If you are looking for the fish with the most protein, yellowfin tuna stands out clearly. After that, the gaps become much smaller: mackerel, trout, swordfish, cod and salmon are separated by only a few grams of protein.
The next table keeps the comparison consistent by using cooked fish per 100 grams. Canned and salted products come later because draining, oil, water loss and salt can substantially change both concentration and calories.
Protein and calories per 100 g cooked
| Fish | Protein | Calories |
|---|---|---|
| Yellowfin tuna | 29.2 g | 130 |
| Atlantic mackerel | 23.9 g | 262 |
| Farmed rainbow trout | 23.8 g | 168 |
| Swordfish | 23.5 g | 172 |
| Wild rainbow trout | 22.9 g | 150 |
| Atlantic cod | 22.8 g | 105 |
| Farmed Atlantic salmon | 22.1 g | 206 |
| Haddock | 20.0 g | 90 |
Two things matter more than the exact order of every row. First, tuna is genuinely higher: it provides about 5–9 g more protein per 100 g than the other fish listed. Second, among fish clustered around 22–24 g, ranking by tenths of a gram creates a precision that usually does not matter at the table.
Mackerel and cod are a good example. They provide 23.9 and 22.8 g protein — only 1.1 g apart — but 262 versus 105 calories per 100 g. That much larger difference is mostly about fat.
Tuna: high protein with relatively few calories
Cooked yellowfin tuna provides about 29.2 g protein and 130 calories per 100 g. A 5-ounce / 142 g serving supplies roughly 41 g protein, so it is a very concentrated protein food without much fat.
That does not mean every product called “tuna” has the same nutrient profile or the same mercury guidance. Species and product type matter, especially for pregnant or breastfeeding people and children.
Mackerel, salmon and cod: similar protein, very different fat
Atlantic mackerel provides about 23.9 g protein and 262 calories per 100 g; farmed Atlantic salmon about 22.1 g and 206 calories; cod about 22.8 g and 105 calories. Salmon and cod differ by only 0.7 g protein, but salmon is about 100 calories higher per 100 g.
The main reason is fat. Salmon commonly contains more than 10–12 g fat per 100 g, while cod is close to 1 g. Mackerel and salmon also provide EPA and DHA long-chain omega-3 fats. A higher calorie number is therefore not automatically a disadvantage; it reflects a different nutritional package.
Trout sits in the middle
Farmed rainbow trout is around 23.8 g protein per 100 g and wild rainbow trout about 22.9 g. In a 5-ounce / 142 g serving, that is roughly 34 versus 33 g protein — a difference of about one gram.
For a real meal, taste, price, availability and fat content are likely to matter more than that small protein gap.
Mercury can matter more than the protein ranking
Mercury does not track protein. A fish can provide about 23 g protein and still come with different consumption advice because of the species. Swordfish is the clearest example here: it provides about 23.5 g protein per 100 g, almost the same as trout and mackerel, but FDA/EPA places swordfish in its “Choices to Avoid” category for people who are pregnant or breastfeeding and for children.
Tuna also needs species-level context. FDA/EPA lists canned light tuna among “Best Choices,” albacore/white tuna among “Good Choices,” and bigeye tuna among “Choices to Avoid” for those groups. The word “tuna” by itself is not enough to describe mercury exposure.
For most adults, protein can be one useful comparison. For groups who need to pay closer attention to mercury, the exact species can be more important than gaining one or two extra grams of protein.
Fresh cod, salted cod and canned fish are different products
The cooked fresh cod in the table provides about 22.8 g protein and 105 calories per 100 g. Salted cod loses water during curing and becomes much higher in sodium; desalting changes it again. It should not be treated as nutritionally identical to simply cooked fresh cod.
Canned fish changes for similarly concrete reasons. Drained sardines in oil provide about 24.6 g protein per 100 g, and drained anchovies can approach 28.9 g. Less water makes the protein more concentrated, while added oil can raise calories and salt can raise sodium substantially.
Serving size changes the picture too. Twenty grams of anchovies provides about 5.8 g protein. A high per-100-g number does not mean anchovies are usually eaten in the same quantity as a fish fillet.
Protein in a normal serving
| Fish | Serving | Protein |
|---|---|---|
| Cooked tuna | 5 oz / 142 g | 41 g |
| Mackerel | 5 oz / 142 g | 34 g |
| Trout | 5 oz / 142 g | 34 g |
| Cod | 5 oz / 142 g | 32 g |
| Salmon | 5 oz / 142 g | 31 g |
| Canned sardines | 3.75 oz can / ~106 g | ~26 g |
At a normal serving size, mackerel, trout, cod and salmon still cluster closely at about 31–34 g protein. Tuna remains the one that clearly separates itself, at roughly 41 g in a 5-ounce serving.
So which fish is best if protein is the goal?
For a lot of protein with relatively few calories, tuna, cod and haddock perform especially well. If you also want more long-chain omega-3 fat, salmon and mackerel provide similar protein to cod but come with more fat and energy.
If mercury guidance applies to you or your child, the exact species matters more than a small difference in the ranking. The useful takeaway is not that one fish wins every category, but that some protein differences are meaningful while many others are too small to outweigh fat, omega-3s, mercury, sodium in processed products, price or preference.
Sources
- USDA FoodData Central — Fish composition.
- FDA/EPA — Advice about Eating Fish — Mercury-based fish guidance.