Blackhead Seabream

Fascinating facts about the Blackhead Seabream

• When Pieter Bleeker first described this fish in 1854, he placed it in a different genus entirely, naming it Chrysophrys schlegelii. The type specimen came from Nagasaki, linking the species to Japan’s historic scientific expeditions. Its name still honors Hermann Schlegel, a 19th-century German ornithologist, showing how taxonomy often preserves personal stories.
• A dorsal fin with 11 or 12 spines and 11 soft rays, plus an anal fin with 3 spines and 8 soft rays, sets this seabream apart from its cousins whose fin counts differ. Those pale-colored fins contrast with its generally black or grey body.
• The fish can grow up to 50 cm (20 in) in standard length. That size lets it inhabit shallow rocky reefs and brackish bays down to 50 m (160 ft) deep, where it hunts molluscs and polychaete worms.
• Unlike many fish, this seabream changes sex as it ages, starting life as a male and later becoming female, a strategy called protandrous hermaphroditism. Males live up to 20 years, while females can reach 28 years, meaning the oldest individuals are the egg-layers that sustain populations. This life-history twist explains why smaller size classes are dominated by males.
• In 2022 China harvested 123,000 tonnes of this species for aquaculture. Vietnam relies on it as a staple food fish, and Korea and Japan also farm it intensively.

At a glance

About the Blackhead Seabream

The blackhead seabream, Acanthopagrus schlegelii, glides through the sheltered bays and shallow rocky reefs of the northwestern Pacific, its sleek body cloaked in a muted black-grey mantle that shimmers silver along the belly. Light-colored dorsal, caudal, anal and pelvic fins contrast with faint vertical stripes that run the length of its form, while a distinctive round spot crowns the upper edge of the operculum. Growing to a standard length of up to 50 cm (20 in), this ray-finned fish is built for both agility and endurance, its dorsal fin supported by 11 or 12 spines and 11 soft rays, and an anal fin bearing 3 spines and 8 soft rays. In the dimming light of early evening, the blackhead seabream gathers in coastal waters to spawn, a ritual triggered by the falling light levels that cue its protandrous hermaphroditic cycle. Males, which dominate the younger size classes, can live to 20 years, while females may reach 28 years, underscoring a life history tuned to the seasonal rhythms of spring and summer. Their predatory diet of molluscs and polychaete worms reflects a keen foraging instinct, but perhaps the most surprising trait is their ability to thrive in brackish waters down to 50 m (160 ft), bridging the gap between marine and estuarine ecosystems, a flexibility that fuels their prominence in regional fisheries and aquaculture.

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