Catch-and-release fishing causes measurable physical harm and physiological stress to fish, though whether fish experience that harm as conscious pain remains one of the most contested questions in animal biology. What is not contested is the physical reality: a hook pierces tissue, a fish fights to exhaustion, stress hormones surge, gills collapse when exposed to air, and the animal returns to its environment in a compromised state. How much lasting damage all of this causes depends on a web of variables, from water temperature and hook placement to how long the fish spends out of the water. The science here is richer and more specific than most anglers realize.
Can Fish Actually Feel Pain?
This question has been debated by researchers for over two decades, and the answer depends partly on what you mean by “pain.” Fish have the biological hardware for detecting harmful stimuli. Rainbow trout, for example, possess specialized nerve receptors called nociceptors on their heads and faces that respond to mechanical pressure, dangerously high temperatures, and irritating chemicals like acetic acid, with properties similar to the pain-detecting receptors found in mammals.1PubMed Central. Do fishes have nociceptors? Evidence for the evolution of a vertebrate sensory system The nerve fibers that carry these signals (A-delta and C fibers, the same types involved in sharp and dull pain in humans) have been confirmed in trout through both anatomical and electrical-activity analysis.2PubMed. Anatomical and electrophysiological analysis of the trigeminal nerve in a teleost fish, Oncorhynchus mykiss
Fish also display behavioral responses that go beyond simple reflexes. When exposed to harmful stimuli, they show changes in normal activity patterns, reduced feeding, increased breathing rate, and rocking behavior, all of which are considered indicators of distress in other animals.3ILAR Journal. Pain Perception in Fish: Indicators and Endpoints Some researchers argue that if the definition of pain in animals cannot require direct measurement of subjective experience (since we can never truly ask an animal how it feels), then fish meet the working criteria for pain perception.
Not everyone agrees. A prominent counter-argument holds that fish lack the neocortical brain structures thought to generate conscious experience in mammals, and that their responses to noxious stimuli are essentially reflexive rather than felt.4PubMed Central. Fish do not feel pain and its implications for understanding phenomenal consciousness This camp points out that humans tend to project their own experience of pain onto animals that react to harmful stimuli, which may or may not be justified. The debate remains unresolved, but the trend in the scientific literature has moved increasingly toward acknowledging that fish pain perception is plausible enough to take seriously from both a welfare and a management perspective.
What Happens Inside a Fish During Catch and Release
Regardless of the pain question, the physiological stress response to being caught is well documented and unambiguous. When a fish is hooked and fights against a line, its body floods with cortisol (a stress hormone) and lactate (a byproduct of anaerobic exertion, the same compound that makes your muscles burn during intense exercise). In rainbow trout caught from wild populations, cortisol levels rise significantly within an hour of capture and can stay elevated for up to 24 hours, even after the fish is back in the water.5Journal of Fish Biology. Effects of capture and recovery on plasma levels of cortisol, lactate and gonadal steroids in a natural population of rainbow trout Lactate levels climb faster, often within minutes of capture, but tend to return to normal sooner. The same study also found that reproductive hormones were depressed a full day after capture, hinting at costs that extend beyond immediate stress.
How fish handle this stress varies by species. Research on winter ice-angling found that bluegill had cortisol concentrations about 58% higher than yellow perch under the same conditions, and bluegill also showed substantially greater impairment of basic reflexes like equilibrium and tail-grab response.6PubMed Central. Chill out: physiological responses to winter ice-angling in two temperate freshwater fishes Reflex impairment scores did decline over the following hours, meaning recovery was happening, but the variation between species underscores that generalizing from one fish to another is risky. A bass is not a trout is not a bonefish when it comes to resilience.
Where the Hook Lands Changes Everything
The single biggest factor determining whether a released fish lives or dies is where the hook ends up. This is not a small difference. In a study of spring chinook salmon, jaw-hooked fish had a mortality rate of just 2.3%, while gill-hooked fish died at a rate of 81.6% and esophagus- or stomach-hooked fish died at 67.3%.7North American Journal of Fisheries Management. Hooking Mortality by Anatomical Location and Its Use in Estimating Mortality of Spring Chinook Salmon Caught and Released in a River Sport Fishery The good news is that the vast majority of fish in that fishery (about 82%) were hooked in the jaw. But for the unlucky ones hooked deeper, the prognosis was grim.
