Fish is okay. Just shellfish.
The top 8 food allergens (the ones that food products have to label) are:
Milk
Eggs
Peanuts
Tree nuts (such as almonds, cashews, walnuts)
Fish (such as bass, cod, flounder)
Shellfish (such as crab, lobster, shrimp)
Soy
Wheat
Of these, I know that Peanuts are the most extreme (they're the most likely to generate airborne proteins and/or aerosolize while cooking) and Tree nuts and Shellfish can be very severe (anaphylaxis) when ingested. I'm not as familiar with the others, plus I imagine it's very hard to have things avoiding all of those.
I'll amend my previous suggestion to say that shellfish, peanuts, and tree nuts should be avoided. For the rest, people should please be considerate and label which of these ingredients are in the dish. (It's not always as obvious as "Warning. Peanut butter contains peanuts.")
Also if anyone else has a specific allergy, whether or not it's one of the above, please mention it here so we can be aware.