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Fish can feel pain and react to it like humans

By Gary Bogue
Tuesday, May 5th, 2009 at 7:22 am in Fish.

King salmon by USFWS
king salmon1

Fish don’t make noises or contort their faces to show that it hurts when hooks are pulled from their mouths, but a Purdue University researcher believes they feel that pain all the same.

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

A paper detailing the finding was published in the early on-line version of the journal Applied Animal Behaviour Science.

Sockeye salmon by USFWS
sockeye salmon1

“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 doctoral student in 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 a 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 behaviors.

“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 behaviors, indicating wariness, or fear and anxiety.”

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

Cutthroat trout by USFWS
cutthroat trout1

“The experiment shows that fish do not only respond to painful stimuli with reflexes, but change their behavior also 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 — either because the responses were reflexive or because the morphine blocked the experience of pain, but not the experience of an unusual stimulus.

“If you think back to when you have had a headache and taken a painkiller, the pain may go away, but you can still feel the presence or discomfort of the headache,” Garner said.

Those with saline both experienced pain in the test, as well as responding to it, and were able to cognitively process that pain, thus causing the later fear and anxiety.

“The goldfish that did not get morphine experienced this painful, stressful event. Then two hours later, they turned that pain into fear like we do,” Garner said. “To me, it sounds an awful 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.

This should definitely give fishermen something to think about. /Gary

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4 Responses to “Fish can feel pain and react to it like humans”

  1. Carny Asada Says:

    Curious! But I have to say, when it comes to fish, that goldfish are smarter than average — for instance, you can train them to fetch, perform simple tricks and swim in formation. I would like to see these findings replicated with some different species. In the meantime, be kind to your wet pets!

  2. ROBERT LEE Says:

    I am amazed that testing had to be down to prove that hypothesis. Every creature on this planet has an ability to communicate and express emotion in what ever form that is species specific. It is simply the fact the we are not yet sophisticated or obviously intelligent enough to demonstrate this truth.
    Plants respond to positive and negative stimuli and do better in an environment of other plants then alone.
    The continued loss of the flora and fauna of this earth because of the viruliferous nature of the human race is already foreshadowing our future – lets respond as the sentient beings we claim to be and demonstrate world wide, as one race of humans, our superior intellect.

  3. Gary Bogue Says:

    Robert: I couldn’t agree more. Your response is EXACTLY the reason I printed this study. Curious, isn’t it? Thanks for your great reply. /Gary

  4. poo Says:

    Makes me afraid to eat fish…

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