Japanese horse mackerel
Fish · Last reviewed 2026-08-25
The aji — the fish Japanese light-tackle fishing is built around, and the reason the rods and jigheads a Canarian species hunter uses exist at all.
Safety: injury while handling fish — minor injury.
Catching Japanese horse mackerel
Everything here on fishing for it. Each entry opens the page behind it.
If you have fished a one-gram jighead on a solid-tipped rod anywhere in the world, you have used tackle designed for this fish.
*Trachurus japonicus* is the aji: a slim silver scad of the north-west Pacific, from southern Japan and the Korean peninsula into the East China Sea, reaching a FishBase maximum of 50 cm and an age of twelve years. It shoals, it comes into harbours and along walls after dark, and it feeds on small crustaceans and larval fish drifting in the current.
Those habits produced a whole discipline. **AJING** is the Japanese term for fishing for it with ultralight gear — a soft-tipped rod, a tiny tungsten jighead, a one- or two-inch soft plastic, and a retrieve slow enough to keep the lure in the drift where the fish is feeding. The tackle categories that came out of it are the ones a European light-rock angler now buys as a matter of course, and the fish they were designed around is this one.
It is caught from harbour walls, breakwaters and piers, most productively at night under lights where the current concentrates plankton and the shoals come to it. It is also one of the most heavily fished species in the north-west Pacific and is assessed by the IUCN as **Near Threatened**, on a criterion of observed population reduction.
It is separated from the other Pacific scads by the extent of its armoured lateral line, which carries scutes along almost its whole length, and by the shape of the curve where the straight and arched sections meet.
How it is caught
Identification
No photograph of Japanese horse mackerel has passed identity review yet, so none is shown. FishingHQ publishes a species photograph only once somebody has confirmed the animal in it against the species record’s own diagnostic features.
- Scientific name
- Trachurus japonicus
- Family
- Carangidae
- Water
- Saltwater
- Conservation status
- Near Threatened
- Regions
- East Asia, South-East Asia, Indo-Pacific
- Bony scutes along almost the whole lateral line, running from behind the gill cover to the tail — more extensive than in the Atlantic horse mackerels.
- A dark blotch on the rear edge of the gill cover.
- Slim, silvery, with a greenish or bluish back and a large eye.
- Two dorsal fins, the second long and low, and a deeply forked tail on a narrow wrist.
- FishBase records a maximum of 50 cm, 0.66 kg and an age of 12 years.
Size
- Typical
- 80–250 g (3–9 oz)
- Large
- 350–600 g (12 oz–1.3 lb)
Exceptional: FishBase records a maximum of 50 cm, 0.66 kg and an age of 12 years
Lifecycle and reproduction
Pelagic-neritic and oceanodromous over a depth range of 0 to 275 m and usually 50 to 275 m, shoaling over the shelf and moving inshore to feed. Medium resilience and a maximum age of twelve years. It is among the most heavily fished species in the north-west Pacific, which is the context for its conservation status.
Not detailed on the FishBase record beyond the age data. What matters for the fishery is the combination the assessment rests on: a shoaling species with a twelve-year life, taken in very large quantities commercially as well as recreationally, and assessed on observed reduction rather than on inference.
Feeding and senses
Takes small crustaceans, larval fish and zooplankton drifting in the current, feeding in the water column rather than on the bottom. That single fact is the whole basis of ajing: the lure is not retrieved past the fish, it is held in the drift at the depth the shoal is feeding, which is why the rods are soft and the weights are tiny.
Sight in low light, and strongly associated with artificial light after dark — harbour and quay lights concentrate plankton, the plankton concentrates the shoal, and the fishing follows the light rather than the structure.
Through the year
Moves inshore and offshore with temperature through the year, with the inshore shoals most reliable in the warmer months and around lit structure after dark. It is fished for year-round where shoals remain within reach.
Distribution
Northwest Pacific: southern Japan, Korean Peninsula to the East China Sea. Pacific Ocean off the coast of southeast Asia
This is a biological range — where the species occurs, not a prediction that you will catch one. To browse the fishing geography FishingHQ holds, start at fishing places.
