Fish & Marine Animals comparison

Tuna vs Mackerel: Key Differences Explained

The short answer

Both sit in the family Scombridae and share finlets behind the dorsal and anal fins plus a keeled tail base. Tunas belong to the tribe Thunnini and are deep-bodied, torpedo-shaped ocean fish that use counter-current heat exchangers to hold swimming muscle, and in some species the eyes and viscera, above the surrounding water temperature. Mackerels are slimmer, usually far smaller, patterned with bars or spots, and the common Atlantic kinds stay at water temperature throughout.

The main difference

Tunas are deep-bodied Thunnini that keep swimming muscle warmer than the sea, whereas mackerels are slimmer scombrids that generally stay at ambient temperature.

Fish counters, menus and market names use tuna and mackerel loosely, and both cover several genera, so readers often want to know whether a mackerel is simply a small tuna and what actually separates the two groups within one family.

At a glance

Comparison of Tuna and Mackerel across 6 dimensions, with an interpretation of each difference.
What differs	Tuna	Mackerel	What it means
What each name covers	The tribe Thunnini, around fifteen species in genera such as Thunnus, Katsuwonus, Euthynnus and Auxis	Several separate scombrid genera, including Scomber, Scomberomorus and Rastrelliger	Tuna is a reasonably tight group, while mackerel is a looser label applied across parts of the family.Regional markets stretch both names further, and some fish sold as mackerel or as tuna belong to neither group.
Typical size	From skipjack at under a metre to Atlantic bluefin regularly over two metres and several hundred kilograms	Atlantic mackerel usually about 30 to 45 cm; king and Spanish mackerels reach well over a metre	Size separates the extremes reliably but fails in the middle, where a large Scomberomorus overlaps small tunas.
Body temperature	Regionally endothermic, using retia mirabilia to keep muscle and often eyes and viscera above ambient	Ectothermic in the common Scomber mackerels, tracking surrounding water temperature	Warm muscle lets tunas sustain speed in cold water and range into higher latitudes than most scombrids.Endothermy is not uniform across Thunnini; the degree and the tissues warmed differ between species.
Body shape	Deep, robust, tapering sharply to a narrow keeled peduncle, with fins that fold into body grooves	Slender and near-cylindrical, less deep-bodied, with a comparatively slim profile	Tuna proportions are shaped for continuous high-speed cruising; mackerels are built for a more variable pace.
Markings	Mostly plain metallic blue to dark above and silver below, sometimes with pale spots or bars on the flanks	Usually strongly marked, with wavy dark bars in Atlantic mackerel or spots in Spanish and king mackerels	Flank pattern is the quickest field or counter check when size is not decisive.
Swimming and ventilation	Continuous swimming with a stiff body and lunate tail, relying on ram ventilation to move water over the gills	Also a fast schooling swimmer, though with a more flexible body; Atlantic mackerel lacks a swim bladder	Both are built to keep moving, but the tuna carries that requirement much further into its anatomy.

What each name covers: TunaThe tribe Thunnini, around fifteen species in genera such as Thunnus, Katsuwonus, Euthynnus and Auxis
MackerelSeveral separate scombrid genera, including Scomber, Scomberomorus and Rastrelliger
Tuna is a reasonably tight group, while mackerel is a looser label applied across parts of the family.Regional markets stretch both names further, and some fish sold as mackerel or as tuna belong to neither group.
Typical size: TunaFrom skipjack at under a metre to Atlantic bluefin regularly over two metres and several hundred kilograms
MackerelAtlantic mackerel usually about 30 to 45 cm; king and Spanish mackerels reach well over a metre
Size separates the extremes reliably but fails in the middle, where a large Scomberomorus overlaps small tunas.
Body temperature: TunaRegionally endothermic, using retia mirabilia to keep muscle and often eyes and viscera above ambient
MackerelEctothermic in the common Scomber mackerels, tracking surrounding water temperature
Warm muscle lets tunas sustain speed in cold water and range into higher latitudes than most scombrids.Endothermy is not uniform across Thunnini; the degree and the tissues warmed differ between species.
Body shape: TunaDeep, robust, tapering sharply to a narrow keeled peduncle, with fins that fold into body grooves
MackerelSlender and near-cylindrical, less deep-bodied, with a comparatively slim profile
Tuna proportions are shaped for continuous high-speed cruising; mackerels are built for a more variable pace.
Markings: TunaMostly plain metallic blue to dark above and silver below, sometimes with pale spots or bars on the flanks
MackerelUsually strongly marked, with wavy dark bars in Atlantic mackerel or spots in Spanish and king mackerels
Flank pattern is the quickest field or counter check when size is not decisive.
Swimming and ventilation: TunaContinuous swimming with a stiff body and lunate tail, relying on ram ventilation to move water over the gills
MackerelAlso a fast schooling swimmer, though with a more flexible body; Atlantic mackerel lacks a swim bladder
Both are built to keep moving, but the tuna carries that requirement much further into its anatomy.

