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