Mottled spinefoot

Lore & Background

Siganus fuscescens was first formally described in 1782 as Centrogaster fuscescens by the Dutch naturalist Martinus Houttuyn, with the type locality given as Nagasaki. This taxon is largely sympatric with the white-spotted spinefoot (Siganus canaliculatus) and these taxa are also very similar in appearance. Molecular analyses in 2011 found three separate lineages within S. canaliculatus and S. fuscescens, that these lineages interbred, and that each lineage had specimens which referred to either taxon. The authors concluded that S. canaliculatus is in fact a synonym of S. fuscescens, though FishBase does not take this position, and the Catalog of Fishes recognises a third lineage as the species Siganus margaritiferus. Further molecular analyses have suggested that there may be cryptic species within S. fuscescens. The specific name fuscescens means 'darkened', thought to refer to the dark upper body.

The mottled spinefoot has a moderately slender, laterally compressed body, with a greenish-grey to brown colour fading to silvery on the lower body, and many small light-bluish spots on the flanks. It has a slender brown bar along the upper margin of the operculum and frequently a dark patch under the start of the lateral line. When asleep or threatened, adults adopt a mottled pattern. The front spine on the dorsal fin points forwards. It is found in shallow coastal waters in algae, sea grass, and coral or rocky reefs, and frequently in large estuaries. It is a schooling, mostly diurnal fish; juveniles feed on filamentous algae while adults prefer leafy algae and sea grass. Larvae aggregate in schools of up to 5,000, declining to about 12 by three months old. Spawning occurs on the 4th or 5th day of a new moon, with each female laying around 300,000 eggs.

Reader's Guide

The mottled spinefoot is a species of rabbitfish found in the Western Pacific Ocean, from the Andaman Sea east to Fiji and Samoa, north to Japan and south to Australia. It is caught using small seine nets, set nets, fish traps, and by spearfishing. Adults are sold as fresh fish, while juveniles are frequently preserved as dried fish and sold in large quantities. The species has venomous spines in the dorsal and pelvic fins, with venom similar to that found in stonefishes; the venom is usually non-lethal but can cause sharp pain, bleeding, and numbness. Soaking the affected area in water of around 45°C could help eliminate or ease the pain. There is a single record from the Italian Mediterranean Sea, but it is thought to refer to an individual transported by shipping. The taxonomic status of Siganus fuscescens remains disputed, with molecular analyses suggesting it may be a species complex and that Siganus canaliculatus may be a synonym, though this is not universally accepted. The species attains a maximum total length of 40 cm, though 25 cm is more typical.

Did You Know?

• The mottled spinefoot was first formally described in 1782 by Dutch naturalist Martinus Houttuyn with the type locality given as Nagasaki.
• Molecular analyses in 2011 found three separate lineages within S. canaliculatus and S. fuscescens, leading some authors to consider S. canaliculatus a synonym of S. fuscescens.
• Each female lays around 300,000 eggs in a single spawning, and fish more than two years old may spawn more than once in a season.