How they are related

Both belong to Scombridae, the mackerel and tuna family, within the wider group that also holds bonitos and wahoo. Tunas form the tribe Thunnini, roughly fifteen species across genera including Thunnus, Katsuwonus, Euthynnus and Auxis. Mackerel is applied across several separate genera, so it is a looser label than tuna and not a single lineage. That means a mackerel is not a small tuna, but they are relatives inside one family with a great deal of shared anatomy.

A note on naming: Both names cover groups. Tuna refers to the tribe Thunnini, but mackerel is a market and vernacular label spread across Scomber, Scomberomorus, Rastrelliger and others, and some fish sold under either name are not scombrids at all.

Telling them apart

Look first at depth of body and at flank pattern. A tuna is a thick, deep-bodied fish that narrows abruptly to a slim tail base carrying lateral keels, with a stiff crescent tail and mostly plain metallic sides. A mackerel is slimmer and more cylindrical, and usually well marked, with wavy dark bars across the back in Atlantic mackerel or rows of yellowish spots in Spanish and king mackerels. Both show the small separate finlets behind the dorsal and anal fins.

Thick-bodied, plain silver flanks, a very narrow keeled tail base and fins that tuck into grooves: tuna. Slimmer, strongly barred or spotted flanks, less bulk through the shoulder: mackerel. Both show finlets, so finlets alone will not settle it. If the fish is over two metres and deep-bodied, it is a tuna; if it is a well-marked half-metre schooling fish from the shelf, mackerel is the safer call.

Habitat and distribution

Tunas are largely oceanic, crossing basins and diving through the thermocline, with bluefin ranging into cold northern water and skipjack concentrated in the tropics. Mackerels are more coastal and shelf-associated, schooling in surface and mid-water over continental shelves and moving seasonally along coastlines. The ranges overlap widely, and both groups turn up in the same fisheries, but a fish taken far offshore in deep blue water is more likely a tuna than a Scomber mackerel.

Diet and ecological role

Both are pursuit predators of the open water. Mackerels feed heavily on zooplankton, small crustaceans and larval and small schooling fish, with Atlantic mackerel filtering copepods at some sizes and switching to fish as it grows. Tunas take fish, squid and crustaceans, with larger species specialising on schooling fish and cephalopods and diving deep to feed. Both groups sit mid-chain, eating abundant small prey and in turn feeding sharks, billfish, seabirds and marine mammals.

Behaviour

Schooling defines both. Mackerels form dense surface schools that shift shape rapidly and often mix with other small pelagic fish. Tunas school by size and species, sometimes in association with floating objects, dolphins or seamounts, and undertake long directed migrations that tagging has traced across whole ocean basins. Neither group holds territory. Movement in both is driven by temperature fronts, prey concentrations and spawning, so distribution changes between seasons and between years.

Senses and adaptations

The tuna heat-exchange system is the standout adaptation: dense networks of small arteries and veins, the retia mirabilia, run counter to one another so that heat from working muscle is retained rather than lost at the gills. Several species also warm the eyes and brain, which is thought to keep vision responsive during rapid dives into cold water. Mackerels lack that arrangement and rely instead on manoeuvrability, schooling and large surface area of gill for oxygen uptake.

More on this topic: Animal senses and adaptations.

Lifespan and life stages

Lifespans differ by roughly an order of magnitude across the two labels. Atlantic mackerel is often aged to somewhere around ten to twenty years, with growth slowing markedly after maturity. Large tunas live longer, and Atlantic bluefin has been aged well beyond twenty years using otolith and spine sections. Skipjack, at the small end of the tuna tribe, is short-lived and fast-growing by comparison. All ageing estimates depend on method, region and the sample of fish examined.

People and these animals

Both are among the most heavily fished marine fish in the world and both are central to global seafood markets, from canned skipjack to salted and smoked mackerel. That pressure has driven decades of management effort through regional fisheries bodies, with quota systems, gear rules and stock assessments. Some populations have rebuilt after tight management while others remain depleted, and status varies by stock, not just by species, which is why blanket claims about either group are unhelpful.

Conservation context

Assessment for both groups is done stock by stock rather than species by species, since an eastern and a western population of the same fish can be in very different condition. Several tuna stocks have shown rebuilding under stricter quotas, while others remain a concern, and mackerel stocks fluctuate with recruitment and with disputes over shared quotas. Consult the current IUCN Red List entry and the relevant regional fisheries assessment rather than assuming a fixed status.

Tuna and mackerel status is assessed by stock as well as by species and changes with each assessment cycle. Check the current IUCN Red List entry and the relevant regional fisheries management assessment.

