Sole is not high in mercury. It is one of the lowest-mercury fish you can eat, with an average concentration of just 0.056 parts per million (ppm) across all flatfish species that include sole. The FDA places sole in its “Best Choice” category, the safest tier in its fish consumption guidelines.
Mercury Levels in Different Sole Species
Not all sole is identical, but every commercially available variety tests well below the 1.0 ppm threshold the FDA considers concerning. FDA monitoring data from the 1990s through 2010 shows a narrow range across species:
- Yellowfin sole: 0.03 ppm (lowest)
- Generic sole: 0.042 ppm
- Petrale sole: 0.08 ppm
- Dover sole: 0.09 ppm
- Rex sole: 0.10 ppm
Even Rex sole, the highest on this list, contains roughly one-tenth the mercury limit. For context, high-mercury fish like swordfish and king mackerel typically average 0.7 to 1.0 ppm or more.
Why Sole Stays So Low in Mercury
Mercury accumulates as it moves up the food chain, a process called biomagnification. Large predatory fish that eat other fish for years build up the highest concentrations. Sole sits near the bottom of the food chain. It’s a small, bottom-dwelling flatfish that feeds primarily on worms, tiny crustaceans, and other invertebrates found in ocean sediment.
Because sole feeds on the seafloor, it does have some direct exposure to mercury that settles into sediments. Research comparing common sole to other species found that sole accumulates intermediate mercury levels in its liver tissue compared to predatory fish (which accumulate more) and plant-feeding fish (which accumulate less). But even with that sediment exposure, sole’s small body size and short food chain keep its mercury levels very low in the parts you actually eat.
Sole Compared to Other Popular Fish
If you’re choosing between common white fish at the grocery store, sole compares favorably to nearly all of them. Here’s how it stacks up using FDA data (mean mercury in ppm):
- Tilapia: 0.013 ppm
- Pollock: 0.031 ppm
- Whiting: 0.051 ppm
- Haddock: 0.055 ppm
- Flatfish (sole, flounder, plaice): 0.056 ppm
Sole lands right alongside haddock and whiting. Tilapia and pollock edge slightly lower, but the differences at these concentrations are negligible from a health standpoint. All of these fish fall comfortably in the “Best Choice” range.
How Much Sole You Can Safely Eat
Because the FDA categorizes sole as a “Best Choice” fish, adults can eat two to three servings per week (a serving is about 4 ounces). Pregnant and breastfeeding women get the same recommendation. Children can also eat sole freely within age-appropriate portion sizes, which are smaller: about 1 ounce for children ages 1 to 3, scaling up to 4 ounces by the teen years.
This is notably more generous than the guidelines for “Good Choice” fish like albacore tuna or halibut, which are limited to one serving per week due to moderate mercury levels.
Selenium Offers Additional Protection
Sole contains selenium, a mineral that helps your body counteract mercury’s harmful effects. What matters is the ratio between the two: when selenium outweighs mercury (a ratio above 1), the selenium can bind to mercury and reduce its toxicity. Common sole has a selenium-to-mercury ratio of about 3.95, meaning it contains nearly four times more selenium than mercury on a molar basis. This is among the highest protective ratios measured in seafood, which means the small amount of mercury in sole is further offset by its own mineral content.
A typical serving of common sole contains roughly 0.28 micrograms of selenium per gram of fish, alongside just 0.16 micrograms of methylmercury (the form your body absorbs). You’re getting meaningful nutritional benefit with minimal risk.
Fish to Avoid if Mercury Concerns You
If you’re watching your mercury intake closely, the fish to limit or skip entirely are large, long-lived predators. The FDA’s “Avoid” list includes shark, swordfish, king mackerel, tilefish from the Gulf of Mexico, bigeye tuna, marlin, and orange roughy. These species can carry mercury levels 10 to 20 times higher than sole. Swapping any of these for sole is one of the simplest ways to keep eating fish while minimizing mercury exposure.