Japanese jack mackerel (Trachurus japonicus) is a saltwater species recorded in Hong Kong, Taiwan. It is found at depths of 0–275 m. The main season in Hong Kong, Taiwan runs all year.
Scientific name: Trachurus japonicus · Water: Saltwater · Season: All year
Size: up to 50 cm
Weight: up to 0.66 kg
The Japanese jack mackerel is a small carangid with a row of scutes along the flank, common in Taiwanese inshore surface and mid-water schools; adults live over continental shelf waters in the open sea, while juveniles travel with drifting seaweed. Its range is the north-west Pacific, from southern Japan and the Korean Peninsula down through the East China Sea, plus the Pacific off south-east Asia. Greedy and abundant, it is easy for beginners to catch on feather rigs, lures or small hooks fished on the bottom, and it ranked 7th in the Ocean Conservation Administration's second-quarter 2021 report. Taiwan fishes it mostly from shore or from boats, and Hong Kong has it all year. Maximum about 50 cm total length and 0.66 kg, with a lifespan of about 12 years. IUCN lists it as Near Threatened.
It is recognised by a black blotch on the gill cover, a greyish-blue back over a silver belly, dusky dorsal and pectoral fins set against pale pelvic and anal fins, and above all by its bright yellow caudal fin. It most closely resembles the yellowtail horse mackerel of Australia and New Zealand, differing in its greater number of gill rakers and larger eyes. It feeds mainly on small crustaceans such as copepods, along with shrimp and small fish, working over sandy and muddy ground. In Japan it is the aji, one of the most familiar food fishes there, most often deep-fried or salt-grilled.
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