Fish and Humans May Share Pain Reactions

WEST LAFAYETTE, Ind. — Fish don't make noises or contort their faces to show pain when hooks are removed from their mouths, but a Purdue University researcher believes they feel that pain all the same.

Joseph Garner, DPhil, an assistant professor of animal sciences at Purdue, helped develop a test that showed goldfish can feel pain and that their reactions to it are much like that of humans. "There has been an effort by some to argue that a fish's response to noxious stimuli is merely a reflexive action and that the fish 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 doctoral student at the Norwegian School of Veterinary Science, attached small foil heaters to the goldfish and slowly increased the temperature. To prevent any physical damage to tissue, the heaters were designed with sensors and safeguards that turned the heaters off at certain temperatures.

For the test, half of the fish were injected with morphine and the others received saline. The researchers believed that those receiving 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. The reflexive response is similar to people involuntarily moving their hand off a hot stove.

However, subsequent observation of the goldfish in their home tanks found that each group exhibited different behaviors.

"The fish given the morphine acted like they always had: swimming and being fish," Garner said. "The fish that had received saline — even though they responded the same in the test — later acted differently. They showed defensive behaviors that indicated wariness, fear or anxiety."

Nordgreen said those behavioral differences demonstrated that fish can feel both reflexive and cognitive pain.

"The experiment shows that fish not only respond to painful stimuli with reflexes but also change their behavior after the event," Nordgreen said. "Together with what we know from experiments carried out by other groups, this indicates that the fish consciously perceive the test situation as painful and switch to behaviors indicative of having been through an aversive experience."

Garner believes that the morphine blocked the experience of pain, but not behavioral responses to the heat stimulus itself.

"If you have a headache and take a painkiller, the pain may go away, but you can still feel the presence or discomfort of the headache," Garner said. "The goldfish that did not get morphine experienced a painful, stressful event. Then 2 hours later, they turned that pain into fear," Garner said. "To me, it sounds a lot like how we experience pain."

The findings could raise questions about slaughter methods and how fish are handled in research. Garner said standards of care could be revisited to ensure fish are being treated humanely.

A paper detailing the finding was published in an online version of Applied Animal Behaviour Science.

source : http://www.vettechjournal.com