This is the healthiest seafood, according to experts

A cornerstone of the widely revered Mediterranean diet, seafood has a number of benefits for the heart, brain, skin, immune system and more.

Seafood is a broad category — from fish to shellfish, mollusks, crustaceans, bivalves and everything swimming in between.

Although experts recommend varying the types of seafood you eat to get the most health benefits, some types of seafood are better for you and contain fewer contaminants than others. Which of these water-dwelling delicacies is best for your health?

We asked dietitians to share the healthiest types of seafood and which types to limit or avoid.

Is seafood healthy?

"Seafood is a wonderful food for overall health," Frances Largeman-Roth, a registered dietitian nutritionist, tells TODAY.com.

Seafood is an excellent complete protein. Often leaner and lower in unhealthy fats than red meat, most seafood options pack in the nutrients and benefits for fewer calories.

In addition to being a great source of lean protein, seafood provides brain-boosting, heart-protective omega-3 fatty acids, says Largeman-Roth. Omega-3 fatty acids are healthy fats that support many bodily functions. These include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DPA), per the Cleveland Clinic.

Omega-3s are essential nutrients, which means the body does not produce enough of them to survive and we have to get them from dietary sources, Kate Patton, registered dietitian with the Cleveland Clinic Center for Human Nutrition, tells TODAY.com.

Many seafood options are also rich in vitamins and minerals like vitamin D, vitamin B-12, zinc, calcium, iodine and magnesium, Largeman-Roth adds.

The Dietary Guidelines for Americans recommends adults eat at least eight ounces or two servings of seafood each week. People who are pregnant or breastfeeding should eat between eight and 12 ounces seafood per week, per the U.S. Food and Drug Administration.

What is the healthiest seafood?

In general, the healthiest fish and shellfish are:

• High in omega-3 fatty acids

• High in protein

• Low in mercury

• Sustainable

The healthiest seafood choices are very high in omega-3s, says Patton. “These have been show to lower inflammation, triglycerides, blood clots and lower risk of CVD (heart disease),” Patton adds.

These include fatty or oily fish. “All seafood is a great source of protein and nutrients, but choosing fatty fish will provide the added benefit of omega-3 fatty acid DHA and EPA, which are not available in many other foods,” says Largeman-Roth.

Healthier seafood options are also low in mercury and sustainable, Patton adds. Nearly all seafood, including fish and shellfish, contains trace amounts of mercury from the surrounding water, which they absorb when they feed, per the U.S. Food and Drug Administration.

For most people, the health risks of mercury through eating fish is not a concern, TODAY.com previously reported. However, fish and shellfish containing higher levels of mercury may be harmful to an unborn baby or young child, per the FDA, which is why it's advised that pregnant women and children eat fish lower in mercury.

There are many seafood options that are low in mercury and high in omega-3s. If you're looking to up your seafood intake, these are the best options according to dietitians.

Wild salmon

"Salmon is a seafood star," Largeman-Roth adds. Salmon, especially wild caught, is rich in healthy fats, protein, and has a delicious flavor that makes it a great choice for beginners and seafood lovers.

According to the U.S. Department of Agriculture, one serving or three ounces of wild salmon, cooked in dry heat (such as roasting or grilling), provides:

• 155 calories

• 22 grams of protein

• 6 grams of fat

"Wild salmon provides a ton (1570 mg in a 3-ounce serving) of omega-3s ... If you’re looking for the protective benefits of omega-3 for heart and brain health, salmon is the clear winner," says Largeman-Roth.

Salmon is a great source of lean protein, Kimberly Snodgrass, registered dietitian nutritionist and spokesperson for the American Academy of Dietetics, tells TODAY.com. "It also has vitamin D, vitamin E, it several B vitamins. It's a really good fish, it's usually one of my first choices," Snodgrass adds.

Wild sockeye salmon provides the highest vitamin D content of all salmon species, Largeman-Roth adds, and it's more sustainable than the farmed types.

Sardines

Sardines are another top choice. These tiny fish are nutritional powerhouses and often more affordable and accessible options.

According to the USDA, one serving (or about a half-cup drained) of canned sardines in oil provides about:

• 200 calories

• 22 grams of protein

• 13 grams of fat

Sardines are a good source of healthy fats, including EPA and DHA omega-3 fatty acids. In addition to essential fatty acids and protein, sardines are rich in calcium, vitamin D, vitamin B12, potassium, selenium, iron, zinc and choline, TODAY.com previously reported.

Sardines are also naturally very low in mercury, “because they’re low on the food chain,” says Largeman-Roth. They're inexpensive and shelf-stable, lasting for years unopened — making them an excellent choice for your health and your wallet, too.

Sablefish (black cod)

Also known as black cod, sablefish is a delicious and sustainable cold water fish that's packed with nutrients.

