Madai (Red Seabream) from Hinata

You actually won’t find Tilapia very often at a sushi restaurant as nigiri. According to zukan-bouz, it’s mostly eaten as sashimi or grilled. The only times I’ve heard about Tilapia (Izumidai) at a sushi restaurant is when the restaurant is trying to pass it off as the more expensive Red Seabream (madai) prized for its delicate flavors or as the Red Tilefish (amadai).

As such, many of us are far removed from the source of the food that we eat. As a result we consumers don’t really know what actual food is suppose to look like. For example, how do you know what fresh fish looks like?

It’s a bit easier if the fish is sold whole — one thing to look for are clear jet black eyes. But some fish, like tuna, are too big to sell whole, so we only see the flesh in the supermarket or sushi counter. In those cases, we use the color of the fish as a proxy to whether the fish is good to consume or not. And usually, we think of the brighter the color, the fresher it is.

However, color isn’t as reliable indicator as you might think at first. First, is that sushi is often aged, so color is not necessarily indicative of deliciousness. Second, for fish like tuna and tilapia, some fish processors and packagers might treat them with carbon monoxide to help the fish retain its red color. This process is usually called “tasteless smoke” or “clearsmoke”.

Carbon monoxide treatment results in the formation of carboxymyoglobin in fish flesh that alters or fixes the color of the fish. It’s relatively stable when frozen and can last beyond the shelf-life of the fish.

Unlike sitting in the garage with your engine running, the amount of carbon monoxide used to treat the meat is small (0.4% of the air in a contained volume), and considered non-lethal by the FDA in the United States. Actually, the agency has never formally approved the practice, but rather looked at information provided by companies, and decided not to object. However, countries in the European Union, Japan, and Canada have banned the practice. Tilapia farmers from Latin America object to the practice, saying it is deceptive. In fact, China bans the sale of carbon monoxide treated tilapia for internal sales, but oks them for export, since the United States market accepts product with the practice.

The issue is contentious not only for seafood, but also for red meats as well.

Why is the issue so contentious?

Red Tilefish (Amadai) from Sushi Tomi

On one hand, when there’s two packages of tuna with the same expiration date on the supermarket shelf, where one is bright-red and the other one is brownish-red, which would you reach for? Both are actually safe to consume, but we eat as much with our eyes as we do with our taste and smell. Proponents argue that the seafood industry is responding to consumer demand for fish at all times of the year, even in land-locked places, that look fresh, at a low cost. To meet that demand, they found carbon monoxide treatment to be safe for consumption, and they believe themselves to be stewards of food safety by posting sell-by and use-by dates on all products.

On the other hand, while the treatment helps retain the color of the fish and may even help deepen it, carbon monoxide treatment doesn’t retain the quality of the fish. In fact, the retained color may last well beyond the shelf-life of the fish. Hence, opponents say this can easily trick consumers into buying fish that is well into realm of spoilage. Much of the tilapia in the United States market comes from China, and aquaculture there is poorly regulated with mixed results. That makes it difficult to make quality consumer judgements when visual cues are taken away as a tool to judge product quality.

On this, it seems to fundamentally come down to control and trust. In this day and age, consumers trust in large corporations and institutions has eroded significantly compared to 50 years ago. In addition, consumers want to be in control of how they evaluate what they consume. An increased transparency in industry practices, education of the public in the techniques and processes, and independent party evaluation and reviews of these practices will help win consumers over again.

Not so bright

So how do you tell the difference between one that’s been treated with carbon monoxide or not? It’s hard to tell, but the general giveaway is flesh that’s usually bright. Fresh, untreated tilapia tends to have a pink vein (the bloodline) running down the center of the filet. Carbon monoxide treated tilapia has a red and almost orange vein.

Check out the color of recently filleted tilapia. It’s more of a faded red and dark pink.

Recently filleted tilapia without carbon monoxide treatment

Even the side right underneath the skin isn’t bright red. Check out this video of the other side of the fillet.

Other side of recently filleted tilapia without carbon monoxide treatment

In contrast, tilapia that has been treated will either be marked on the packaging or it will appear bright red.

Carbon monoxide treated tilapia. source

Tilapia from Latin American farmers tend to be untreated and Chinese and Taiwanese farmers tend to be treated when exported, you can ask your local fish monger about the provenance of the fish. If it’s from Latin America, it’s probably not treated, according to a New York Times article from 2011 as it references Monterey Bay’s Seafood Watch. Checking it out in 2017, it ranks tilapia from China and Taiwan as “Good Alternative” when farmed in ponds, though data has been hard to obtain and there’s evidence that banned or illegal chemicals were used. While Latin American countries like Ecuador and Peru still rank as “Best Choice”, Mexico, Columbia when farmed in pens, and Honduras are ranked “Good Alternative”.

Tsukiji tuna buyer can tell fish quality by sight. Source

As for tuna, it’s a bit tougher. I’m sure the fish bidders in Tsukiji can tell just by looking at it under a flashlight.

Tuna treated with carbon monoxide is bright red when first defrosted, and fades within a couple of days to a watermelon pink.

- Tuna’s Red Glare? It Could Be Carbon Monoxide.

In my limited experience, supermarket sushi always looks oddly watermelon pink, whereas when I visit higher end sushi joints, tuna is never that lollipop color. Now, I strongly suspect that watermelon color is the result of carbon monoxide treatment. However, that’s not to say none of the other shades of red have or haven’t. I don’t have the experience to say one way or the other.

At the end of the day, ask your sushi chef

Though tilapia isn’t usually eaten as sushi, the practice of carbon monoxide treating other types of fish isn’t uncommon. Tilapia is just the most striking example.

As a consumer, we should be educated in the practices of the industry so they can properly judge the quality of product. In this case, know that the color of the fish isn’t as reliable indicator of quality as you might think, due to industry practice of carbon monoxide treatment. You will need other proxies for judging the fish’s quality.

In addition, consumers should also learn when different fish are in and out of season. By demanding fish that are in season, there will be less pressure on industry to provide fish out of season. Currently, the only way to provide fish out of season is to freeze and gas-treat it to make it look fresh. If we as consumers only eat seasonally, there’s less pressure for the seafood supply chain to resort to these techniques.

Lastly, vote with you wallet. By asking your sushi chef about which countries and where he gets his fish from will go a long way in letting them know you care about the food you eat, and they in-turn will ask the same of their fishmongers and suppliers. If they can’t answer your questions or are unwilling to, then you should find your sushi fix somewhere else.