Color change in exercising crabs: evidence for a hormone

Three species of crabs exercised to fatigue showed a blanching and/or reddening of the body and legs. In Uca pugilator this effect was due to white and red pigment dispersion in the leucophores and erythrophores, respectively, and a black pigment concentration in the melanophores. The pigment movements were induced by factor(s) present in the blood of exercising Uca; blood (hemolymph) removed from an exercised crab and injected into the isolated leg segment of another individual cause pigment movements similar to those seen in intact fatigued crabs. The blood of exercised Uca also caused similar chromatophore changes in isolated leg segments of the crab Sesarma cinereum. The evidence suggests that blood-borne factor(s) related or identical to chromatophorotropins are released during vigorous exercise in crabs. We speculate that the effects of these exercise factor(s) are secondary to possible effects on carbohydrate and lipid metabolism associated with exercise.