274 
FIG. 5. Juvenile of Ctenochaetus binotatus Randall 
from the Gilbert Islands; standard length 35 mm. 
5 of the present paper. As a result of the exam- 
ination of specimens of C. binotatus taken in 
the Society Islands, it is now apparent that the 
one from the Gilbert Islands is a juvenile of 
this species. The upper teeth with seven instead 
of six denticulations and the bright yellow 
caudal coloration are juvenile characteristics. 
No positive record of the life color of adults 
was available for the description of C. binotatus. 
The following color notes made from specimens 
speared in Papetoai Bay, Moorea, are therefore 
presented. A 130 mm. adult was chestnut brown 
on the head and body with narrow, blue, length- 
wise lines on the body and small blue spots on 
the head and thorax; the median fins were 
brown; the caudal, however, was observed to be 
dull yellow underwater and after the fish was 
speared the color of the fin alternated from 
entirely brown to brownish yellow on the upper 
half and brown on the lower; also evident while 
the fish was still alive was a temporary suffusion 
of brownish yellow over the body and dorsal 
and anal fins; faint diagonal-lengthwise bands 
of dull orange were visible in the dorsal fin, and 
the dorsal and anal had a narrow blue-black 
margin and the diagnostic black spot at rear base 
of each of these fins; the pectoral membranes 
were hyaline, the rays yellowish brown; the iris 
was deep blue. A 31 mm. specimen in a late 
phase of transformation from the acronurus to 
the juvenile state was brown with vivid yellow 
caudal fin, caudal peduncle, and posterior part 
of dorsal and anal fins (thus emphasizing the 
black spot at rear base of the latter two fins ) ; 
blue spots were present anteriorly on the body 
and blue lengthwise lines posteriorly. 
Juveniles are commonly seen on the shore 
reef of Papetoai Bay at a depth of about 3-6 
PACIFIC SCIENCE, Vol. XIV, July I960 
ft.; adults occur in the bay at a depth of 30-40 
ft. at the base of the vertical front of the shore 
reef. Acanthurus thompsoni was observed and 
collected from the same general habitat, though 
more over the sand adjacent to the vertical reef 
front. 
Ctenochaetus strigosus is here recorded from 
the Society Islands and Marquesas for the first 
time. This species in French Oceania also dis- 
plays a striking color change from juvenile to 
adult. The young are entirely bright yellow- 
the fourth species of surgeonfish known to have 
a yellow juvenile stage (the others are Acanthu- 
rus pyroferus, A. olivaceus, and A. coeruleus 
Bloch and Schneider; curiously, none of these 
species appear to be closely related) . In the Ha- 
waiian Islands, however, the young of C. strig- 
osus are not yellow but are brown like adults. 
As previously discussed (Randall, 1955^: 159) 
a notable color difference exists between adults 
in the Hawaiian Islands and the Philippines 
and those in the Tuamotus. The caudal fin of 
Hawaiian and Philippine fish is brown, whereas 
it is white in specimens from the Tuamotus 
(and the Societies and Marquesas). Specimens 
from all of these areas (except the Philip- 
pines), when alive have a bright yellow ring 
around the eye or a rim of yellow adjacent to 
the posterior edge of the eye. Even the yellow 
juveniles clearly show a posterior rim of yellow, 
for the yellow color is brighter adjacent to the 
eye than on the rest of the head. 
In the Society Islands the change from yellow 
juvenile to dark brown, white-tailed adult colora- 
tion takes place at a standard length of about 
50 mm. There is considerable variation in size 
at which this occurs, however. Yellow speci- 
mens have been taken which are as large as 
54 mm., and brown with white tail have been 
taken as small as 45 mm. in standard length. 
At Takaroa, Tuamotus, a specimen was collected 
which was changing from yellow juvenile to 
brown adult color at a standard length of 67 
mm. A 32 mm. specimen was speared in Moorea 
at a depth of 20 ft. which was in a late stage 
of transformation from the acronurus to the 
juvenile form (there was still a trace of silver 
over the abdomen, and the scales on the body 
were not fully formed ) . The specimen was dull 
yellow-orange with bright orange caudal fin, a 
