July 19, 2021
By Cory Schmidt
Dog-day muggy in the middle of September. A damp, breathless swelter incites anger in the biting flies. The sun roasts your neck, while the boat floor burns like a wok. Through it all, the river’s flow conceals a quiet, primal pulse fueled by the incandescent orb above—a force that energizes metabolic machines known as catfish.
For its relatively small size, the Red River of the North has legions of enormous channel catfish. After boating the fifth 20-pounder inside an hour, you find yourself pondering how this river can contain such a mass of life; how it breeds enough food to sate the glutinous appetites of its apex predator; and that a single small brushpile can conceivably hold a dozen or more big fish. You get the feeling each time your bait lands, the rod will lurch and load.
Cutting another round of bait, Captain Brad Durick doesn’t seem surprised when your prophesy comes true. “I guess the drive-through window is open,” Durick says, wrenching the bent rod from its holder for the umpteenth time.
“That’s what happens when a few days of hot weather interrupt the cooling waters of fall,” says the busiest guide on the U.S. side of the Red River of the North. He’s an analytical catman and meticulous keeper of catch records. For over a decade, he’s logged daily data such as water temperature, barometric pressure, depth, and other factors for each catfish that enters his boat. Several years ago, he published Cracking the Channel Catfish Code, an intriguing glimpse into climatic, aquatic, and metabolic factors affecting success of catfish anglers. His observations have uncovered intriguing micro seasons—short periods of intense feeding occurring within traditional In-Fisherman Calendar Periods.
Metabolism and Monkey Wrenches
“Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life,” Durick says. “These processes allow organisms to grow and reproduce, and help dictate the way they respond to their environment. We’ve known for a long time that the world of catfish is driven by water temperature. Because fish are cold-blooded, their bodies have no choice but to respond to their surroundings. When water warms, fish need to eat more because their bodies are working harder to stay alive. The opposite is true when water temperature is cooling or cold.”
Much of the data on catfish feeding and metabolism come from commercial catfish farmers, he explains. The studies show that in captivity, when water is 50°F to 53°F, a catfish can survive by consuming just one percent of its body weight once per week.
He believes the “real feeding” begins when water temps reach 53°F and rise to around 70°F. “This phase of fast-rising water temperature corresponds with the prespawn bite. Catfish metabolism rises with temperature.”
According to data from catfish farmers, channel cats in the low-50°F range require one percent of their body weight as food three times per week. When it reaches 70°F, Durick says catfish in captivity need to eat the equivalent of at least 3 percent of their body weight each day, for survival and maximum growth. “That’s 7 times the amount of food required per week compared to when water is below 50°F,” he says.
While metabolism and feeding data from catfish raised in commercial ponds closely follow those of fish living in public lakes and reservoirs, rivers offer other challenges. Navigating river current alone is enough of an energy drain to elevate the food needs of catfish. Durick cites a study published in the Canadian Journal of Fisheries and Aquatic Sciences by David J. Rowan and Joseph B. Rasmussen, who found wild river fish require nearly double the food (roughly 5 pounds of food per pound of catfish per year) required by those living in captive ponds.
“A 10-pound river channel cat, on average, requires about 50 pounds of food per year to achieve maximum growth, recuperate from the spawn, and maintain ample energy to fight current and hunt for prey,” Durick says.
Caveats such as differing water temperatures by latitude and oxygen levels also affect the food needs of catfish. One U.S. Fish and Wildlife Service study by Thomas E. McMahon and James W. Terrell revealed the optimal temperature ranges of adult channel catfish. The ideal range for growth occurred between 78°F and 84°F. The study reported “poor” channel catfish growth at 69°F and below, with growth ceasing below 64°F.
The same study found that oxygen levels of 7 mg/liter (parts per million) and higher are optimal for channel cat survival. Feeding is reduced when dissolved oxygen falls below 5 mg/l, while growth is severely hindered at 3 mg/l. As you’d expect, rarely does oxygen in most rivers drop below 5 mg/l, although it can happen when low water and reduced current coincide with high summer water temperatures. Portions of July and August on gauging stations along the Red River, for example, often see oxygen dropping below 6 mg/l and into the 5 mg/l range.
Could it be that slowing mid- to late-summer bites are due in part to stressed catfish languishing in low oxygen water? Certainly, postspawn recuperation, which also extends into early July in northern latitudes, can play a role in negating the normally positive effects of an increasing need for food.
“In summer 2012, the river was low and hot and the USGS gauging station at Grand Forks (North Dakota) showed dissolved oxygen levels down near 5 mg/l for an extended number of days,” Durick says. “The bite was slow, prompting me to speculate about the negative impact of low oxygen, even at a time when catfish metabolism should be high with high water temps, well after the postspawn slump.”
Peak Feeding Windows
Durick’s catch data show a connection between rising water temperature, metabolism, and fishing success. His most productive and consistent fishing occurs during prolonged periods of gradually warming water. “Beginning around May 1 each year, when water temps hit 50°F, fishing can be off the charts,” he says. “The bite’s typically on fire during those years when we hover between or slide gradually from 55°F to 65°F.
“Something similar happens in the dog days, following postspawn. The key is getting water temps up around 78°F to 80°F and holding steady. Catfish become predictable at this time, with no big movement patterns. If you’ve got good, consistent flow, that 80°F mark can put a lot fish into small areas, such as small shallow snags. With enough flow, we’ve often caught over a dozen big fish from a single tiny snag lying in 2 feet of water. It’s like the fish get in line behind the snag and wait for their turn to eat. When you hook a 20-pounder that shallow the water explodes in all directions.”
