Black cod (sablefish) contains moderate levels of mercury, averaging 0.361 parts per million (ppm) according to FDA monitoring data. That places it well below high-mercury fish like swordfish and shark, but notably higher than many popular seafood choices like salmon, shrimp, or regular cod. The FDA classifies black cod as a “Good Choice,” meaning it’s safe to eat but in smaller weekly quantities than the lowest-mercury options.
How Much Mercury Black Cod Contains
The FDA tested 26 samples of sablefish between 2004 and 2009. The average mercury concentration was 0.361 ppm, with a median of 0.265 ppm. Individual samples ranged widely, from as low as 0.09 ppm to as high as 1.052 ppm. That wide spread matters: the piece of black cod on your plate could contain anywhere from a modest amount of mercury to a level that exceeds what’s found in some higher-mercury species.
For context, the FDA’s action level for mercury in fish is 1.0 ppm. Most black cod falls comfortably below that threshold, but the occasional sample does brush up against it. The median of 0.265 ppm is a more useful number than the average here, since a few high readings pull the mean upward. Most fillets you encounter will be closer to that median figure.
Black Cod vs. Regular Cod
Despite sharing a name, black cod and regular cod are completely different species. Black cod is actually a sablefish, not a true cod, and the difference in mercury levels is significant. Atlantic cod averages roughly 0.082 ppm of mercury across FDA samples, and Pacific cod is even lower at about 0.078 ppm. That makes black cod roughly four to five times higher in mercury than the fish most people picture when they hear “cod.”
If you’ve been eating black cod thinking it carries the same low-mercury reputation as standard cod, this is worth knowing. Regular cod is classified as a “Best Choice” by the FDA, with three servings per week recommended. Black cod, at the “Good Choice” tier, comes with a lower recommended intake.
Why Black Cod Accumulates More Mercury
Two biological traits explain why sablefish carry more mercury than most whitefish. First, they live an exceptionally long time, with a maximum recorded age of 94 years. Mercury builds up in fish tissue over a lifetime, so longer-lived species simply have more years to accumulate it. Second, sablefish feed at a high trophic level, meaning they’re near the top of their food chain. Each step up the food chain concentrates mercury further, a process called bioaccumulation. A fish eating other fish that have already absorbed mercury ends up with compounding levels in its own flesh.
These same traits are why large, long-lived predators like swordfish, king mackerel, and tilefish top the mercury charts. Black cod doesn’t reach their extremes, but it follows the same biological pattern at a smaller scale.
How Often You Can Safely Eat It
The FDA’s “Good Choice” designation means one serving per week for adults. The Washington State Department of Health is more specific: one serving per week, with a serving size of about 8 ounces for a 160-pound adult (roughly 1 ounce per 20 pounds of body weight). If you eat black cod that week, you should skip other fish from the same mercury tier.
For pregnant or breastfeeding women and young children, the moderate mercury level is more relevant. These groups are typically advised to stick to “Best Choice” fish (two to three servings per week) and limit “Good Choice” fish to one serving. Black cod’s mercury content doesn’t make it off-limits, but it does mean being intentional about how often it appears in your rotation.
The Omega-3 Tradeoff
Black cod is one of the richest sources of omega-3 fatty acids among all fish. A 100-gram serving (about 3.5 ounces) delivers approximately 1.4 grams of EPA and DHA combined, split evenly between the two. That’s comparable to salmon and far exceeds what you’d get from standard cod, tilapia, or most other whitefish.
This creates a genuine nutritional tradeoff. The same deep-water, high-fat biology that makes sablefish an omega-3 powerhouse also makes it a more effective mercury accumulator. For most adults eating one serving per week, the cardiovascular and anti-inflammatory benefits of those omega-3s likely outweigh the mercury exposure. But if you’re eating black cod specifically for omega-3s and want to minimize mercury, wild salmon offers a similar fatty acid profile at a fraction of the mercury, typically around 0.022 ppm.
Keeping Mercury Exposure Low
If you enjoy black cod regularly, a few practical strategies help manage your overall mercury intake. Rotate it with lower-mercury, high-omega-3 options like salmon, sardines, herring, or anchovies. Pay attention to serving size, since mercury exposure scales directly with how much fish you eat. And avoid doubling up on moderate-mercury fish in the same week. Pairing a black cod dinner with a tuna lunch, for example, stacks two moderate-mercury sources in a short window.
Mercury levels can also vary from fish to fish. Larger, older sablefish tend to carry more mercury than younger, smaller ones. If you’re buying whole fish or selecting fillets, smaller portions from smaller fish are generally a safer bet, though this isn’t always information you can get at the counter.