The wobbling pull of the big crankbait stalls suddenly, and as the angler raises his rod, there’s a strong thumping pull 20 yards out and 18 feet down. After several runs, the bass approaches the boat and the angler loosens the drag to avoid pulling out hooks. After leading the fish around the boat carefully, his partner nets the 6-pounder. High fives all around and the anglers decide to weigh the lunker. A few photos are in order. And because the lake is managed with a 22-inch length limit, the measuring board is dug out. Then back she goes, with the anglers in a celebratory mood. But the fish is not feeling as well. It may be days until her metabolism returns to normal, and if her stress response is extended, a deadly disease may attack since her immune system has been suppressed.

Protected slot limits and other length limits are management tools essential to the future of bass fishing in most regions. At In-Fisherman, we’ve long championed selective harvest. But such regulations or decisions to voluntarily release fish only work if released fish survive and prosper. Dr. Bruce Tufts, Professor of Biology at Ontario’s Queens University and an expert on the physiology of catch and release, has pried and probed into the bodily functions and processes of fish and has carefully monitored how they react when we hook, fight, photograph, and set them free. In-Fisherman Field Editor Gord Pyzer, a fishery biologist himself, sat down with Tufts to review his key results.

“To maintain high-quality fisheries,” Tufts says, “we have to be selective of the fish we keep. In some waters, we’re already catching the same fish several times a year. A released fish must be able to quickly return to normal behavior—feeding and avoiding predators. Also, seriously stressed fish are more susceptible to disease.”

Tufts and his colleagues have made major discoveries involving catch-and-release angling in recent years. What they’ve observed bodes well for the future, but only if anglers heed the information and practice careful catch and release.

Counting Casualties

“In the early days,” Tufts explains, “information about catch and release came from studies that simply counted dead fish after they were caught, handled, and released under various conditions. Though limited in scope, these studies demonstrated to many skeptical anglers and some fishery managers that most bass and other species survive when released. But much biological information was missing.

“As with humans, fish can be in pretty rough shape, but still be alive. Today, we have considerably more information, obtained through physiological studies, to determine what goes on inside a fish when it’s caught and released. We’ve monitored many physiological variables and assembled a picture that tells us the condition of the fish after a disturbance like being caught.

“When a medical doctor needs to diagnose a disease,” Tufts explains, “he first takes a blood sample and analyzes it. In the hospital, an intravenous cannula is implanted in your arm to take samples anytime. We do the same with fish, surgically implanting tubes in blood vessels to determine how the fish is doing.

“We may also surgically implant tiny transmitters to monitor heart rate and muscle contractions. Sometimes we need to obtain physiological information from other tissues, which involves terminal sampling after the fish has been killed with anesthetic. We often use a combination of strategies to get a complete picture of the physiological response to angling under certain conditions. We keep conditions constant except for one particular factor, such as angling time, fish size, or water temperature.”

Fight Or Flight

Tufts says the first things that happen inside a fish when we hook it are similar to what takes place inside us when we realize we’ve hooked it. The initial physiological changes involve what he calls a “hormonal axis” commonly known as the “flight or fight response.”

Once this has been triggered, he says, the body releases large quantities of the hormones adrenaline and noradrenaline. These hormones then trigger secondary responses—increased heart rate and blood flow to the working muscles and a decrease in flow to nonessential areas like the gut. This improve a fish’s ability to flee or fight.

“That shot of adrenaline increases blood flow to the gills,” Tufts continues, “so all the respiratory structures of the gills, the secondary lamellae, become involved in gas exchange. At rest, only about half of these respiratory structures receive blood. The increase in adrenaline levels also stimulates the release of extra red blood cells from the spleen into the circulation. This, too, improves the transport of oxygen.”

Thus, many of the most important physiological adjustments a fish makes are intended to ensure that it receives an adequate supply of oxygen when it’s hooked. Important metabolic changes also take place in the fish’s muscles. “To make long runs and jumps on the end of your line,” Tufts reports, “fish rely on energy reserves in their white muscle tissue, primarily phosphocreatine, adenosine triphosphate, and glycogen. These compounds can be mobilized quickly, even in the absence of oxygen. We call them anaerobic energy stores for this reason. Once these reserves are depleted, however, the fish no longer can jump or struggle, and it appears worn out.

“Consumption of anaerobic energy reserves also increases the levels of some important metabolic end products in the fish’s muscles, such as lactic acid. The hydrogen ions that result from the production of lactic acid can have important negative consequences in the fish.”

