The healthiest fish are small, oily, cold-water species: salmon, mackerel, anchovies, sardines, and herring. These five fish deliver the highest concentrations of omega-3 fatty acids, the lowest mercury levels, and a broad range of vitamins and minerals per serving. Nutritionists use the acronym SMASH (salmon, mackerel, anchovies, sardines, herring) as a shorthand for this group, and for good reason: a 3.5-ounce portion provides anywhere from 1,000 to 2,300 milligrams of omega-3s depending on the species.
Why Omega-3s Matter So Much
Omega-3 fatty acids are the primary reason fish stands apart from other protein sources. Your body can’t produce the two most beneficial forms, EPA and DHA, in meaningful quantities on its own. These fats reduce inflammation throughout the body, lower triglyceride levels, and help maintain healthy blood vessel function. Eating at least two servings of oily fish per week is associated with a 10% to 15% reduction in cardiovascular mortality risk, based on a large study published in JAMA Internal Medicine that tracked people both with and without existing heart disease. Oily fish specifically drove the benefit more than leaner varieties.
Fish consumption also appears to protect brain health over time. Research from the USDA’s National Agricultural Library has linked regular fish intake to lower rates of dementia and slower cognitive decline in aging adults. The DHA in fish is a structural component of brain cell membranes, so this connection makes biological sense.
The SMASH Fish, Ranked by Strengths
Salmon is the most popular of the group for good reason. It’s widely available, mild in flavor, and versatile in the kitchen. Fresh or frozen salmon contains just 0.022 ppm of mercury, making it one of the cleanest fish you can buy. It’s rich in both omega-3s and vitamin D, a nutrient many people are deficient in.
Sardines punch well above their weight nutritionally. A 3-ounce serving of canned sardines with bones delivers roughly 300 milligrams of calcium, about the same as a glass of milk. The soft, edible bones are the reason. Sardines are also extremely low on the food chain, which means they accumulate very little mercury over their short lifespans.
Mackerel has a tender texture and milder flavor than most people expect. Atlantic mackerel falls in the “Best Choices” category for mercury. King mackerel, however, is a completely different story and should be avoided due to high mercury, so always check which variety you’re buying.
Anchovies are one of the most omega-3-dense fish available relative to their size. They work especially well as a flavor ingredient rather than a standalone protein. When cooked into sauces or dressings, they dissolve completely, adding a savory depth without any fishy taste.
Herring is a staple across Scandinavian countries and delivers a nutrient profile comparable to sardines. It’s commonly sold pickled, smoked, or canned, making it a convenient option that requires no cooking.
Mercury Levels Across Common Fish
Mercury is the main safety concern with fish, and the differences between species are dramatic. FDA data shows fresh salmon averages 0.022 ppm of mercury, while swordfish averages 0.995 ppm, roughly 45 times higher. The general rule: the bigger and longer-lived the fish, the more mercury it accumulates.
Tuna falls somewhere in the middle and deserves special attention because so many people eat it regularly. Skipjack tuna (the type in most “chunk light” cans) averages 0.144 ppm. Albacore tuna, sold as “white” canned tuna, nearly triples that at 0.350 ppm. This is why federal guidelines classify skipjack as a “Best Choice” but albacore as only a “Good Choice,” meaning you should limit albacore to one serving per week.
The EPA and FDA recommend eating 2 to 3 servings of fish per week from the “Best Choices” category, or 1 serving per week from the “Good Choices” list. One serving is about 4 ounces. Fish to avoid entirely due to mercury include swordfish, shark, king mackerel, tilefish from the Gulf of Mexico, marlin, orange roughy, and bigeye tuna.
One protective factor worth knowing about: selenium, a mineral found naturally in most fish, can counteract some of mercury’s toxic effects. Research from the U.S. Geological Survey found that Chinook salmon has a selenium-to-mercury ratio of 27 to 1, meaning the protective mineral vastly outweighs the contaminant. This is another reason salmon consistently ranks at the top of healthy fish lists.
Wild Salmon vs. Farmed Salmon
This is one of the most common questions people have, and the answer is more nuanced than “wild is always better.” A 3-ounce fillet of wild salmon has fewer calories and half the total fat of the same amount of farmed salmon. Farmed salmon does contain more omega-3s in absolute terms, but it also carries more than double the saturated fat.
The bigger concern with farmed salmon is contaminant load. Levels of PCBs, a class of industrial pollutants linked to cancer and hormone disruption, are 16 times higher in farmed fish than in wild fish, according to Cleveland Clinic reporting. This gap has narrowed as farming practices have improved, but wild-caught salmon remains the cleaner option. If cost or availability makes wild salmon impractical, farmed salmon is still a net positive for your health compared to most other protein sources. The omega-3 benefits don’t disappear just because the fish was farmed.
Other Fish Worth Eating
The SMASH group gets the most attention, but several other fish are excellent choices. Trout, particularly rainbow trout, is high in omega-3s and low in mercury. Cod and haddock are lean white fish that provide high-quality protein with minimal fat, a good option if you’re watching calorie intake even though their omega-3 content is lower. Pollock is the fish used in most fish sticks and fast-food sandwiches, and in its unprocessed form it’s a solid, affordable protein source.
Shellfish like shrimp, scallops, and oysters also appear on the EPA’s “Best Choices” list. Oysters are particularly notable for their zinc content, providing several times the daily recommended amount in a single serving.
How Preparation Changes the Equation
A piece of salmon loses most of its health advantages when it’s battered and deep-fried. The frying oil adds inflammatory omega-6 fats that work against the omega-3s you’re trying to get. Baking, grilling, broiling, and poaching all preserve the nutritional profile. Canned fish is nutritionally comparable to fresh in most cases, and it’s significantly cheaper. Canned salmon actually retains its omega-3 content well, and canned sardines with bones provide that calcium bonus you won’t get from a fresh fillet.
For people who are pregnant or breastfeeding, the federal guidelines recommend 8 to 12 ounces of low-mercury fish per week. This is a recommendation to eat more fish, not less. The omega-3s in fish are critical for fetal brain development, and the benefits of eating low-mercury species outweigh the risks of avoiding fish altogether. Sticking to the SMASH fish, trout, pollock, and shrimp keeps mercury exposure minimal while maximizing nutritional value.