Hook type makes a real difference here. Circle hooks, which are designed to rotate and catch in the corner of the jaw rather than lodging in soft throat tissue, generally reduce the rate of deep hooking compared to traditional J-style hooks. One study on red drum found the lowest deep-hooking rate (just 4%) when using large circle hooks on short leaders with fixed weights.8Fisheries Research. Large circle hooks and short leaders with fixed weights reduce incidence of deep hooking in angled adult red drum For species like tuna, billfish, and striped bass, circle hooks drastically cut injury and mortality while maintaining capture efficiency.9Aquatic Conservation: Marine and Freshwater Ecosystems. Are circle hooks an effective tool for conserving marine and freshwater recreational catch‐and‐release fisheries?
The story is not universally positive, though. In bluegill, circle hooks actually caused more severe injury than some other hook types, and for largemouth bass, they offered minimal conservation benefit while reducing capture efficiency.9Aquatic Conservation: Marine and Freshwater Ecosystems. Are circle hooks an effective tool for conserving marine and freshwater recreational catch‐and‐release fisheries? Research on bluegill specifically showed that J-hooks increased the odds of deep hooking relative to circle hooks, but they also increased capture success, so the tradeoff is real.10Fisheries Research. Influence of angler hook-set behaviour relative to hook type on capture success and incidences of deep hooking and injury in a teleost fish Bait type compounds the problem. Walleyes caught on artificial lures are typically hooked in the lips, while those caught on live bait like leeches tend to swallow the hook deeper into the throat and gut.11North American Journal of Fisheries Management. Hooking Mortality of Walleyes Caught on Live and Artificial Baits This makes intuitive sense: a fish takes longer to work on live bait, giving it time to swallow, while a hard strike on a lure tends to set the hook early in the lip.
The Danger of Air Exposure
Every second a fish spends out of the water matters. Air exposure causes the delicate gill filaments, which are designed to float freely in water, to collapse against each other. This both starves the fish of oxygen and physically damages the gill tissue, and the harm scales directly with how long the fish is held out of the water.12Fisheries. Fish Out of Water: How Much Air is Too Much? The phrase “keep ’em wet” has become a mantra in catch-and-release fishing circles for good reason. Even brief air exposure of 30 seconds or more begins to register in stress and injury metrics, and longer exposures compound the problem. Photographing a trophy catch may feel like it only takes a moment, but for a fish already depleted from fighting, those seconds are consequential.
Water Temperature and Mortality
Warm water holds less dissolved oxygen and drives up a fish’s metabolic rate, creating a double bind: the fish needs more oxygen to recover but has less of it available. The result is dramatically higher mortality when catch and release happens in warm conditions. A study on muskellunge found that at water temperatures below 25°C, catch-and-release mortality was about 10%. Above 25°C, it jumped to over 43%.13Transactions of the American Fisheries Society. Evaluating Muskellunge catch‐and‐release mortality at elevated summer water temperature The relationship was steep and nonlinear: modeled mortality rose from under 1% at 22°C to about 38% at 30°C when handling time was held constant.
Salmonids show a similar pattern, though their thresholds differ. Rainbow trout mortality peaked at 16% in one river and 9% in another when daily maximum temperatures reached 23°C or above. Brown trout were hardier, staying below 5% mortality across all temperature ranges. Mountain whitefish were the most vulnerable, with mortality hitting 28% in the hottest conditions. At temperatures below 20°C, no mortality was recorded for any of these species.14North American Journal of Fisheries Management. Effects of Catch‐and‐Release Angling on Salmonids at Elevated Water Temperatures The practical takeaway is simple: fishing during the hottest part of summer, especially for coldwater species, carries a significantly higher risk of killing the fish you intended to release. Some jurisdictions now implement hoot-owl restrictions, closing fishing during the warmest hours of the day for exactly this reason.
