Animal Diversity Web

Di­ver­sity

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. (Nel­son, 1994; Wheeler, 1975)

Ge­o­graphic Range

Siganids are nat­u­rally con­fined to the trop­i­cal Indo-Pa­cific, but are now found in the east­ern Mediter­ranean as well. Siganus rivu­la­tus 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. (John­son and Gill, 1998; Nel­son, 1994; Wheeler, 1975)

• Biogeographic Regions
• palearctic
  • native
• indian ocean
  • native
• pacific ocean
  • native

Habi­tat

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 ver­mic­u­la­tus, is truly es­tu­ar­ine. Some pri­mar­ily es­tu­ar­ine species have been suc­cess­fully in­tro­duced into fresh­wa­ter lake and pond habi­tats as well. (Helf­man, et al., 1997; Nel­son, 1994; Thresher, 1984; Wheeler, 1975)

• Habitat Regions
• tropical
• saltwater or marine

• Aquatic Biomes
• pelagic
• reef
• coastal

• Other Habitat Features
• estuarine
• intertidal or littoral

Sys­tem­atic and Tax­o­nomic His­tory

A de­tailed phy­lo­genic analy­sis of the sub­or­der Acan­throidei was com­pleted by Tyler et al. (1989) and should be con­sulted for a list of synapo­mor­phies (from Nel­son 1994). (Nel­son, 1994)

Siganids are one of sev­eral re­cently de­rived fam­i­lies (Acan­thuri­dae, Monacan­thi­dae, Po­ma­cen­tri­dae, Scari­dae, Blenni­idae) ca­pa­ble of ex­ploit­ing reef algae and small colo­nial in­ver­te­brates. Reef her­bivory was pri­mar­ily re­stricted to post-Cre­ta­ceous per­ci­formes until these fam­i­lies un­der­went rapid evo­lu­tion dur­ing the early Ter­tiary, 50 to 30 mil­lion years ago. (Harmelin-Vivien, 2002)

Phys­i­cal De­scrip­tion

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). (Helf­man, et al., 1997; John­son and Gill, 1998; Nel­son, 1994)

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. (Kuiter, 1993; Thresher, 1984)

• Other Physical Features
• ectothermic
• bilateral symmetry
• polymorphic
• venomous

• Sexual Dimorphism
• sexes alike
• female larger

De­vel­op­ment

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. (John­son and Gill, 1998; Nel­son and Wilkins, 1993; Nel­son, 1994; Thresher, 1984; Wheeler, 1975)

Re­pro­duc­tion

Siganids char­ac­ter­is­ti­cally school in small to large groups, with some species, such as Siganus rivu­la­tus 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. (Thresher, 1984)

• 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. (Thresher, 1984)

• 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. (Thresher, 1984)

• Parental Investment
• no parental involvement

Lifes­pan/Longevity

Gen­er­ally, smaller reef fishes such as siganids live be­tween three and five years. (Moyle and Cech, 2000)

Be­hav­ior

Siganids are com­monly known as rab­bit­fishes partly be­cause of their peace­ful tem­pera­ment. They are di­ur­nal her­bi­vores, hid­ing in reef crevices dur­ing night­time and brows­ing over reefs to feed dur­ing the day. Some species school while oth­ers browse in­di­vid­u­ally among corals. (Dr. Fos­ter and Dr. Smith, 2000; Froese, et al., 2003; Moyle and Cech, 2000)

• Key Behaviors
• natatorial
• diurnal
• motile
• social

Com­mu­ni­ca­tion and Per­cep­tion

No spe­cific in­for­ma­tion was found con­cern­ing com­mu­ni­ca­tion meth­ods used by this group.

• Communication Channels
• visual

• Perception Channels
• tactile
• vibrations
• chemical

Food Habits

Most siganids are her­biv­o­rous and feed on phy­to­plank­ton or at­tached algae. (John­son and Gill, 1998; Nel­son, 1994; Wheeler, 1975)

• Primary Diet
• herbivore
  • folivore
• planktivore

Pre­da­tion

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. (Kuiter, 1993; Moyle and Cech, 2000; Wheeler, 1975)

• Anti-predator Adaptations
• aposematic
• cryptic

• Known Predators

  • humans (Homo sapiens)

Ecosys­tem Roles

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). (Froese, et al., 2003; Moyle and Cech, 2000)

• Ecosystem Impact
• creates habitat

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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. (Froese, et al., 2003; Kuiter, 1993; Thresher, 1984)

• Positive Impacts
• pet trade
• food

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

No spe­cific in­for­ma­tion was found con­cern­ing any neg­a­tive im­pacts to hu­mans.

