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Blue runner (Caranx crysos): the jack that conquered the Mediterranean northwards in 30 years — as far as the Ligurian Sea

Among the Mediterranean's jacks, it is the small, fast schooling predator with the blue-green back: *Caranx crysos* — in English the blue runner, less often bluestripe jack or hardtail jack (English Wikipedia), in Italian carango mediterraneo or carango dorato (Italian Wikipedia), in French carangue coubali, in Catalan sorella del sud, in Portuguese xaréu-azul, in Spanish jurel azul among others, in Dutch zwarttip makreel, in Danish blå løber, in Finnish sinipiikkimakrilli or turkoosipiikkimakrilli, in Russian золотистый каранкс, in Turkish trakun balığı, in Greek κοκάλι, in Japanese クロカイワリ and in Arabic شيم أزرق (GBIF, Wikidata, Wikipedia). German has no name of its own for it: GBIF lists only the family name Stachelmakrele (jack), and the German Wikipedia only the scientific one. For Croatian, Slovenian and Albanian we found no confirmed species name. Here is how to recognise it, where it lives, what it eats, how it has spread northwards in the Mediterranean — and why the sources can't even agree on which side it came from.

A “yellow mackerel” from New York

It was described by the American naturalist Samuel L. Mitchill in 1815, from a fish caught in New York Bay — at the time as *Scomber crysos* (English Wikipedia, FishBase). Mitchill proposed the name “yellow mackerel”; according to the English Wikipedia, the species name *crysos* refers to the Greek word for gold. The species was later described anew three more times, among others as *Caranx fusus* — a name that, according to the English Wikipedia, some authors still use wrongly today. Whether the eastern Pacific *Caranx caballus* (green jack) is in fact the same species is considered unresolved: according to the English and German Wikipedias, the two differ only in the number of gill rakers.

How to recognise it

  • The shape: elongated, moderately deep-bodied and laterally compressed, with the dorsal and ventral profiles about equally curved and a slightly rounded snout (English Wikipedia, FishBase). The pectoral fins are sickle-shaped and longer than the head (FishBase).
  • The colour: back light olive-green to bluish-green, flanks silvery grey to golden or brassy (FishBase, English Wikipedia). The Italian Wikipedia describes silvery flanks with a mother-of-pearl sheen, sometimes with golden reflections.
  • The spot: at the top of the gill cover sits a dark spot, which according to the English Wikipedia can be indistinct; the Italian Wikipedia calls it black and taller than it is long. The tips of the tail fin are dark (Italian Wikipedia) — probably the origin of the Dutch name *zwarttip makreel*.
  • The lateral line: a short, pronounced arch at the front, then a straight section at the back with very strong bony scutes, which form keels on the caudal peduncle (English Wikipedia, FishBase). Hence the English names *hardtail* and *hardnose*.
  • The fins: two dorsal fins, the first with 8 spines, the second with 1 spine and 22–25 soft rays; the anal fin with 2 detached spines, then 1 spine and 19–21 soft rays (English Wikipedia, FishBase).
  • The juveniles: usually carry seven dark vertical bars on the flanks (FishBase, English and Italian Wikipedias).

How big it gets

The confirmed maximum length is 70 cm, the maximum weight 5.05 kg (English Wikipedia) or, rounded, 5.1 kg (FishBase). This record is also the IGFA world record: caught in 1997 off Dauphin Island in the Gulf of Mexico (English Wikipedia). Most fish are considerably smaller — how much smaller is covered below. For the Mediterranean, the Italian Wikipedia writes that the fish there are smaller and weigh no more than 1.5 kg. According to the English Wikipedia, the oldest known specimen was 11 years old, aged by the rings in its ear stones (otoliths).

