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Fish can feel pain like humans

india Updated: May 04, 2009 13:49 IST

IANS
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Like humans, fish too can feel extreme pain when hooks are pulled off their mouths, even though it doesn't show on their faces, according to researcher Joseph Garner at Purdue University.

Garner, assistant professor of animal sciences, helped develop a test that found that goldfish do feel pain, and their reactions to it are similar to that of humans.

"There has been an effort by some to argue that a fish's response to a noxious stimuli is merely a reflexive action, but that it didn't really feel pain," Garner said. "We wanted to see if fish responded to potentially painful stimuli in a reflexive way or a more clever way."

Garner and Janicke Nordgreen, a student at the Norwegian School of Veterinary Science, attached small foil heaters to the goldfish and slowly increased the temperature.

The heaters were designed with sensors and safeguards that shut off the heaters to prevent any physical damage to the fish's tissue.

Half of the fish were injected with morphine, and the others received saline. The researchers believed that those with the morphine would be able to withstand higher temperatures before reacting if they actually felt the pain. However, both groups of fish showed a response at about the same temperature.

Because both groups of fish wriggled at about the same temperature, the researchers thought the responses might be more like a reflex than a cognitive reaction to experiencing pain.

The reflexive response is similar to a person involuntarily moving a hand off a hot stove with which they had come into contact. The reaction happens before a person actually experiences pain or understands that they have been hurt.

Upon later observation in their home tanks, however, the researchers noticed that the fish from each group were exhibiting different behaviours, said a Purdue release.

"The fish given the morphine acted like they always had: swimming and being fish," Garner said. "The fish that had gotten saline, even though they responded the same in the test, later acted different, though. They acted with defensive behaviours, indicating wariness and anxiety."

Nordgreen said those behavioural differences showed that fish can feel both reflexive and cognitive pain.

These findings were detailed online in Applied Animal Behaviour Science.