Siganus rivulatus
A gregarious herbivore that colonized the Mediterranean via the Suez Canal.
Siganus rivulatus, commonly called the marbled spinefoot, rivulated rabbitfish, or surf parrotfish, is a schooling, mostly plant-eating ray-finned fish belonging to the family Siganidae. It naturally lives in the western Indian Ocean and the Red Sea, and it entered the Mediterranean Sea through the Suez Canal—a movement known as Lessepsian migration. This species is the type species for the genus *Siganus*.
The genus name comes from New Latin, derived from the Arabic word *sijan*, meaning "rabbitfish." The species name *rivulatus* refers to irregular streaking, describing the yellow streaks along its sides. Swedish zoologist Peter Forsskål named it, and his friend Carsten Niebuhr published the description posthumously in 1775 in *Descriptiones animalium, Flora Aegyptiaco-Arabica*. If a 2007 proposal to split the genus *Siganus* into three subgenera is accepted, the exact placement of *S. rivulatus* remains uncertain, and no names for these new groupings have been established.
The fish has a laterally compressed body, with a standard length 2.7 to 3.4 times its greatest depth. Its dorsal fin has 14 spines and 10 soft rays; the anal fin has 7 spines and 9 soft rays. It has 23 vertebrae and a slightly forked tail fin. The longest dorsal spine is shorter than the distance from the front of the eye to the rear edge of the gill cover, and the longest dorsal ray is no longer than the snout. The slender spines are barbed and contain venom. Its teeth are incisor-like with side cusps, arranged in a single row. Small, embedded scales cover the body except along the midline of the underside. Color varies but usually includes dark spots and yellow wavy lines on the sides. The upper body is grey-green to brown, with a yellow belly or silvery-white underside. It typically grows to 10–20 cm, sometimes up to 27 cm in standard length, with a maximum recorded size of 40 cm.
Like other rabbitfish, *S. rivulatus* has venom glands linked to its fin spines, which can envenomate a person if handled carelessly. The sting is very painful, but no fatalities have been recorded. The venom is a heat-sensitive protein, so any sting site should be treated at as high a temperature as possible—43 to 46 °C. Medical treatment for possible infection is also recommended.
Quick Facts
- Taxon
- Siganus rivulatus
Facts from the source article.
Lore & Background
Siganus rivulatus was named by Swedish zoologist Peter Forsskål and published posthumously in 1775 in a book edited by Carsten Niebuhr. Its generic name derives from the Arabic 'sijan', meaning rabbitfish, while the specific name 'rivulatus' refers to the irregular yellow streaks on its sides. The fish has a laterally compressed body with venomous barbed spines in its fins, and its color varies from grey-green to brown with a yellow abdomen. It typically grows to 10–20 cm but can reach 40 cm.
Its natural range extends along the east African coast from South Africa to the Red Sea, including the Comoros, Madagascar, and the Seychelles. It was first recorded in the Mediterranean off Palestine in 1927 after entering through the Suez Canal, and it is now common throughout the eastern Basin. The fish forms schools of 50 to several hundred individuals, feeds mainly on algae, and spawns when water temperatures reach 24–27 °C, with spawning occurring later in the Mediterranean (May to July) than in the Red Sea (March to May).
Reader's Guide
Siganus rivulatus holds significance as the type species of the genus Siganus and the monogeneric family Siganidae. Its Lessepsian migration through the Suez Canal into the Mediterranean has made it a prominent invasive species, where together with Siganus luridus it has created 'barrens' off the coast of Turkey by overgrazing algae, reducing the complexity and biodiversity of algal communities. The fish is a quarry for artisanal fisheries, caught mainly by beach seines and gill nets, and while landings are combined with other siganids, data from the Red Sea suggests overexploitation. Research into its aquaculture potential is ongoing, as its herbivorous diet may offer a more sustainable alternative to carnivorous farmed species. It can be matured and spawned in captivity, readily consumes artificial feeds, and has good market demand. However, it has been linked to ciguatoxin-like toxins and hallucinatory poisoning when consumed, particularly from polluted waters. Its venomous spines cause painful envenomation treatable with heat at 43–46 °C, with no recorded fatalities.
Did You Know?
- Siganus rivulatus is the type species of the genus Siganus and of the family Siganidae.
- It was first recorded in the Mediterranean off the coast of Palestine in 1927.
- Its venom is a heat-labile protein; envenomation should be treated at 43–46 °C.
- Adults have been observed feeding on ctenophores and moon jellyfish in the northern Red Sea.
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