Question: how to know if you're allergic to fish?
Answer: Hives or a skin rash.
Nausea, stomach cramps, indigestion, vomiting and/or diarrhea.
Stuffy or runny nose and/or sneezing.
Headaches.
Asthma.
Anaphylaxis (less common), a potentially life-threatening reaction that impairs breathing and can cause the body to go into shock.