When you order fish, you make a decision based on a name. You may choose it for its flavor, its price, or what you have learned about its health benefits. You may also care about where it came from and how it was caught. All of those decisions depend on the fish actually being what you think it is.

Once a fish has been cut into a fillet, breaded, or served with sauce, you have much less to go on. The label becomes your connection to information you cannot see. If that connection is wrong, even a thoughtful purchase can lead somewhere you did not intend.

This has been found right here in Honolulu

A study published in 2020 used DNA barcoding to examine 75 fish samples from restaurants, grocery stores, and sushi bars in the greater Honolulu area. Researchers found that 21% were mislabeled. Swai was the most common substitute, appearing under names including red snapper, sea bass, and mahi-mahi.

That finding describes the samples in that study. It does not establish today's rate across Hawaiʻi. The researchers also cautioned that comparisons between locations can be misleading when studies sample different mixtures of restaurants and stores.

Still, the local finding gives us a concrete reason to ask questions. This is a problem that has been documented in familiar places where people buy meals and groceries.

A legal name can still leave you guessing

There are two issues worth separating. One is substitution: selling one species under the name of another. The FDA identifies selling less expensive fish as red snapper as an example of economic fraud.

The other is a name that covers several species. It may meet labeling requirements while leaving out information you would find useful. Here in Hawaiʻi, ʻahi commonly refers to both yellowfin and bigeye tuna. Asking which one is being offered gives you a more precise starting point.

The Honolulu researchers also identified conservation concerns hidden beneath generic, acceptable market names. A broad name can obscure the species even when the label does not count as mislabeling. “Is this label allowed?” and “Does this label tell me enough?” are different questions.

The consequences can reach beyond the price

Paying a premium price for a lower-cost substitute is the most obvious loss. It also interferes with your ability to decide what is worth buying. A less expensive fish may be perfectly welcome on your plate when it is honestly identified and priced.

Species identity can matter for health, too. Escolar and oilfish contain indigestible wax esters that can cause oily diarrhea and abdominal discomfort in some people. Hong Kong's Centre for Food Safety has documented complaints after fish labeled as cod were consumed. Cooking or freezing does not break down those wax esters.

Mercury is another reason identity matters. If you are choosing fish using species-based advice, a substitution can undermine that choice. It does not mean every mislabeled fish is hazardous, but it means you cannot reliably apply advice to a species you have not actually identified.

What can you ask at the counter?

You do not need to become a fish identification expert. Start with questions that make the seller's description more useful:

• What species is this? If the answer is ʻahi, ask whether it is yellowfin or bigeye. If it is sea bass, ask which kind.
• Where was it caught or raised? Ask about the harvest location, especially if buying local matters to you.
• Is it wild-caught or farmed? This helps describe the product and gives you information for any sourcing research you want to do.
• Can you check the supplier's label? When a menu gives only a broad name, the restaurant may have more detail in its purchasing records.
  
  

A person at the counter may need to check rather than know immediately. The useful distinction is whether the business can find a specific answer and is willing to provide it. Asking also tells sellers that identity matters to their customers.

What labels and appearances can tell you

A whole fish retains identifying features that a fillet has lost. That can help someone who knows the species, but it does not make every shopper an expert. A familiar-looking fillet or an attractive display is not proof of identity.

Traceability certification can add useful oversight. The Marine Stewardship Council's Chain of Custody system tracks certified seafood through the supply chain and uses checks that include DNA testing. It provides an additional reason for confidence, rather than a guarantee that mistakes never occur.

Buying locally can give you more opportunities to ask who caught the fish and where. The value is the information you can obtain and verify. A local label alone does not establish the species or the sustainability of a particular catch.

Make your next purchase more informative

Start with a fish you buy regularly. Find out its species, then use that information to look into the health or environmental questions that matter to you. Once you have a clear answer, it becomes easier to compare prices and recognize when another seller is offering something different under a similar name.

You should be able to enjoy seafood without having to investigate every meal. Clear identification is part of what you are paying for, and a specific question can help bring that expectation into the conversation.

Sources and further reading

• Seafood mislabeling in Honolulu, Hawaiʻi: 2020 study
• University of Hawaiʻi: Honolulu seafood study findings
• FDA: Seafood Species Substitution and Economic Fraud
• Centre for Food Safety: Oilfish Consumption and Oily Diarrhoea
• FDA: Mercury in Food
• Marine Stewardship Council: Tackling seafood fraud