FISH can feel pain, according to a controversial study. The finding will inflame arguments over whether angling should be considered a cruel blood sport alongside fox hunting and hare coursing.
A team of researchers in Scotland reached this conclusion after observing abnormal behaviours in trout given injections known to cause pain in people. They say their results provide the first concrete evidence that fish feel pain. Some experts disagree, arguing that the researchers鈥� definition of pain is too vague. But others say that whatever the fish are feeling, they show similar symptoms of distress as mammals.
Lynne Sneddon at the Roslin Institute near Edinburgh and her colleagues anaesthetised trout, then prodded their heads and applied acid and heat. While doing this they measured the activity of neurons to identify those that could transmit a pain signal. They found 22 neurons that gave a response to heat and mechanical pressure, of which 18 also responded to acid. Crucially, they found that the neurons show a similar firing pattern to that found in the human nervous system when transmitting a pain signal.
Advertisement
Having confirmed that a trout鈥檚 nervous system can transmit a pain signal, the crucial question is whether this is actually registered by the fish鈥檚 brain. You can never know for sure if another person is in pain, let alone another species, says Patrick Bateson, an animal behaviour expert at the University of Cambridge, who in 1997 conducted a major investigation into whether deer hunting caused the animals unreasonable stress. The best you can do, he says, is to look for behavioural responses that might indicate whether the animal is suffering pain.
The Roslin researchers studied the behaviour of trout after bee venom or acetic acid (vinegar) had been injected into their lips. The team will report in a future issue of Proceedings of the Royal Society B that the fish showed clear signs of physiological stress. Compared with fish that were simply handled or others that were given a harmless saline injection, they took 1陆 hours longer to resume feeding, and they breathed as rapidly as a fish swimming at full speed.
Most strikingly, they displayed unusual behaviours such as rocking from side to side, which Sneddon likens to repetitive behaviours sometimes seen in zoo animals. The fish injected with acid also rubbed their lips on the sides and bottom of their tank. These behaviours are akin to those shown by people suffering from prolonged pain, says Sneddon. 鈥淭hey are not just reflex responses.鈥�
But James Rose, an expert in fish neurobiology at the University of Wyoming in Laramie, insists that conscious self-awareness is a prerequisite for experiencing pain. He points out that fish lack a neocortex, the brain region that mammals use to process pain signals. 鈥淭he fish brain just hasn鈥檛 got the hardware to experience pain,鈥� he says.
Humans in a persistent vegetative state are also capable of complex behavioural reactions 鈥� such as crying out or screwing up their faces 鈥� to painful events, without ever being conscious of the pain, adds Rose. Sneddon argues that Rose sets the bar too high, and that his definition means that only primates could experience pain.
Bruno Broughton, a fisheries consultant based near Stafford who represents Britain鈥檚 National Angling Alliance, believes the work suggests that angling is relatively benign. He points out that the researchers used two controls 鈥� fish injected with a saline solution and others that are simply handled. The fish given the saline solution behaved in a similar way, with slight elevation in gill breathing and slight delay in feeding, as handled fish. He thinks this is more similar to a hook than injecting a poison, suggesting angling isn鈥檛 cruel.
What is clear from Sneddon鈥檚 work is that fish experience prolonged discomfort following an injection that would be painful to humans. And that is good enough for Bateson. 鈥淭here seems, already, to be a good argument to say that fish should be treated carefully,鈥� he says.