According to the USDA, one serving or three ounces of black cod or sablefish, cooked in dry heat, provides roughly:

• 212 calories

• 15 grams of protein

• 16 grams of fat

• 0 grams of carbohydrates

"Sablefish is an omega-3 powerhouse that is buttery and rich in flavor. One 3-ounce serving boasts more than 1,500 mg of omega-3 DHA and EPA combined, making it a top source of omega-3s," says Largeman-Roth.

In addition to healthy fats, sablefish is also a good source of protein and packed with other nutrients, including potassium, magnesium, and vitamins B12 and B6.

"Look for wild-caught sablefish from Alaska, which means it’s guaranteed to be sustainable. Sablefish is also low in mercury, making it a healthy pick for pregnancy," says Largeman-Roth.

Atlantic mackerel

Atlantic mackerel is another top choice among experts.

According to the USDA, one serving or three ounces of Atlantic mackerel, cooked in dry heat, provides:

• 223 calories

• 20 grams of protein

• 15 grams of fat

• 0 grams of carbohydrates

Atlantic mackerel is an oily fish that's rich in omega-3s and other nutrients, says Snodgrass. These include calcium, phosphorus, vitamin D and vitamin E.

It's important to opt for Atlantic mackerel or smaller mackerel, as larger mackerel can contain more contaminants like mercury.

Shrimp

Shrimp are delicious and easy to cook. That’s why they are one of the most popular types of seafood eaten in the U.S., TODAY.com previously reported.

According to the USDA, one serving or three ounces of cooked shrimp provides roughly:

• 99 calories

• 24 grams of protein

• 13 grams of fat

• 0 grams of carbohydrates

While shrimp are lower in omega-3s than the other fish on this list, they are an incredible source of protein while very low in fat, making them a great low-calorie protein choice.

Shrimp are also rich in phosphorus, B vitamins and contain high amounts of a carotenoid called astaxanthin. Research suggests astaxanthin has antioxidant and anti-inflammatory properties.

Since it’s smart to include a variety of seafood in your diet, mix it up with salmon, shrimp and other types of seafood," says Largeman-Roth.

Canned vs. fresh seafood

Canned or tinned seafood is often just as healthy as fresh, the experts note. "Both can be great choices," says Largeman-Roth.

Fish and shellfish that's canned provides the same nutrients and benefits as the fresh versions but in a pre-cooked, shelf-stable, convenient package, TODAY.com previously reported.

"Canned seafood is an excellent choice when you’re trying to stick to a budget. It’s also great to keep on hand because it lasts for months in the pantry," says Largeman-Roth.

However, depending on what the canned seafood is packed in and the added ingredients, it can be higher in fat or salt, Largeman-Roth notes. Opt for tinned seafood that is packed in water or extra virgin olive oil, lower in sodium, safe-caught and in BPA-free cans.

Which seafood is best to eat for weight loss?

If you're looking for a low-calorie seafood, the experts recommend shrimp, halibut, cod or tuna.

"One 3-ounce serving of baked halibut is less than 100 calories, with 19 grams of protein. The same serving of cod has just 71 calories and 17 grams of protein," says Largeman-Roth.

Mollusks such as clams, oysters and mussels are also low in calories and often packed with nutrients such as zinc, Largeman-Roth adds.

"There is no magic bullet when it comes to certain fish helping (with) weight loss," says Patton. Moderation is key, and ensuring your seafood intake is part of a well-balanced diet with plenty of vegetables, fruits, whole grains and legumes, Snodgrass adds.

What fish is safest to eat every day?

“While all seafood is generally healthy, if you plan to eat it every day or more than the recommended twice per week, it’s best to opt for species lower in mercury," says Largeman-Roth. These fish include sardines, wild salmon, shrimp, tilapia, clams and scallops.

While it may be safe for some adults to eat these fish daily, it depends on your health status. People who are pregnant and breastfeeding should choose low-mercury seafood but limit intake to 12 ounces per week, according to the FDA.

Seafood that’s higher in mercury should not be eaten daily and limited to once a week, at most.

Which seafood is least healthy?

The least healthy fish is high in mercury, the experts note. "It's recommended to avoid species very high on the food chain," says Largeman-Roth. These include swordfish, shark, albacore tuna, yellowfin tuna, tilefish and Spanish mackerel, according to the FDA.

If you can, avoid or limit eating farm-raised seafood and always opt for wild caught, the experts note.

"Wild caught means the fish was caught from its natural habitat, while farm raised can be raised in penned off areas of water and are fed different diets compared to wild fish, changing the quality of the fish itself," Patton adds.

"When it comes to contaminants and food safety, I think the source matters as much as the species, so I seek out wild, sustainable sources, ideally caught within the U.S.," says Largeman-Roth.