After a fish is released, it has several ways of dealing with the build-up of harmful by-products resulting from the vigorous exercise. Research shows that it takes anywhere from a few hours to a full day for a fish to reduce the levels of lactate and protons and to restore muscle energy reserves.

In extreme cases, some bass may not be able to recover from the stress of being caught. They typically die several hours into the recovery phase. This is the early phase of “delayed mortality” anglers often hear about but rarely witness unless they visit harbors routinely used for tournaments. When Tufts observed it during his research, he said the fish often appeared normal when released.

“Fortunately,” Tufts notes, “this delayed mortality syndrome is probably more prevalent in experimental studies, where fish are also experiencing other stresses, such as surgery and confinement for observation, than it is on the lake.”

Are Some Fish Tougher Than Others?

Researchers in this field have concluded that the same physiological processes occur in all fish species, but specifics vary among species. Different fish have varying amounts of muscle energy reserves that are depleted during angling. Levels of muscle energy reserves typically match the lifestyle of a species. Steelhead and salmon, for example, whose lifestyle requires them to leap tall waterfalls and power through rapids during long migrations, have higher levels of muscle energy reserves than more sedentary species like bass, walleyes, and crappies.

“These differences provide a physiological basis for what anglers observe—some fish fight harder than others. Other factors are involved, including the shape and size of the fish, but species differences in muscle energy reserves largely explain why some fish fight harder and longer than others.”

Other factors affect the way a fish responds physiologically to being hooked, fought, landed, and released. “Many studies have shown that the time it takes to land a fish can have important consequences to a fish’s health and survival,” Tufts says.

“A few years ago, we conducted a study that showed that angling time can be a critical issue for nesting bass caught in spring. We found that male bass landed in just 20 seconds quickly returned to their nests. Exhausted bass (fought for 2 minutes or more) took much longer to resume guarding the bed. Moreover, nests of the exhausted bass experienced much higher levels of predation.”

Ego Kills

It’s ironic that many anglers practice catch and release, but only do it properly with bass that easily can shake off the effects of the event—the little ones. They’re released without fanfare. But when they catch a big bass, out comes the net, then long admiring glances, photos, and perhaps a ride in the livewell.

“From a conservation standpoint, big fish are extremely valuable. They’re the best spawners and the ones we should be releasing. Unfortunately, big bass are most damaged by catch and release. They’re battled longer and held out of water longer. This contributes to a greater physiological disturbance.

“We’ve found that the buildup of lactic acid in the muscles of big fish can be almost twice that found in smaller individuals following the same amount of burst exercise. Although much of the research in this area has been conducted on trout and salmon, similar physiological changes could affect big bass, muskies, and walleyes.”

Deadly Effects Of Warm Water

Water temperature also affects the physiological disturbance of fish. Tufts notes that most anglers know that warm water can make catching fish more difficult, but they fail to realize the effects of warm water on fish after they’re hooked.

“Water temperature increases the severity of the physiological disturbance in the blood of a caught fish,” Tufts says. “In species most sensitive to temperature increases, the ability to tolerate angling, handling, and confinement in livewells declines markedly as water warms.

“When water temperatures rise in summer, fish are more fragile and become more susceptible to delayed mortality following catch and release. Holding fish in livewells under these conditions exacerbates the problem. In extremely warm water, anglers should be careful not to fight fish to exhaustion. And they should release fish immediately.”

Help . . . I Can’t Breath

Needlessly exposing fish to air is the final factor that anglers need to consider, and it’s one over which they have full control. Many of the physiological responses initiated in a fish when you hook it are designed to facilitate the transport of oxygen.

“When you remove a fish from the water, however, the delicate secondary lamellae in the gills collapse, inhibiting gas exchange. This can be serious in a fish fought to near exhaustion.”

Consider the consequences of holding your own breath under different conditions. When you’re resting, it’s not a problem to stick your head under water and hold your breath for a short time. It’s another story, however, after you just ran a 100-yard dash. From a bass’ point of view, the consequences of hindering gas exchange after exercise can be devastating. The longer you hold the fish out of water the greater the physiological disturbance.

Experts agree that fish handling is one important hurdle we must pass to ensure healthy fisheries in the future. The old adage says that you must think like fish in order to catch them. Another angle is that to safely release fish, you must understand the basics of their physiology. n

*Dr. Bruce Tufts is Professor of Biology at Queen’s University, Kingston, Ontario. He has worked on the physiology of catch and release since the late 1980s and has published many scientific papers on this topic.

In-Fisherman Field Editor Gord Pyzer has a Masters degree in Resource Management. He was a senior manager with the Ontario Ministry of Natural Resources for almost 30 years.