Acoustical Behavior of Myripristis berndti — Salmon 
365 
centridae) produce sounds. Studies to date have 
been made on two species in the genus Holo- 
centrus. Fish (1948) first reported sound pro- 
duction in the group. Moulton (1958) studied 
H. ascensionis in Bimini and described two 
types of sounds produced in the field, a single 
sound (the grunt) and one composed of 
several thumplike sounds produced in a series 
(the staccato). Winn, Marshall, and Hazlett 
(1964) were the first to study the significance 
of these sounds experimentally. They found 
that the nonreproductive social organization of 
H. rufus, which produced the same types of 
sounds as H. ascensionis, was territorial. When 
a conspecific individual entered the territory of 
another squirrelfish, the resident produced 
many grunt sounds and rarely staccatos, some- 
times acompanied by fin erection, nipping, and 
lateral displays in which the two fish moved 
parallel to each other. Intruders of other species 
elicited both staccatos and grunts, but more 
staccatos were produced toward larger fish or a 
potential predator, such as a moray eel. Lab- 
oratory populations were maintained in large 
tanks and each fish defended a territory con- 
sisting of the inside of a large can, open at one 
end, and the area immediately before the open- 
ing. When staccato sounds were played back to 
these populations from one of two speakers on 
each side of the tank, the fish at first retreated 
into their cans. Some then swam to the sound 
source, while others turned their heads toward 
the speaker from just outside the can, indicating 
that the fish were probably able to localize the 
source of sound. Diel recording showed that 
more sounds were produced during the day 
than at night, when the fish were active and 
feeding. Peaks in sound production occurred at 
dawn and dusk. It was hypothesized that the 
peaks were caused by movements of nocturnal 
and diurnal species into and out of the reef 
and through the territories of squirrelfishes 
under conditions of reduced light intensity. 
Moulton (1958) stated that contractions of 
the body wall musculature associated with the 
first three ribs and the air bladder were re- 
sponsible for sound production in H. ascen- 
sionis. In a series of ablation experiments, 
Winn and Marshall (1963) showed that the 
muscles involved in sound production were 
bilateral and attached to the posterior part of 
the skull, the air bladder, and the first two 
dorsal ribs in H. rufus. Removal of one muscle 
reduced the intensity of sounds produced by 
hand-held specimens, but did not significantly 
change sound duration or number of pulses per 
sound, indicating that the two muscles con- 
tracted simultaneously to produce each sound. 
Gainer, Kusano, and Mathewson (1965) 
studied the electrophysiological and mechanical 
properties of the sound-producing muscle in the 
same species. The muscle was capable of con- 
tracting at a frequency of 100/second with 
no mechanical summation, while fast white 
muscle from the same fish showed considerable 
summation at 50/second. 
Myripristis is the second largest genus in the 
family. These fish live in schools and move over 
the reef more than do members of the genus 
Holocentrus (Herald, 1961), which are soli- 
tary-territorial. Other reports indicate that the 
schools remain in caves or under ledges during 
the day and scatter to feed at night (Hobson, 
1965). The presence of sand-dwelling annelids 
in the stomachs of M. berndti from the Mar- 
shall Islands indicated that the fish move to 
open areas, away from the reef during noc- 
turnal feeding (Hiatt and Strasburg, I960). 
There have been no published studies on the 
acoustical behavior of any species in this genus. 
Nelson (1955) described the antero-bilateral 
projections of the air bladder which, in M. 
argyromus, completely covered the auditory 
bullae and were thus more extensively modified, 
presumably for an auditory function, than in 
H. ascensionis and H. rufus. 
MATERIALS AND METHODS 
All observations and experiments were carried 
out at Oahu, Hawaii, from February to July 
1965. Most of the field observations were made 
in Pokai Bay, Waianae, in water 3-9 m deep. 
The study area spanned a 1-km distance along 
the coast. Several other schools were observed 
in similar habitats offshore at Black Point and 
Ilikai Harbor. The topographic features of the 
habitats and estimates of school size in number 
of fish were recorded with the aid of an under- 
water flashlight and drawing pad or were pho- 
tographed directly with a Nikonos underwater 
camera. 
