Is tuna in the same food class as shellfish?

Tuna and Shellfish Classification: Different Food Categories

Tuna is not in the same food class as shellfish. 1

Taxonomic Classification

Seafood is divided into distinct biological groups with different taxonomic classifications:

• Fish (including tuna)

  • Vertebrates
  • Belong to the phylum Chordata
  • Examples: tuna, salmon, cod

• Shellfish

  • Invertebrates
  • Divided into two major groups:
    1. Crustaceans: shrimps, crabs, lobsters (phylum Arthropoda)
    2. Mollusks: clams, oysters, mussels, scallops (phylum Mollusca)

Allergen Differences

The distinction between fish and shellfish is particularly important from an allergenic perspective:

• Fish allergens: The major allergen is parvalbumin (12 kDa protein) 2

  • Controls calcium flow in muscular sarcoplasm
  • Heat-resistant and resistant to enzymatic digestion

• Shellfish allergens: The major allergen is tropomyosin (38-41 kDa protein) 3, 4

  • Essential for muscle contraction in invertebrates
  • Other shellfish allergens include arginine kinase, myosin light chain, sarcoplasmic calcium-binding protein, and hemocyanin 4

Clinical Implications

This classification difference has important clinical implications:

1. Allergic cross-reactivity:

   • Cross-reactivity is common within fish species (50% risk) 2
   • Cross-reactivity is common within shellfish species (75% risk) 2
   • Cross-reactivity between fish and shellfish is uncommon 5

2. Dietary considerations:

   • Patients allergic to shellfish can typically consume fish safely
   • Patients allergic to fish may be able to consume shellfish safely

3. Food challenge testing:

   • In clinical food challenges, fish and shellfish are treated as separate categories 1
   • Canned tuna is sometimes even used as a masking agent for other fish in oral food challenges, indicating its distinct properties 1

Important Distinctions in Seafood

The term "seafood" encompasses three distinct groups:

1. Fish (finfish) - vertebrates
2. Crustaceans - invertebrates
3. Mollusks - invertebrates

While crustaceans and mollusks are often collectively called "shellfish" for culinary purposes, they belong to different phyla biologically 5. Tuna specifically belongs to the Scombroidea family of fish, which is taxonomically and allergenically distinct from shellfish 2.

Potential Confusion

One area of potential confusion is that both tuna and shellfish are found in marine environments and are considered "seafood." However, from biological, allergenic, and dietary classification perspectives, they are distinct food classes.

Note that while tuna can cause allergic reactions, these are typically due to either fish-specific allergens or, in the case of canned tuna, possibly due to scombroid poisoning (histamine fish poisoning) rather than shellfish-related allergens 6.