Mercury in Fish: How to Choose Seafood That's Low in Mercury (and High in Omega-3s)
If you've ever stood in the seafood aisle wondering whether that piece of fish is "safe," you're not alone. Mercury is one of the most common seafood concerns we hear about at Sena Sea, and the good news is that choosing low-mercury fish doesn't have to be complicated. A few simple factors — fat content, lifespan, size, and where the fish comes from, tell you almost everything you need to know.
Here's how to think about it, so you can keep eating the fish you love with confidence.
The Short Answer: Choose High-Fat Fish With a Short Lifespan
In general, when you're concerned about mercury content, your best bet is high-fat fish with a shorter lifespan, think salmon. Here's why that combination matters so much, broken down by the four factors that actually drive mercury levels in seafood.
1. Fat Content
Fat content and mercury content are inversely correlated, meaning fattier fish are typically much lower in mercury. Mercury tends to bind to protein in fish tissue rather than fat, so the higher a fish's fat content, the more diluted its mercury concentration tends to be.
Copper River King salmon has the highest fat content of any wild salmon, followed by Copper River sockeye and coho — Copper River salmon in particular runs higher in fat than other wild salmon populations. Black cod (also known as sablefish) is another standout here, prized for its naturally high fat content.
2. Lifespan
Mercury accumulates in fish over time, so the longer a fish lives, the more mercury it tends to carry by the time it reaches your plate. This makes lifespan one of the most reliable predictors of mercury content.
Salmon have a short lifespan of just 4–5 years, which is a major reason they stay so low in mercury. Compare that to halibut, which can live anywhere from 25 to 50 years, giving it far more time to accumulate mercury. Sablefish falls somewhere in the middle with a medium lifespan.
3. Size
Size follows the same logic as lifespan: smaller fish generally contain less mercury than larger fish. Scallops, sardines, and shrimp are good examples of low-mercury seafood thanks to their size, while large predatory species like bigeye tuna and swordfish tend to carry much higher mercury loads.
4. Location
Where a fish is caught matters too. Alaskan fish, wild Alaskan salmon especially — is known for having very low mercury levels. Alaska health officials have actively monitored residents and have not found any cases of unsafe mercury exposure resulting from eating Alaska fish, and FDA testing data backs this up as well.
So Which Fish Should You Choose?
Putting it all together: Alaskan salmon is one of the best choices you can make, thanks to its high fat content, short lifespan, and the clean waters it comes from. Sablefish is also a great option — it's high in fat, though its medium lifespan means it accumulates a bit more mercury than salmon over time.
Halibut is where a little moderation comes in. It's lean, grows large, and lives a long time — all three factors that tend to raise mercury levels. That's exactly why, at Sena Sea, we specifically select smaller, younger halibut, which keeps mercury levels lower while still giving you that firm, flaky halibut texture you love.
Fish That Are High in Omega-3s and Low in Mercury
According to guidelines from the Alaska Department of Health, these are the fish to reach for more often:
- Wild Alaska salmon
- Black cod (sablefish)
- Herring
- Sardines
- Canned chunk light tuna
The 10 Fish Highest in Mercury
On the other end of the spectrum, the FDA's mercury testing data identifies these as the species with the highest mercury levels — worth limiting or avoiding, especially for pregnant women and young children:
- Tilefish
- Swordfish
- Shark
- King Mackerel
- Bigeye Tuna
- Orange Roughy
- Marlin
- Spanish Mackerel
- Grouper
- Bluefish
The Bottom Line
Mercury doesn't have to be scary once you understand what actually drives it: fat, lifespan, size, and location. Wild Alaskan salmon checks nearly every box for a low-mercury, high-omega-3 choice, which is exactly why it's been a staple of our family's fishing business for generations. And when it comes to fish like halibut, a little extra care in sourcing — like choosing smaller, younger fish — makes all the difference.
Have questions about mercury in a specific type of fish? Drop them in the comments — we love digging into the science behind what's on your plate.
