It could look like any other allergic reaction, of which symptoms may include:

• Hives and generalized itching
• Nausea, vomiting
• Diarrhea
• Abdominal pain or cramping
• Skin redness
• Nasal congestion
• Cough

Many people on this site have also said that their lips swell up if they eat fish they are allergic to.

You should also be aware of anaphylaxis, a potentially deadly allergic reaction that can have the same symptoms listed above, but may also lead to:

* Difficulty breathing
* Wheezing
* Abnormal (high-pitched) breathing sounds
* Confusion
* Slurred speech
* Rapid or weak pulse
* Blueness of the skin (cyanosis), including the lips or nail beds
* Fainting , light-headedness , dizziness
* Anxiety, panic of a sense of "impending doom"
* Heart palpitations

Generally, a shot of epinephrine as soon as anaphylaxis symptoms come on if the first, best and almost only treatment.