• Negative Impacts
• injures humans
  • bites or stings
  • venomous

Con­ser­va­tion Sta­tus

Cur­rently, there is no known con­ser­va­tion threat to any mem­ber of this fam­ily. (The World Con­ser­va­tion Union, 2002)

• IUCN Red List [Link]

  Not Evaluated

Other Com­ments

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). (Nel­son, 1994)

Con­trib­u­tors

R. Jamil Jonna (au­thor), An­i­mal Di­ver­sity Web.

Ref­er­ences

Allen, G., D. Robert­son. 1994. Fishes of the Trop­i­cal East­ern Pa­cific. Hon­olulu, HI: Uni­ver­sity of Hawaii Press.

Böhlke, J., C. Chap­lin. 1994. Fishes of the Ba­hamas and Ad­ja­cent Trop­i­cal Wa­ters. Wyn­newood, Pa: Pub­lished for the Acad­emy of Nat­ural Sci­ences of Philadel­phia by Liv­ingston.

Dr. Fos­ter, , Dr. Smith. 2000. "PetEducation.​Com" (On-line). Drs. Fos­ter and Smith's source for ex­pert pet in­for­ma­tion. Ac­cessed May 05, 2003 at http://​www.​peteducation.​com/​.

Froese, R., D. Pauly, D. Wood­land. 2003. "Fish­Base" (On-line). Fish­Base World Wide Web elec­tronic pub­li­ca­tion. Ac­cessed May 05, 2003 at http://​www.​fishbase.​org/​.

Harmelin-Vivien, M. 2002. En­er­get­ics and Fish Di­ver­sity on Coral Reefs. Pp. 268-269 in P Sale, ed. Coral Reef Fishes: Dy­nam­ics and Di­ver­sity in a Com­plex Ecosys­tem. San Diego, CA: Aca­d­e­mic Press.

Helf­man, G., B. Col­lete, D. Facey. 1997. The Di­ver­sity of Fishes. Malden, MA: Black­well.

John­son, G., A. Gill. 1998. Perches and Their Al­lies. Pp. 191 in W Es­chmeyer, J Pax­ton, eds. En­cy­clo­pe­dia of Fishes – sec­ond edi­tion. San Diego, CA: Aca­d­e­mic Press.

Kuiter, R. 1993. Coastal fishes of South-east­ern Aus­tralia. Hon­olulu: Uni­ver­sity of Hawaii Press.

Moyle, P., J. Cech. 2000. Fishes: An In­tro­duc­tion to Ichthy­ol­ogy – fourth edi­tion. Upper Sad­dle River, NJ: Pren­tice-Hall.

Nel­son, J. 1994. Fishes of the World – third edi­tion. New York, NY: John Wiley and Sons.

Nel­son, S., S. Wilkins. 1993. Growth and res­pi­ra­tion of em­bryos and lar­vae of the rab­bit­fish Siganus ran­dalli (Pisces, Siganidae). Jour­nal of Fish Bi­ol­ogy, 44: 513-525.

The World Con­ser­va­tion Union, 2002. "IUCN 2002" (On-line). 2002 IUCN Red List of Threat­ened Species. Ac­cessed May 05, 2003 at http://​www.​iucnredlist.​org/​.

Thresher, R. 1984. Re­pro­duc­tion in Reef Fishes. Nep­tune City, NJ: T.F.H. Pub­li­ca­tions.

Wheeler, A. 1975. Fishes of the World, an il­lus­trated dic­tio­nary. Lon­don: Fer­n­dale Edi­tions.

Wood­land, D. 1990. Re­vi­sion of the fish fam­ily Siganidae with de­scrip­tions of two new species and com­ments on dis­tri­b­u­tion and bi­ol­ogy. Indo-Pa­cific Fishes, 19: 136.