Sound Production in Triggerfishes — Salmon, Winn, and Sorgente 
19 
In R. rectangulus, sounds produced after the 
operations were significantly shorter in duration 
than were those of normal fish. However, when 
hand-held underwater for over a minute, even 
unoperated fish of this species gradually pro- 
duced more abbreviated sounds. We believe that 
the effect after operations reflected this species- 
specific response to prolonged handling, and 
was not causally related to the operations them- 
selves. 
The octave band analyses of the sounds pro- 
duced by seven species showed similarities in 
frequency spectra. Most of the acoustic energy 
was concentrated in the lower frequencies, as 
was shown by Moulton (1958) in his sono- 
graphic displays of sounds produced by B. vetula 
and M. piceus. 
Triggerfishes produced sounds in the field 
under conditions involving agonistic interactions. 
These sounds were quite loud and, when pro- 
duced by a fish chased into a narrow hole in 
the reef, could function to startle a predator. 
Sound production under these circumstances is 
probably a behavior adaptation which, in addi- 
tion to the bony plates and trigger mechanism, 
serves to promote survival of these relatively 
slow-moving fish. 
Intraspecific aggressive behavior, with sound 
production, was infrequently observed in the 
field and only in two species ( B . bursa and B. 
vetula ) . Triggerfish were usually observed swim- 
ming alone, and when they did meet conspecifics 
they were quite aggressive. Wide spacing be- 
tween individuals seemed to be the normal so- 
cial organization of each species at the time 
studied. Individual fish, observed from the sur- 
face, were seen swimming near the bottom, 
stopping occasionally to feed and inspect a ledge 
or hole in the reef. Sometimes a suitable hiding 
place was defended for a brief period. It may 
be that a fish which has found a suitable vacant 
hiding place nearby would be better able to 
escape from a predator. Several R . rectangulus 
consistently returned to the same hole when 
approached several times during a 2 -hour pe- 
riod. It would be interesting to mark fish and 
determine if they swam regularly over a def- 
inite home range, returning at dusk to the same 
hole which would be defended as are territories 
by other vertebrates. 
When placed in groups in the fish pen and 
in the circular concrete tank, Bimini species fre- 
quently produced sounds and, in B. vetula, 
showed color changes associated with aggressive- 
ness by fish in the field. Under these conditions, 
interactions were more common due to the 
crowding of several fish within a small area. 
Sounds with correlated color changes were pro- 
duced by individual fish when chasing one an- 
other, when defending their shelters, and when 
displacing other fish from the inside of the 
shelter. 
Triggerfish sounds may function in other 
situations, particularly in reproductive behavior, 
but at present no information is available about 
these situations. The hand-held sounds show 
species-specific differences in duration, but little 
difference in frequency content. It is quite prob- 
able that temporal variation in the rate and inter- 
vals at which pulses are produced could carry 
information to distinguish between signals of 
different species, especially when the sounds are 
used in conjunction with changes in body colora- 
tion. Further study of these fish is certainly 
indicated. 
SUMMARY 
Triggerfishes produce sounds correlated with 
movements of the pectoral fins against the side 
of the body. The air bladder evaginates to form 
two bilateral lobes covered by thin scales at the 
area of contact between the fins and body wall. 
A series of operations were performed on these 
structures in Balistes vetula, Melichthys piceus, 
and Rhinecanthus rectangulus in order to ana- 
lyze their contribution to the sounds. The single 
stout pectoral fin spine contributed to produc- 
tion of most of the sound energy, but some was 
contributed by the fleshy muscular lobe of the 
fin. Removing the gas from the air bladder re- 
sulted in markedly reduced sound intensities. 
The sounds of these fish, and those of B. capi- 
stratus, B. bursa, M. vidua, and M. buniva were 
found to be quite similar in frequency spectra, 
with most of the acoustic energy below 1200 Hz. 
Field and laboratory observations also were 
made on all species. The production of pectoral 
fin sounds during escape and aggressive behavior 
was described. In some species, these interactions 
were accompanied by color changes as well, 
usually in the aggressive or dominant fish. 
