If people have such a serious allergy then they should be driving, not flying. Someone could very easily have a brought fish/peanuts/whatever on board with them and off you go. People who only notify the carrier, especially if they are serving food, should either not get on the plane or go hungry. Also, the last time I checked, a smell of fish doesn't cause anaphlactic shock. In the case where it does, as mentioned before, the person should drive.