Most fish are good sources of dietary protein while also supplying essential minerals and heart-healthy omega-3 fatty acids. However, it's important to limit intake of larger, predatory fish like shark and swordfish, as they may contain high levels of mercury. In addition to fish, other foods that represent excellent sources of dietary protein include cheese, beans, lean red meats, seeds, poultry, yeast extract and legumes.
Tuna has the highest protein content compared to other types of fish. The bluefin and yellowfin species of tuna are especially high in protein, with bluefin offering up 29.91 g of protein per 100 g of dry-cooked fish, and yellowfin providing 29.15 g, according to the USDA National Nutrient Database for Standard Reference, Release 23. Canned light tuna, usually made from a blend of yellowfin and skipjack tuna, is also an excellent source of protein, supplying 29.13 g of protein per 100 g.
Besides tuna, other fish with high protein content, ranging from about 26 to 29 g per 100-g serving, include: anchovies, salmon, halibut, snapper and tilapia. Swordfish and cod also contain high amounts of dietary protein, each providing about 23 g per 100 g of fish. Lobster and other shellfish are good sources of protein as well, with lobster supplying 26.41 g per 100 g. Shrimp and crab meat are other high-protein sea crustaceans. While usually consumed in smaller amounts than fish flesh, fish eggs are also very protein-dense, offering about 29 g of protein per 100 g.
It's important to choose wisely when selecting high-protein fish in order to limit mercury exposure risk. While providing the highest protein content in fish, bluefin tuna, primarily consumed in sushi dishes, has been associated with high mercury levels. Light canned tuna, on the other hand, while providing only slighlty less protein than bluefin, has relatively low levels of mercury, according to the American Heart Association (AHA). Shrimp, salmon, cod and crab are also low in mercury, while swordfish and snapper contain higher amounts of mercury.
The AHA recommends eating at least two servings of fish per week, choosing mostly omega-3-rich, low-mercury fish like salmon and tuna -- both of which are also high in protein. Pregnant women and children should be especially careful to limit their fish intake to low-mercury fish and should not exceed two 6-oz. servings of fish per week. In addition to fish, the AHA also recommends eating the protein- and omega-3-rich plant foods tofu, soybeans, walnuts and flaxseed.