Do fish feel pain? Pain like humans do? Study done in April of 2009 says they do.
In this study, there were two groups of fish, one injected with morphine, a pain reliever, and the other with a placebo, saline, which is a kind of medicine used to relieve physical pains psychologically (a fake pain killer). After injected, they were treated to a burning sensation, which would not damage any tissue. Both groups of fish wriggled as a response to the burning. However, after time, the fish with morphine went on their day unaffected, while the fish that had gotten saline were weary.
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This shows that fish feel pain because the fish with the painkillers were unaffected and went on the day as if nothing happened, while the fish with the fake painkillers were obviously affected.
From this study, scientists begin to think that fish do feel pain like humans, as previously thought that they do not.
For more information on this study go to: http://www.livescience.com/animals/090430-fish-feel-pain-too.html