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PACIFIC SCIENCE, Vol. XV, April 1961 
tures in the Hawaiian Islands vary from about 
75° to 81° F. Enlargement of the gonads ap- 
pears to coincide with decreasing water tem- 
perature in the fall. 
18. An estimate of about 2 Vi months for the 
duration of larval life of the manini in Hawaii 
was made by noting the time between the find- 
ing of the first ripe females and first transform- 
ing young of the season and the last ripe fish 
and last incoming acronuri. 
19. Ripe female manini ( Acanthurus trioste- 
gus triostegus) were found in collections made 
at islands of the tropical Pacific (where mean 
sea surface temperatures exceed 80° F. through- 
out the year) in all months of the year, as were 
transforming or early juvenile specimens, thus 
indicating year-round spawning in more equa- 
torial waters. 
20. A lunar periodicity in the number of 
transforming manini was discovered from tide- 
pool collections on Oahu, with the peak in 
spring occurring a few days before new moon. 
Since a collection of young from the Gilbert 
Islands, where water temperatures average about 
7° F. higher (and hence development is prob- 
ably more rapid) , indicates peak influx of acron- 
uri approximately at the time of full moon, the 
periodicity is not attributed to any lunar effect 
on the young but to greater spawning by adults 
at one time of the month than another. Thirty- 
nine ripe female fish were found among 2,552 
adult manini examined from 12 days before to 
2 days after full moon during the spawning 
season and 4 among 1,311 fish seen in the re- 
maining half of the lunar month. 
21. Individual manini appear to spawn more 
than once during the season. Large and small 
ripe females were found near the start and end 
of the season. No completely spent ovaries were 
observed until July and August. In graphs of 
egg diameters of mature ovaries, a mode of egg 
size about intermediate to the diameter of trans- 
parent ripe eggs and primordial ova was in- 
variably present during the season. 
No specimens were found with modes of egg 
size lying between the intermediate-size mode 
and that of fertilizable eggs, thus suggesting that 
ripe eggs develop rapidly from the opaque ova 
of the intermediate group. 
22. Although the spawning of manini was 
never witnessed in the Hawaiian Islands, A. 
triostegus triostegus was observed to spawn in 
the Tuamotu Archipelago. Several hundred fish 
were seen in a milling aggregation at dusk dur- 
ing the time of full moon. Many had broader 
bars on the body and darker fins than normal; 5 
of these were speared and proved to be ripe 
males. Two normally colored manini were fe- 
males, 1 running ripe. Spawning occurred at the 
apex of sudden rapid upward movements by 
small groups of fish. A current carried the eggs 
to the open sea. 
23. The smallest running ripe female manini 
which was found on Oahu was 101 mm. in 
standard length; the smallest male, 97 mm. Ma- 
nini probably do not spawn in their first year. 
24. The number of ripe eggs in the ovary of 
one 123 mm. manini was estimated at 40,000. 
25. Early development was studied following 
artificial fertilization of the eggs. The eggs aver- 
age 0.67 mm. in diameter, have a single oil 
globule, and float at the surface. Hatching occurs 
in 26 hr. at 24° C. As yolk is used up, the larvae 
show a progressive tendency to sink. They com- 
bat this by upward swimming movements. Feed- 
ing begins at the age of 51/2 days. No young 
were maintained in aquaria more than 6 V 2 days; 
however, 3 postlarval manini, 6.6 to 7 mm. in 
total length, could be identified from plankton 
collections by fin-ray counts. The most striking 
feature of their morphology is very elongate sec- 
ond dorsal, second anal, and pelvic spines. 
2 6. Manini acronuri come into shoal water to 
transform only at night. They are discoid, scale- 
less, and transparent with a silvery abdomen. 
Their second dorsal, second anal, and pelvic 
spines are poisonous. During transformation, 
which requires 4-5 days, adult-type configura- 
tion and coloration is attained, scales form, and 
the venomous quality of the spines disappears. 
27. Light appears to be essential to transfor- 
mation. Two acronuri taken at midnight were 
placed in a darkened 2 l /z gal. battery jar. They 
failed to transform, whereas 3 others in a com- 
parable but not darkened container completed 
their metamorphosis to juvenile form. 
28. A variation in standard length from 22 
to 29.5 mm. was noted in 175 manini acronuri 
from Oahu in their first day of transformation. 
One hundred and sixteen were collected in tide 
