April 30, 2003
Fish 'capable of experiencing pain'
by James Randerson
Fish are capable of experiencing pain. This is the conclusion of researchers who observed rainbow trout behaviour after the animals were given injections that would be painful to people. Other scientists reject their interpretation, but the study could still be used by anti-angling campaigners.
The argument over whether fishing is a "blood sport" in the same vein as fox hunting and hare coursing has hinged on whether fish feel pain in a similar way to animals. If they do not, as most researchers currently believe, then the animal welfare argument against angling largely falls apart.
Lynne Sneddon at the Roslin Institute, near Edinburgh, Scotland, and her colleagues, took measurements from individual neurons in anaesthetised fish while they poked the fish's heads and applied acid and heat.
They identified up to 22 neurons that fire in response to the stimuli. What is more, the firing pattern looked much the same as neurons in humans that transmit the pain message. So fish have the neural hardware to transmit the message but does it register as pain in the fish brain?
It is of course impossible to really know whether another person is feeling pain, let alone another species, notes Patrick Bateson, an animal behaviour expert at Cambridge University, UK. But the next best thing, he says, is to look for behavioural responses that resemble those exhibited by a human in pain.
The team compared the behaviour of fish that had either bee venom or acetic acid injected into their lips with animals that had received harmless saline.
The fish given the nasty chemicals showed clear signs of physiological stress, the researchers found. They took 90 minutes longer to resume feeding and their rate of gill breathing was characteristic of a fish swimming at top speed.
More surprisingly, they displayed very unusual behaviours such as rocking from side to side. Sneddon believes this may be similar to repetitive behaviours sometimes seen in zoo animals. The fish treated with acid also rubbed their lips on the sides and bottom of the tank.
"These behaviours are not just reflex responses," argues Sneddon. If a human touches a hot iron then, before any pain is registered, a local neural reflex circuit pulls the hand away to prevent damage. But the throbbing discomfort felt after the event is pain. She believes that the strange trout behaviours are evidence of something similar.
But James Rose, an expert in fish neurobiology at the University of Wyoming in Laramie disagrees: "It has nothing to do with pain -- the fish brain just hasn't got the hardware to experience pain."
He points out, for example, that even people in a persistent vegetative state are able to make complex responses to painful stimuli. They can cry out or screw up their faces without ever being conscious of their surroundings.
Whether it can be classed as pain or not, Sneddon's work has identified that fish experience prolonged discomfort following an injection that would be painful to humans.
For Bateson that is a significant step forward in the argument: "There seems, already, to be a good argument to say that fish should be treated carefully."
Journal reference: Proceedings of the Royal Society B (DOI 10.1098/rspb.2003.2349)
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