Barotrauma in Deep-Water Fish
Fish caught from depth face an additional hazard that surface-dwelling species do not. Species with closed swim bladders, like many rockfish, cannot rapidly vent expanding gas as they are hauled upward. The result is barotrauma: the swim bladder over-inflates, sometimes pushing the stomach out through the mouth, and the fish arrives at the surface bloated, unable to swim back down, and with potential internal organ damage.15Canadian Journal of Fisheries and Aquatic Sciences. Sink today, swim tomorrow: barotrauma symptoms and effectiveness of descending Pacific rockfishes
Two main approaches have been tried to help these fish: venting (puncturing the swim bladder with a hollow needle to release gas) and descending (using a weighted device to send the fish back down to depth where the gas recompresses). A review of 76 published comparisons across dozens of species found that both methods improved survival compared to simple surface release, but neither was clearly superior to the other, and the positive effects were often modest.16North American Journal of Fisheries Management. Venting and Descending Provide Equivocal Benefits for Catch-and-Release Survival: Study Design Influences Effectiveness More than Barotrauma Relief Method Descending devices are now legally required in some jurisdictions for releasing rockfish, but research has documented challenges including fish resurfacing after being sent down and inaccurate release depths.15Canadian Journal of Fisheries and Aquatic Sciences. Sink today, swim tomorrow: barotrauma symptoms and effectiveness of descending Pacific rockfishes For deep-water species, catch and release is inherently more harmful than for shallow-water fish, and there is no perfect fix.
Predation After Release
A fish does not have to die from the hook or the handling to die from being caught. Released fish are often exhausted, disoriented, and swimming erratically, which makes them easy targets. In a study of bonefish in the Bahamas, 17% of angled fish were eaten by lemon sharks or great barracuda after release, compared to only 5% of fish captured by net (which causes far less exhaustion). Bonefish that had lost their equilibrium at the time of release were six times more likely to be eaten than those that swam away upright.17Journal of Experimental Marine Biology and Ecology. Effects of recreational angling on the post-release behavior and predation of bonefish (Albula vulpes): The role of equilibrium status at the time of release
Research on fish captured from different depths tells a similar story. Fish brought up from 40 or 60 meters showed significantly greater impairment in their ability to evade a simulated predator compared to fish caught from the surface.18ICES Journal of Marine Science. Sublethal effects of catch-and-release fishing: measuring capture stress, fish impairment, and predation risk using a condition index Post-release predation is an underappreciated source of mortality because it does not show up in studies that track whether a released fish swims away. It swims away, then gets eaten five minutes later. This is especially relevant in environments with high predator densities, like tropical flats or reefs.
Nets, Handling, and Skin Damage
How you handle a fish during unhooking and release matters nearly as much as what happens during the fight. Fish skin is covered in a mucous layer that serves as a barrier against infection and parasites, and that layer is surprisingly fragile. Landing nets, while convenient, strip mucous and scales on contact. A controlled study found that just 30 seconds in a landing net produced measurable increases in fin abrasion, scale loss, and mucous disruption. Mortality rates for netted fish ranged from 4% to 14% over the following week, while no hand-landed control fish died.19Fisheries Research. Effects of landing net mesh type on injury and mortality in a freshwater recreational fishery Fish that died typically showed impaired swimming for about a day before death and developed fungal infections on abraded areas, particularly near the tail. Among net types, knotted mesh was the most damaging, while rubber and knotless mesh caused less injury but still more than bare-hand landing.
Reproductive Costs of Being Caught During Spawning
Catch and release during the spawning season introduces an entirely different category of harm. Many freshwater species, including bass, guard their nests aggressively after spawning. When a nesting male is caught, even briefly, the nest is left undefended. Research on smallmouth bass found that after being caught and released, males were less willing or less able to defend their broods from predators, and the combination of angling stress plus brood predation produced substantially higher rates of nest abandonment.20Transactions of the American Fisheries Society. The Effect of Catch‐and‐Release Angling on the Parental Care Behavior of Male Smallmouth Bass Separate work confirmed that preseason angling pressure on nesting male black bass was sufficient to reduce fry production in some waters.21North American Journal of Fisheries Management. The Impact of Catch-and-Release Angling on the Reproductive Success of Smallmouth Bass and Largemouth Bass The fish survives the release, but a generation of offspring may not. This is one reason many jurisdictions impose closed seasons during spawning periods.
