Streamlined spinefoot
A pelagic-spawning rabbitfish with venomous spines and wide Indo-Pacific range.
The streamlined spinefoot (Siganus argenteus), also called the forktail rabbitfish, schooling rabbitfish, or silver spinefoot, is a marine ray-finned fish in the family Siganidae. It lives across the Indo-Pacific region.
French naturalists Jean René Constant Quoy and Joseph Paul Gaimard first formally described this species in 1825, naming it Amphacanthus argenteus. The type location was Guam in the Marianas. Its species name, argenteus, means "silvery," referring to the silver color on its cheeks and lower body.
The fish has an oval, compressed, slender, and fusiform body. Its standard length is 2.4 to 3 times its depth. The small head lacks a steep dorsal profile but has a pointed snout. A flap on the front nostril extends past the rear nostril. A procumbent spine, enclosed in the skin of the nape, sits at the front of the dorsal fin. The dorsal fin has 13 spines and 10 soft rays; the anal fin has 7 spines and 9 soft rays. The caudal fin is deeply forked. Maximum total length is 40 cm (16 in), though 25 cm (9.8 in) is more typical. The upper body is blue, the lower body silvery. Variable markings, spots, and curved lines often appear, especially on the lower flanks. The eye has a silvery-yellow iris. The pectoral fin’s axil is yellow, and a yellow stripe usually runs along the dorsal fin’s base. A dark brown bar marks the upper edge of the operculum. When alarmed or asleep, the fish changes to pale and dark brown mottling, with dark areas forming seven diagonal zones across the flanks and the fins becoming mottled.
This species has a wide Indo-Pacific range, from the Red Sea south to Mozambique and Madagascar, east to Pitcairn Island, north to Japan, and south to Australia. In Australia, it appears from Shark Bay in Western Australia to Ashmore Reef in the Timor Sea, and on the east coast from the northern Great Barrier Reef near Cape York south to Moreton Bay in Queensland. It also occurs on reefs in the Coral Sea and at the Cocos (Keeling) Islands. One specimen was recorded in the Mediterranean Sea off Libya, but how it got there is uncertain. At remote islands like Rapa, Pitcairn, and the Line Islands, it may be the only rabbitfish present. It lives down to 40 m (130 ft) in lagoons, on reefs, and in seaweed and seagrass beds.
Quick Facts
- Taxon
- Siganus argenteus
Facts from the source article.
Lore & Background
The streamlined spinefoot was first formally described in 1825 as Amphacanthus argenteus by the French naturalists Jean René Constant Quoy and Joseph Paul Gaimard, with the type locality given as Guam in the Marianas. The specific name argenteus means 'silvery', a reference to the silver colour of the cheeks and lower body. Its body is oval, compressed, slender and fusiform, with a standard length 2.4 to 3 times its depth. The small head has a pointed snout, and the front nostril has a flap extending past the rear nostril. There is a procumbent spine at the front of the dorsal fin enclosed in the skin of the nape. The dorsal fin has 13 spines and 10 soft rays, while the anal fin has 7 spines and 9 soft rays. The caudal fin has a deep fork. Coloration includes blue on the upper body with a silvery lower body, variable markings, spots and curved lines, a silvery-yellow iris, a yellow axil of the pectoral fin, a yellow stripe along the base of the dorsal fin, and a dark brown bar on the upper edge of the operculum. When alarmed or asleep, the fish changes to pale and dark brown mottling with 7 diagonal zones across the flanks and mottled fins.
Reader's Guide
The streamlined spinefoot is significant for its unusual reproductive biology among rabbitfish: it is a pelagic spawner with a relatively long larval stage and a unique prejuvenile stage. These long developmental stages allow it to disperse widely and make the species less vulnerable than its congeners to overfishing. It is frequently recorded in markets in parts of its range, both as juveniles and adults, and pre-juveniles are taken as they migrate to reef flat areas in a brief but important part of local fisheries, e.g. in Guam. They are consumed fresh, pickled in brine, or made into fish paste. The species has a wide Indo-Pacific distribution from the Red Sea south to Mozambique and Madagascar and east into the Pacific Ocean as far as Pitcairn Island, north to Japan and south to Australia. It has been recorded once in the Mediterranean Sea off Libya, but how this specimen reached there is uncertain. At remote islands such as Rapa, Pitcairn and the Line Islands, this species may be the only rabbitfish present. It occurs in lagoons, on reefs, and in seaweed and seagrass beds down to 40 m. The streamlined spinefoot is normally found in large, fast-swimming schools in the water column, diving down to feed. Its diet consists of red and green macroalgae, and it is one of the few herbivorous fishes able to eat the chemically rich macroalgae Chlorodesmis fastigata, though this may be only opportunistic. It has spines that can inject venom into an attacker.
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