As the yearly limit on the local bigeye tuna fishery gets closer, Hawaii consumers should be both wary and informed when it comes to purchasing imported fish that have been treated for color using carbon monoxide. In truth, the hazardous effects of eating fish treated with carbon monoxide are not nearly so serious as the hundreds of deaths occurring from carbon monoxide poisoning each year, nor are they in any way related. Still, there are dangers to keep in mind.

Every year, hundreds of people die from carbon monoxide gasses, usually inhaled from improperly ventilated areas where a gasoline burning appliance is running. Carbon monoxide is especially toxic since it goes directly from the lungs to the bloodstream, where it replaces oxygen and destroys the blood’s ability to distribute oxygen throughout the body.

It is in this same fashion, by way of "pigment fixation," that carbon monoxide keeps fish looking fresh after being processed. The progression of oxidation, pertaining to flesh — such as fish or meat — is for the meat to turn a bright red at first, and then eventually a natural brown color. Anyone who has taken a steak out of the package to thaw in the refrigerator over night can attest to the fact that it just does not look the same the next day.

For this reason, processors use carbon monoxide to make sure their fish maintain the bright red color that consumers associate with freshness. Since carbon monoxide is ephemeral, a gas, it does not become absorbed in the fish after it has done its job of preserving the color. You are not breathing it, or even eating it for that matter. The Federal Drug Administration has declared carbon monoxide treatment of tuna to be "generally regarded as safe," even though it has been banned by other countries, including Japan, Canada and the European Union.

The main dilemma for consumers — and the main reason it has been banned in other countries — is that although carbon monoxide will preserve the color of the fish, it will not preserve the freshness. Fish that may otherwise be rotten or rancid will still have the appearance of being fresh. Cases of people buying fish that has expired but looks fresh are common. Consumers need to use other indicators to decide if the fish is truly fresh. The expiration date is a good place to start.

As the catch limit nears, dealers are forced to import and sell fish caught outside the islands. Much of it is treated with carbon monoxide. Use everything but the fish’s color to make your decision before buying. Tuna coloring varies anywhere from pink to red depending on the size of the fish, so again, color is not a great indicator. Quality tuna should be somewhat firm in texture and have no odor, no matter what the color.

If your family eats a lot of tuna, make sure to buy your tuna from quality sources you can trust.