The fossil history of the Siganidae family contains three known fossil genera. From the Eocene epoch there is Ruffoichthys from Italy and Siganopygaeus from Turkmenistan. From the Oligocene epoch there is Archaeoteuthis from Switzerland (Tyler and Sorbini, 1990 from Nelson 1994).
No specific information was found concerning communication methods used by this group.
Communication Channels: visual
Perception Channels: tactile ; vibrations ; chemical
Currently, there is no known conservation threat to any member of this family.
Members of the Siganidae family first produce small adhesive egg sacs, which then become larvae. The larval stage is planktonic and develops into a distinctive post-larval stage called the acronurus, which is characteristic for members of the suborder Acanthuroidei. In the acronurus stage the body is transparent and individuals remain pelagic for an extended period before settling into the adult habitat and rapidly changing into the juvenile form. There is considerable morphological difference between larvae and adults and current information suggests that males reach sexual maturity before females throughout the family.
The Siganidae family is composed of one genus, Siganus, and two subgenera, Siganus with 22 species and Lo with five species (Woodland (1990) from Nelson 1994). Siganids get their common name, rabbitfishes, from their peaceful temperament, rounded blunt snout, and rabbit-like appearance of the jaws. They are important reef herbivores that browse individually or in schools over the reef or feed on plankton within the water column.
No specific information was found concerning any negative impacts to humans.
Negative Impacts: injures humans (bites or stings, venomous )
Some siganids are important food fishes in many areas and colorful species are popular in the aquarium trade. The fast growth rate and shallow browsing habits of siganids make them ideal for aquaculture, as evidenced by numerous studies on their growth and reproduction.
Positive Impacts: pet trade ; food
All siganids are diurnal herbivores and fill the roles of grazer and planktivore. Herbivores are quite important for the reef because they keep thick mats of filamentous and leafy algae from smothering the corals. They keep the mat only 1 to 2 mm thick and can strip vegetation from a 10 m wide ring around the reef. Other siganids use the reef mainly for shelter but “hover above it in brilliant, shifting shoals, while feeding on plankton.” These fish deposit feces in the small crevices where they hide, which is important in promoting the growth and diversity of corals (Hixon 1991; Lewis 1986 in Moyle and Cech 2000).
Ecosystem Impact: creates habitat
Most siganids are herbivorous and feed on phytoplankton or attached algae.
Primary Diet: herbivore (Folivore ); planktivore
Siganids are naturally confined to the tropical Indo-Pacific, but are now found in the eastern Mediterranean as well. Siganus fuscescens is at least one species that has been able to penetrate from the Red Sea through the Suez Canal to the Mediterranean, where it is now locally common.
Biogeographic Regions: palearctic (Native ); indian ocean (Native ); pacific ocean (Native )
Siganids are marine and mainly inhabit reefs, shallow lagoons, sea grasses or mangrove areas. They can be found along reef edges with broken rock, reef flats with scattered coral heads or near grass flats, and often come into very shallow waters to feed in algae. They are rarely found in estuaries, and only one species, Siganus lineatus, is truly estuarine. Some primarily estuarine species have been successfully introduced into freshwater lake and pond habitats as well.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: pelagic ; reef ; coastal
Other Habitat Features: estuarine ; intertidal or littoral
Generally, smaller reef fishes such as siganids live between three and five years.
The siganids have many strong spines with venom glands in dorsal and anal fins that contain a painful toxin. Most siganids are countershaded, but some reef species, Siganus vulpinus, have coloration similar to butterflyfishes. The teeth of siganids are compressed into a single row and asymmetrically bicuspid. The pelvic formula is unique (I, 3, I,) reflecting the hard spines at either end of the fin. The dorsal fin has 13 spines and 10 soft rays and the anal fin has 7 spines and 10 soft rays. There are 23 vertebrate and the maximum length is approximately 50 cm. (Click here to see a fish diagram).
Rabbitfishes are quite colorful and can be easily identified during daylight hours. However, at night or when threatened, they change drastically as color fades and dark blotches appear. Similarly, at death colors fade rapidly, making identification after preservation difficult. Although there are no significant differences between the sexes in this group, females are larger than males in some, if not all, species.
Other Physical Features: ectothermic ; bilateral symmetry ; polymorphic ; venomous
Sexual Dimorphism: sexes alike; female larger
Siganids are most threatened by predation during the planktonic, larval stage and very few larvae survive. On reefs, where most siganids live, predation is the most important cause of death (Hixon, 1991 in Moyle and Cech, 2000). The elaborate defenses in the form of poisonous spines are a testament to predation pressures. The sharp, strong spines are coated with a mucous mixed with venom and can inflict painful wounds. As discussed in physical description above, rabbitfishes lose their color at nightfall and may also change color if threatened.
Known Predators:
Anti-predator Adaptations: aposematic ; cryptic
Siganids characteristically school in small to large groups, with some species, such as Siganus fuscescens and Siganus luridus, breaking off into pairs or small units after spawning begins. Other members of the Siganidae family, such as the foxface, form monogamous pairs. Individual pairs or groups behave aggressively towards one another resulting in wide spacing throughout the reef during spawning. Just before gametes are released, most siganids move in a circular pattern and the males develop a marble color pattern.
Mating System: monogamous ; polygynandrous (promiscuous)
Before spawning, siganids migrate to traditional spawning areas, with the location varying among species. Spawning peaks in spring and early summer, and, as with many other coastal species, siganids show a prominent lunar rhythm. Spawning usually takes place at night or early morning and coincides with outgoing tides. Siganid larvae also respond to the lunar cycle, as most appear inshore (after the initial pelagic stage) three to five days before the new moon.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
There is no evidence of parental care in the Siganidae family.
Parental Investment: no parental involvement
