Allergy to fish appears to be among the most common food allergies in countries with high fish consumption. It is commonly established during early childhood and persists life-long. Allergic reactions are often elicited by several different fish species, but can also be specific for only a few species. Urticaria, eczema and vomiting are common fish allergy symptoms. Fish can elicit respiratory symptoms like severe asthma and inhalation of fish steam/damp during cooking of fish or handling of fish has been reported to trigger fish allergy respiratory reactions, i.e. asthma.
The presence of fish in fish dishes is normally easily recognized but there are a few dishes where the fish ingredient might not be expected. Such examples are Ceasar dressing, liver pâté and Worchester sauce where sprat can be an ingredient. Sprat is also used as taste enhancer in certain sauces/gravies for steaks. Fish products with crab taste (crab sticks) are produced from fish, commonly Alaska pollock, but might contain small amounts of crab meat. Asian fish sauces are prepared from fermented fish.
Other reactions to fish
Fish may contain toxins or high levels of histamine. Histamine is found mainly in tunas and mackerels (scombroid fishes) and is formed during fish handling at elevated temperature or as a cause of less good hygiene. Histamine poisoning gives acute attacks of stomach pain, vomiting and diarrhea.
High levels of histamine have also been found in Escolar, a fish species sometimes mislabeled as butterfish. Escolar and ruvett (also called oil fish) contain a kind of fat called waxy esters. If the fish is not fried or grilled hard enough in such a way that the fat disappears, the waxy esters give gastrointestinal problems during consumption. These symptoms are sometimes wrongly interpreted as being a hypersensitivity reaction.
Labeling
The presence of fish and products thereof in food products must always be declared, see further in LIVSFS 2004:27 Livsmedelsverkets föreskrifter om märkning och presentation av livsmedel [in Swedish] (see link to the right).
Examples of methods of analysis
The presence of fish proteins can be detected with immunodiffusion and specific antibodies to cod. The limit of detection is around 100 mg fish protein/kg (ppm).
One commercial ELISA test kit for the analysis of fish proteins is available. The quantification limit is 5 mg cod/kg.
Allergic reactions / doses
Information about doses of fish that elicit an allergic reaction during provocation is few/scarce. One study reported 400 to 500 mg of fish; another study reported that the lowest eliciting dose was 6 mg of cod. Other reports on eliciting doses during provocation have been from 5 mg of cod and 5 mg of herring up to 6000 mg of plaice.