The key proteins associated with fish allergy are called Parvalbumins, they are found in most species of fish. They are found in different concentrations in different species of fish, if you are allergic to these proteins it can be difficult to tell which fish causes you to have more serious reactions.

Parvalbumins are very stable proteins with the ability to cause reactions when cooked or as vapour during cooking (but food is thought to be 20-60% lower in parvalbumins when cooked). The protein is found in high concentrations in the light muscle of fish rather than the dark muscle, so fish like cod and carp are higher in parvalbumin levels compared to swordfish and tuna which have lower levels as they have more dark muscle tissue.

Parvalbumin is the protein used for allergy testing, if you are negative to these tests then your allergy may be to less common proteins found in fish, namely tropomyosin, enolases, aldolases, collagen and gelatin.

Tropomyosin is a protein found in certain types of fish including tilapia, catfish and salmon.

Some fish contain enolase and aldolase proteins. These are minor panallergens found in fish, chicken, rabbit and snake meat. They are heat stable so are allergens of note.

High sulphites and high histamine often go hand in hand. Fresh fish is low in sulphites, but the amount increases in the fish as it is processed, canned or smoked. Sulphites are inorganic salts used in preservations and have the potential to cause symptoms of food intolerance to those sensitive to sulphites, this food intolerance is more common in asthmatics. An improvement in symptoms can be made with a change to a low sulphite diet.

Fish can be considered to be high in histamine, so is not suitable for people following a low histamine diet. The amount of histamine starts to increase once caught, so improperly handled and refridgerated fish can cause what is called 'scromboid poisoning'. The symptoms of this are very similar to a severe allergic reaction, so are often confused.

Fish is a low FODMAP food. FODMAP stands for Fermentable oligosaccharides, disaccharides, monosaccharides and polyols. Foods high in FODMAPs can cause symptoms of food intolerance, affecting the gastro intestinal system and this can be mistaken for a true IgE food allergy.

You can read more about Food Intolerances on the dedicated Food Intolerance Page.

There is currently no information on syndromes associated with fish allergy.

Occasionally there can be cross reactivity between fish and other products containing gelatin.

Other foods containing aldolase and enolase proteins include chicken, cod, catfish, salmon and tuna.

Other seafood which contains tropomyosin includes shrimp, prawns, crab, lobster, squid, oyster, snail and abalone.

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