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PACIFIC SCIENCE, Vol. XV, April 1961 
such as labrids and chaetodonts, feed greedily 
on the eggs when afforded the opportunity to 
do so by the absence of the guarding parent. 
A study of the kinds of filamentous algae 
eaten by manini was undertaken. It was soon 
apparent that a great many different species of 
algae are eaten, and it is believed that at least 
a few filaments of virtually every filamentous 
alga in the Hawaiian area can ultimately be 
found in the gut of the manini if enough speci- 
mens are examined. 
Dawson, Aleem, and Halstead (1955: 21), 
reporting on the gastrointestinal contents of 42 
Acanthurus triostegus triostegus (size of speci- 
mens not given) from Palmyra, Line Islands, 
found 40 species of benthic algae and a number 
of species of diatoms of several genera. The 
number of algal species exceeded that previously 
known from Palmyra. Five species were most 
common in the stomachs: Pterocladia sp., Spha- 
celaria furcigera , Lyngbya majuscula ( and/ or L. 
aestuarii ) , Bryopsis pennata , and Lophosiphonia 
sp. The authors assumed that these were either 
dominant algae in the grazing grounds of the 
fish or were especially selected as food. It is the 
opinion of this author that these are the dom- 
inant algae, for (as is discussed below) the 
blue-green Lyngbya majuscula and another Lyng- 
bya are not selected by this surgeonfish (at least 
not the Hawaiian subspecies ) . 
A simple piece of apparatus was devised to 
test the preference by manini in Hawaii for 
various kinds of common filamentous algae. Ten 
tongue depressors were attached 2 cm. apart to 
a piece of wood. The free end of each depressor 
was notched and wrapped with a short piece of 
pliable galvanized steel wire. Different kinds of 
algae were fastened to the depressors by wrap- 
ping the wire ends around them. All 10 de- 
pressors with the assortment of algae attached 
were lowered simultaneously into the center of 
an aquarium in which juvenile manini, 26-30 
mm. in standard length, were kept. When ex- 
periments were repeated, the position of the 
algae was always changed. If an alga was not 
eaten during the course of the experiment, it 
was left in the aquarium as long as it appeared 
edible to see if it would ultimately be devoured. 
The results are given in Table 3. 
Many of the above algae were offered in a 
comparable manner to two adult manini, 123 
and 128 mm. in standard length, with similar 
results. 
Some species of algae not listed in the table 
were offered but not eaten; these, however, were 
probably too coarse for the juveniles. Included 
were two species of Laurencia , a species of 
Gelidium , a Gracilaria , and a species of Dictyota. 
A thallus of one of the species of Laurencia was 
placed in the aquarium with the adult manini. 
The small branches were eaten, leaving the ma- 
jor branches denuded. 
Of the seven kinds of algae fine enough to be 
eaten but ignored in the preference experiments, 
one is a red (Asparagopsis taxiformis , well 
known for its high iodine content), one is 
brown (Ecto carpus breviarticulatusj , and the 
rest are blue-greens. These were the only blue- 
greens tested. 
Blue-green algae, some of which are the same 
species as those in the preference experiments, 
have been found in the stomachs and intestines 
of manini by the author ( and, as noted, by Daw- 
son, Aleem, and Halstead, 1955). This seems in- 
consistent with the results of the experiments. 
It was noted, however, that the blue-greens were 
never the exclusive food material, but were al- 
ways mixed with large amounts of other algae, 
usually reds or greens. 
In May, 1952, in water 10-20 ft. deep in 
Hanauma Bay, Oahu, the bottom was examined 
for the kinds of fine algae which reach a height 
of about 5 cm. or more. Three species this size 
were common: Lyngbya majuscula , Asparagop- 
sis taxiformis , and Plocamium sandvicense (a 
red alga). Since surgeonfishes are abundant in 
the bay and at least two of the three algae are 
distasteful to one surgeonfish, the success of 
these algae might be associated with distasteful 
qualities. 
Although there was little question from the 
observations that the manini requires no animal 
food, an experiment was designed to demon- 
strate that this species can subsist and grow on 
algae alone. A 2 3 -gallon aquarium was divided 
into two compartments with a piece of plexi- 
glass. Six manini, 26-31 mm. in standard length, 
were placed on each side and provided with 
cover in the form of several rocks grouped in 
the center of each compartment. The fish on one 
