Siganus sutor

Lore & Background

Siganus sutor was first formally described in 1835 as Amphacanthus sutor by French zoologist Achille Valenciennes, with the type locality given as the Seychelles. The specific name sutor means 'cobbler' or 'shoemaker', referencing the local name in the Seychelles and Mauritius; Valenciennes did not explain this, but it is thought to refer to the sharp spines that may have been used to puncture leather like an awl. The fish is endemic to the Indian Ocean, from Indonesia to Comoros, and occurs in the Western Indian Ocean off East Africa from Somalia to South Africa, as well as around Madagascar, Réunion, Mauritius, the Comoros Islands, Rodrigues, and in the Gulf of Aden off Yemen. Records elsewhere require confirmation. During the daytime, the body is usually silver with white spots, sometimes with blue spots within the white spots; at night, it has a mottled green or grey color, and it can immediately change between these patterns. The spines are slender, pungent, and venomous; venom glands can cause great pain but are unlikely to be fatal to a healthy adult. The long flap of the anterior nostril shortens as the fish ages. S. sutor is an herbivore feeding mainly on macro-algae, is diurnal, and shows schooling behavior. When threatened, it raises its dorsal fin for protection. It returns to the same offshore coral patch reef aggregation site to spawn on subsequent full moons, migrating at most 3.3 km from fishing grounds.

Reader's Guide

Siganus sutor holds significant commercial and ecological importance in the Western Indian Ocean. It is one of the most common fish species in Kenyan marine fisheries, accounting for around 40% of artisanal fishery landings, and is ubiquitously caught in Tanzania and along the entire East African coast. Various fishing gears are used, but basket traps are preferred. Management efforts by the Wildlife Conservation Society, Kenya Marine and Fisheries Research Institute, and State Department of Fisheries have promoted modifying basket traps with an escape gap to reduce bycatch of juveniles and small fish.

The species has two spawning seasons, January/February and May/June, determined by temporal changes in condition factor, gonad weight, maturity stages, and seasonal appearance of juveniles. It is a mangrove/seagrass-associated coral reef fish inhabiting littoral areas at depths between 1 and 12 m, frequently recorded in seagrass beds. Its venom, similar to that of stonefishes, is treated by immersing the wound in hot water (as hot as one can take) for 60 to 90 minutes. Research on bioaccumulation of heavy metals in S. sutor from Dar es Salaam, Tanzania, found that levels of aluminum, cadmium, copper, iron, lead, and zinc in its muscles were below FAO/WHO maximum levels for contaminants and toxins in food for human consumption, though fins were not suitable as non-destructive monitoring organs for most metals.

Did You Know?

• Siganus sutor can immediately change its color pattern from silver with white spots during the day to mottled green or grey at night.
• The specific name sutor means 'cobbler' or 'shoemaker', thought to refer to the sharp spines possibly used to puncture leather like an awl.
• This species accounts for around 40% of artisanal fishery landings in Kenya.
• If envenomated by its spines, treatment involves soaking the wound in hot water for 60 to 90 minutes.