14 
PACIFIC SCIENCE, Vol. XXII, January 1968 
Rhinecanthus rectangulus 
— nm — -HifiHW - 
Melichthys piceus 
u i h hi 1 , 1 1 ill 
: a 
-#4— ill- 
Balistes vetula 
M ,1 
'd 1 " — — i it~M — — *f— 4 
f-4 
200 400 600 
MILLISECONDS 
800 
Fig. 2. Pectoral fin sounds of three species of triggerfishes. Note that most of the sounds can be re- 
solved into groups of two or more pulses (each pulse is indicated by a solid line under recording). Each 
pulse corresponds to one sweep of the pectoral fins across the drumming membrane. 
not result in significant changes in sound pres- 
sure. When a small hole was made in the drum- 
ming membrane (but only a few bubbles of gas 
were allowed to escape from the airbladder), 
again there was no significant change in sound 
pressures. However, when the hole was held 
open with the syringe, allowing most of the gas 
to escape, sound pressures averaged 13.7 db be- 
low those of fish with only a small hole in the 
drumming membrane. 
TABLE 1 
Peak Sound Pressures Produced by Triggerfishes after Operatons on Parts of the 
Pectoral Fins and Air Bladder 
PEAK SOUND PRESSURE 1 
CONDITION 
X 
S. D. 
T-VALUE 
PROBABILITY 
One fin removed 2 
Both fins removed 2 
—2.2 
-16.4 
1.1 
3.2 
15.2688 
0.005 
One spine removed 
Both spines removed 
— 1.8 
— 13.0 
3.3 
2.7 
11.6792 
0.005 
Unilateral removal of rays 
Bilateral removal of rays 
0.73 
—0.33 
1.4 
1.7 
0.7067 
0.5 
Small hole in air bladder 
Gas removed from air bladder 
-0.4 
— 13.7 
1.4 
5.3 
9.4785 
0.005 
1 Sound pressures are expressed as positive db (above) or negative db 
2 Experiments performed on Rhinecanthus rectangulus only. 
(below) 
peak sound pressures of normal 
fish. 