What they have in common

Both belong to Scombridae and share finlets, a keeled caudal peduncle and a stiff crescent tail.
Both are fast schooling pelagic predators that feed on small fish, squid and crustaceans.
Both support very large commercial fisheries managed through regional assessment bodies.
Both cover multiple species, so any single figure is a range across a group.

Key differences

Tunas are deep-bodied and heavy through the shoulder; mackerels are slim and near-cylindrical.
Tunas use counter-current heat exchangers to hold muscle above ambient temperature; common mackerels do not.
Mackerels are usually strongly barred or spotted, while tunas are mostly plain metallic on the flanks.
The largest tunas exceed two metres, whereas most mackerels stay well under one.
Tuna is a defined tribe, Thunnini, while mackerel is applied across several unrelated scombrid genera.

Where people go wrong

Assuming mackerel is simply the small end of the tuna group, when it spans several separate scombrid genera.
Using finlets as a diagnostic, when both groups carry them as a shared family feature.
Treating all tunas as equally warm-bodied, when the extent of endothermy differs between species.

Frequently asked questions

Is a mackerel just a small tuna?

No. Both are scombrids, but tunas form the tribe Thunnini while mackerel is applied across several other genera in the family, so the two labels are not nested. Size supports the impression, since most mackerels are far smaller, but it breaks down with king and Spanish mackerels that outgrow small tunas. The real division is anatomical: body depth, tail base structure and the presence or absence of heat exchangers.

Which tunas are warm-bodied, and are any mackerels?

Regional endothermy is characteristic of the tuna tribe, though the degree varies: bluefin species warm muscle, viscera and eyes substantially, while smaller tunas warm less tissue. Among mackerels the familiar Scomber species are ectothermic. Elsewhere in the family the butterfly kingfish has cranial heat-exchange tissue, so the trait is not perfectly aligned with the tuna label. Treat endothermy as a strong tendency in tunas rather than an absolute rule.

What separates a Spanish mackerel from a small tuna on the counter?

Look at body depth and flank pattern. Spanish and king mackerels are elongate and comparatively slim, with rows of spots or bars along the sides and a long low second dorsal. Small tunas such as skipjack or little tunny are noticeably deeper through the shoulder, plainer on the flanks apart from stripes low on the belly in skipjack, and have a stouter tail base with prominent keels.

Why must tunas keep swimming continuously?

They rely on ram ventilation, driving water over the gills by forward motion rather than pumping it with the mouth and opercula, so stopping means losing oxygen flow. Continuous swimming also maintains lift, since tunas are denser than seawater and several species have reduced or absent swim bladders. Many mackerels swim near-continuously too, and Atlantic mackerel lacks a swim bladder, so this is a family-wide tendency taken furthest by tunas.

Do tuna and mackerel both have those little fins behind the dorsal?

Yes. The small separate finlets running from the second dorsal and anal fins back to the tail are a shared scombrid feature present in both groups, along with a narrow keeled caudal peduncle. They are thought to influence flow along the tail and reduce drag at speed. Because both groups have them, finlets confirm you are looking at a scombrid but do not distinguish a tuna from a mackerel.

Read the full profiles

Sources and methodology

How this comparison is built: FaunaHub comparisons are assembled from the sourced animal profiles behind them rather than written as standalone claims. Figures such as size, mass, and lifespan are typical ranges that vary by subspecies, population, region, sex, age, and — where relevant — whether an animal lives in the wild or under human care, so they are presented as ranges rather than fixed values. Where a common name covers a group rather than a single species, the page says so instead of implying a species-to-species match. Conservation status changes over time and should be confirmed against the current IUCN Red List. Dimensions that could not be supported from the underlying profiles are omitted rather than filled in.

What this page does not do: it does not rank the two animals, predict the outcome of a confrontation, or present either one as stronger, smarter, or better. It is not veterinary, medical, first-aid, handling, capture, hunting, or pest-control guidance. For an animal in your care, or any situation involving injury, contact a qualified veterinarian, your local wildlife authority, or emergency services.

Sources and further reading

Authoritative references used for general educational context. External links open in a new tab. These sources do not endorse FaunaHub.

UniversityAnimal Diversity Web — Thunnus thynnus (Atlantic bluefin tuna) — University of Michigan species account
GovernmentNOAA Fisheries — Pacific Bluefin Tuna — U.S. government species page for bluefin tuna
Wildlife referenceIUCN Red List of Threatened Species — Authoritative source for current conservation status
GovernmentNOAA Fisheries — Marine Life — U.S. government science agency for marine species and habitats
ReferenceWoRMS — World Register of Marine Species — Authoritative register of marine species names
ReferenceEncyclopaedia Britannica — Animals reference — Editor-reviewed encyclopedia overview entries
UniversityAnimal Diversity Web — University of Michigan Museum of Zoology — Peer-edited reference accounts for animal species

Last updated: 2026-08-04