The tuna fish sandwich has a bad odor these days. A slow decline in sales of canned tuna became a free fall in 2004, the same year the FDA and EPA issued a joint recommendation that children and pregnant women limit tuna consumption because of concerns over mercury levels. Per capita intake of the fish has fallen by a third since then.

Bay Area father-son duo Malcolm and Sean Wittenberg were convinced that mercury was scaring consumers away from the kitchen staple. So, in 2005, they and their partners developed a proprietary technology that, for the first time, allowed fishermen, processors, and grocery stores to quickly and cheaply test every fish onsite for the toxic heavy metal. They launched Micro Analytical Systems Inc. to market the testing services.

But it was a harder sell than they expected. Seafood processors balked at the added cost. Tuna brands weren't interested. And enforcement of FDA mercury limits is minimal. So "everyone does just enough testing to satisfy the [FDA] rules," says Sean.

Even as the rejections rolled in, the Wittenbergs and one of their partners, Bryan Boches, saw a confluence of health and social trends transforming the super­market. If consumers would pay more for gluten-free bread or Greek yogurt, why not low-mercury tuna? High in protein and beneficial fatty acids, "tuna is pretty much a superfood, outside of the purity issue," says Boches, a former investment banker who wrote MASI's original business plan.

So they pivoted, with Sean and Boches buying MASI's assets and reformulating it as Safe Catch. (Malcolm is not involved.) In February, they began selling online the only commercially available canned skipjack tuna to guarantee a mercury content of less than 0.1 part per million, 1/10th the FDA limit. National grocery chains have already come calling, and Sean expects national retail distribution sometime in the first quarter of 2015. Safe Catch is betting that the $1.8 billion-a-year U.S. shelf-stable-tuna market will follow the path of other premium food categories, and that it will soon be reeling in sales.