Acoustical Behavior of Myripristis herndti — Salmon 
375 
made for 1-3-hour periods. The majority of 
the sounds produced were staccatos and grunts. 
Within 1 hour after the lights were turned off, 
all fish had assumed a pale red color, typical 
of individuals caught by fishing at night in 
the field. 
Over 90% of all aggressive interactions 
consisted of brief chasing (1-3 seconds), usu- 
ally accompanied by knock sounds. In a few 
cases physical contact between the aggressive 
and fleeing fish occurred. In five such instances 
the aggressive fish produced growl sounds just 
after nipping took place. On these occasions 
the attacked fish was about the same size as the 
aggressor and did not flee. The oscillograph 
in Figure 4 illustrates a typical growl se- 
quence. The impact sound caused by body 
contact between two fish (within brackets) 
preceded the growl by several milliseconds. In 
four other observations, nipping did not occur 
but one aggressive fish dashed rapidly toward 
another, stopping just short of contact, and 
then produced the sound with his opercula 
slightly extended and mouth open. Aggressive 
behavior infrequently involved two fish which 
assumed parallel head-to-tail or head-to-head 
positions and slowly circled, beating their tails 
toward one another as they rotated, with oper- 
cula and mouth open but only the caudal fins 
spread. Knocking sounds were produced after 
one fish broke away and was chased by the 
other. 
Usually it was not possible to determine 
which of the two fish produced the knock 
sounds during a chasing episode. In cases where 
the aggressor chased a fish from the front to 
the rear of the cave, both fish involved had 
their heads facing away and opening of the 
mouth and opercula, associated with sound 
production, could not be observed. When chas- 
ing across the front of the cave took place, the 
aggressive fish often stopped swimming near 
the hydrophone while the fleeing fish continued 
moving across the front or into the cave. In 
such cases, knock sounds increased in intensity 
as the aggressive fish approached the hydro- 
phone while the fleeing fish moved several 
centimeters away. Often another faint series of 
knocking sounds occurred just after those of 
the attacking fish. These differed in pitch from 
those of the aggressive fish, indicating that the 
chased fish might also be producing sounds. 
The general impression (not documented) was 
that more sounds were produced during longer 
periods of chasing. The majority of all aggres- 
sive interactions were initiated by a larger fish. 
A summary of the aggressive interactions of 
all populations is shown in Table 5. 
Several of the smaller fish in three popu- 
lations often adopted a characteristic posture 
when approached by an aggressive and larger 
fish. They elevated their heads while simul- 
taneously tilting the ventral region toward the 
aggressor, exposing the pectoral area. In all 
cases, the aggressive fish broke off further con- 
tact and moved away. No staccato or grunt 
sounds were emitted during any aggressive 
interactions. 
Locomotory Activity of Individual Fish 
The number of pen deflections caused by 
single fish in the activity chamber were tallied 
per hour (Table 4). All fish showed consis- 
tently greater locomotory activity at night from 
1900 to 0800 hours. Two fish showed con- 
tinued activity through 0900. There were indi- 
vidual differences in the degree of daytime 
activity. There appeared to be a gradual rise 
to peak nocturnal activity during the first 3 
hours after midnight. 
Response to Introductions of Other Fish 
The number of grunt and staccato sounds 
produced by populations 1 minute after other 
fish were introduced is shown in Table 6. In 
no case did these sounds precede the intro- 
duction. A few grunts and one staccato sound 
were produced by three populations to one 
FI. xantherythrus, P. meeki, and P. porphyreus. 
In all cases, introduced fish immediately en- 
tered the cave. The greatest number of sounds 
was produced when a moray eel was presented. 
After entering the cave the eel immediately 
curled around one of the blocks with its head 
protruding inside and its tail outside the cave, 
and remained motionless. The majority of stac- 
cato sounds were produced when the eel ap- 
peared initially, but grunts were produced 
throughout the 1 -minute period. Other behav- 
ior by menpachi in addition to sound produc- 
tion consisted of orientation to the eel’s head 
and rapid swimming movements inside the 