Where it lives

Its range covers the entire Atlantic: in the west from Nova Scotia in Canada to Brazil, including the Gulf of Mexico and the Caribbean; in the east from Angola along the West African coast to Morocco and into the Mediterranean (English Wikipedia, FishBase). North of Portugal it is rare; individual catches come from Madeira and Galicia, the northernmost from southern England — two fish in 1992 and 1993 according to the English Wikipedia, and by now around 13 records from Dorset and Cornwall according to the Italian Wikipedia. In the Canary Islands, where it was rarely seen in the past, it is now said to have stable populations; some authors attribute this to rising sea temperatures (English Wikipedia).

It mostly lives close to the coast, often over reefs and — according to the Italian Wikipedia — especially along sandy shores, but goes down to 100 m and deeper (FishBase, English Wikipedia). Juveniles like to shelter in the shade of drifting sargassum weed or large jellyfish and move into lagoons and estuaries, including brackish water (FishBase, Italian Wikipedia). Its preference for structures in the water is striking: it gathers around fish aggregating devices (FADs), oil and gas platforms, artificial reefs and aquaculture cages (English Wikipedia).

The road north

For Mediterranean anglers, this is the most exciting part. According to the Italian Wikipedia, the species used to live only in the south and east of the Mediterranean. Between the 1990s and the new millennium, in the course of warming — in Italian *meridionalizzazione* — it spread first into the centre of the basin and then into the north, as far as the Ligurian Sea. A 2023 study in the journal *Thalassas* describes the northernmost records in the north-western Mediterranean (Italian Wikipedia, reference list). The English Wikipedia now states that it has been reported from almost all Mediterranean coastal states.

What it eats

It is a fast predator that, near the coast, mainly hunts small, bottom-dwelling fish (English Wikipedia). It also takes crabs, shrimps, copepods and other invertebrates; a study in Cape Verde also found spiny lobsters and jellyfish in its stomach (English Wikipedia). Juveniles feed mainly on zooplankton, as do fish living far offshore or around platforms. At platforms in the Gulf of Mexico it fed equally intensively by day and night — at night preferring larger prey such as fish, by day small crustaceans (English Wikipedia). It often hunts in small schools, rarely in aggregations of up to 10,000 fish, and sometimes follows hunting spinner dolphins to pick up the leftovers (English and German Wikipedias). It is itself prey for larger fish — the Italian Wikipedia names dolphinfish (mahi-mahi), great barracuda and Atlantic sailfish — as well as for seabirds and dolphins.

Spawning and growth

It reaches sexual maturity at 22.5 to 28 cm depending on the area (English and German Wikipedias); FishBase gives 27.4 cm as the mean length at maturity. According to the English Wikipedia, all maturity studies come from the western Atlantic. It spawns in the open sea; eggs and larvae drift freely in the water. A female releases on average between 41,000 and 1,546,000 eggs, large fish more than small ones (English and German Wikipedias). When it spawns is answered differently by the sources — see below. According to FishBase, its resilience is medium: a population needs 1.4 to 4.4 years to double.

Angling, the kitchen and a warning

The English Wikipedia calls it an excellent sport fish on light tackle that takes fish baits as readily as plugs, spoons, metal jigs and soft plastics; fly anglers in saltwater target it too. In the Mediterranean, according to the Italian Wikipedia, it is caught by trolling and spinning. Very often it serves as live bait itself for larger predators such as marlin and sailfish, cobia and amberjack (English Wikipedia). How good it tastes is disputed — see below. Important: FishBase and the English Wikipedia report cases of ciguatera poisoning after eating it; according to the English Wikipedia, it is mainly larger specimens that carry the toxin, and several cases come from the US Virgin Islands. So the fish is dangerous to humans not when caught, but on the plate — and we found no ciguatera report from the Mediterranean in our sources.

Status — and what you can do

On the IUCN Red List it is classed as “Least Concern”, assessed on 4 February 2009 (FishBase). According to the Italian Wikipedia, it is common or very common across large parts of its — growing — range, and there is no sign of overfishing. FishBase rates its vulnerability to fishing as low to moderate (34 out of 100), but its vulnerability to climate change as moderate to high (53 out of 100). In Europe and Africa, according to the English Wikipedia, it is not recorded separately in catch statistics but lumped together with other jacks — so nobody knows exactly how much is caught there.

