240 
PACIFIC SCIENCE, Vol. XV, April 1%1 
Two other surgeonfishes, Ctenochaetus stri- 
atus (Quoy and Gaimard) and Zebrasoma sco- 
pas (Cuvier), were observed to spawn in the 
Society Islands. Like the manini, they exhibited 
the sudden upward rush prior to spawning. Pos- 
sibly the release of eggs and sperm is facilitated 
by the expansion of the airbladder from the de- 
creasing pressure caused by the upward swim- 
ming movement. Like the manini in the pass 
at Tikahau, both of these surgeonfishes were 
spawning in a region of strong current to the 
open sea. 
Size and Age at Maturity 
The smallest running ripe female seen by me 
was 101 mm. in standard length. The smallest 
running ripe male was 97 mm. in standard 
length. These are probably near the minimum 
lengths for mature manini around Oahu. 
Ten manini were reared in a large concrete 
tank of the Hawaii Marine Laboratory at Coco- 
nut Island from a size of 25 to 27 mm. in stand- 
ard length beginning on March 17, 1953 (see 
detailed discussion in section on growth). Two 
fish of this group, an 89.5 mm. male and a 99 
mm. female were killed for gonad study on July 
24, 1953. The female had an immature gonad, 
clear gray in color, and only 5 mm. in length. 
The ova were minute, only 0.015 to 0.03 mm. 
in diameter. The male was detected because it 
was possible to strip a small amount of milt 
from it, although considerable pressure on the 
abdomen was necessary. The sperm, however, 
were not motile. Its testis was slender and 6 
mm. long. Subsequent examination of the gon- 
ads of the remaining 8 captive manini was not 
made because of arrested growth of these fish 
following inadvertent destruction of the algal 
food supply when seining the tank. 
There appears to be considerable variability 
in the size at maturity. This variability is ap- 
parent when the 101 mm. ripe female manini 
is contrasted with the 127 mm. immature speci- 
men whose egg diameters are graphically illus- 
trated in Figure 8, C. 
It is doubtful that any female manini spawn 
during the season in which they first arrived 
as acronuri in tide pools. Even if the W mm. 
female, which was killed on July 24 following 
its growth in captivity from a small juvenile on 
March 17, had been among the first few arrivals 
to shallow water of the season (middle Febru- 
ary), another month of growth and gonad de- 
velopment would hardly seem sufficient to bring 
a tiny immature ovary such as that seen in this 
specimen on July 24 to full maturity before the 
season ended. It also seems unlikely that males 
will spawn within their first season following 
recruitment to tide pools. 
It seems probable, from a knowledge of 
growth (see growth section) and the approxi- 
mate size at maturity, that some manini will 
spawn in the season following their first sojourn 
as juveniles in inshore waters. This would be 
very likely for the first young of the season; 
the last young of the season would net seem to 
have sufficient time to develop to sexual matu- 
rity before the following spawning season ended. 
Such a situation would probably increase the 
variation in the size of the fish at maturity. 
Fecundity 
Fecundity is defined as the total number of 
ripe eggs produced by a female in 1 year. It is 
impossible to ascertain this for fish like the 
manini which may spawn more than once a 
year, when the number of spawnings per year 
is unknown. Therefore only the number of eggs 
released at one spawning can be determined. 
This was attempted for only a single manini. 
The fish chosen for the egg count was the 
123 mm. June 21 specimen, the egg diameters 
of which are plotted in Figure 8, 7. This fish had 
a very large ovary (42 mm. in length) which 
contained a high percentage of large eggs. These 
eggs were not completely transparent, and none 
appeared to have been expelled by the fish. The 
ovary was vigorously shaken in the vial in which 
it had been preserved with a minimum of fluid. 
The agitation released nearly all of the near-ripe 
eggs from ovarian tissue and placed them in 
uniform suspension. The contents of the vial 
were then placed in a graduated cylinder, al- 
lowed to settle, and the small amount of excess 
fluid poured off. A sample of the ovarian mass 
was drawn off. After its removal, the volume 
was computed as 26 per cent of the total. All of 
the large eggs in this sample were counted in 
successive lots placed in a Petri dish under a 
binocular dissecting microscope. The sample 
