236 
Fig. 7. Collection of Acanthurus triostegus trios- 
tegus from tide pools of the outer reef flat, Onotoa 
Atoll, Gilbert Islands, August 21, 1951. Sample size, 
108. Nine specimens 21—25 mm. in standard length 
are transforming from the acronurus to the juvenile 
stage; the rest are juveniles. Time of full moon, Aug. 
16 . 
males ) examined from September to November, 
11.8 per cent were running ripe males; 23 per 
cent of 2,419 adult manini (an estimated two- 
thirds of which were males) examined from 
February to June were running ripe males. No 
variation in degree of ripeness was apparent 
within the period of a single month. It should 
be emphasized, however, that no sharp dividing 
line exists between the condition of a running 
ripe male and one that is not quite running ripe, 
and these data tend to be subjective in this re- 
gard. 
Ripe females are more easily distinguished. 
Fertilizable eggs of female manini are about 
0.7 mm. in diameter, prefectly transparent, and 
are released when the abdomen is only slightly 
squeezed. The data on ripe females in terms of 
the lunar month are summarized in Table 6. As 
may be seen in this table, the number of fish 
examined on the different days ranged from 9 
to 252. This variability is entirely due to varia- 
tion in the catches. Also there is no regular 
sequence in time when the catches were exam- 
ined. Scheduled sampling was not possible 
largely because of the great dependence of trap 
fishing on hydrographic conditions. In addition 
to being impeded by rough seas, trap fishermen 
are restricted by turbid water (traps are not 
found by surface markers but by observing 
through a glass-bottom box). Although the fish- 
ermen ordinarily tend their traps twice a week, 
they may be held in port several weeks by dirty 
water. A successful sampling day was also con- 
tingent on being at Kewalo Basin when the 
catches were unloaded. Frequently the fishermen 
PACIFIC SCIENCE, Vol. XV, April 1961 
came in unexpectedly early and their fish were 
promptly taken to market. Market fish were not 
sampled because catches of previous days may 
accumulate and the date when fish are caught is 
usually not available. 
A total of 43 running ripe females were 
found. Thirty-nine of these were taken from 12 
days before to 2 days after the full moon and 
only 4 from the remaining half of the lunar 
month. A total of 2,552 adult manini were 
examined in the former period, however, and 
only 1,311 in the latter; therefore a correction 
is necessary for this discrepancy in sample size. 
A corrected figure of 7.8 ripe females instead of 
4 is the proper number to compare with 39. 
Nevertheless, it still remains obvious that a sig- 
nificantly greater number of ripe females, and 
hence probably greater spawning, occurs before 
and shortly after full moon than before and 
shortly after new moon. Since at least a few 
acronuri of all sizes (see section on transforma- 
tion) enter tide pools at all times during the 
month and not totally in one portion thereof, 
some spawning might be expected throughout 
the month. 
One sample of adult manini was examined on 
July 29, 1955. There were 7 running ripe female 
fish among the 57 manini comprising the sam- 
ple. Full moon occurred on August 3. 
It is not known whether spawning by the 
same fish takes place every month. There is evi- 
dence, however, that individual fish spawn more 
than once a season. The long season in itself 
suggests repeated spawning. If large ripe females 
were found at the start and progressively smaller 
ones throughout the rest of the season, a long 
spawning season might be indicated with each 
individual spawning only once, but no obvious 
trend in size of the 43 ripe females was apparent. 
The first ripe female of the season, which was 
found December 1, measured 138 mm. in stand- 
ard length. The last (July 21) was also large, 
140 mm. The shortest found were 106 mm. 
(March 13) and 101 mm. (July 14). More con- 
vincing is the failure to see any completely 
spent ovaries in fish during the spawning sea- 
son and the observation of spent and regressing 
ovaries in all of the females at the end of the 
season. The strongest evidence concerns the find- 
ing in ripe females of a second mode of egg size 
