Acanthurus triostegus sandvicensis — Randall 
217 
the plankton net. The lack of specimens shorter 
than 4.2 mm. may be the result of a paucity of 
small larvae so far offshore. 
That acanthurid larvae, in general, are more 
abundant close to land has been shown by 
Reintjes and King ( 1953). These authors found 
a total of 1,067 acanthurid larvae in the stomach 
of 184 of 1,097 yellowfin tuna ( Thunnus ma- 
cropterus) sampled from the region of the Line 
and Phoenix islands. They stated that the acan- 
thurids were common in the stomachs of near- 
shore yellowfin, along with balistids and caran- 
gids. Representatives of the Bramidae, Exocoe- 
tidae, and Gempylidae predominated in the 
stomachs of offshore yellowfin. 
King kindly allowed me to examine the stom- 
ach content work sheets in order to compare the 
occurrence of larval acanthurids in the stomachs 
of tuna caught at the surface by pole-and-line 
fishing and by trolling with those caught at 
depths of about 30 to 160 mi. by long-lining. 
The comparison revealed more acanthurid larvae 
in the stomachs of surface-caught fish. 
The acronurus larval form of the manini, av- 
eraging about 26 mm. in standard length in the 
Hawaiian Islands, leaves the pelagic realm and 
enters very shallow water, often tide pools, to 
transform to the juvenile stage. Although ju- 
veniles tend to remain in shallow water, there 
is a progressive movement with increasing size 
to somewhat deeper water. Adults are not en- 
tirely absent from tide pools, however. Several 
were seen in pools 1-3 ft. deep cut off from the 
open sea at low tide on Moku Manu and Ma- 
nana (Rabbit) islands. Also, at night on Oahu, 
manini as large as 70 mm. were occasionally 
found in high tide pools. 
TOLERANCE TO TEMPERATURE AND SALINITY 
In order to determine if the manini is cap- 
able of surviving the extremes of temperatures 
and salinity which it encounters on Oahu, a sur- 
vey of these factors in tide pools and brackish 
areas known to be penetrated by the species was 
undertaken and compared with the tolerance of 
the species to these factors as determined by 
laboratory experiments on both juveniles and 
adults. 
Environmental Extremes 
The survey of environmental temperature and 
salinity was not made on any regular schedule. 
Only when conditions occurred which suggested 
that high and low values of temperature and 
salinity might be found, were measurements of 
these factors made. Temperatures were taken at 
mid-depth of the tide pools tested. Water sam- 
ples from which chlorinity was determined were 
obtained after stirring the pools. The Mohr 
method was used to determine chlorinity, and 
the results are expressed as grams of chlorine 
per kilogram of sea water (%o). 
The maximum temperature, 35.1° C., was 
recorded in a tide pool with basalt bottom (al- 
most black) at Makapuu Point on August 31, 
1953, at 2:00 P.M. A reverse stratification of 
temperature existed in the pool at that time. 
A +0.2 low tide had occurred at 1:50 P.M. 
The maximum air temperature at Makapuu 
Point for August 31 was 79° F. (26.2° C.). 
Other fishes observed in the tide pool along with 
manini included aholehole ( Kuhlia sandvicen- 
sis ) and kupipi ( A budefduf sordidus ) . 
The minimum temperature, 16.2° C., was 
recorded in a small tide pool at Diamond Head 
on March 5, 1954, at 11:15 P.M. A -0.2 low 
tide had occurred at Honolulu at 10:42 P.M. 
The minimum air temperature during the night 
was 60° F. ( 15.5° C.) . A strong northerly wind 
was blowing. The wind velocity for the hour 
prior to the temperature reading was as high 
as 33 knots. 
The extremes of environmental temperature 
recorded by Tester and Takata (1953: 48) for 
the aholehole on Oahu are 20.1° C. and 32.1° 
C. Like the manini, young aholehole are tide- 
pool residents. Although found in the highest 
pools of the intertidal zone, they are less in- 
clined than the manini to enter small pools. A 
more notable difference of these two species is 
the ability of the aholehole to live in streams 
with little or no salt content. 
The lowest chlorinity recorded from pools 
where manini were observed was 2.65 %c. This 
reading was obtained from a high tide pool at 
Diamond Head during a heavy rain at 9:00 
A.M. on March 1, 1954. A +0.1 low tide oc- 
curred at 9:02 A.M. A rivulet of rain water was 
observed entering the pool. 
