266 
quarry. A long stick was used to prod the pos- 
terior end of the fish which often responded by 
swimming into the net. 
The following observations on sleep were 
made on 10 juveniles, 27 to 40 mm. in standard 
length, which had been maintained in an aquar- 
ium for 12 days. 
With the onset of darkness the fish settled 
to the bottom of the tank, although they con- 
tinued to move about, and occasionally these 
movements would take them above the bottom. 
After total darkness ensued, 25 min. were re- 
quired before they entered the state of suspended 
animation completely. This state was ascertained 
by lightly stroking the fish with a glass rod. 
When they ceased to flee from such contact, it 
was assumed that they were asleep. Since the 
period of attaining sleep was prolonged by the 
interruptions, a series of observations on succes- 
sive nights was necessary to determine the nor- 
mal period. 
The stimulus to sleep was shown to be the 
onset of darkness and not merely the passage 
of a definite number of hours of diurnal exist- 
ence, for the manini remained active for many 
hours when a light was kept burning above the 
tank after darkness set in. In one experiment 
the fish were kept awake for a period of 24 hr. 
They remained active during the time; however 
they ceased to feed toward the end of this pe- 
riod and displayed "restless” swimming. 
When the fish were kept in total darkness 
for 24 hr., they remained relatively quiet on the 
bottom during the entire period. At the end of 
this period, however, it was noticed that they 
perceived the immersion of a hand into the 
tank regardless of how slowly it was inserted. 
After 3 hr. of uninterrupted sleep, beginning 
with onset of darkness, lights were turned on 
to see how long the state of torpor would per- 
sist. In 13 to 14 min. the first 3 fish awakened 
and began to swim around the aquarium. These 
were the largest of the 10 manini. The remain- 
ing fish awakened according to size; the 2 
smallest required 25 and 28 min., respectively. 
All of the fish displayed very restless swimming, 
moving constantly back and forth in the aquar- 
ium. When the lights were turned off, they re- 
quired 39 min. to re-enter the state of torpor. 
PACIFIC SCIENCE, Vol. XV, April 1961 
No distinction could be detected in the time 
needed for the different-size fish to go back to 
sleep. 
SUMMARY 
1. In the Hawaiian Islands the common sur- 
geonfish, Acanthurus triostegus sandvicensis 
(known in Polynesia as the manini), is found 
in many different habitats, although never far 
from coral or rock for shelter and algae for 
food. The young are abundant in tide pools. 
Manini are not numerous in regions of heavy 
coral cover, although certain other surgeonfishes 
are surprisingly common there. 
2. The eggs and larvae of the manini are pe- 
lagic. Eleven acanthurid larvae, 4.2 to 8.7 mm. 
in length, were taken in eight plankton tows 
10-140 mi. from the nearest Hawaiian island. 
All were from the upper 50 m., although more 
tows were made in from 100 to 300 m. A higher 
percentage of acanthurid postlarvae have been 
found in surface-caught yellowfin tuna than 
those taken with long line at depths of about 
30 to 160 m. Acanthurid larvae are more com- 
monly found in the stomachs of tuna caught 
inshore than offshore. 
3. The limits of temperature tolerated for 1 
hr. by manini (both young and adults) appear 
to be about 12° and 37° C. Chlorinity tolerance 
for 24 hr. approximates 1.4 %o to 37 %c. The 
most extreme readings of temperature found on 
Oahu in waters inhabited by manini were 16.2° 
and 35.1° C. and of chlorinity, 2.65 %c and 
21.3 %o. 
4. Apart from the postlarval acanthurids found 
in tunas nothing is known of predation on the 
pelagic stages of the manini. In Hawaii, juve- 
nile manini probably constitute prey to carangid, 
muraenid, synodid, scorpaenid, sphyraenid, cir- 
rhitid, holocentrid, and antennariid fishes, and 
possibly certain large crabs. In view of the pau- 
city of large piscivorous fishes in Hawaiian wa- 
ters adult manini are probably relatively free 
of predation ( man excluded ) . 
5. The manini was found to be parasitized by 
one species of hydroid, four trematodes, four 
nematodes, two leeches, and six copepods. 
6. Difficulty was experienced at one time 
maintaining manini in aquaria. They died in 
