A slim, fast, blue-and-gold fish to 1.8 m (6 ft), with two blue stripes down the flank and a gold band between them. The identification is at the back: a single small finlet stands behind both the dorsal and the anal fin, which no other jack here has.
Those finlets are borrowed from the tunas. They break up the water rolling off the fins in front of them, cutting drag at speed, and the fact that a jack and a tuna arrived at the same solution independently says how narrow the options are for a fish built to cross open water.
It hunts small fish and squid in fast-moving schools that appear off a drop-off, cross the blue and are gone. Rainbow runners often turn up alongside larger animals - sharks, mantas, whale sharks - taking whatever the larger animal disturbs and, in the case of sharks, occasionally rubbing against the skin to scrape off parasites.
It is a strong food fish and a game fish, and large individuals carry ciguatera in some regions, which is a common tax on reef-associated predators.
slim torpedo body with two blue stripes running the length of the flank, gold between them
small separate finlet behind the dorsal and anal fins - unique among the jacks here
deeply forked tail on a narrow stalk
length up to 1.8 m
Why it's threatened
Biological resource use
Unintentional effects: (large scale) [harvest]
Some populations may be locally impacted due to excessive bycatch in the tuna purse seine fishery. In the tuna fishery in the Eastern Indian Ocean, it was a major component of the bycatch (6% of the total catch from October 1993 to February 2005). Aggregating behaviour around fish aggregating devices (FADs) may render them vulnerable to overfishing. However, there are no indications at present time of regional or global declines from harvesting. In the Gulf of Mexico off Mexico, it is taken as bycatch in fisheries targetingsardines (SAGARPA 2012).
Threat classification from the IUCN Red List.
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