Effect of cadmium chloride on physiological color changes of the fiddler crab, Uca pugilator

The effects of cadmium exposure on the color change system of the fiddler crab, Uca pugilator, were determined. Crabs were either immersed in 10 ppm cadmium chloride solutions or injected with 8.5 micrograms cadmium/g body weight. The crabs exposed to cadmium, either by injection or immersion, were less able to bring about dispersion of the pigment in their integumentary melanophores than were the unexposed crabs. Cadmium did not affect the melanophores directly. This decreased black pigment dispersion was apparently due to effects of cadmium on the neuroendocrine processes that control the melanophores. The neuroendocrine complex in the eyestalk is the source of a black pigment-dispersing hormone (BPDH). Eyestalks of crabs kept in clean water contained 3.27 times more BPDH than did the eyestalks of the cadmium-exposed crabs. Histological studies revealed that cadmium exposure results in depletion of the neurosecretory material in the eyestalks and brain. It is hypothesized that cadmium inhibits BPDH synthesis in neurosecretory (neuroendocrine) cells, resulting in decreased ability of exposed crabs to disperse their black pigment.