Are Crabs With Black Spots Safe to Eat?

December 15, 2011

Question: I just bought two crabs and found one with black spots on the outside shell. I’ve seen these before and usually avoid them, but this time the seller sneaked it into my package. When I called him about it, he said he didn’t know what it is, but it doesn’t permeate the shell. This isn’t true—I’ve seen this stuff on the flesh at the joints. It looks like oil. Can you enlighten me? Besides being ugly, is it unsafe? (Mari V., Berkeley)

Answer: According to our senior fish pathologist Jim Moore, black spots on the shells of crustaceans are typically composed of melanin, which is the end product of a series of immunological reactions. This means the crab was likely responding to some shell damage that could be caused by physical trauma or a disease agent. In this case, the black spotted crab is probably safe if cooked correctly. However, if the discolored shellfish tissue has an unpleasant taste or texture, or looks or smells unusual, we always recommend not eating it.