Many a seafood fan has parroted the popular idea that fish and crustaceans do not feel pain. New research, however, suggests that they may, revealing that their nervous system may be more complex than we thought—and our own awareness of pain may be much more evolutionarily ancient than suspected. [For more on pain, see the special section beginning here.]

Joseph Garner of Purdue University and his colleagues in Norway report that the way goldfish respond to pain shows that these animals do experience pain consciously, rather than simply reacting with a reflex—such as when a person recoils after stepping on a tack (jerking away before he or she is aware of the sensation). In the study, the biologists found that goldfish injected with saline solution and exposed to a painful level of heat in a test tank “hovered” in one spot when placed back in their home tank. Garner labels that “fearful, avoidance behavior.” Such behavior, he says, is cognitive—not reflexive. Other fish, after receiving a morphine injection that blocked the impact of pain, showed no such fearful behavior.

Although Garner’s findings fit with previous work that tentatively suggests that fish feel pain, some experts remain unconvinced that the reaction was not an instinctive escape behavior. Still, the new study raises ethical concerns. “If we’re going to use animals in experiments, and we’re going to use animals as food, then it is really important to understand the consequences of our actions for those animals,” Garner says.

Note: This article was originally printed with the title, "Underwater Suffering?"