Nichol and Acuna: Annua! and batch fecundity of Limanda aspera in the eastern Bering Sea 
109 
Figure 1 
Location of yellowfin sole (Limanda aspera ) ovary collections within the 
eastern Bering Sea trawl survey area, 1993. Stations where yellowfin sole 
ovaries were collected are circled. The diagonal line separates the northwest 
from the southeast sampling areas. 
Identifying partially spawned ovaries can 
be difficult with unaided macroscopic obser- 
vation. With microscopic observation, how- 
ever, identification of postovulatory follicles 
(POFs) within an ovary verifies that at least 
one batch has been spawned (Hunter and 
Macewitz, 1985a; Hunter et al., 1992). Histo- 
logical analysis of collected ovaries was em- 
ployed in our study in part to identify POFs. 
Second, annual fecundity may be overesti- 
mated if the eventual loss of oocytes due to 
atresia (oocyte resorption) is not taken into 
account. Oocyte atresia can occur in vary- 
ing degrees throughout the spawning sea- 
son, depending on the species and environ- 
mental conditions (Hunter and Macewicz, 
1985b; Macewicz and Hunter, 1994; Walker 
et al., 1994; McFarlane and Saunders, 1997). 
This bias can be minimized if ovaries chosen 
for fecundity estimates are well developed 
and near spawning condition. 
Understanding the spawning character- 
istics along with other life-history param- 
eters may help determine how fish abun- 
dance varies with changing environmental 
or fishing conditions. Moreover, knowledge 
of the fecundity and the spawning charac- 
teristics can help define how species, such 
as yellowfin sole, relate to other species 
from a phylogenetic perspective. In our study, we evaluate 
the annual and batch fecundities of yellowfin sole with ref- 
erence to its spawning habits. 
Materials and methods 
Summary of collections 
A total of 767 ovary pairs were collected in June and July 
of 1993 during a groundfish trawl survey in the eastern 
Bering Sea, conducted by the Alaska Fisheries Science 
Center (Nichol, 1995). Collections were made at 83 sta- 
tions at depths shallower than 50 in (Fig. 1). Whole ova- 
ries were extracted from approximately 10 females per 
station and then preserved in 10% formalin (3.7% form- 
aldehyde) buffered with 19 g/liter sodium acetate-trihy- 
drate. Females were selectively chosen by size: 2 females 
25-30 cm total length (TL), 4 females 31-35 cm TL, and 
4 females >35 cm TL. All females less than 25 cm TL 
were immature and therefore were not collected. Each pre- 
served ovary lobe was weighed to the nearest milligram. 
Ovaries were assigned a maturity code based on a 5-point 
maturity classification scale for macroscopic examination 
(Table 1). These assignments were verified with histologi- 
cal evaluation. 
Histological evaluation of ovaries 
Histological cross sections were prepared from the middle 
portion of one ovary from each fish. Most sections (93%) 
were taken from the blind side; however, sections were 
occasionally taken from the eyed-side if fixation was not 
complete. Ovary tissues were embedded in paraffin, sec- 
tioned at 6 pm, then stained with hematoxylin and eosin. 
Each ovary section was examined for the following oo- 
cyte stages: early perinuclear, late-perinuclear, partially 
yolked (PY), advanced-yolk (AY), migratory-nucleus (MN), 
unovulated hydrated (HY), and ova (ovulated, hydrated) 
(Howell, 1983). We also noted the presence of postovula- 
tory follicles (POF), atretic oocytes, and residual chorion 
tissue. 
The maximum diameter of AY through MN oocytes were 
measured with an ocular micrometer. Oocyte diameters 
were measured from five of the largest spherical nonatretic 
oocytes with a centrally located nucleus. The average maxi- 
mum oocyte diameters were then computed for each fish. 
Examination of oocyte atresia 
Occurrence of alpha (a) stage atresia (Hunter and Mace- 
wicz, 1985b) among advanced vitellogenic oocytes (AY, MN, 
and HY) and PY oocytes was recorded for 75 females by 
using histological ovary cross sections. Samples included 
28 maturing (maturity-code 2) females with AY-stage 
oocytes and no evidence of POFs, 13 fish with AY and HY 
oocytes and no POFs, 23 fish that had spawned at least 
one batch (POFs present), and 11 fish with evidence of 
residual chorion tissue in the ovary lumen and no other 
evidence of batch spawning (no HY, ova, POFs). A 2 x 
2 mm grid was used to count atretic and nonatretic PY 
oocytes, and AY through HY oocytes. One ovary section 
