Head to head
Tuna vs Salmon
Tuna and salmon are both large, powerful, commercially vital fish, but almost everything about how they live is different. One is built to cross oceans without pausing, the other to shuttle between fresh water and salt and stake everything on a single journey home.
| Tuna | Salmon | |
|---|---|---|
| Family | Scombridae (mackerel family) | Salmonidae |
| Warm-blooded | Partly, in several species | No, fully cold-blooded |
| Life cycle | Entirely at sea | Born in fresh water, grows at sea, returns to spawn |
| Can it stop swimming | No, it must swim to breathe | Yes |
| Breeding fate | Survives, spawns many times | Fatal for Pacific salmon; repeatable for Atlantic |
| Body shape | Stiff spindle, crescent tail | Streamlined but flexible |
| Swim bladder | Reduced or absent | Present |
| Typical water | Warm and temperate open ocean | Cold rivers and the North Atlantic or North Pacific |
Tuna vs Salmon: common questions
Is tuna or salmon healthier to eat?
Both are nutritious oily fish rich in protein and omega-3 fats, but they differ in a few ways. Salmon, especially farmed Atlantic salmon, is generally higher in total fat and omega-3s and in vitamin D. Tuna is leaner and very high in protein, and canned tuna is an inexpensive staple. The main caution is mercury: large predatory tuna such as bluefin and bigeye accumulate more mercury than salmon does, so health agencies advise limiting them, particularly for pregnant people and young children, while skipjack, the small tuna in most cans, is lower. Salmon is consistently low in mercury.
Why does a tuna have to keep swimming but a salmon does not?
It comes down to how each breathes and floats. Tuna use ram ventilation, meaning they keep the mouth slightly open and rely on forward motion to push water over the gills, so stopping means suffocating. Tuna have also reduced or lost the gas-filled swim bladder that lets most fish hover in place, so a motionless tuna sinks. A salmon, like most fish, actively pumps water over its gills using its mouth and gill covers and can do this while stationary, and it has a working swim bladder for buoyancy, so it can hold position in a current or rest in a pool.
Are tuna and salmon related?
Not closely. Tuna belong to the family Scombridae, alongside mackerel and bonito, within the large group of spiny-rayed fishes. Salmon belong to the family Salmonidae, together with trout, char, and grayling, in a separate and more ancient lineage. Their similar torpedo-ish shape and strong swimming reflect the shared demands of life as an active predatory fish rather than common ancestry. In cooking terms they are also different: salmon flesh is pink from carotenoid pigments in its diet, while tuna flesh is deep red from high concentrations of the oxygen-storing muscle protein myoglobin that supports its endurance swimming.