Zhukova et al.: Gonadal maturation of Aptocyclus ventricosus 
157 
nP 
(Ss 
OJ 
o 
c= 
<D 
§25 
O 
8 20 
O 15 
o 10 
c 
8 5 
gf CU¬ 
LL. 0 
Oocyte diameter (pm) Oocyte diameter (pm) 
Figure 3 
Photographs of the ovaries of smooth lumpsucker (Aptocyclus ventricosus) in the (A) developing 
phase and (B) actively spawning subphase and the oocyte size frequency in ovaries of the (C) 
developing phase and (D) actively spawning subphase. The following features are indicated: pri¬ 
mary growth (PG); cortical alveoli (CA); vitellogenic (Vtg); and mature (M) oocytes. The length 
of the scale bars in the photographs represents 1 mm. 
60. 
1000 
1200 
1000 
down oocytes” (Brown-Peterson et al. [2011]) with yolk 
homogenization was present in the ovary. The diam¬ 
eter of advanced oocytes increased by about 2.5 times 
(1401-1658 pm), and the thickness of their zona ra- 
diata ranged from 39 to 61 pm. Primary growth oocytes 
and oogonia, which served as the reserve fund of germ 
cells, occurred among mature oocytes (Fig. 2E). 
Regressing and regenerating gonads were detected 
in 3 females, which were caught at depths of 86-138 
m at distances of 26-58 nmi from the coast. The TL 
of these spent fish ranged between 261 and 300 mm, 
body weight varied between 523 and 615 g, gonadal 
weight varied between 32 and 64 g, and mean GSI 
was 7.4% (SD 4.7). Ovaries at the regressing phase 
were identified in 2 of these females by the presence 
of postovulatory follicles; primary growth oocytes were 
located among them. In gonads of 1 of the 3 females, 
we found late-stage atretic eggs, postovulatory follicles, 
and early primary vitellogenic oocytes that indicate a 
regenerating phase (Fig. 2F). No sperm were found in 
any of the ovaries. 
The results from examination of oocyte diameters 
indicated group-synchronous oocyte development. In 
developing ovaries (Fig. 3, A and C), 3 groups of oo¬ 
cytes were clearly distinguishable on the basis of size. 
The first group was characterized by primary growth 
oocytes of 250-pm diameter, the second by cortical al¬ 
veolus oocytes of 600-pm diameter, and the third by 
vitellogenic oocytes of 850-pm diameter. In actively 
spawning subphase gonads (Fig. 3, B and D), the ma¬ 
jority of germ cells were in the germinal vesicle break¬ 
down stage and ranged in diameter from 1800 to 2000 
pm. There were also a reserve fund of oocytes, includ¬ 
ing primary growth and cortical alveolus oocytes of the 
same size as developing gonads. 
Gonad maturation begins in individuals longer than 
129 mm TL. Spawning and spent fish range from 218 
to 300 mm TL. Therefore, mature individuals have 
dominated trawl catches during research surveys and 
commercial fishing operations in the Pacific waters off 
the northern Kuril Islands and southeastern Kamchat¬ 
ka (Orlov and Tokranov, 2008). 
Our histological study on the smooth lumpsucker 
has shown a discontinuous type of oogenesis or deter¬ 
minate type of fecundity, which is characterized by 2 
oocyte generations (vitellogenic oocytes and reserve 
fund of sex cells) in ovaries at the developing and 
spawning-capable phases. The reserve fund of sex cells 
