Proteins

Horse Mackerel (Aji)

Oily, full-flavored small fish grilled whole or served as sashimi in Japan (aji).

Horse mackerel, called aji in Japan, is a small oily fish with rich, savory flesh. It is grilled whole with salt, dried into himono, or served raw as sashimi and tataki. Its high oil content gives a deep umami flavor that pairs with ginger, citrus and soy.

Horse mackerel (aji) is a small, oily fish prized throughout Japan for its rich, full-flavored flesh and high fat content, particularly in the belly section known as toro. Unlike mild white fish, aji delivers pronounced umami and a distinctive fishy character that intensifies with freshness—making it both demanding and rewarding to work with. The flesh is firm and dense, holding together well during grilling while the belly meat renders into an exceptionally fatty, melt-in-mouth texture that sushi chefs regard as a premium cut. Aji is considered a working-class fish in Japan—affordable and ubiquitous—yet among sushi chefs it commands respect as a challenge: its high fat and quick spoilage demand precise timing and handling. The fish is so closely tied to freshness that Tokyo's Tsukiji traders used to say aji tells the truth about a fishmonger's care within hours of catch. For home cooks, the single most important rule is: buy the morning of service, cook or eat immediately, and never refrigerate whole aji for more than a day regardless of how it looks.

Measured in: g
Storage: Fridge

Allergens

Fish

Types & varieties

Ma-aji

True horse mackerel; the standard market species with high fat content and firm flesh

Hime-aji

Smaller species (up to 20 cm); milder flavor, thinner flesh; common in Setouchi region, often grilled whole as piri-piri

Muro-aji

Often sold as aji but actually white croaker (Pennahia argentata); milder, less oily; common in Western Japan markets

Common uses

Sashimi and nigiri sushi—the belly toro section is especially prized; aji is a classic Edomae sushi ingredientGrilled whole with salt (shioyaki)—the quintessential preparation; skin crisps while flesh stays moistKabayaki-style—butterflied, basted with sweet soy and grilled; popular in TokyoSimmered (nitsuke)—head-on, braised in soy, mirin, sake; the fat renders into the sauceTsukudani—whole fish or fillets simmered aggressively in sweetened soy until reduced to a preserve-like consistencyAs sushi toppings—often marinated briefly in vinegar or lightly seared (aburi)Pasta—poached in olive oil with garlic and chili, adapted from Spanish cuisine

Tips & pitfalls

Never substitute frozen aji for sashimi—the texture becomes mealy and the flavor flat; only use sashimi-grade fresh fish raw
For grilling: score the thickest part of the body (behind the head) 2–3 times to allow heat penetration and prevent curling; this is essential for even cooking
The blood line running along the spine is bitter; remove it with a thin knife for cleaner flavor, especially important for raw preparations
Season grilled aji at the table, not before cooking—salt draws moisture and will steam the flesh rather than crisping the skin
When buying whole for sashimi, request the fish be killed by the spike method (ikejime) if available—this preserves the flesh quality significantly
Aji spoils faster than most fish; if the eyes have clouded even slightly or the gills have dulled, cook it rather than serving raw
The liver (shimo) and roe are considered delicacies—ask your fishmonger to save them; liver is briefly seared and served with ponzu, roe is pickled or grilled
The belly meat (toro) is the most prized part; if buying whole, negotiate to have it reserved or learn to remove it yourself for maximum yield

Nutrition

No USDA FoodData Central match for Horse Mackerel (Aji) yet. We surface a per-100 g profile once a generic whole-food entry is matched and verified.

In the shops

Matched grocery products

No matched grocery products for Horse Mackerel (Aji) yet.

Good to know

Scientific Name: Trachurus symmetricus (Pacific horse mackerel)
Japanese Name: Aji (鯵)
Peak Season: Late autumn through winter (November–February) for wild catch; aquaculture available year-round
Flavor: Rich, full-bodied with pronounced umami backbone and sweet undertone; pronounced fishiness when very fresh
Texture: Firm, dense flesh that holds together well; high fat content especially in the belly (toro)
Size: Typically 20–40 cm; market size 25–35 cm preferred for grill; larger specimens called "o-agane"
Freshness Indicators: Bright red gills, clear bulging eyes, iridescent scales, firm flesh that springs back; belly should feel heavy with fat
Nutritional Notes: High in omega-3 fatty acids (EPA, DHA); excellent source of vitamin B12 and selenium
Storage: Use within 24 hours of purchase for sashimi; wrap tightly, refrigerate at 0–2°C; freeze only if absolutely necessary (degrades texture)
Yield: Head-off, gutted: ~55–60%; filleted: ~40–45%; belly (toro): ~15% of flesh, the premium cut
Common Forms: Whole (market standard), filleted, as sashimi-grade blocks; frozen HGT (head-gutted-trimmed) common for foodservice

Substitutes

Spanish Mackerel (Goma-saba) — Similar fat content and firm texture; slightly stronger flavor; good one-to-one substitute for grilling or baking
Blue Mackerel (saba) — Higher fat, more pungent; reduce cooking time slightly; excellent for kabayaki but overpowering for sashimi
Yellowtail/Amberjack (buri or kanpachi) — Milder flavor, larger flakes; works for sashimi and grilled preparations but lacks aji's characteristic richness
Atlantic Mackerel — Closely related species; nearly identical culinary properties; widely available outside Japan

Pairs with

Daikon (grated or sliced)Ponzu and scallionsGinger (shoga)Shiso leavesSoy sauce and grated wasabiYuzu koshoSake (for cooking)

Also called

Aji · Scad