What we know about hooks, nets and fish pain

What happens to a fish’s body when it is hooked or netted is well documented and severe. Whether the fish consciously suffers through it is still debated. Anyone who tells you the second question is settled, in either direction, is overselling the evidence.

The case that fish can feel pain

The modern debate runs through a 2003 study by Lynne Sneddon and colleagues, who identified nociceptors, the sensory receptors that detect potentially damaging stimuli, on the face and head of rainbow trout. That alone doesn’t prove pain, since a receptor is only the first step. So the team went further: they injected the lips of trout with bee venom or acetic acid, the acid in vinegar. The fish rocked from side to side, rubbed their lips against gravel and tank walls, and behaved abnormally for roughly three hours. Fish given a saline control showed far less of this.

Sneddon’s argument is that these responses are too prolonged and too complex to be simple reflexes, and that the sensible default is to assume fish can feel pain unless shown otherwise.

The case against

The main sceptics, including James Rose and Brian Key, argue that nociception is not pain. Pain, on their view, requires conscious experience, which in mammals depends on the neocortex, a structure fish lack. Rose’s critique of the trout study is that complex behaviour can occur without consciousness, that injecting large volumes of irritants is a crude test, and that fish routinely feed on spiny prey and can be caught repeatedly within minutes, which he reads as evidence of low responsiveness to oral injury. Rose and colleagues also point out that sharks and rays lack some of the neural pathways that carry pain signals in mammals.

Sneddon’s reply is that sceptics mostly review the literature selectively rather than publishing experiments of their own. Neither side has landed a decisive blow, and the question remains open.

What happens when a fish is hooked

The physiology is much less contested than the philosophy. A fish fighting a line goes through burst exercise and a stress response that can be measured in the blood.

  • Stress hormones and metabolites. Studies of angled rainbow trout, freshwater drum and California sheephead consistently show rises in cortisol, glucose and lactate. In trout, cortisol climbs above baseline within two to three minutes of angling and keeps rising with longer fights and handling.
  • Injury. Hook placement matters. In one freshwater drum study, about a third of the fish were hooked deep in the esophagus. In trout, J-hooks caused more internal hooking than circle hooks, and novice anglers injured proportionally more fish.
  • Aftereffects. Warmer water produces a stronger stress response. Sheephead that fought the line for more than three minutes had higher stress markers, and tracked fish moved less and covered less ground for hours after release.
  • Longlines. In commercial longline fishing, a Portuguese study found stress markers already high when fish were hauled up, likely from a prolonged struggle on the hook. Within an hour, many red porgies stopped responding to stimuli.

None of this proves the fish felt anything. It does show that a hooked fish is under serious physiological strain.

What happens when a fish is netted

Commercial nets add different problems, mostly from scale and duration.

  • Exhaustion. Trawled fish are chased until they tire, then funnelled into the narrow end of the net.
  • Crushing. As the tow continues, fish in the net’s end are packed together and suffer scale loss, skin damage and crushing. One report cited by the animal welfare journal Animal Welfare put deaths before landing at around 29% in a two-hour trawl and 61% in a four-hour trawl.
  • Decompression. Fish hauled from deep water can suffer pressure injuries, such as bulging eyes and ruptured internal organs, according to welfare groups.
  • Gillnets. Fish snared by the gills can hang for long periods.
  • Death on deck. Most fish are not killed quickly. Many are left to suffocate in air, and studies cited in the same report put the time to insensibility at 55 to 250 minutes, though this varies by species and conditions.
  • Bycatch. Discarded fish are often assumed to survive. One observed herring trawl put discard mortality at 77 to 100%.

A caveat on sourcing: much of the capture-welfare literature comes from advocacy groups such as Fishcount and Eurogroup for Animals. Their figures are drawn from peer-reviewed studies, but they are presented with a purpose, and the numbers vary widely by gear, species and conditions.

What we can and can’t say

Three things hold up well:

  1. Fish have nociceptors and show strong, measurable stress responses to capture.
  2. Many capture methods cause injury, exhaustion and slow death, regardless of what the fish consciously experience.
  3. Most of the behavioural pain research is on a few species, mainly rainbow trout and zebrafish. Generalising to the many thousands of fish species is risky, and sharks and rays may genuinely differ.

One thing remains unresolved: whether fish have subjective experience of that suffering. The honest position is probabilistic. Given the evidence, a meaningful chance that fish suffer seems hard to dismiss, and the scale of fishing means even a modest probability carries a large moral weight.

The takeaway

You don’t need to settle the consciousness debate to see that how fish are caught and killed could be much better. Shorter trawl tows, pumping fish aboard instead of hauling them in crowded nets, circle or barbless hooks, shorter fights and quick stunning would reduce injury and stress whatever the answer turns out to be.

Sources
  • Sneddon, Braithwaite & Gentle (2003), “Do fishes have nociceptors?”, Proceedings of the Royal Society B
  • Rose et al. (2014), “Can fish really feel pain?”, Fish and Fisheries; Rose, critique of Sneddon et al.
  • Key (2016), review on fish and pain
  • Mood (2010), Worse Things Happen at Sea, Fishcount.org.uk; summarised in Animal Welfare 19(4)
  • Eurogroup for Animals, wild capture fisheries reports (2021, 2022)
  • Meka & McCormick (2005), Fisheries Research 72, on trout angling stress
  • Carefish/catch consortium, longline welfare report (2025)