(1) A black discoloration found in canned fish and shellfish. Caused by defects in the plating or lacquering of the insides of steel cans such that sulphides present in the product can interact with the exposed steel to form black iron sulphide. The blackening might be seen only on the walls of the can, but can extend into the contents. Not the same as black spot. (2) Intense black, localised, discoloration arising from the copepod parasite Sarcotaces articus, the ink bag parasite, found in blue ling, Molva dypterigia. It is a black liquid, and if the sac (ink bag) is cut during filleting the surrounding flesh is stained black. Otherwise the parasite can be carefully excised without causing staining.