Fish and seafood species, freshness, safety, storage, nutrition, buying cues and cooking techniques.
Cooked Atlantic mackerel provides about 262 calories, 23.9 g protein and 17.8 g fat per 100 g, including roughly 1.2 g EPA+DHA. It is also exceptionally rich in vitamin B12. Atlantic mackerel should not be confused with high-mercury king mackerel.
Raw Atlantic cod is about 82 calories, 17.8 g protein and less than 1 g fat per 100 g. Dried salted cod concentrates protein and sodium as water is removed; desalting then changes the composition again.
Tuna often provides roughly 20–26 g protein per 100 g in water-packed products. Oil raises calories, and mercury varies by species: canned light, albacore and bigeye tuna should not be treated as interchangeable.
Hake is among the leaner fish choices: different raw species can range roughly from 65 to 90 calories and 1–2 grams fat per 100 grams. Protein may appear anywhere from about 12 to 18 grams because “hake” is not one species or one database entry.
Sardines combine three nutrients that are rarely this concentrated in one food: roughly 24–25 grams protein, more than 1 gram EPA+DHA, and—when canned with edible bones—around 300–400 milligrams calcium per 100 grams.
Hake and salmon can provide similar amounts of protein in a serving, but their energy profiles are very different. Hake is lean; salmon carries roughly 10 g more fat per 100 g and far more EPA and DHA.
Salmon and sardines are surprisingly close in protein and calories. Both provide EPA and DHA; cooked Atlantic salmon can land around 2 grams EPA+DHA per 100 grams, while canned sardines are often around 1.4 grams, depending on species and product.
Salmon combines roughly 18–22 g protein per 100 g with considerably more fat than lean white fish. That fat raises calories, but it is also where salmon carries substantial EPA and DHA.
Canned tuna can be a healthy protein food, but the type matters. FDA/EPA lists canned light tuna, usually skipjack, as a Best Choice and albacore/white tuna as a Good Choice because albacore typically contains about three times more mercury. For people who are pregnant or breastfeeding, canned light can fit 2–3 fish servings per week, while albacore is limited to one serving in a week.
The white material that appears on salmon during cooking is protein from the fish pushed out with water and then coagulated by heat. It is commonly called albumin. It is safe to eat and does not by itself mean the fish is spoiled or contains parasites. More tends to appear when cooking is especially hot or prolonged.
Canned sardines and tuna can both provide roughly 24–26 grams of protein per 100 grams, so protein is basically a tie. The difference appears in the rest of the package: sardines provide far more EPA and DHA, can add substantial calcium when the bones are eaten and average very low mercury. Tuna mercury varies by species.
Lean white fish often falls around 80–130 calories per 100 grams cooked, while many oily fish reach 180–250 because they contain more fat. That same fat explains their large advantage in EPA and DHA. Protein is much closer than the labels suggest: both groups commonly provide roughly 18–25 grams per 100 grams.