What are the symptoms of shellfish or crab allergy?

A variety!: Depending on the patient, food allergy symptoms can include:itchy mouth/throat, facial &/or airway swelling, difficulty breathing or talking, cough, wheeze, nausea, vomiting, diarrhea (can be bloody), flushing, hives, eye redness, itch, &/or swelling, runny, itchy, &/or stuffy nose, sneezing, abdominal pain, feeling of impending doom and even shock or cardiac arrest!