Acanthurus triostegus sandvicensis — RANDALL 
Fig. 16. Size of Acanthurus triostegus sandvicensis 
from Oahu during the first day of transformation 
from the acronurus to the juvenile stage. The solid 
line represents all of the specimens collected from 
Apr. 11 to May 8, 1953; the dotted line indicates 
those collected from Jul. 7 to Oct. 4, 1953 - 
drawn by chance from a population in which 
the transformation length was the same through- 
out the season. It is therefore concluded that a 
relationship as indicated above exists between 
the size of transformation of the manini and 
the temperature of the water. 
Breder (1949a) stated that the complete trans- 
formation of Acanthurus chirm gus occurred 
in a period of about 48 hr. He did not, how- 
ever, define the morphological state that con- 
stitutes complete transformation. In the manini, 
adult coloration is nearly acquired after about 
48 hr., but other major changes are less than 
half completed after this length of time. Ad- 
mittedly it is difficult to define a precise stage 
at which larval characteristics have completely 
disappeared and miniature adult structure is 
assumed. Probably the most convenient criterion 
is the stage at which the scales have completely 
formed. Drawings of developing scales have 
been made by Poey (1875: pi. 3) for the West 
Indian species, Acronurus caeruleatus ( — Acan- 
thurus coeruleus ) and Acronurus nigriculus 
{— Acanthurus bahianus) . The first evidence 
of the formation of the scales is the appearance 
of scattered thornlike outgrowths which project 
upward as well as posteriorly from the narrow, 
vertical, fleshy ridges of the body (these spines 
do not occur on the anterior half of the body ) . 
249 
The spines are present on manini acronuri 
caught offshore at a night light, but they can be 
seen on these specimens only with the aid of a 
microscope. They enlarge and become visible 
(when wet) with the naked eye on the majority 
of first-day transforming individuals as early as 
7:00 A.M. Each such spine on later stages was 
found to be a central stout ctenius of a single 
developing scale; the majority of scales, how- 
ever, do not possess these. As scale development 
proceeds, the large ctenii flatten and become 
overlaid with epidermis. When this occurs, scale 
development is essentially complete as are other 
major changes of the transformation process. 
Scale development normally requires 4-5 days. 
In an aquarium the whole process seems de- 
layed, and about 6 days are necessary. 
Figure 17 shows transforming manini on the 
first, second, third, and fourth to fifth days. The 
second-day and third-day stages were identified 
with assurance by comparison with specimens 
recovered in tide pools following fin clipping 
on the first day of transformation. No older 
marked specimens were recovered at the stage 
when scale structure is just complete, and the 
time this required had to be inferred from the 
percentage of specimens in the different stages 
collected in the weekly poison stations of the 
Diamond Head tide pool of Figure 4. 
Fig. 17. Transformation of Acanthurus triostegus 
sandvicensis from the acronurus to the juvenile stage. 
Upper left, first day; upper right, second day; lower 
left, third day; lower right, fourth or fifth day. 
