Chilton: Maturity and growth of Sebastes variabilis in the central Gulf of Alaska 
73 
Table 2 
Maturity criteria for staging gonads of female dusky rockfish ( Sebastes variabilis ) based on macroscopic and microscopic obser- 
vations. Adapted from Chilton (2006). 
Maturity stage 
Macroscopic description 
Histological description 
Oocyte stages 
1 Immature 
Thin and thready ovaries, 
pink or light red in color; 
oocytes are not visible 
Oogonial nests and unyolked 
oocytes, oocyte diameter is 
between 80 and 150 ^m 
Oogonia organized into nests 
(ON) with some oocytes at 
early perinucleus (EP) and late 
perinucleus (LP) development 
2 Maturing or 
intermediate 
Ovaries cream to light yellow 
in color with thin ovarian 
wall; oocytes visible 
Initial yolk accumulation in 
oocytes with yolk globules very 
small, oocyte diameter 160 to 
320 f/m 
LP and stage-1 through stage-2 
yolk accumulation in oocytes, 
ON and EP stage oocytes are 
also present 
3 Vitellogenesis 
Individual eggs are visible, 
bright yellow in color; ovarian 
wall thickening and darkly 
pigmented 
Yolk globules and oil vesicles 
present, oocyte diameter 400 to 
600 ju m 
Tertiary yolk stage and initial 
oil vacuoles coalescing in oocytes 
4 Fertilized 
Large translucent eggs with 
pink to yellow tint, ovaries 
enlarged to accommodate 
large hydrated eggs 
Embryo diameter is 600 to as 
large as 950 ,wm 
Stage-8 migratory nucleus 
through early embryonic 
development 
5 Eyed larvae 
Ovary enlarged with eyed 
larvae, ovarian wall thin and 
transparent, easily torn or 
broken open 
Embryos with dark pigmented 
eyes 
Eyed larvae 
6 Postparturition 
Ovary flaccid and dark red 
in color, some eyed larvae are 
visible 
Postovulatory follicles (POF) and 
atretic oocytes, residual larvae 
are present 
Evidence of parturition based 
on POF, atretic oocytes and 
residual embryos 
7 Resting 
Ovary pink to reddish grey 
in color, eggs are small and 
opaque 
Oogonial nests and resorption of 
POF as well as atretic oocytes 
ON through EP stage oocytes, 
POF and atretic oocytes present 
in the weight-length relationship. The residuals of the 
log-transformed weight-length data were approximately 
normally distributed and no transformations were made 
(Gerritsen and McGrath, 2007). Student’s t-test was 
used to test for a significant difference in the weight- 
length relationship from the maturity-estimate samples 
compared to female dusky rockfish from the NMFS 
GOAS samples (Snedecor and Cochran, 1989). 
Results 
A total of 193 ovaries with corresponding otoliths and 
fish lengths were collected to estimate A 0 5 and L 0 5 
of female dusky rockfish. Three otoliths were unread- 
able, resulting in 190 samples used for the age at 50% 
maturity estimate analysis of which 166 samples were 
collected along the east and south side of Kodiak Island 
and 24 were collected during May and June 2001 from 
the NMFS GOAS along the Alaska Peninsula. The ages 
of female dusky rockfish ranged from 3 to 50 years 
and lengths ranged from 190 mm to 500 mm FL. The 
age at 50% maturity was estimated at 9.2 years (95% 
CI=8.2-10.2; Fig. 2A) and the length at 50% maturity 
was estimated at 365 mm FL (95% CI=354-378; Fig. 
2B and Table 3). 
Histological methods used to evaluate ovary devel- 
opment in this study resulted in observations of vitel- 
logenic oocytes present in all seven months sampled; 
January through June, and November. Stage-4 fertil- 
ized ova, and stage-5 eyed embryos were observed only 
in April, and stage-6 postparturition was not observed 
until May, although a small number of ovaries were at 
stage 7 in April (Fig. 3). These results indicate that 
the peak of dusky rockfish fertilization in the central 
GOA occurred in April followed by parturition in May 
when postovulatory follicles (POFs) were present. The 
ovaries exhibiting POFs and extrusion of larvae, stage 
7, in April were from females ranging in size from 
300 to 360 mm (7 to 9 years of age) and could be an 
example of delayed oocyte development due to their 
smaller size. 
