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Fishery Bulletin 107(2) 
parent objects such as PVF, cortical alveoli, hydrated, 
and POFs. After PAS staining, manual measurements 
of follicle diameter (F dm ) compared closely to automatic 
measured follicle diameter (F di ) calculated from the 
image analysis: 
F di = 1.0016 xF dm + 0.0405 (6). 
(n=42, r=0.997, 220 < manual reading < 1900 pm) 
Although the eosin solution stained both vitellogenic and 
hydrated follicles in European plaice, it was much less 
effective when applied to either Atlantic cod or Atlantic 
mackerel follicles. A further disadvantage was that the 
stain was not bound by a chemical reaction and tended to 
leach out more rapidly compared to PAS stained tissue. 
This could be countered by extensive washing but this 
LA LM LP RA RM RP Fish mean 
Sample site in ovary 
Figure 1 
Comparison of mean follicle diameter (A) and leading 
cohort diameter (B) ±2 standard error taken from three 
sites, anterior (LA and RA), middle (LM and RM), and 
posterior (LP and RP), in each pair (left L or right R, 
respectively) of seven ovaries of Atlantic cod ( Gadus 
morhua) caught by commercial vessel using gill nets 
landing at Andenes, Norway in 2007 (Table 1). Lines 
join the sites for each fish. Approximately 200 unstained 
follicles were measured using image analysis by the 
Institute of Marine Research Norway at each site. Fish 
mean refers to the overall mean follicle diameter of all 
sites for each fish. 
progressively affected the follicle size determined by 
image analysis. The rose bengal stain was also based on 
affinity rather than chemically bound and excess stain 
had to be washed from the sample. It was an effective 
aid to automatic measurement of PVF and POFs from 
Atlantic cod, European hake, and Atlantic mackerel, 
though the coloration was not as intense compared to 
PAS. Also the PAS stain was particularly useful when 
applied to whole mounts from Atlantic cod making it 
easier to identify the outline of small POFs compared 
to PVF that were less intensely stained. 
Comparison of whole-mount method 
with histological method 
A whole mount prepared from a female Atlantic cod 
caught during ovulation (Fig. 2A) revealed small POFs 
from earlier ovulations (Fig. 2B left) and also much 
larger POFs (Fig. 2B right). The latter appeared as large 
round membrane structures, about the size of hydrated 
follicles formed by the thecal and granulosa layers that 
remain in the ovary to form the POF. A burst zone in 
the circular membrane was also visible, probably made 
during the expulsion of the ripe egg. POF shape and 
morphology was equivalent in whole mounts and section 
and characterised by deep red staining in section and 
denser grey scale in stained and unstained whole mount 
respectively (Fig. 2B left and middle). PVFs in unstained 
whole mounts appeared quite translucent with a central 
nucleus that was consistent with their shape and form 
in section and easily distinguished from POFs. 
Atretic follicles were rather easily identified in un- 
stained whole mounts and their morphology could be 
equated to that seen in histological section (Fig. 3). 
Comparing these preparations the chorion appeared 
to be progressively broken down and provided a useful 
criterion to identify late alpha atretic follicles in whole 
mounts. A comparison of alpha atretic intensity between 
the two methods (Fig. 4) indicated that the whole mount 
preparation could provide an indication of both preva- 
lence and intensity of atresia. 
Fecundity maturation and down regulation 
Atlantic cod fecundity data from the North and Irish 
Sea collected in 2003 and 2004 (Table 1) was ana- 
lysed to investigate whether the relative fecundity 
declined during maturation. As the ovary matured 
and D f increased from 350 to 800 pm the prevalence of 
atresia increased (Fig. 5). Relative intensity of atresia 
was absent in ovaries with a D f of 350 pm and tended 
to remain at a fairly low level but with one much higher 
value when the mean follicular diameter was 650 pm. 
Also during this maturation period there was a drop 
in predicted mean relative fecundity for all fish in the 
sample amounting to 49.6% whilst fecundity diameter 
measured manually or automatically (F d ) increased 
from 355 to 794 pm. Analysis of the data from the 
1995 survey indicated that fecundity was overestimated 
between 11% (Atlantic cod) and 13% for European plaice 
