Chilean sea bass has a moderate mercury level, averaging 0.354 parts per million (ppm). That places it in the FDA and EPA’s “Good Choice” category, meaning it’s not among the highest-mercury fish you need to avoid, but it does carry enough mercury to limit how often you eat it.
How Much Mercury Chilean Sea Bass Contains
Based on 74 samples tested by the FDA between 1994 and 2010, Chilean sea bass has a mean mercury concentration of 0.354 ppm, with a median of 0.303 ppm. The range is wide: some samples came back with no detectable mercury at all, while the highest recorded sample hit 2.18 ppm. That kind of variability is common in large, long-lived predatory fish, where mercury levels depend heavily on the size and age of the individual animal.
For context, the FDA’s action level for mercury in fish is 1.0 ppm. The average Chilean sea bass fillet sits well below that threshold, but the fact that some individual fish exceed it explains why this species lands in the middle tier rather than the safest category.
Why Mercury Varies So Much in This Fish
Chilean sea bass is actually Patagonian toothfish, a deep-water predator found in cold Southern Ocean waters. These fish can live more than 50 years and grow to around a meter in length by age 10. They’re primarily fish-eaters, feeding on smaller fish and squid throughout their lives. Both of these traits, long lifespan and predatory diet, drive mercury accumulation.
Mercury builds up in fish tissue over time through a process called bioaccumulation. Research on toothfish populations in Antarctic waters found a clear positive correlation between fish length and mercury concentration: bigger, older fish carry more mercury. A small Chilean sea bass fillet and a large one from the same waters can have very different mercury loads. You have no practical way to know the age or size of the fish that produced your fillet at a restaurant, which is why blanket serving limits exist.
How It Compares to Other Popular Fish
Chilean sea bass sits in the middle of the mercury spectrum. To put its 0.354 ppm average in perspective, here’s how it stacks up against fish you’re likely to encounter:
- Lower mercury (under 0.1 ppm): Salmon, shrimp, tilapia, pollock, catfish. These are FDA “Best Choices” you can eat two to three times per week.
- Similar range (0.2 to 0.5 ppm): Albacore tuna, halibut, snapper, grouper. All are “Good Choices” with the same one-serving-per-week guidance.
- High mercury (above 0.5 ppm): Swordfish (0.995 ppm), king mackerel (0.73 ppm), shark, bigeye tuna, tilefish from the Gulf of Mexico. The FDA says to avoid these entirely if you’re pregnant or feeding young children.
Chilean sea bass is roughly comparable to albacore tuna in terms of mercury exposure. Neither is dangerous in occasional servings, but neither belongs on your plate every day.
How Often You Can Safely Eat It
The FDA and EPA classify Chilean sea bass as a “Good Choice,” which translates to one serving per week for adults. A serving is about 4 ounces (113 grams) of cooked fish. Washington State’s Department of Health echoes this with a specific note: if you eat one serving of a “Limit” fish like Chilean sea bass in a given week, you shouldn’t eat other fish that week.
For children ages 1 to 11, serving sizes are smaller (roughly 1 to 3 ounces depending on age), and the same one-serving-per-week cap applies. Children are more vulnerable to mercury’s effects on the developing nervous system because of their smaller body weight and ongoing brain development.
Pregnancy and Nursing Considerations
Pregnant and breastfeeding women can eat Chilean sea bass, but should stick to the one-serving-per-week limit. It is not on the FDA’s “Choices to Avoid” list, which includes swordfish, shark, king mackerel, and bigeye tuna. The concern during pregnancy is that methylmercury crosses the placenta and can affect fetal brain development, so the goal is keeping total weekly mercury intake low rather than eliminating fish entirely.
Fish is a valuable source of omega-3 fatty acids that support fetal brain and eye development, so the FDA actively encourages pregnant women to eat fish, just lower-mercury options. If you love Chilean sea bass, having it once a week is within guidelines. If you want to eat fish more frequently during pregnancy, fill the remaining meals with “Best Choice” species like salmon, sardines, or shrimp.
The Selenium Factor
Most ocean fish contain selenium, a mineral that may offer some protection against mercury’s toxic effects. Selenium binds to mercury in the body and can reduce its ability to cause damage. Research has explored whether the ratio of selenium to mercury in a given fish species could refine safety advice, since a fish high in both selenium and mercury might pose less risk than its mercury number alone suggests.
Ocean fish generally have selenium-to-mercury ratios well above 1:1, which is considered the threshold where selenium’s protective effect kicks in. However, scientists haven’t yet reached consensus on how to apply these ratios to consumption guidelines. For now, the standard mercury-based serving limits remain the most reliable tool for managing your exposure.