Yellowtail Horse Mackerel

Fascinating facts about the Yellowtail Horse Mackerel

• A single yellowtail horse mackerel can grow to 50 cm (20 in), about the length of a school ruler, yet it lives up to 15 years, an unusually long lifespan for a fish of that size, showing how slow-growing marine species can persist in coastal waters.
• When you spot a school of these fish, you’re likely seeing individuals that prefer waters shallower than 150 m (490 ft) and warmer than 13 °C (55 °F), a niche that keeps them close to rocky offshore reefs where they can quickly dart for prey.
• Juveniles between 91 mm and 150 mm focus almost entirely on crustaceans, but once they exceed 151 mm they switch to hunting small fish, a dietary shift that mirrors their rapid growth and changing role in the food web.
• In some Australian regions, a tongue-replacing parasite, Cymothoa exigua, invades the fish, eating the tongue and taking its place, yet it leaves the host otherwise unharmed and poses no risk to humans, illustrating a bizarre yet harmless host-parasite partnership.
• Since 1997, New South Wales fisheries have hauled 300–500 tonnes of this species each year, though much ends up as bait or discard, highlighting how a commercially valuable fish can still be underutilized despite steady catches.

At a glance

About the Yellowtail Horse Mackerel

The yellowtail horse mackerel (Trachurus novaezelandiae), colloquially called yakka, cuts a striking figure in the coastal waters of Australia and New Zealand. Its body is a moderately compressed oval, cloaked in a bright olive green dorsally that fades to a golden green on the sides before turning silvery white beneath. Nine to sixteen faint grey bars run vertically along its flanks, and a small black spot sits just above the eye on the operculum. Adults reach up to 50 cm (20 in) and bear 68–73 lateral-line scutes, a key metric that separates them from the closely related greenback horse mackerel. In the shallower, soft-bottom nurseries juveniles gather in large schools, while mature fish favor rocky reefs offshore, typically staying below 150 m (490 ft) and in water no colder than 13 °C (55 °F). Their diet shifts dramatically with size: fish 91–150 mm long feast on crustaceans, whereas those over 151 mm become almost exclusive predators of small fish, cruising the midwater column in coordinated sweeps. A surprising quirk of the species is its susceptibility to the tongue-replacing parasite Cymothoa exigua in some Australian locales, an odd hitch that harms neither the fish nor its human consumers, though the parasite should be removed before cooking. Their longevity, up to 15 years, and their versatility on the plate, fresh, smoked, canned, or frozen, make them a prized target for both commercial and recreational fisheries, with New South Wales alone pulling 300–500 tonnes annually since 1997, much of which ends up as discard or bait.

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