Why anglers care
The single most significant fish in Japanese light shore angling, and the species an entire tackle category was designed around. Ajing — ultralight rods, tungsten jigheads under a gram or two, one-inch soft plastics and a retrieve slow enough to stay in the drift — is fished from harbour walls, breakwaters and piers, most productively at night under lights. The same tackle is now used worldwide for entirely different fish, which is worth knowing when a European angler wonders why their rod is built the way it is.
Handling and returning
The scutes along the lateral line are sharp and backward-facing, so a hand slid from tail to head is cut by the fish's own armour. It also bleeds and softens quickly. Grip from the head end, unhook with pliers on a small hook, and cool anything kept at once.
Safety
Injury while handling fish — Minor injury
The bony scutes running most of the lateral line are sharp and point backwards, so a hand drawn along the flank towards the head is cut by the fish itself.
What reduces it: Hold across the body from the head end rather than sliding a hand down the flank, and unhook small jigheads with pliers.
Where to go next
Similar and related fish
Where it lives
More fish
Not related to this page — just the rest of the section. There is little else joined to this subject yet, and a short page should still lead somewhere.
Sources and evidence
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Family, maximum size, depth range, environment, distribution and the IUCN assessment for Trachurus japonicus.States this directlyPassage read and verified
- The IUCN Red List of Threatened Species — International Union for Conservation of Nature (Conservation authority)Relied on for: The Near Threatened assessment for Trachurus japonicus, assessed 20 July 2017.States this directlyCitation checked — the work exists and is described correctly
- FAO Species Identification Guides for Fishery Purposes and the FAO Species Catalogues — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Identification, distribution, habitat and fishery description from the FAO species identification guides for fishery purposes.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: The widely restated practitioner account of how this species is fished — tackle, method and the ground it is taken over.Background and mechanism onlyCitation checked — the work exists and is described correctly
Why the 4 connections on this page are here, and the sources
Similar and related fish
Backed by research — 2 connections
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
Atlantic horse mackerel
Trachurus japonicus reaches 50 cm in the north-west Pacific and Trachurus trachurus reaches similar sizes on the northern European shelf. Both are shoaling scads taken on small baited and lure traces from harbour structure, and the tackle developed for the first is now used on the second.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: The morphology, size, depth range and distribution that separate these two species from one another.States this directlyPassage read and verified
Blue jack mackerel
Trachurus japonicus carries bony scutes along almost the whole lateral line and is a north-west Pacific fish; Trachurus picturatus carries them on the rear half and is an eastern Atlantic island fish. Both are called by a regional name — aji and chicharro — that a reader is likely to meet before the binomial.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: The morphology, size, depth range and distribution that separate these two species from one another.States this directlyPassage read and verified
How it is caught
What experienced anglers do — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Light rock fishing
Fished with ultralight rods, tungsten jigheads under a gram or two and one-inch soft plastics, from harbour walls, breakwaters and piers, most productively at night under lights. The retrieve holds the lure in the drift at the depth the shoal is feeding rather than pulling it past the fish, which is why the rods are soft-tipped and the weights are tiny — and why that tackle now catches wrasse in the Canaries.
- FAO Species Identification Guides for Fishery Purposes and the FAO Species Catalogues — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Identification, distribution, habitat and fishery description from the FAO species identification guides for fishery purposes.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: The widely restated practitioner account of how this species is fished.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where it lives
Backed by research — 1 connection
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
Harbours, piers and breakwaters
Pelagic-neritic and oceanodromous over 0 to 275 m, shoaling over the shelf and moving inshore to feed on drifting plankton and larval fish. Artificial light on harbour structure concentrates that food, which is why the fishery follows the light rather than the wall.
- FishBase: a global information system on fishes — Froese, R. and D. Pauly, eds. — FishBase Consortium (Scientific institute)Relied on for: Environment, depth range, habitat association and distribution for Trachurus japonicus.States this directlyPassage read and verified
How FishingHQ labels evidence is explained in the evidence policy.