Is tuna considered a shellfish?

Tuna is Not a Shellfish

No, tuna is not a shellfish. Tuna is a finfish, which belongs to a completely different biological classification than shellfish 1.

Classification of Seafood

Seafood is broadly categorized into two main groups:

1. Finfish (such as tuna, salmon, cod)

   • These are vertebrates with fins and scales
   • Tuna specifically belongs to the Scombroidea family 2
   • Major allergen in finfish is parvalbumin (12 kD protein)

2. Shellfish

   • Crustaceans: Shrimp, lobster, crab
   • Mollusks: Clams, oysters, mussels, scallops
   • Major allergen in shellfish is tropomyosin (38-41 kD protein)

Biological and Allergenic Differences

The distinction between tuna and shellfish is important for several reasons:

• Different allergens: The primary allergen in fish like tuna is parvalbumin, while in shellfish it's tropomyosin 2
• Cross-reactivity: While there is significant cross-reactivity within fish species (about 50% risk) and within shellfish species (about 75% risk), there is minimal cross-reactivity between fish and shellfish 2
• Consumption patterns: In the US, tuna is one of the most commonly consumed seafoods (2.2 lb per capita per year), alongside shrimp, salmon, tilapia, and pollock 1

Nutritional Considerations

Tuna has distinct nutritional properties compared to shellfish:

• Omega-3 content: Tuna, especially bluefin and albacore, is considered an oily fish high in long-chain omega-3 fatty acids (EPA and DHA) 1
• Mercury concerns: Tuna can contain mercury, with levels varying by species. Some large predatory tuna species may have higher mercury concentrations 3
• Fat content: The fat content in tuna products can vary significantly (3-33% of energy from fat), with water-packed tuna generally having a more favorable omega-3 to omega-6 ratio than oil-packed varieties 4

Clinical Implications

Understanding that tuna is not a shellfish has important clinical implications:

• Allergy management: Patients allergic to shellfish are not automatically allergic to tuna and vice versa
• Dietary recommendations: The American Heart Association recommends consuming fish, especially oily fish like tuna, at least twice a week for cardiovascular benefits 1
• Food challenge testing: When conducting oral food challenges, tuna and shellfish are handled differently. Interestingly, canned tuna (if tolerated) can sometimes be used to mask the aroma of other fish during testing 1

Important Distinctions for Patient Education

When educating patients about seafood:

• Clearly distinguish between finfish (like tuna) and shellfish
• Explain that allergies to one category don't necessarily mean allergies to the other
• Note that tuna from the Scombroidea family is often better tolerated even among those with other fish allergies 2
• Be aware that rare cases of Kounis syndrome (allergic acute coronary syndrome) have been reported after tuna consumption 5