Acanthurus triostegus sandvicensis — Randall 
239 
2 4 6 8 10 12 14 16 18 20 22 24 26 
Diameter of eggs 
125 mm. specimen. Oct. 27, 1952. Ovary length 20 mm. 
2 4 6 8 10 12 14 16 18 20 22 24 26 
Diameter of eggs 
142 mm. specimen. Dec. 5, 1952. Ovary length 18 mm. 
• Diameter of eggs 
146 mm. specimen. Feb. 6, 1953. Ovary length 32 mm. 
106 mm. specimen. March 13, 1953. Ovary length 20 mm. 
138 mm. specimen. March 17, 1953. Ovary length 35 mm. 
2 4 6 8 10 12 14 16 18 20 22 24 26 
Diameter of eggs 
123 mm. specimen. June 21, 1953. Ovary length 42 mm. 
FIG. 8. Egg diameters of Acanthurus triostegus sandvicensis plotted as units of an ocular micrometer. 
Scale: 1 unit = .035 mm. Except for A, where the number of eggs of 1 and 2 micrometer units were esti- 
mated at 1,575 and 627, respectively, no eggs less than 3 micrometer units were measured. 
Spawning 
The spawning of A. triostegus sandvicensis 
was never witnessed, in spite of considerable 
observation both at night and during the day 
and at various times of the month. On June 12, 
1957 (full moon) A. triostegus triostegus was 
observed to spawn at the atoll of Tikahau in the 
Tuamotu Archipelago at dusk (5:30 P.M.). It 
is believed that the failure to see the Hawaiian 
manini spawn was due to the lack of effort at 
dusk. The following account of the reproduction 
of the Tuamotu manini is probably similar to 
that for the Hawaiian subspecies. 
Several hundred spawning A. triostegus trio- 
stegus were observed in the pass at a depth of 
about 25 ft. Many of the fish displayed a marked 
color change. The black bars on the side of the 
body were much broader (but the added width 
on either side of each bar was not as intense a 
black as the center ) ; the median fins were dark, 
almost black, except for the middle of the caudal 
which remained pale; the dark median band on 
the forehead was prominent. Five fish of this 
color pattern were speared (when pursued, an 
individual dark-colored manini resumed normal 
coloration within about 10 sec.) ; all 5 were ripe 
males. As many as 4 or 5 of these more melanis- 
tic fish were repeatedly observed chasing single 
fish which were unchanged in color pattern. Two 
of the normally colored manini were speared. 
One was a running ripe female and the other a 
female with opaque eggs which were squeezed 
from the body only with considerable pressure; 
thus not all females in the spawning aggrega- 
tion are capable of reproduction at the same 
time, which is in keeping with the finding of 
running ripe female manini in Hawaii along 
with fish with maturing ova on many different 
days of the lunar month (Table 6). Actual 
spawning took place among small groups of fish 
within the large school which became increas- 
ingly active and suddenly darted upward about 
8 ft. above the rest. Eggs and sperm were re- 
leased at the apex of this movement. Swimming 
was more rapid as the apex was approached. The 
fish dispersed as they swam back down to mingle 
with the school. At times two or more small 
groups joined together in the first few feet of 
the upward movement, resulting in a dozen or 
more fish in a compact mass at the top. The 
attempts to spear individual fish broke up the 
one large aggregation into several lesser ones in 
which spawning took place infrequently. 