Do Fish Learn to Avoid Hooks?
One of the more surprising findings in this field is that fish learn from being caught, and they learn fast. Common carp that were hooked once became roughly 57% less likely to be caught again just two hours later. Even more striking, carp that merely witnessed a tankmate being hooked (without being caught themselves) showed an almost identical reduction in vulnerability.22Transactions of the American Fisheries Society. Hook Avoidance Induced by Private and Social Learning in Common Carp This social learning component means that the behavioral effects of catch and release ripple beyond the individual fish.
Juvenile red sea bream learned to avoid angling gear after being caught just once or twice, distinguishing between food attached to a fishing line (avoided) and the same food presented without a line (eaten freely). About half of the fish retained this learned avoidance for at least two months.23Journal of Experimental Biology. Angling gear avoidance learning in juvenile red sea bream: evidence from individual-based experiments This has implications beyond animal welfare. If heavily fished populations become progressively harder to catch, fishery-dependent stock assessments can underestimate population size because the remaining fish are not biting, not because they are not there.
The Longer View on Growth, Survival, and Evolution
When a fish is hooked in a non-critical location and released properly, the evidence for lasting physical damage is surprisingly thin. A study tracking rainbow trout found no differences in growth (length or weight gained) between fish that had been caught and released and those that had not been caught at all over a one-month period, as long as hooking was in the mouth.24Fisheries Management and Ecology. Effect of catch‐and‐release angling on growth and survival of rainbow trout, Oncorhynchus mykiss Fight duration itself appears to be a relatively minor stressor for some species. Research on largemouth bass found that fight intensity was not a major driver of physiological stress, likely because fights with typical angling gear last less than two minutes.25Conservation Physiology. The influence of water temperature and accelerometer-determined fight intensity on physiological stress and reflex impairment of angled largemouth bass
At the population level, though, the picture gets more complex. Heavy fishing pressure, even with full release, can exert evolutionary selection on fish populations. Traits like metabolic rate, swimming performance, stress responsiveness, and even visual acuity all influence how vulnerable a fish is to being caught. Over generations, sustained catch-and-release pressure could shift these traits within a population, potentially producing fish that are less active, less aggressive, or otherwise physiologically different from their ancestors.26PubMed Central. A physiological perspective on fisheries-induced evolution This kind of fisheries-induced evolution is still poorly understood, but the theoretical concern is real: we may be inadvertently breeding the boldness and vigor out of popular sport fish.
How Different Countries Handle the Ethics
The question of whether catch and release causes unacceptable harm is not just scientific but regulatory, and different countries have landed in very different places. In Germany and Switzerland, acceptance that fish are sentient and can suffer has led to strict constraints. Competitive fishing, put-and-take stocking, and the use of live baitfish have all been severely restricted or banned in some areas. In several German federal states, voluntarily releasing a legal-sized fish is actually illegal. The reasoning is that catch-and-release fishing causes suffering to the fish, and the recreational benefit to the angler does not outweigh that suffering.27ICES Journal of Marine Science. Welfare of aquatic animals: where things are, where they are going, and what it means for research, aquaculture, recreational angling, and commercial fishing The contrast here is revealing: mandatory release for conservation purposes (undersized fish, protected species) is considered acceptable because the conservation benefit justifies the harm. But releasing a fish you are legally allowed to keep, purely for sport, is not.
In North America and much of the English-speaking world, the ethical calculus tilts the other direction. Catch and release is widely encouraged, sometimes mandated, as a conservation tool to maintain fish populations under heavy recreational pressure. The emphasis is on minimizing harm through best practices rather than prohibiting the practice. Both approaches rest on the same biological evidence; they just weigh recreational value, conservation outcomes, and animal welfare differently. The fact that reasonable legal frameworks can reach opposite conclusions from the same data tells you something about how much of this question lives outside the bounds of science alone.