Do Fish Feel Pain? What the Studies Found, and What to Do

Hands holding a fish with its mouth open and a hook lodged inside — Photo: U.S. Air Force (public domain)

Key takeaways

Fish sense damage: a rainbow trout has 58 receptors on its face and head, 22 of them nociceptors. Injured trout rocked, rubbed their lips and stopped eating for about 170 minutes.
Whether fish suffer is contested. Sneddon and Braithwaite say the behavior is more than reflex; Rose and Key say no neocortex and almost no C-fibers means no felt pain.
Across 274 estimates from 53 studies, 18% of released fish died on average. Hook location is the biggest factor; barbed versus barbless changes almost nothing (4.5% vs 4.2%).
Air is the lever you control: exhausted trout survived 88% with no air, 62% after 30 seconds, 28% after 60. Keep it to about 10 seconds.
Hook wounds on bass were still visible on 91% of fish a week later; by day 6, 27% had healed in May against 12% in July. In warm water, fight fast and release faster.

Fish sense damage: a rainbow trout carries 22 pain receptors on its face and head, and it reacts when they fire. A caught fish also shows a stress response you can measure in its blood; whether fish suffer the way we do is where scientists still disagree. None of that settles what matters most at the water: whether the fish you let go swims off and lives. That question has clear numbers, and most of them are in your hands.

Exhausted rainbow trout survived at 88% when they were never lifted from the water, 62% after 30 seconds in the air and 28% after 60 seconds.

Alarm or pain: what is the argument about?

Two words carry the whole argument. Nociception is the body’s alarm system: nerve endings that fire when something is cut, crushed or burned. Pain is what a mind makes of that alarm. Fish have nociception, and nobody serious disputes it anymore. Lynne Sneddon, then at the Roslin Institute near Edinburgh and later at the University of Liverpool, led the work that proved it. James Rose of the University of Wyoming led the case against: the alarm rings, but there is no one home to hear it.

Think of a smoke detector. A fish has one, and it works. The argument is about whether anything in the fish notices the noise.

How do we know? The trout study

In 2003 Sneddon, Victoria Braithwaite and Michael Gentle mapped the nerves on the face of the rainbow trout. They found 58 receptors on the face and head. Twenty-two were nociceptors, firing at hard pressure and at heat above 104 °F (40 °C). Eighteen of those also fired at a 1% acetic acid solution, which makes them polymodal nociceptors.

Then some trout got bee venom or acid injected into the lips, and others got plain saline. The venom and acid fish rocked from side to side on the gravel, breathed faster and refused food for about 170 minutes. The acid fish also rubbed their lips on the gravel and the tank walls. The saline and untreated fish were feeding again after about 80 minutes, less than half that time. In a second paper the same year, Sneddon gave injured fish morphine. The rocking and rubbing dropped sharply, and so did the breathing rate. Fish have working detectors, and a painkiller changes what they do about it.

What the doubters say

Rose and six colleagues answered in 2014 with “Can fish really feel pain?” Their case rests on the brain. In humans, the felt part of pain happens in the neocortex, the folded outer layer. Fish have no neocortex. Nociception on its own, they argue, is a reflex, the way your hand leaves a hot stove before you feel the burn.

They also point at the wiring. In a human skin nerve about 83% of the fibers are C-fibers, the slow ones tied to the dull, lasting ache. In the trout’s face nerve about 4% are, and in a carp’s tail nerve about 5%. Their conclusion: claims that fish feel pain “remain unsubstantiated.” Brian Key of the University of Queensland made the same case in 2016 under the title “Why fish do not feel pain.” It drew more than 40 published commentaries, most of them critical.

On the other side, Braithwaite’s 2010 book Do Fish Feel Pain? and Culum Brown’s 2015 review argue that fish pain is comparable to that of other vertebrates. The trout did not just flinch; they changed what they did for hours, and a painkiller damped the change.

So here is where the science stands. Nociception is a fact. Stress is a fact. Suffering is inferred, in both directions, and no experiment yet can settle it.

Do fish feel pain when hooked?

A hook goes through the lip or jaw, exactly where Sneddon mapped the receptors. So the detectors fire. You may have heard that fish lips have no nerve endings. No study says that, and the 2003 map says the opposite. The defensible version is narrower: lips carry nociceptors, but very few of the slow C-fibers. What the fish makes of that is the contested part above.

What is known is that the hook wound itself rarely kills. Fernholz and colleagues followed hooked largemouth bass in 2018. Every wound was visible on day 0, and 91% still were on day 7. Healing depended on the season: 27% of wounds had closed by day 6 in May, against 12% in July. In 2023 Skov and colleagues followed small sea trout in 39–50 °F (4–10 °C) water for 26 to 29 days after release. None died and none lost growth. By the end, only about 6% of the lure-caught fish still had an unhealed or infected wound.

Do fish feel pain when caught? The stress response

Whatever a fish feels, its body reacts like any body under threat. Suski and colleagues sampled tournament largemouth bass within five minutes of weigh-in in 2003. Cortisol, the stress hormone, and blood glucose were far above the levels in rested bass and in bass just caught and sampled at once. Lactate, which builds up in muscles worked to exhaustion, was about five times the resting level. In a follow-up in 2004, the same team found lactate back at control levels in bass given 24 hours to recover.

