Scientific Name: Cyprinus carpio
Occurrence: Usually eaten cooked but also as sushi.
Allergy to fin fish is relatively common (0.4% of adults in the USA
according to one telephone survey), and can be associated with severe
symptoms such as anaphylactic shock. Symptoms can also occur after
ingestion of only a small quantity of fish with one reported reaction
in an individual after receiving a kiss from someone who had recently
eaten fish. Allergy to fish is not to be confused with a toxic reaction
to histamine in spoiled fish (scombroid fish poisoning).
Almost all fish allergy seems to involve the protein parvalbumin, which
is found in the muscle of most fish. As the parvalbumins are similar in
all fish species, individuals allergic to one fish are likely to react
to a range of different fish species. Thus after a diagnosis of allergy
to one fish species, patients are normally advised to avoid all fin
fish. Some individuals also react to frog. Although fin fish and
shellfish allergies are not linked, individuals can be allergic to both
Parvalbumin remains able to cause a reaction after cooking. Thus fish
remains allergenic after cooking and other treatments. Fish can be a
"hidden" allergen in, for example, pizza toppings. Consequently, the EU
labelling regulations require foods containing fish and products
thereof to be labelled.
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Fish and fish products play an important role in human nutrition. Fish
is a valuable source of proteins and contains large amounts of healthy
fats (so called polyunsaturated fatty acids) and fat-soluble vitamins.
However, it also is one of the most common causes of food allergy. Fish
allergy is a so-called IgE-mediated food allergy. IgE (Immunoglobulin
E) is the allergy antibody.
Allergy to fish is caused by a reaction to protein in fish meat
(muscle). The dominating allergen is a muscle protein called
parvalbumin. In professional literature this allergen is often referred
to as “Gad c 1” from the Latin name for cod fish Gadus callarias. This
major allergen is extremely stable to heat, which means that boiling or
frying of fish does not destroy the allergen. Other proteins in fish
have been described as allergens, but most reactions to cod (and other
fish; see under Related foods) are most likely caused by this one
Reactions can be severe and even life-threatening. The severity of
symptoms may vary according to the amount ingested and the sensitivity
of the person. Often the first symptom is irritation and itching in
mouth and throat appearing few minutes after the intake. It can be
followed by other allergic reactions such as nausea, vomiting, stomach
ache, diarrhoea, hives (also called urticaria or nettle rash), swelling
under the skin (also called angioedema), itching and reddening of the
skin, worsening of eczema, asthma (wheezing, breathlessness, coughing),
hay fever (itchy nose and eyes, sneezing/runny nose), swelling of the
airways, and sometimes fatal episodes of allergic shock. Usually a
combination of several symptoms is seen.
Spoiled fish can contain a substance called histamine. This is the same
substance that is produced by cells of an allergic patient during an
allergic reaction. It is involved in the induction of symptoms. Spoiled
fish can elicit symptoms in every person having eaten it. The reaction
is similar to an allergic reaction, i.e. swelling, hives, wheezing
etc., but it is poisoning.
Related foods (cross-reactions)
Most information on fish allergy is gathered on codfish. The variety of
fish eaten around the world is immense. Despite this, fish species
known to cause allergy belong to a few closely related orders: codfish
and hake (Gadiformes), mackerel, tuna and perch (Perciformes), salmon
and trout (Salmoniformes), plaice and sole (Pleuronectiformes),
herring, anchovy and sardine (Clupeiformes), carp and catfish
(Cypriniformes), and eel (Anguilliformes). Patients with allergy to
codfish are often allergic to the other fish species as well. This can
be explained by similarity of the allergen parvalbumin in all fish
species. Allergic reactions based on such similarity are called
cross-reactions. The cross-reactivity between fish species is certainly
not complete. Some patients are allergic to one and tolerate other
Allergy to fish does not mean that other seafood like shellfish is not
tolerated. Cross-reactivity is irrelevant between fish and shellfish.
Of course, patients can develop allergy to both independently. Fish roe
(or caviar) has been reported to cause food allergy but there is no
relation to allergy to the fish from which the eggs originate.
Finally, it has been reported that parvalbumin in frogs legs can in
some cases also cause allergy in fish allergic patients. This again is
cause by cross reactivity.
Who, when, how long and how often?
Food allergy to fish is seen both among children and adults
(approximately 0.1-0.2%). Varieties in food habits according to country
influence the frequency patterns of fish allergy, with the number of
fish allergics being higher in those countries where fish is a major
component of the local diet. In general, fish allergy is not outgrown
but it persists through life.
How much is too much?
Care has to be taken since very small amounts (few mg, in other words a
tiny flake) of fish can elicit a reaction in very sensitive persons. A
dose of only 5 mg of cod has been described to cause reaction.
Furthermore, some fish allergic persons can get allergic symptoms due
to the steam (airborne allergens) from cooking fish. Fish allergy is
therefore sometimes a problem in the fish industry and among restaurant
cooks, where handling and inhalation might cause eczema and asthma.
Finally, even a kiss of somebody that has eaten fish can induce a
reaction in a fish allergic person.
An indication for IgE-mediated fish allergy can be obtained from skin
prick testing and from serum IgE testing. The presence of a positive
skin prick test or of fish protein-specific IgE-antibody in serum is
indicative of an IgE-mediated fish allergy, but both tests may be
false-positive or false-negative. Therefore, a definitive diagnosis has
to be based on strict, well-defined elimination and re-introduction
protocols or on controlled fish challenge procedures. Fish allergy is
confirmed if symptoms disappear after elimination and re-appear upon
re-introduction or if a so-called double-blind placebo controlled food
challenge gives a positive result. During such a challenge both doctor
and patient do not know which challenge meal contains fish and which
does not. Such challenge procedures are also helpful in determining the
threshold dose of reactivity, and to verify if a person has outgrown
the food allergy, although this is rarely seen with fish allergy.
Where do I find fish?
It is important to study the labels on processed foods since various
products can contain fish: surimi (fish product imitating crabmeat),
fish meal, animal fat, liver pâté, some sausages, crab salad, sushi,
oyster sauce, Worcestershire sauce, Caesar salad, tapenade, and pizza
toppings. Fish oils/animal oil can also contain fish proteins,
depending on the degree of refining of the oil. Fish gelatine made from
skin and bones and used in food products is not considered to present a
risk to fish allergic persons at the doses typically used.
Fish gelatine is applied in pharmaceutical products like vaccines, but it is not considered a risk to fish allergic persons.
If suffering from fish allergy, strict avoidance of fish in any form
and food containing fish-derived ingredients is the only way to prevent
a reaction. This can sometimes be difficult because they can be hidden
in food products. According to the new EU labelling directive
(2003/89/EC) and the list of the Codex Alimentarius Commission, any
fish-derived ingredient has to be listed on the label. Even if labels
are carefully read, unintentionally and accidentally consumption of
fish may happen. Fish allergic individuals should especially be
cautious when eating away from home. When ordering a “non-fish meal” at
a restaurant it may be contaminated with fish proteins from utensils,
cooking oil or a grill exposed to fish.
Other Information: The carp image was created by Duane Raver and is from the USFWS National Image Library.
Taxonomic Information: NEWT 7962 (common carp). Several other related
fish include carp in their name i.e. bighead carp, crucian carp, grass
carp, mud carp, noble carp and silver carp.Just Goin Fishin' Message forum
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