In children, fish is the third most common allergic cause after milk and eggs. It may disappear over the years, but very often it persists.
A person allergic to fish such as tuna or salmon is not necessarily allergic to shellfish. While the recommendation to a person allergic to one type of fish is not to eat fish in general, it is possible to be allergic to one type and not another. Symptoms are generally mild, with vomiting and diarrhoea, but can lead to episodes of anaphylaxis and cause death.