Whether a minimum size, a closed season or a catch limit applies to it is governed by national and regional regulations — there is no universally valid number, and we deliberately don't give one. Check locally what currently applies, especially in marine protected areas. And because its northernmost occurrence in the Mediterranean is only now being documented: a photo with location and date is worth more to science than you might think.

Seven contradictions in the sources

  • Which side did it come from? The Turkish Wikipedia writes that it migrated from the Red Sea into the Mediterranean from the mid-1990s. The Italian Wikipedia says the opposite: it is one of the few Mediterranean species to have migrated through the Suez Canal in the reverse direction, at least as far as Lake Timsah. None of our other sources calls it a Red Sea species.
  • Where does it live in the Mediterranean? FishBase and the Spanish, Catalan and German Wikipedias: only in the western Mediterranean. English Wikipedia: in the entire Mediterranean. Italian Wikipedia: formerly only in the south and east, since the 1990s also in the centre and north.
  • How big is it usually? English and Greek Wikipedias: mostly under 35 cm. FishBase and the Italian and Finnish Wikipedias: commonly 40 cm. FishBase also cites a source with a maximum length of only 55 cm instead of 70 cm.
  • Is it any good to eat? FishBase: “excellent food fish”. Italian Wikipedia: “ottimo pesce da tavola”. English Wikipedia: a rather inferior food fish, “mediocre”.
  • Is the breast scaled? English Wikipedia and FishBase: fully scaled — FishBase explicitly notes that other sources have wrongly described it as naked. That is exactly what the German Wikipedia does: “The breast is scaleless.”
  • When does it spawn? English Wikipedia: year-round, with peaks in summer. FishBase and the Finnish Wikipedia: January to August. Italian Wikipedia: in the eastern Mediterranean in summer in coastal waters — all the others say it spawns out in the open sea.
  • How many bony scutes? English Wikipedia: 46–56. FishBase: 45–56. Italian Wikipedia: 39–45. And the Finnish Wikipedia moves the species straight into the eastern and western Pacific — but according to all other sources, it is not this fish that lives there, but its possible twin *Caranx caballus*.

Five naming traps

  • “Pompano” is the wrong fish. The Swedish Wikipedia lists *Caranx crysos* under the title Pompano — in English, that name refers to the species of the genus *Trachinotus*, in the Mediterranean for example the pompano or derbio (*Trachinotus ovatus*). For Swedish and Norwegian, GBIF gives only taggmakrill / taggmakrell, the family name.
  • “Τραχούρι” is used twice over. The Greek Wikipedia calls *Caranx crysos* τραχούρι — which in Greece usually means the horse mackerel or scad (*Trachurus*). English horse mackerel and French chinchard, both listed by GBIF for this fish, also normally mean the scad.
  • “Leccia” and “akya” are a different fish. GBIF also lists Italian leccia for *Caranx crysos*; that name otherwise refers to the leerfish *Lichia amia*. The Turkish Wikipedia explicitly warns that it is confused with the akya — likewise *Lichia amia*.
  • “Jurel”, “palometa”, “crevalle” are catch-all names. The Spanish and English names on GBIF refer to many different jacks depending on the country. For Spain we found no unambiguous Mediterranean name.
  • “Caranx fusus” is an old name. Anyone reading *Caranx fusus* or *Carangoides fusus* in the scientific literature means, according to the English Wikipedia, the same fish — the name is invalid.

That leaves the question every article in this series starts with: when. With a fish that moves fast along structures in small schools and feeds by day and night alike, the right day matters more than any rig. Habitat, prey and spawning season are listed above, and they're fixed. What changes every day are the conditions on your water — StrikeAhead calculates them and tells you when the trip is worth it. And because you don't know the edges and rules of unfamiliar waters from day one, StrikeAhead Pathfinder tells you who to go out with: curated guides and skippers, personally vetted before listing — licence and insurance —, with verified catches instead of promo photos, no paid ranking and, for you as an angler, no booking fee. The app says when, Pathfinder with whom.