Purchase wild caught shellfish. Prawns are large swimming crustaceans or shrimp, they are high in protein and low in saturated fat. A source of niacin, vitamin B6 and folate. They contain the minerals, calcium and iron, also some zinc and magnesium. Shellfish is prone to contamination, so extra care should be taken when buying, preparing and cooking. Shellfish can provoke allergic reactions in some people.