Sole is not high in mercury. It’s one of the lowest-mercury fish you can eat, with an average concentration of just 0.056 parts per million (ppm). The FDA and EPA jointly classify sole as a “Best Choice” for seafood consumption, their highest safety rating.
How Sole Compares to Other Fish
To put 0.056 ppm in perspective, high-mercury fish like swordfish and king mackerel contain mercury levels above 0.7 ppm, roughly 12 times higher than sole. The FDA groups sole with other flatfish (flounder and plaice), and the entire category averages the same low number. Among individual sole species, the differences are minimal: Dover sole tested at 0.09 ppm and Petrale sole at 0.08 ppm in FDA monitoring samples.
Sole falls in the same low-mercury range as other popular white fish like cod, tilapia, and pollock. If you’re choosing between common white fish at the grocery store or a restaurant, mercury levels are similarly low across all of them. The fish that cause concern are large, long-lived predators: shark, swordfish, tilefish, king mackerel, and bigeye tuna. Sole is none of those things. It’s a small, bottom-dwelling flatfish with a short food chain, which is why mercury doesn’t accumulate in its flesh the way it does in apex predators.
Safety During Pregnancy and for Children
Because sole carries the “Best Choice” label, pregnant and breastfeeding women can safely eat two to three 4-ounce servings per week. Children can have two servings per week, with portion sizes adjusted by age. This is the most generous recommendation the FDA offers for any fish category, reflecting just how low the mercury risk is.
For the general adult population, there is no practical mercury concern with sole at normal eating patterns. You would need to eat enormous quantities consistently to approach any meaningful mercury exposure from this fish.
Nutritional Profile of Sole
Beyond its low mercury content, sole offers a solid nutritional package. A 100-gram serving of raw Dover sole provides about 14.8 grams of protein, 200 milligrams of omega-3 fatty acids, and 30 micrograms of selenium. That selenium content is particularly relevant because selenium helps the body counteract mercury’s effects, giving sole a natural built-in safety margin on top of its already low mercury levels.
Sole is a lean fish, so its omega-3 content is lower than fatty fish like salmon or mackerel. But it’s an excellent source of high-quality protein with very little fat, making it a good option if you’re looking for a light, clean protein source that you don’t need to worry about from a contaminant standpoint.
Why Some Fish Have More Mercury Than Others
Mercury enters waterways primarily through industrial pollution and natural geological processes. Bacteria in the water convert it into methylmercury, which gets absorbed by tiny organisms at the base of the food chain. Each step up the chain concentrates the mercury further, a process called bioaccumulation. A large tuna that has spent a decade eating smaller fish accumulates far more mercury than a sole that feeds on worms and small invertebrates on the ocean floor.
Three factors determine a fish’s mercury level: its size, its lifespan, and its position in the food chain. Sole checks all three boxes for low mercury. It’s small, relatively short-lived, and feeds low on the food chain. This is why flatfish as a group consistently test among the lowest-mercury seafood available commercially.