Centreboard Leatherjacket

Fascinating facts about the Centreboard Leatherjacket

• A fish that barely reaches the length of a school ruler, about 40 cm (16 in), carries a striking upturned snout and a fan-shaped tail tipped with a filament, making it look like a tiny marine kite.
• When it drifts over mussel beds, its skin is dark, while over sand it is cream-tan; its colour varies with the environment.
• Its dorsal fin sports a single long, erectile spine up front, followed by a shorter one, while the rear dorsal fin bears 28–34 soft rays and the anal fin bears 27–34 soft rays, a skeletal fingerprint that helps scientists tell it apart from other filefish.
• Living from Malaysia to eastern Australia, it roams shallow waters down to about 50 m (164 ft), preferring estuaries, algae-clad rocks, muddy bottoms and seagrass meadows, essentially any nook where food hides.
• Though it munches on algae and seagrass, about 40% of its diet is animal matter, with the remainder being plant material, showing the fish relies heavily on the tiny creatures that cling to sea-grass.

At a glance

About the Centreboard Leatherjacket

The fan-bellied leatherjacket, Monacanthus chinensis, is a laterally-compressed filefish that reaches about 40 cm (16 in) in total length. Its most striking features are the upturned, pointed snout, a large dewlap beneath the body, and a fan-shaped caudal fin tipped with a delicate filament. The foremost dorsal fin bears a long, erectile spine followed by a shorter one, while the hind dorsal and anal fins carry 28-34 soft rays each. Its coloration shifts with the surroundings, dark hues blend with mussel beds, whereas cream or tan tones match sandy flats, all broken by irregular darker blotches and streaks, giving it a masterful camouflage on reefs, seagrass meadows, and silty bottoms. A diurnal, omnivorous forager, this leatherjacket relies heavily on sight to locate food. It grazes on algae and seagrass while also hunting a suite of tiny invertebrates, amphipods, caridean shrimps, copepods, tanaids, bryozoans, hydroids, polychaete worms, and tunicates. Although its gut does not efficiently break down plant material, it still extracts a surprising amount of carbon compounds from those sources. Roughly 40 % of its diet is animal matter, making the fish particularly dependent on the encrusting organisms and epiphytic algae that carpet seagrass meadows, a niche that ties its survival to the health of these underwater gardens.

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