads arrived.⁹

This top position comes from a combination of factors: flatheads eat other predatory fish, they are large enough that almost nothing in the river preys on adults, and their diet skews heavily toward animal protein rather than plant matter or detritus. In the James River, diet studies similarly confirmed that flatheads function as apex predators.⁴ A 60-pound flathead sitting under a submerged log has essentially no natural predators in a river system. Only alligators, in southern rivers, and humans with rod and reel realistically threaten full-grown adults.

What Happens When Flatheads Invade New Rivers

Flathead catfish are native to the Mississippi, Missouri, and Ohio river basins and their tributaries across the central United States. Over the past several decades, they have been introduced, either deliberately or accidentally, into Atlantic coastal drainages where they never historically occurred. The consequences for native fish communities have been substantial, and understanding the flathead’s diet is central to understanding why.

In the Chesapeake Bay drainage, flatheads were introduced in the 1960s and 1970s and have since spread through the James and Potomac river systems.⁴ In the Susquehanna, they were first detected in 2002 and have built a rapidly growing population since.⁹ In North Carolina, they have colonized coastal rivers far from their native range.¹

The concern is straightforward: a large, gape-unlimited, nocturnal apex predator has been dropped into rivers whose native fish did not evolve alongside it. Researchers in North Carolina found that introduced flatheads fed randomly across available prey species, which initially sounds benign but is actually troubling. It means flatheads eat native species in proportion to their abundance, showing no avoidance of species that may already be struggling.¹ Rare native fish get no reprieve simply because they are uncommon; flatheads eat them whenever they encounter them.

The ripple effects go beyond direct predation. In the Susquehanna, the arrival of flatheads altered the feeding behavior of species already living there. Channel catfish, which occupy a broadly similar niche, showed a probable decline in trophic position at sites where flatheads were present compared to sites without them. The isotopic data showed that the food web’s overall structure shifted, with niche expansion and overlap across multiple species. Researchers interpreted this as support for what ecologists call trophic disruption: the introduction of a dominant predator forces resident species to change their diets to cope with new competition and predation pressure.⁹

In the Susquehanna specifically, flatheads consumed prey species of both recreational and conservation importance, including species like the margined madtom, a small native catfish that is already rare in much of its range.³ For fisheries managers in eastern states, the flathead catfish diet is not an academic curiosity. It is the mechanism through which an invasive species is reshaping entire river communities.

Choosing Bait Based on What Flatheads Actually Eat

The research on flathead catfish diets maps directly onto what anglers have known through experience for generations: flatheads overwhelmingly prefer live bait. Unlike channel catfish, which readily hit stink baits, dough baits, chicken liver, and other prepared offerings, flatheads are far more likely to eat something that is still moving. This tracks with the stomach-content studies showing live fish and crayfish as the dominant food items.

Live sunfish, particularly bluegill and other Lepomis species, are the most popular bait among dedicated flathead anglers, and the diet data explains why. Sunfish are common prey in virtually every river system where flatheads have been studied. Live shad, suckers, and creek chubs also work well and reflect the flathead’s willingness to eat whatever fish species is available. Crayfish, given their consistent presence in flathead stomachs across all size classes, are another proven bait, especially for fish on the smaller end.

The nocturnal feeding pattern also matters for bait presentation. Because flatheads rely on sensing movement and chemical cues in the water rather than sight, a lively bait that puts off vibration and scent in the water column is more effective than a dead one. Flathead specialists typically fish at night, set baits near heavy cover like log jams and undercut banks where flatheads spend the day, and use fresh, vigorous baitfish. Cut bait, which works perfectly well for channel cats and blue cats, is famously poor for flatheads. The science behind why is simply that flatheads evolved as predators of living prey and their sensory systems and behavior are tuned accordingly.

How Researchers Figure Out What Flatheads Eat

Studying the diet of a large, nocturnal, structure-dwelling catfish is not easy, and the methods researchers use shape what we know. The traditional approach is stomach content analysis: capturing fish and examining what is inside their stomachs. For flatheads, this can be done through gastric lavage, which pumps water into the stomach to flush out contents, or through pulsed gastric lavage and stomach tubes. A comparison of these methods found that pulsed gastric lavage recovered about 96% of stomach contents by weight, while stomach tubes recovered about 87%, with no significant difference between the two.¹⁰ Both methods allow the fish to be released alive, which matters for studying populations that managers may want to conserve or control.

Stomach content analysis tells you exactly what a fish ate recently, but it has limitations. Soft-bodied prey get digested quickly and may be underrepresented, while hard parts like crayfish shells persist longer and can be overrepresented. Fish that were captured may have regurgitated food during handling. And a single stomach snapshot does not capture long-term dietary patterns.

Stable isotope analysis offers a complementary view. By measuring the ratios of carbon, nitrogen, and sometimes sulfur isotopes in a fish’s muscle tissue, researchers can infer what a flathead has been eating over weeks to months rather than just the last meal. This technique was used in studies of both the Susquehanna River and coastal river systems to understand broader dietary patterns and trophic position.¹¹ The isotopic approach confirmed what stomach contents suggested: flatheads sit at the top of riverine food webs and consume primarily animal prey. In coastal rivers, isotopic signatures have even revealed that some flatheads incorporate marine-derived nutrients, likely by eating prey fish that move between freshwater and saltwater environments.

The combination of these methods has given biologists a fairly complete picture of flathead catfish feeding. Decades of research across river systems from the Mississippi to the mid-Atlantic coast tell a consistent story of a powerful, opportunistic, live-prey specialist that occupies the apex of whatever food web it enters.¹²

1
Transactions of the American Fisheries Society. Diet Selectivity of Introduced Flathead Catfish in Coastal Rivers
2
Transactions of the American Fisheries Society. Feeding habits and ecological implications of the invasive Flathead Catfish in the Susquehanna River basin, Pennsylvania
3
Transactions of the American Fisheries Society. Feeding habits and ecological implications of the invasive Flathead Catfish in the Susquehanna River basin, Pennsylvania
4
Journal of Fish and Wildlife Management. Growth and Mortality of Invasive Flathead Catfish in the Tidal James River, Virginia
5
North American Journal of Fisheries Management. Gape: Body Size Relationship of Flathead Catfish
6
The American Midland Naturalist. Summer Diel Activity and Movement Paths of Flathead Catfish (Pylodictis olivaris) in Two Missouri Streams
7
PubMed Central. Tracking wakes: the nocturnal predatory strategy of piscivorous catfish
8
Transactions of the American Fisheries Society. Feeding habits and ecological implications of the invasive Flathead Catfish in the Susquehanna River basin, Pennsylvania – Section: Conclusion
9
PubMed Central. Invasive predatory fish occupies highest trophic position leading to expansion of isotopic niches in a riverine food web
10
North American Journal of Fisheries Management. Evaluation of Stomach Tubes and Gastric Lavage for Sampling Diets from Blue Catfish and Flathead Catfish
11
Marine and Coastal Fisheries. Specialized Feeding Patterns and Marine Resource Use by Nonnative Catfished in a Coastal River Ecosystem Revealed by Dietary and Stable Isotopic Analyses
12
North American Journal of Fisheries Management. Two Decades of Advancement in Flathead Catfish Research