Shellfish include several species of crustaceans and bivalve mollusks with distinct morphological and ecological features. The nutritional characteristics also vary among species, reflecting different health benefits. Overall, shellfish can provide a healthy diet because they are excellent protein sources; contain higher carbohydrate content (stored as glycogen); are especially good sources of minerals (selenium and copper) and vitamin B12; are low in fat, especially low in saturated fat; and have a great source of the omega-3 fatty acids. However, despite crustaceans' brown meat being highly appreciated, it contains higher levels of fat, cholesterol, and cadmium in contrast to muscle tissue.