fish and shellfish allergy

Adverse reactions to shellfish are rare in young children and are usually not seen until the teenage years or adulthood. This may be a reflection of the fact that shellfish is not normally a part of the diet of young children.

Allergy to fish may begin in childhood and is likely to be life-long. The fish commonly known to cause allergic reactions include cod, flounder, hake, trout, haddock, halibut, herring, mackerel, pike, salmon, shark, snapper, sole and tuna. New Zealand fish include hapuka, kahawai, moki, parore, tarakahi, and warehou. Occasionally the allergy may not be to the fish itself but to a parasite that can be present in fish.

Allergies to shellfish or fish are potentially serious and there may be a rapid onset of symptoms. A GP’s advice should be sought in all cases and a referral made to see an allergy specialist. Patients known to be at risk may be prescribed an auto-injector containing adrenaline.

Someone who reacts to one type of fish — even if the symptoms are mild — may be advised to play it safe and eliminate all fish from their diet. This is partly because they may react to another type of fish, but also because of the high risk of cross-contamination in restaurants, markets and open fish counters. If the same pair of tongs is used to hand different types of fish and shellfish, or if you suspect one type of fist or shellfish many have spilled over and had contact with another, you should avoid buying or consuming.

Different types of shellfish

Biologically speaking, shellfish are aquatic invertebrates rather than fish. They can be divided into four main groups:

Crustaceans

e.g. crab, lobster, crayfish, shrimp, prawn

Molluscs

1. Bivalves 

e.g. mussels, oysters, scallops, clams, paua, pipi, tuatua, toheroa

2. Gastropods

e.g. limpets, periwinkles, snails

3. Cephalopods

e.g. squid, cuttlefish, octopus, kina

People who have reacted to one type of shellfish (e.g. crab) are likely to react to other members of the same group (in this case, crustaceans). If you react to crab, avoid that and the rest of the crustacean group. If you react to squid, avoid that and the rest of the cephalopod group. Shellfish from the other groups may not necessarily present a problem, although they may do for some people. It is advisable to avoid them all anyway. A special reason for being cautious is that there is a relatively high risk of cross-contamination among different types of seafood.

Eating out

In restaurants, inform staff if you have a shellfish or fish allergy. Find out what your food is fried in and whether the oil has been used for anything else. Check the ingredients of all stocks and soups. Ideally your companions should avoid eating fish/shellfish in your presence, as there is a small risk that breathing in the cooked food may cause a reaction. People have also been known to go into anaphylactic shock after breathing in airborne particles of shellfish in open fish markets.

Fish and shellfish can be present in food in other forms

Dishes to look out for include paella, bouillabaisse, gumbo and fruits de mer (seafood). Oriental food tends to contain lots of different kinds of fish at once, and chopped pieces can be difficult to spot.

Anchovies may be found in caesar salad dressing, caponata, a traditional sweet and sour Sicilian relish, and Worcestershire sauce.

Other dishes to watch out for include kedgeree (smoked fish), jambalaya (fish and shrimps), surimi, crabsticks (contain processed fish that are sold separately or in fish salads and fish cocktails), caviar, fish roe, fish paste, fish sauce, fish stocks, fish soup/chowder, cheese based dips and spreads with fish or shellfish e.g. salmon dip. Fish sauce may be added in dressings and sauces, especially to Asian dishes.


Fish oils are used as a diet supplement as a single oil capsule, or as part of a combination oil mix. If you want to take these supplements, discuss this with your allergy specialist.

Fish, crustacea and molluscs in foods are required to be labelled in New Zealand. If in doubt, check carefully with manufacturers, caterers or restaurant staff.

Non-allergic reactions

Adverse reactions to seafood are not always symptomatic of genuine allergy:

• Histamine, sometimes present in spoiled fish (especially tuna and mackerel), can cause a condition not unlike allergy called scrombroid poisoning. Unlike allergy, this would affect everyone who consumed the offending fish.
• Shellfish/fish sometimes absorb poison from toxic algal blooms, which appear in the waters at certain times of the year. This can cause syndromes known as amnesic, diarrhetic, paralytic and neurotoxic shellfish poisoning. People with syndromes react to the toxin.

Acknowledgements: Dr Jan Sinclair — Paediatric Immunologist, and Jennifer Heyward
 — Paediatric Dietitian, of Starship Children's Health, 
and the Anaphylaxis Campaign