Acanthurus triostegus sandvicensis — Randall 
259 
Fig. 22. Growth of Acanthurus triostegus sandvicensis on Oahu during the period Jul. 6 to Nov. 19, 
1954. The points represent growth increment of tagged fish recovered after at least 1 month in the water. 
Circles indicate the superposition of one point on another. The dotted line is the regression of growth on 
standard length. 
a month or more in the water following being 
tagged were utilized for growth study. In Fig- 
ure 22 the data from 68 such fish, tagged be- 
tween July 6, 1954, and September 28, 1954, 
are plotted. The dotted line represents the re- 
gression of millimeters of growth per month on 
standard length. The regression coefficient "b” 
(slope of the regression line) is — 0.0292. The 
t value testing whether this regression differs 
significantly from zero is 2.085. With 66 degrees 
of freedom, the probability of getting a larger 
value of t is 0.04; thus the null hypothesis of 
no significant regression is rejected. 
The comparison of the regression line with 
the upper part of the growth curve of Figure 18 
is favorable. The average growth rate of the 
captive fish from August 6 to September 27 
was given as 1.8 mm. per month. The average 
rate for this size range (90.0 to 94.3 mm.) from 
the regression line is 1.74 mm. per month. 
In order to further confirm the finding of ces- 
sation of growth in winter, 155 manini were 
tagged on November 19 and November 23, 
1954, by Nemoto. Twenty-five of these fish were 
recovered from December 23, 1954, to Febru- 
ary 18, 1955 (see Fig. 23). Their average rate 
of growth is — 0.112 mm. It therefore seems 
likely that no growth occurred during this 
period. 
Tagged manini, recovered after a month or 
more in the sea, which were at liberty during 
winter and either fall or spring months have not 
yet been considered. Data from these fish are 
presented in Table 11. 
If it is assumed that these 22 fish did not 
grow during any part or all of the 3 -month 
period beginning November 19, and the growth 
rate of each is computed only from remaining 
months, an average growth rate of 1.8 mm. per 
month is obtained. This compares favorably with 
the rate of growth as indicated in Figure 22 
(the average standard length in Table 11 is 
110.6 mm.) . 
AGE 
In view of the lack of winter growth of the 
manini it was hoped that annuli might be de- 
tected on the scales; however, none could be 
seen. Even the circuli of the tiny scales of this 
species are not very distinct. Cross-sections of 
vertebrae and otoliths were also examined, but 
with negative results. It was necessary to grind 
otoliths to about 1 mm. thickness and view them 
with subdued light under a compound micro- 
scope before any concentric rings could be seen. 
These were numerous and variable, and none 
were more sharply defined or grouped closer 
together than others. 
