Accmthurus triostegus sandvicensis — RANDALL 
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TABLE 3 
Preference Feeding Experiments on Juveniles of Acanthurus triostegus sandvicensis 
PREFERRED 
COMPLETELY EATEN 
SPARINGLY EATEN 
NEVER EATEN 
Polysiphonia sp. 
Hypnea sp. 
Ectocarpus indicus 
Lyngbya majuscula 
Enteromorpha sp. 
Hypnea sp. 
Sphacelaria sp. 
Lynghya sp. 
Lophosiphonia sp. 
Liagora sp. 
Hormothamnion 
Ceramium sp. 
Jania sp. 
enteromorphoides 
Centroceras sp. 
Rosenvingia sp. 
Hydrocoleum 
Gracilaria sp. 
Trichogloia sp. 
cantharidosmum 
Rhizoclonium sp. 
fixed diatoms 
Calothrix confervicola 
Dasya sp. 
Enteromorpha sp. 
Cladophora sp. 
Grateloupia sp. 
Herposiphonia sp. 
Microdictyon setchellianum 
( many species ) 
Ectocarpus breviarticulatus 
Asparagopsis taxiformis 
side were fed with a Polysiphonia and those on 
the other with an Enteromorpha (these were 
the algae upon which manini fed most vigor- 
ously in the preference experiments ) . 
These algae are among the first macroscopic 
organisms to appear on the bottom of boats in 
harbor areas on Oahu. They are fast growing, 
especially the Enteromorpha which increased its 
length an average of 27 mm. per day on the 
eastern side of a boat during a period of 5 
sunny days in April. If collected when the thalli 
first develop, they are almost devoid of animal 
life. A fresh mass of the Enteromorpha weigh- 
ing 1.75 g. contained one ciliate, one nematode, 
one copepod, and a few epiphytic pennate dia- 
toms and blue-green algal cells. Nevertheless the 
algae were thoroughly washed and picked over 
for animals before being fed to the fish. Fresh 
algae were added to the aquarium every day, 
and the previous day’s algae removed. At the 
end of 2 weeks the fish were measured. Those 
fed on Polysiphonia grew an average of 2.9 mm.; 
those fed on Enteromorpha grew an average of 
3.1 mm. During the 2 -week interval the tem- 
perature in the aquarium was cool, varying from 
23.0° to 23.8° C. 
The preference experiments indicated that 
neither of these algae was eaten more readily 
than the other. Manini often alternated between 
feeding on the two. After 2 weeks of feeding 
on one of these, both kinds were added at the 
same time. It was immediately apparent that the 
fish had been conditioned to the alga on which 
they had been feeding. The "new” alga was un- 
touched initially and only occasionally sampled 
an hour later. The preference was no longer 
obvious by the end of the day, however. 
Manini feed almost constantly during the day, 
both in an aquarium and their natural habitat. 
They do not feed at night (see section on be- 
havior ) . 
The volume of algae consumed is large. Four 
juvenile manini, 28.5-45 mm. in standard length 
and weighing a total of 8.3 g., were fed a known 
mass of Enteromorpha in an aquarium early in 
the morning. The alga was weighed after firm 
squeezing followed by blotting on paper towels. 
At the end of the day the remaining fresh algal 
material was weighed in the same manner. Fresh 
Enteromorpha is grassy green and can easily be 
distinguished from fecal alga which is brownish 
or blackish green and tends to remain in pellets. 
The manini ate 10.8 g. of this alga one day and 
8.8 g. the next. The same procedure was utilized 
for two adult fish, 123 and 128 mm. in stand- 
ard length and 83.2 and 94.5 g. in weight, re- 
spectively. These two fish ate 27.4 g. of En- 
teromorpha in one day. The second day 16.3 g. 
of Polysiphonia was consumed. After being un- 
fed during the morning of the third day, they 
ate 25.2 g. of Enteromorpha during the remain- 
ing 6 hr. of the day. Although these two adult 
manini in the above experiment were well 
adapted to aquarium life (they were reared to 
this size as captive fish in a pond of the Hawaii 
Marine Laboratory at Coconut Island and were 