Put simply, the fish’s body does what yours does at the finish line of a race. Heart hammering, muscles burning, sugar dumped into the blood. A fish fights the way a rabbit runs, to get away. It spends most of the next day recovering, resting much as it does at night (do fish sleep?). Whether that alarm comes with anything like fear is the next question: do fish have feelings?

What decides whether a released fish lives

Bartholomew and Bohnsack pooled 274 estimates of catch-and-release mortality from 53 studies in 2005. The average was 18% (median 11%), and the range ran from 0% to 95%. That spread is the point. The same fish caught two different ways lives or dies, and one factor towered over the rest: where the hook sits. A fish hooked in the lip mostly lives. A fish hooked deep in the throat or the gills often does not. The same review found natural bait raised mortality, and so did J-hooks against circle hooks, digging hooks out of deep-hooked fish, warm water and long fights and handling. Treble against single hook made no significant difference.

The barb matters less than most anglers believe. Schill and Scarpella pooled the trout studies in 1997: on flies and lures, 4.5% mortality on barbed hooks against 4.2% on barbless, and only 1 of 11 comparisons was significant. Schaeffer and Hoffman found barbless hooks came out faster, and barbed hooks landed 22% more fish.

Air is the lever. Ferguson and Tufts exercised rainbow trout to exhaustion, then held them out of the water: 88% survived the next 12 hours with no air time, 62% after 30 seconds, 28% after 60. Cook, Lennox, Hinch and Cooke reviewed the air-exposure studies in 2015 and are cited for a limit of about 10 seconds. A photo takes less than that if the fish waits in the water between shots.

Factor	The number	Source
Where the hook sits	18% mean mortality across 274 estimates, range 0–95%; deep and gill hooking fill the high end, lip hooking the low	Bartholomew and Bohnsack 2005
Bait or lure	Natural bait raised mortality, as did J-hooks against circle hooks; treble against single hook showed no significant effect	Bartholomew and Bohnsack 2005
Time in the air	88% survival with no air, 62% after 30 s, 28% after 60 s; about 10 s is the cited limit	Ferguson and Tufts 1992; Cook et al. 2015
Barbed or barbless	4.5% against 4.2% mortality, 1 of 11 comparisons significant; barbed landed 22% more fish	Schill and Scarpella 1997; Schaeffer and Hoffman 2002
Season and water temperature	Warm water raised mortality; 27% of bass hook wounds healed by day 6 in May, 12% in July; 91% still visible at day 7	Bartholomew and Bohnsack 2005; Fernholz et al. 2018
The fight	Long fights and handling raised mortality; cortisol and glucose high within 5 minutes of weigh-in; lactate back to normal after 24 hours	Bartholomew and Bohnsack 2005; Suski et al. 2003; Suski et al. 2004

A careful release, from hook to swim-off

Decide before the cast. If you fish bait for bass or catfish and plan to let them go, a circle hook sets in the corner of the mouth instead of the throat. Hook location is the biggest number in the table, and J-hooks raised mortality against circle hooks in Bartholomew and Bohnsack’s review.
Pinch the barb if unhooking speed is your problem. Barbless hooks come out faster and, in Schaeffer and Hoffman’s bait fishery, cost you about one fish in five. Mortality itself barely moves in Schill and Scarpella’s trout studies, so treat this as a handling choice, not a rescue.
Land the fish fast. Every extra minute of fight is more lactate to clear over the next day, and long fights and handling raised mortality in the review. Use tackle that ends the fight, not tackle that prolongs it.
Unhook in the water when you can. Wet hands, pliers ready before the fish arrives, the fish resting in the net or beside the boat while you work.
Count the air. Ten seconds is the number. Lift for the photo, put the fish back to breathe, lift again. A fish held up for a full minute has, on the trout numbers, about one chance in four.
Deep-hooked? Cut the line close and leave the hook. Digging in the throat or gills turns the worst hook position into a fatal one; removing hooks from deep-hooked fish raised mortality in the review.
Hold it upright until it kicks free. Face it into any current and let go when it swims out of your hand, not when you are ready. In July, fish early and release faster; by day 6, fewer than half as many wounds have healed as in May.

What does it mean when you fish?

Fish detect injury, and their bodies go into full alarm when caught. Whether they suffer is a question science has argued for more than twenty years and has not closed. Sneddon, Braithwaite and Brown say yes; Rose and Key say no. You do not have to settle it to fish well. Where the hook sits and how long the fish is out of the water decide, far more than anything else, whether it lives.

Do fish feel pain when they die? The same open question applies, so the welfare advice plays it safe. RSPCA Australia says a fish kept to eat should be stunned first, with a firm blow just above the eyes or a spike into the brain, then bled. It lists suffocation out of the water, chilling in iced water and bleeding without a stun as methods that “do not result in a rapid or humane death.” The steps are in ikejime.

The full routine is in catch and release, and the other questions kids ask about fish, each with a number behind it, are in fish facts.

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