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Fishery Bulletin 107(4) 
Table t 
Classification of ovary maturity stage, macroscopic and microscopic descriptions, gonadosomatic index (GSI), and mean diameter 
of the most advanced group of oocytes (MAGO) of ovary maturity stages of the blue marlin Makaira nigricans. n h is the number of 
ovaries sampled for histological examination, and n d is the number of samples for which the mean diameter of MAGO was estimated. 
Ovary 
maturity 
stage 
Macroscopic characteristics 
Microscopic characteristics 
GSI 
(mean ± 
standard error) 
Mean 
diameter 
(± standard error) 
of MAGO 
Immature 
(OM1) 
Ovaries were solid or resilient, 
pinkish, with smooth 
streamline shape. 
Ovaries are packed with unyolked or 
perinucleolar oocytes (Fig. 2A). No 
vitellogenic oocytes. 
0.26 ±0.19 
(n h =66) 
43.92 ±27.08 
(n d =15) 
Maturing 
(OM2) 
Ovaries became yellowish or 
orange with the ova developing. 
Oocytes were visible by eye. 
Early yolked or previtellogenic oocytes 
were present (Fig. 2A). Some advance 
yolked oocytes were also observed. 
0.56 ±0.24 
(n h =24) 
83.91 ±53.85 
(n d =17) 
Mature 
(OM3) 
Ovary became firm and large, 
and the color turned orange 
or reddish. The surface of 
ovary was vascularized and 
translucent. 
The MAGO was advanced yolked 
oocytes (vitellogenic oocytes, Fig. 2B). 
Unyolked, early yolked oocytes were 
also observed. No atresia of yolked 
oocytes were observed. 
0.98 ±0.34 
(n h =31) 
314.19 ±73.83 
(n d =30) 
Spawning- 
spawned 
(OM4) 
Ovaries reached the maximum 
size before spawning, and the 
hydrated oocytes were visible 
by eye. After spawning, the 
ovaries were flaccid. The wall 
of the ovary was thick. 
The MAGO of the spawning fish were 
composed of the migratory nucleus 
and hydrated oocytes (Fig. 2B). 
Unspawned hydrated oocytes and the 
postovulatory follicles (Fig. 2C) were 
observed for spawned fish. Some early 
yolked oocytes were present. 
4.65 ±2.78 
(n h =45) 
759.01 ±173.68 
(n d =45) 
Recovery 
(OM5) 
Ovaries become small and 
smooth. A few yolked oocytes 
and hydrated oocytes were still 
visible. 
The MAGO were composed of 
unyolked oocytes. Some of the yolked 
and the atresia of advanced yolked 
oocytes were present. 
3.13 ±1.12 
(n h =101) 
729.30 ±135.28 
(n d =31) 
Resting 
(OM6) 
Ovaries were flaccid and 
threadlike. Oocytes could not 
be observed by the naked-eye. 
No vitellogenic oocytes were observed, 
and unyolked oocytes appeared 
loosely in the lumen of the ovary. 
A few atretic yolked oocytes (Fig. 2C) 
were observed. 
0.98 ±0.5 
(n h =127) 
304.92 ±123.37 
(n d =52) 
Spermatogenesis and testicular development 
The testes of 442 males could be staged into five testicu- 
lar development stages by microscopic characteristics 
and the composition of germ cells. The five cellular stages 
were based on 1) spermatogonia (Fig. 3A); 2) primary 
spermatocytes (Fig. 3B); 3) secondary spermatocytes 
(Fig. 3B); 4) spermatid (Fig. 3C); and 5) spermatozoa 
(Fig. 3C). Testes were classified as immature (TM1) if 
they contained spermatogonia and primary spermato- 
cytes, and no spermiogenesis was observed. The testes 
were regarded as maturing (TM2) when they contained 
spermatogonia, secondary spermatocytes, spermatid, 
and spermatozoa (<50% of total number). Testes were 
staged as mature (TM3) if the lobular lumens contained 
more than 50% spermatozoa, and the vas deferens was 
full of spermatozoa. Males were classified as having 
spawned (TM4) if the numbers of spermatozoa were 
decreasing in the lobular lumens and a few unspawned 
spermatozoa were observed in the vas deferens. Resting 
testes (TM5) were similar to immature testes, although 
a few unspawned spermatozoa were observed in the vas 
deferens. 
Spawning season 
GSI (gonadosomatic index) was relatively high between 
May and September for females, and between April 
and September for males (Fig. 4; boxplots). The condi- 
tion factor, an index reflecting the interaction between 
biotic and abiotic factors on physiological condition, 
exhibited a pattern that was roughly the inverse of 
that of the GSI of males (Fig. 4; points-lines). There 
was a significant relationship between the MOD (mean 
oocyte diameter) and the GSI: MOD = 291.80+327.90 
Ln(GSI) (r 2 = 0.79, n=191), and we propose that MOD 
