Zhukova et al.: Gonadal maturation of Aptocydus ventricosus 
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Table 1 
Macroscopic maturity scale for ovaries of the smooth lumpsucker (Aptocyclus ventricosus), with corresponding histological 
gonadal phases and oocytes stages (Brown-Peterson et al., 2011). Histological features include primary growth (PG) oocytes; 
cortical alveolus stage (CA) oocytes; primary (Vtgl), secondary (Vtg2), and tertiary vitellogenic (Vtg3) oocytes; atretic (A) 
follicles or eggs; oocyte maturation (OM); germinal vesicle maturation (GVM); germinal vesicle breakdown (GMBD); and 
postovulatory follicles (POFs). GSI=gonadosomatic index. 
Maturity phases 
Main histological 
features of each phase 
Main macroscopic features of each phase 
Immature 
Oogonia, PG 
Ovaries small, translucent, gray, white, milky, or 
pink, occupy less than 1/5 of the body cavity. In 
some cases, ovary envelope is characterized by black 
color. GSI<0.6%. 
Early developing subphase 
PG, CA 
Ovaries yellow, milky, pink, or reddish, occupy about 
1/4 the volume of the body cavity. No eggs are vis¬ 
ible to the eye. GSI 2.7-5.6%. 
Developing 
PG, CA, Vtgl, Vtg2 
Ovaries opaque, orange, milky, pink, or reddish, 
occupy about 1/3-2/3 the volume of the body cavity. 
Small eggs are visible to the eye, with diameter <1 
mm. GSI 3.7-39%. 
Spawning capable 
PG, CA, Vtg3, OM 
Ovaries gray, milky, or pink, occupy about 2/3 the 
volume of the body cavity. Eggs are visible to the eye 
and had diameter >1 mm. GSI 31-45% 
Actively spawning subphase 
PG, GVM, GVBD, hydration, ovulation 
Ovaries occupy all the volume of the body cavity, 
opaque, gray, or pink. Visible eggs (diameter >2 mm) 
are presented. Oocytes are 2 times larger than in 
the spawning-capable gonads. GSI 31-56%. 
Regressing 
POF, PG, some CA or Vtg, residual eggs 
present 
Ovaries red or black, flaccid, with enlarged blood 
vessels. Gonads are reduced in size, occupy less 
than 1/3 of the body cavity. GSI 5.5-10.5% 
Regenerating 
PG, A, some CA, gamma/delta atresia 
and old POFs may be present 
Ovaries occupy about 1/3 the volume of the body 
cavity, gray or reddish, with distinguished blood 
vessels. GSI 6%. 
rino, Russia) at 8x2 zoom. Absolute (F a b s ) and relative 
fecundity (F re] ) were estimated as 
where n 
w 
GW 
BW 
F'abs 
nxGW 
w 
s -^rel 
nxGW 
wxBW ’ 
( 2 ) 
the number of advanced oocytes in subsample; 
the weight of the subsample (in grams); 
the gonad weight (in grams); and 
the fish body weight (in grams). 
Results 
Immature ovaries were observed in the smallest fe¬ 
males, which had a mean TL of 159.0 mm (standard 
deviation [SD] 55.2), a mean BW of 305.4 g (SD 228.0), 
and a mean GW of 6.2 g (SD 5.6). The most advanced 
germ cells in immature ovaries were represented by 
primary growth oocytes. Also observed were early pri¬ 
mary growth (chromatin nucleolar) oocytes, which are 
characterized by a basophilic cytoplasm stained with 
hematoxylin and a large round nucleus with the nucle¬ 
olus arranged at the periphery. Their diameters ranged 
from 46 to 101 pm (Fig. 2A). Advanced primary growth 
(perinucleolar) oocytes had diameters from 93 to 188 
pm. Primary growth oocytes were characterized by the 
presence of oil droplets at the oocyte cytoplasm periph¬ 
ery. The GSI of the immature female was 3% (SD 0.6). 
Gonads in an early development subphase were 
found in larger females, which had a mean TL of 220.5 
mm (SD 39.9), a mean BW of 362.3 g (SD 150.7), a 
mean GW of 19.1 g (SD 9.7), and a mean GSI of 4% 
(SD 0.7). Cortical alveoli oocytes, as the most devel¬ 
oped oocyte present, were diagnostic of this subphase. 
Their diameters at the early stage ranged from 218 to 
359 pm and had a zona radiata width of 2-3 pm (Fig. 
2B). 
Gonads of the developing phase, observed in still 
larger females that had a mean TL of 257.2 mm (SD 
35.1), a mean BW of 828.5 g (SD 193.6), were the most 
variable in terms of the size and weight of the gonads, 
and having a mean GW of 213.5 g (SD 142.5) and a 
