Welcome to PPRuNe Lizi,
I wouldn't worry too much, I have been allergic to shellfish my whole life. I actively avoid eating shell fish, and have never had a problem with that. I have been declaring that allergy for my class 1 medical for 50 years, and have never had a problem. State the truth for your medical, but don't overstate what you know to put it into the needless worry category!