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Sea of Cortez 810

Families Balistidae and Monacanthidae
Triggerfishes and Filefishes
Class: Actinopterygii (ray-finned)
Order: Tetraodontiformes

Key Features:
Diamond-shaped laterally compressed deep bodies.  Three substantial spines in first dorsal fin (Balistidae), or two in Monacanthidae.  First dorsal spine may be locked into an erect position witgh a trigger mechanism released by the second spine.  Strong jaws with large incisiform teeth.  Movement is by undulation of second dorsal fin and anal fin, with caudle fin being only utilized for rapid bursts of speed.   

     
Notable Species in the Sea of Cortez

Balistes polylepis
Finescale Triggerfish
Sufflamen verres
Orangeside Triggerfish
Pseudobalistes naufragium
Blunthead Triggerfish
Xanthichthys mento
Redtail Triggerfish
 
 

Finescale triggerfish Balistes polylepis Photographed Scuba Diving Isla San Pedro Nolasco, San Carlos, Sonora Mexico

Balistes polylepis
Finescale Triggerfish

San Carlos, Sonora, Mexico

Families Balistidae and Monacanthidae
Triggerfishes and filefishes (Peces puerco y peces lija)


Triggerfishes are an odd group of fish best known for their highly developed defensive adaptations.  They derive their name from a set of three dorsal spines. The first spine can lock into an erect position that can subsequently be released by a trigger mechanism, activated by depressing the second dorsal spine.  The large dorsal spine allows triggerfish to wedge themselves into crevices and lock themselves in, making extrication by predators nearly impossible. 

Triggerfish are also known for possessing strong jaws and well-developed incisor teeth that are sufficient to crush the shells of mollusks and bypass the spines and bony tests of sea urchins.  There is little in nature that they won’t try to eat.  Triggerfish are one of the few fishes that will prey on the crown of thorns sea star, Acanthaster planci, as well as spiny sea urchins and even venomous fireworms. 

The shape of the triggerfish body is also an identification characteristic of the family. Triggerfish have a diamond-shaped body that is laterally compressed and pelvic fins are reduced in most species.  Filefishes in the family Monacanthidae are similar in appearance and were originally classified within the triggerfish family but have since been given their own family designation.  Filefishes may be differentiated in that they posses two dorsal spines rather than the three present in triggerfishes. 

There is only one species of triggerfish that is common in the Sea of Cortez, the fine scale triggerfish, Balistes polylepis.  Most commonly found in the northern and central Gulf, it is often seen near rocky and sandy bottoms.  Adults tend to cruise along rocky reefs where they may quickly seek cover from predators whereas juveniles are more prone to venture into open areas away from rocks. 

Finescale triggerfish over nest by Olin Feuerbacher, Loreto, Baja MexicoTriggerfishes may be observed blowing jets of water into sand to uncover their prey.  This behavior is also utilized to roll over sea urchins so that they can attack from below, where there are fewer spines to contend with.   Scuba divers may be curious when they discover large fields of concave holes encircled with pebbles, stones and assorted rubble.  In late summer and early fall, triggerfish will build nests in sandy bottoms consisting of shallow depressions, sometimes several feet in diameter, that are ringed by small rocks that the female has placed to mark her nest site. 

 

Updated August 28, 2009

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