Acanthurus triostegus sandvicensis — Randall 
attack hastily withdraws, a response which gen- 
erally satisfies the attacker for the moment. 
When there is no immediate retreat the two 
fish circle at close quarters and make pugnacious 
movements, mostly with the posterior part of 
the body. When a new manini was placed in 
the tank, it was attacked with ferocity by all of 
the other manini, but rarely more than one at 
a time. The hapless fish was pecked over the 
head and body, strongly bumped, and lashed at 
with the caudal spines of the others as it scurried 
from one part of the tank to the next. A manini 
twice the size of any in the tank was given the 
same treatment. After about half hour of inces- 
sant attack, this oppressed fish was observed to 
lie on its side on the bottom and submit com- 
pletely to the relentless abuse. It was caught and 
examined shortly thereafter. Only a few small 
scratches on the fins and two small cuts on the 
body could be seen. The manini has a much 
smaller caudal spine than other species of Acan- 
thurus and is not capable of inflicting much 
damage with it. Also the jaws do not seem strong 
enough to injure other fishes of equal size. 
Manini were never observed to fight with 
other species of fishes. They appear to display a 
dominant behavior pattern to at least some, how- 
ever. Six small pomacentrids ( Abudefduf ab- 
dominalis ) ranging from an estimated 18 to 38 
mm. in standard length were observed to inter- 
mingle with 4 juvenile manini about 28 to 36 
mm. in standard length at the shore of the Ala 
Wai Yacht Basin. Although the pomacentrids 
swam close to one another, they usually avoided 
coming within a body length of any manini. 
When one did and this was observed by a ma- 
nini, the latter responded by a slow sideward 
movement of the body toward the intruding 
fish. The posterior half of the manini’s body 
was curved toward the pomacentrid and vibrated 
slightly. The pomacentrid invariably retreated 
a short distance. 
Breder (1948: 293) observed similar behav- 
ior in an aquarium with A. chirm gus. He noted 
that a peck order was established among certain 
fishes in an aquarium. This involved 4 pomacen- 
trids and 1 gerrid. A small specimen of A. 
chirurgus was added which was about equal in 
size to the largest pomacentrid. Although the 
surgeonfish was not bothered much by the other 
265 
fish at first, it seemed to be low or lowest on the 
peck order. It was never noted to pursue the 
others, but was occasionally pecked at by the 
others. Fourteen days later the peck order was 
modified and the acanthurid was definitely num- 
ber one. There was little fighting but all kept 
clear of the surgeonfish which "showed” its 
peduncular spine to the more timorous. 
I have never observed fighting among adult 
manini. Larger individuals may display dom- 
inance over smaller ones, however. 
Behavior at Night 
At night, both in the natural habitat and in 
the aquarium, manini rest on the bottom, usually 
with the pelvic fins and anal fin touching the 
substratum, in what appears to be a state of 
torpor or sleep. In general the body color is 
darker than during the day. Large dark blotches 
which may be seen faintly during the day be- 
tween the vertical dark bars are more conspicu- 
ous at night. This resting phase is not without 
movement, for the pectoral fins are almost in 
constant slow motion and there are vertical un- 
dulations of the median fins. When a light was 
flashed on a darkened aquarium at night, short 
movements over the bottom were occasionally 
found to be in progress. These were directed 
backward more often than forward. 
Usually the manini in an aquarium or a tide 
pool at night are well dispersed. In the normal 
environment most of the fish choose a sheltered 
although not a confining location. Many, how- 
ever, may be seen in very exposed locations. 
Breder (1948: 294) observed that A. chirurgus 
rested on the bottom of an aquarium at night 
in the proximity of some shells, but in no case 
did it enter or hide in the shells. 
If light is turned on a sleeping manini at 
night, and no sharp movements are made, the 
fish can be lightly touched or even picked up 
without its making any effort to escape. If a 
sharp movement is made in the water of the 
aquarium, or if the fish is roughly handled, it 
will dart away for a considerable distance over 
the bottom. This behavior was put to good use 
for the collection of this species alive. Using a 
head lamp at night to locate a sleeping fish, a 
dip net was cautiously placed in front of the 