When current slows during this same late-summer phase, he often finds lots of fish packed into small areas of concentrated current, without cover. “With no current, there’s nothing telling the fish they have to get behind cover,” he says. “These low-flow conditions tell me to start looking for subtle or not-so-subtle current seams, places where two currents come together. Dam tailraces are obvious spots, too, but they often produce mostly small cats due to constant fishing pressure.
“One of the best spots I found last August formed a visible V in the water. The spot wasn’t on a river bend, but within a straightaway adjacent to a sharp cutbank. So, you never know where these little fast-water seams show up. We stayed and caught fish from that spot for several days, including big ones. Turned out, a friend fishing well upstream had discovered the same pattern at the same time. We were the only two boats catching fish on a long stretch of river.”
While stable flows and slowly rising water temps spur feeding, Durick says that rapidly declining water temperature—whether from a cold front or an influx of cool rainwater—can kill a consistent bite. His multi-year records also reveal that some of his poorest fishing occurs when water temperatures rise extraordinarily fast. Both conditions likely parallel major changes in barometric pressure, too—one more factor bearing on metabolism and a catfish’s desire to feed from day to day.
“I think there’s a shock factor involved with the fish when temp rises 10 to 12 degrees within a week or so,” he says. “We were on a terrific bite through most of last May, until the weather turned hot. Later, I checked the USGS site and noted that between May 22 and June 1, water temps had increased from 61°F to almost 76°F. The cats had moved from fast to slow current and appeared to feed less. We stayed on the fish, but had to sit on them longer and work harder for fewer fish.”
In August 2018, a strong cold front dropped water temperature at least 5 degrees within two days, producing a similar movement of catfish off current and a tougher bite. But as water temperature began to gradually rise again, catch rates picked up. “We worked our tails off to boat 12 fish as water temps hit their low point of 73°F on August 2,” he says. “But as the water gradually warmed back up to the upper 70s, subsequent days yielded 14 cats, then 22 to 32 fish per day up to August 10.”
Among all peak phases for catching catfish on a metabolic feeding spree, Durick reminds me of an outstanding early fall bite we shared several years ago. “As the water gradually cools in fall, you get occasional warming trends, usually in September, that can move the needle in the other direction,” he says. “As water temperatures fall and metabolism slows, fish require slightly less food. But when you get these minor warm-ups over several days, bites can take off accordingly.”
By September 9, 2018, for example, early fall water temps had dropped to 66°F. But a warming trend through September 17 pushed temps back close to 70°F, before a major cold front chilled the water into the low 60s by the 21st of the month. During the week-long warm-up, however, catfish bit aggressively, with lots of fish feeding in shallow snags associated with moving water.
I’ve observed a divergent trend with coolwater species such as walleyes and pike. While unseasonable fall warming trends seem to spur excellent fishing for warmwater species like bass and catfish, the same trend often produces poor fishing for species with cooler water preferences.
Although Durick wraps up his guiding season around October 1—around the time water temps drop to the low 50s—he often “fun fishes” for cats in deep holes. “We find fish with electronics and fish for them with walleye gear,” he says. “Lower a jig and minnow or a small strip of cutbait and keep it there, and you can still catch plenty of cats. The bites, however, don’t feel anything like the aggressive pull of a catfish. Usually, you just feel a subtle tick, just like a walleye.”
Late fall into winter patterns for channel cats have been well documented, with masses of fish migrating to deep bend holes in rivers and 30- to 50-foot basin areas in lakes and reservoirs. That the fish can still be caught is largely a function of abundance and opportunity. Put a lure or a piece of meat in front of enough fish and eventually one bites.
Metabolic Theory of Ecology
Durick notes that by November, channel catfish have already consumed close to 100 percent of their yearly requirements for food. While that might be true of catfish in the North, fish in Ohio, Texas, or Florida might still be feeding consistently, perhaps even continuing to grow.
Latitude, water temperature, and metabolism, Durick believes, may also reveal part of the reason channel catfish in the North often grow larger than their southern counterparts. “To satisfy their increased metabolic needs (due to warmer water and longer growing season), southern fish must eat more food,” he says. “I believe northern fish live longer, in part because they have a shorter growing season and an extended period of dormancy. Perhaps catfish (and all fish) have a limited ‘metabolic life expectancy.’ A northern fish exhausts its metabolic reserves slower than southern fish, whose metabolism must work longer. This, to me, explains why northern channel cats often live longer and grow larger, so long as ample food is available.”
Supporting Durick’s viewpoint, In-Fisherman Managing Editor Dr. Rob Neumann conducted research on northern pike for his doctoral dissertation. His study results suggested that a similar north-south phenomenon caused pike to manifest what’s been called ‘physiological burnout.’”
“Latitudinal gradients, in part, determine fish growth rates,” he says. “I found that pike in the southern waters I studied grew fast and died young, compared to northern waters where pike are longer lived, and on average attain larger sizes, such as in the Far North. In the waters I studied, when water temps reached near lethal levels in summer, pike stopped growing. And most of their growth occurred during coolwater periods, including some growth in winter.
“There’s been quite a bit written and debated about the metabolic theory of ecology (MTE),” Neumann says. “We’ve speculated that metabolism and lifespan (and sometimes physical size) are related to temperature in cold-blooded animals. Like anything in science, exceptions always exist. One study that compared growth rates of channel catfish didn’t find significant differences in growth rates north to south. Perhaps in the Red River catfish grow large because food is so abundant or they have greater longevity or there are other genetic reasons.”
Or, perhaps the Red truly is an outlier. As Durick says, “Southern channel cats have to fight for real estate and top-dog status with bigger, meaner predators, like flathead and blue catfish. Not to mention navigate around trotlines, limblines, juglines, and the nets of commercial fishermen. Given those landmines, I’d choose to live large and long in the Red River, too.”
*In-Fisherman Field Editor Cory Schmidt is a multispecies angler, long-time catman, and contributor to all In-Fisherman publications.