380 
PACIFIC SCIENCE, Vol. XXI, July 1967 
sound is used in nest defence or male-male 
fighting, for example the "knocks” of N. 
analostanus, and grunts and growls of toadfish 
and midshipman (Gray and Winn, 1961; 
Cohen and Winn, in preparation). In M. 
berndti, an acoustical system involving the pro- 
duction of at least five types of sounds, includ- 
ing the hand-held grunt, has been evolved. 
These sounds are correlated with non reproduc- 
tive behavior patterns. Other sounds may be 
used during spawning, but to date no infor- 
mation is available. It may be supposed that 
the development of increasingly complex acous- 
tical systems (more distinct types of sounds 
correlated with specific behaviors or with dif- 
ferent intensities of one behavior pattern) will 
occur when large numbers of fishes aggregate 
throughout the year, at least for certain periods 
of the day. Such aggregations promote a variety 
of intraspecific contacts in different behavioral 
contexts and increase problems of vulnerability 
to predators. This explanation might account 
for two types of sounds associated with dif- 
ferent intensities of aggressive behavior (knocks 
and growls) and warning (staccatos and 
grunts) in M. berndti. There have been few 
studies to date, but it is interesting that several 
( 3-5 ) types of sounds have been recorded 
from nonreproductive groups of squirrelfishes 
and aggregations of marine catfishes (Tavolga, 
I960). 
Winn (1964) has proposed that fish sounds 
may be categorized into five basic types: vari- 
able interval, fixed interval, unit duration, time- 
length, and harmonic-frequency signals. Inter- 
mediates are not uncommon. He has suggested 
that information could be transmitted by vary- 
ing the intervals as well as the unit lengths, 
although there are cases when these variables 
do not seem to be involved. Differences in in- 
tervals and duration of units appear to differ- 
entiate sounds produced by menpachi, although 
there are also some minor differences in fre- 
quency and intensity between various sounds. 
Since M. berndti responds preferentially to 
some of its own signals, it might be possible 
to test these variables with artificial sound play- 
backs. It is assumed that all types of sounds in 
these fish are produced by different temporal 
patterning of contractions by the same pair of 
muscles associated with the air bladder. 
The squirrelfish are well suited for bio- 
acoustical studies because they will produce 
sounds and can usually be kept under semi- 
natural conditions in the laboratory for obser- 
vations and experiments. At least two other 
species in the Hawaiian area ( Holocentrus 
xantherythrus and H. lacteoguttatus') produce 
different sounds in intraspecific aggressive be- 
havior and warning (Salmon, unpublished 
observations). While H. xantherythrus was 
found in groups under ledges and in caves, 
H. lacteoguttatus appeared to be territorial. It 
appears that quite different types of social or- 
ganization and patterning of sounds may be 
characteristic of each species of squirrelfish. 
Further studies on other species may yield valu- 
able information on the evolutionary devel- 
opment of acoustical communication in the 
Holocentridae, and in marine fishes in general. 
ACKNOWLEDGMENTS 
This study would not have been possible 
without the cooperation of the faculty and staff 
of the Hawaii Marine Laboratory, especially 
Dr. Philip Helfrich and Dr. Ernst Reese. Dr. 
P. E. van Weel devoted much of his time and 
laboratory equipment to record muscle poten- 
tials. The Crown tape recorder and Grass cam- 
era were borrowed from Dr. Hubert Frings. 
Dr. Frings, Mabel Frings, and Carl Frings gen- 
erously cooperated to facilitate this research in 
many ways. Dr. Barry Muir kindly permitted 
me to test several fish in his activity chamber. 
Mr. Robert Morris of the Waikiki Aquarium 
supplied many specimens and the Nikonos 
camera. Miss Anne Sayler assisted in some of 
the experiments and in field work. This re- 
search was supported by grants to Dr. Howard 
E. Winn (United States Public Health Service 
Grant 5 R01 NB 03241) and the author 
(National Science Foundation Grant GB-3430). 
Experiments were completed while the author 
was a National Institutes of Health Postdoctoral 
Fellow (1 F2 MH-18, 887-01). I am grateful 
to Dr. Joseph A. Marshall for criticism of the 
manuscript. 
REFERENCES 
Barber, Saul B., and William H. Mowbray. 
1956. Mechanism of sound production in 
the sculpin. Science 124(3214) :219-220. 
Bergeijk, William A. Van. 1964. Directional 
