Acanthurus triostegus sandvicensis — Randall 
about 48 hr., displaying large sores, eroded fins, 
and excessive mucus on the body. The dominant 
bacterium was a short, gram-negative rod. 
7. The stomachs of 3 postlarval manini 6.7 to 
7 mm. in length were examined for food. Two 
were empty, and 1 contained two appendicular- 
ians and a larval polychaete. Of 57 manini in 
the acronurus (late postlarval) stage taken by 
night light offshore, 45 were empty, and the rest 
contained only occasional fish scales or crusta- 
cean fragments lodged in intestinal folds, thus 
suggesting that the acronuri do not feed at night. 
The guts of 4 unidentified acronuri taken from 
a skipjack stomach caught during the day were 
filled with zooplankton. 
8. During the first day of transformation from 
the acronurus to the juvenile state, most manini 
do not feed at all. Feeding on algae becomes pro- 
gressively heavier as transformation continues. 
Juvenile and adult manini feed almost entirely 
on relatively fine filamentous algae of numerous 
species. Little inorganic sediment was seen in 
the gut contents. When 28 different kinds of 
algae plus diatoms were offered to manini in 
feeding experiments, a red alga ( Polysiphonia 
sp. ) and a green ( Enteromorpha sp. ) were pre- 
ferred. All of the blue-greens, the red Asparag- 
opsis , and one species of the brown alga Ecto- 
carpus were not ingested (although these may 
be found in stomach contents, mixed with other 
algae ) . 
9. Juvenile manini were maintained in aquaria 
on algae alone. Fish 26 to 31 mm. in standard 
length grew at the rate of about 6 mm. per 
month (temperature 23.0° to 23.8° C.) when 
fed either Polysiphonia sp. or Enteromorpha sp. 
10. Manini feed almost constantly during the 
day, and a large volume of algae is passed 
through the gut. Four juveniles weighing a total 
of 8.3 grams consumed 10.8 grams of Entero- 
morpha in 1 day and 8.8 the next. Two adults 
weighing 83.2 and 94.5 grams ate a total of 
27.4 grams of Enteromorpha in 1 day. The adult 
fish did not feed as frequently in aquaria as in 
the natural environment. The larger fish dom- 
inated the smaller one and consumed the major 
part of the algae. 
11. Manini showed no response to extracts of 
algae, and the visual sense alone is needed to 
locate algal food. The olfactory sense appears to 
267 
function in feeding only to avoid unsavory mate- 
rial. Chemoreceptor organs in the mouth and 
possibly tactile organs as well seem to be as- 
sociated with the acceptance of algae and the 
rejection of material not utilized as food. 
12. The morphology of the digestive system 
is briefly discussed. The alimentary tract in- 
creases nearly three-fold during the 4 or 5 days 
of transformation from the acronurus to the ju- 
venile form, reflecting a change in food habits 
from feeding on zooplankton to feeding on al- 
gae. The length of the gut increases from about 
three times the standard length in small juve- 
niles to nearly six times in large adults. 
13. Algae passed through the gut of juvenile 
manini in 1 hr. 45 min. and in about 2 hr. in 
adults. At night when feeding ceases, the gut 
is emptied slowly. 
14. Although sustaining growth, the Entero- 
morpha appeared little affected after passing 
through the gut of manini. Additional work is 
needed to determine what is utilized by the ma- 
nini from its algal food. 
15. The stomach of the manini varies from 
slightly acidic to slightly alkaline. The intestine 
is alkaline (pFl 7.7 to 9.1) and the gall bladder 
acidic (pH 6.2 to 6.4). 
Amylase was detected throughout the diges- 
tive tract, strongest in the pancreas and weakest 
in the stomach. The pH optimum of the amy- 
lase is about 6.7. Maltase was not found. 
Lipase, with a pH optimum of 7.2, was found 
in all digestive organs, strongest in the pancreas 
and pyloric caeca and weakest in the stomach. 
Proteolytic enzymes are weak, especially from 
the stomach; pH optimum of pancreatic pro- 
tease is about 8.4. 
16. About two-thirds of the adult manini 
caught in unbaited traps off Oahu in from 30 to 
90 ft. are males. Of 221 manini in museum col- 
lections from the tropical Pacific mostly taken 
from inshore waters, 134 (60.7 per cent) are 
females. 
17. Although ripe males may be taken through- 
out the year ( fewer, however, in the fall ) , ripe 
female manini have been found in Hawaii only 
from early December to late July (and trans- 
forming young from middle February to early 
October ) . Average monthly sea surface tempera- 
