Stress is not pain. Comment on Elwood and Adams (2015) ‘Electric shock causes physiological stress responses in shore crabs, consistent with prediction of pain’

Elwood & Adams [1] exposed Carcinus maenasto electric shocks. They reported that 6/20 unshocked crabs did not move but all (20/20) shocked crabs did move. No control crabs showed ‘extreme responses’ [1, p. 2] but 4/20 shocked crabs did. Most crabs walked (14 control and 16 shocked). When comparing only walking crabs, haemolymph lactate was higher in shocked crabs. At the end of the discus-sion, they state ‘Although these physiological responses are expected should an animal experience pain, they do not prove the feeling of pain in decapods...’[1, p. 3]. They nevertheless conclude that their results, interpreted in the contextof previous research, ‘...fulfils the criteria expected of a pain experience’ [1, p. 1].We contend that their conclusion that crabs experienced pain (as summarized in the title and abstract) is unfounded, because neither is stress a necessary prerequisite for pain nor is it always coupled with pain...