Acemthurus triostegus sandvicensis — RANDALL 
269 
pools from 5 days before to 5 days after peak 
tide-pool recruitment (2 days before new moon). 
When the lengths of these manini were com- 
pared with the lengths of the 59 acronuri from 
the rest of the lunar month, a smaller range of 
length (23.5-28.5 mm.) was apparent for the 
former group in spite of nearly twice as many 
specimens. Presumably individual acronuri are 
capable of transforming some days before the 
rest of their age group, and hence at a smaller 
size, when they come inshore earlier than the 
others. Similarly, those which reach shoal waters 
later than the majority will have attained larger 
than average size. 
29. A variation in size at transformation was 
found with locality which appears related to 
water temperature. The smallest size occurs in 
the warmest regions (about 20 mm. in the East 
Indies) and the largest in cooler sectors (Phoe- 
nix Islands excepted ) . 
In the Hawaiian Islands the size at transfor- 
mation averaged 26.3 mm. for 39 specimens col- 
lected in April and May and 25.4 mm. for 38 
specimens which were taken from July to Octo- 
ber (thus developing during warmer months). 
30. Growth of juvenile manini, as determined 
by rearing of captive fish, recovery of fish 
marked by clipping rays from the top or bot- 
tom of the caudal fin, and progression of modes 
in successive graphs of tide-pool collections on 
Oahu is about 12 mm. per month. 
The recovery of 281 manini of 1,247 tagged 
with Petersen disk tags fastened with monofila- 
ment nylon provided information on the growth 
of larger fish. The growth of adults 100 to 120 
mm. in standard length is slightly greater than 
1 mm. per month; 120 to 14 1 mm. fish grow 
about 0.8 mm. per month. 
Growth of both juveniles and adults ceases 
during the winter months in the Hawaiian Is- 
lands. 
31. No annular marks could be detected on 
the scales, otoliths or vertebrae of manini from 
which estimates of age could be made. Two 
larger acanthurids, Naso unicornis and Acanthu- 
rus xanthopterus, lived 20 and 15 years respec- 
tively in the Waikiki Aquarium in Honolulu 
where they died as the result of accidents. 
32. Small juvenile manini tend to remain in 
the tide pool or shallow water area to which 
they first come as acronuri. With increasing size 
they move seaward. 
Locality data from the recovery of tagged 
adult manini was too general to determine local 
movements, but adequate to demonstrate that 
no extensive migrations are normally undertaken 
by this surgeonfish. If displaced from their home 
area, however, manini are capable of wandering 
distances as great as 8 mi. 
33. Manini may be seen as solitary fish, in 
small groups, or in large feeding aggregations. 
One large group of fish, although observed to 
remain in one region in the Tuamotus, moved 
as much as 300 yd. in several hours. 
34. Juvenile manini in a large tide pool on 
Oahu were observed to have two hiding places 
beneath ledges, one of which was preferred. In 
order to attain shelter they will swim toward 
an intruder, if necessary. From 4 to 7 hr. were 
required for aquarium fish to accept an inverted 
bowl tilted on edge as shelter. 
Adults are less inclined to seek shelter. Their 
reaction to an approaching swimmer usually 
takes the form of retreat. 
35. Juvenile manini frequently fight among 
themselves, both in the natural environment and 
after being adapted to aquarium life. This does 
not concern territoriality, but is an expression 
of dominance by larger fish over smaller fish or 
old residents (in the case of aquarium fish) 
over new arrivals. A distinct color change, which 
involves an almost complete reversal of color 
pattern, is readily apparent, with the more ag- 
gressive fish becoming the darkest. Generally 
there is no contact between fish, and the fish 
under attack usually retreat. If not, there is a 
circling at close quarters with occasional overt 
movements, especially with the posterior part of 
the body. The manini’s caudal spine is small, 
and the juveniles were observed to inflict at 
most only superficial scratches. 
Manini were not observed to fight with other 
species but they may display a dominance in 
their behavior towards some. 
36. With the onset of darkness juvenile and 
adult manini settle to the bottom, usually with 
pelvic and anal fins in contact, and enter a state 
of torpor or sleep. Occasional short movements 
are made, these more often directed backward 
than forward. Even when remaining in one place 
