Acanthurus triostegus sandvicensis — Randall 
counted. The ability to overcome settling is more 
efficient than 227 movements with an upward 
component out of 300 would indicate. Since the 
head is directed downward, swimming is initi- 
ated in this direction. In most cases the fish 
soon turn sharply and swim upward. If the in- 
terval of movement is short, there may be in- 
sufficient time to end up higher than the start- 
ing position, but usually the fish is not signif- 
icantly lower. The interval between movements 
is highly variable, but it averages about 1 min. 
The distance traveled by the larvae per move- 
ment is usually less than 40 mm. One, however, 
stopped 110 mm. above its starting position. 
In addition to geotaxic responses, swimming 
movements were made to avoid contact with an 
approaching object. This was first observed in 
I mm. 
Fig. 10. Early larval stages of Acanthurus triostegus 
sandvicensis. 
243 
42 -hr. larvae; however, it may be operative sev- 
eral hours earlier. The eyes do not seem suf- 
ficiently well developed to be functional at this 
early age, and a glass rod is detected as easily 
as an opaque one; thus vision would not seem 
to be the sense responsible for perception of an 
approaching object. Before such an object 
touches a larva, and sometimes when it is as far 
as 2 or 3 cm. away, a fleeing movement is ini- 
tiated. A second stimulus soon after the flight 
reaction will usually result in a second swim- 
ming movement. Contact with the bottom due 
to slow settling usually will not result in a swim- 
ming movement. Regular movements occur at 
about the same rate when the fish are on the 
bottom. They may enable a larva to become sus- 
pended again, but usually only for a short time. 
Areas of white pigment are beginning to form 
on the ventral part of the seventh and fifteenth 
somites of the 42 -hr. larva. These are large and 
conspicuous in the 54-hr. larva, and lesser white 
areas may be seen on the ventral part of the 
body anterior to the seventh somite and on the 
head. At this stage the intestine has just formed 
and the yolk mass is small. The melanophores 
over the yolk are large and dendritic. 
Figure 11 consists of microphotographs of 
living 7 5 -hr. and 4-day 1-hr. larvae with the 
light transmitted through the little fish. The 
dorsal fin fold is a prominent feature at 75 hr. 
(it was first noticed in the 66-hr. larva), and 
the pectoral fins are developing. Dark pigment 
around the eye is evident. The 4-day 1-hr. larva 
was observed to sink less rapidly than prior 
stages. One larva of this age sank 2.5 cm. per 
min. and another less than 1 cm. per min. The 
4-day 12 -hr. larva remained suspended head 
down in the water, thus indicating that the air 
bladder was functional. The jaws were observed 
to move in the 4-day 5 -hr. larva (Fig. 12). 
Although still tending to float head down- 
ward, the 5 -day larva is capable of normal ori- 
ented swimming. The pectoral fins can be flut- 
tered rapidly, and the eyes move. The yolk is 
completely gone and the oil globule half re- 
sorbed. By 5 days 12 hr., the 3 individuals which 
survived to this age appeared to be feeding by 
short darting movements. Material from a cul- 
ture of marine ciliates was added to the finger 
bowl in which these 3 larvae were kept. One 
