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 The Triggerfish

TRIGGERFISHES (FAMILY BALISTIDAE)

General Information on Triggerfish

Triggerfish Index

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General Information on Triggerfish

Triggerfishes are the subject for this month’s Fish-Watch article.  The triggerfish takes its name from the  locking mechanism of the stout first dorsal-fin spine and the smaller, slender second spine (the trigger).  When the first spine is erected, the second spine is also pulled up and functions like a cam to wedge the larger spine in a vertical position (Fig. 1).  The first spine cannot be folded down, until the tip of the second spine is pulled posteriorly.  The family name Balistidae is formed from the genus name Balistes, which is derived from the Latin ballista, another name for the Roman catapult, in allusion to the trigger mechanism of the dorsal-fin spines.  

Most triggerfish species occur on coral reefs, and when threatened by a predator, triggerfish dart into a hole or crevice on the reef, lock their dorsal spine erect and depress their pelvic bone to wedge themselves into the reef.  The body is also covered with strong, rough, plate-like scales that serve as armour plating and provide further protection.

The pelvic fins are reduced to a small, bony nubbin at the tip of the long depressible pelvic bone on the ventral midline of the belly.  Triggerfish swim by undulating the soft dorsal and anal fins, and use their tail fin only when they are in a hurry.

Although the mouth is small, the jaws are provided with strong, sharp teeth, and triggerfishes can deliver a painful bite.   They feed on a variety of benthic invertebrates, including crustaceans, molluscs, brittlestars, tunicates, polychaete worms, sponges, hydrozoans, tips of branching coral, and small fishes.  Sea urchins are a favourite food, and even the long spines of Diadema urchins pose no problem for a hungry triggerfish.  The fish just picks the sea urchin off the bottom, flips it over in midwater and then zeroes in on the spineless underside of the urchin. Some triggers, especially the redtooth (Odonus niger) and species of the genus Xanthichthys feed primarily on zooplankton.

Triggerfish are closely related to the filefishes (Family Monacanthidae), and some filefishes also have a locking dorsal-fin spine.  But filefishes have only one or two dorsal-fin spines, all the dorsal, anal and pectoral-fin rays are simple (unbranched), and the scales are modified, forming fine short bristles like on a toothbrush.

Triggerfishes occur worldwide in tropical and warm temperate waters, generally near shore in relatively shallow water (usually less than 100 m), but adults of some species are regularly found out in the open ocean.  Most triggerfish are good eating, although large specimens of some species are occasionally toxic and eating these fish may result in ciguatera poisoning.

When it comes time for spawning, most triggerfish dig a shallow crater in the sand, where the female deposits the eggs.  Both sexes have been reported guarding the nest until the eggs hatch and the larvae float away.  Should you see a trigger circling a spot on the sand, chasing other fishes that approach this location and blowing jets of water at the spot, it is likely that the fish is guarding a nest there.  Steer well clear of these nest guarders, as they are particularly aggressive, and have no hesitation in attacking and biting divers.

Trigger

The Balistidae comprises 12 genera and about 36 species; we have 20 species in our area.

  1. Titan or Giant triggerfish, Balistoides viridescens
  2. Orangestriped triggerfish, Balistapus undulatus
  3. Clown triggerfish, Balistoides conspicillum
  4. Indian triggerfish, Melichthys indicus
  5. Redtooth triggerfish, Odonus niger
  6. Blue triggerfish, Pseudobalistes fuscus
  7. Wedgetail triggerfish, Rhinecanthus rectangulus
  8. Boomerang triggerfish, Sufflamen bursa
  9. Bridle triggerfish, Sufflamen fraenatum
  10. Halfmoon triggerfish, Sufflamen chrysopterum
  11. Whitetail triggerfish, Sufflamen albicaudatum
  12. Gilded triggerfish, Xanthichthys auromarginatus
  13. Striped triggerfish, Xanthicthys lineopunctatus
  14. Outrigger triggerfish, Xanthichthys punctatus  and Bluelined triggerfish, Xanthichthys caeruleolineatus

The following species were omitted from the article as they are quite rare:

  • Abalistes stellatus
  • Balistes vetula
  • Canthidermis maculatus
  • Melichthys vidua
  • Pseudobalistes flavimarginatus
  • Rhinecanthus aculeatus

 
Balistes vetula may not even occur here, however it was listed in Smith's Sea Fishes based on what were presumably  incorrect identifications. No museum has Southern African specimens of this fish.

Please keep your eyes peeled for these fishes if you are a photographer; we would love photographs of these fishes as they are  so rare.

Text and photos Dr Phil Heemstra

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Updated on: 23/03/2001

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