Witthames et al.: Advances in methods for determining fecundity in marine fishes 
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A 
15 i 
400 600 800 1000 1200 1400 1600 
Follicle diameter (pm) 
B 
Figure 2 
Morphology of ovary samples of Atlantic cod ( Gadus morhua) taken from a 
research vessel trawl catch in the Irish Sea during 2003 shown as whole mounts 
and histological preparations. (A) The size frequency distribution measured 
in a whole mount of residual fecundity (black bars) and postovulatory follicles 
(POFs striped bars). The POFs from the most recent and previous ovulations 
appear to the right and left respectively of the residual fecundity. (B) (right 
image) shows the appearance of periodic acid-Schiff stained POF in whole 
mount from the most recent ovulation with an arrow pointing to the burst 
zone in the follicle membrane. B (left image) POFs from previous ovulations 
shown in histological section stained with PAS Mallory (left) and as a whole 
mount (right). The white and black arrows point to POFs and previtellogenic 
follicles respectively and box arrows show vitellogenic (V) and early hydration 
stage (H) follicles. The two scale bars on the left indicate 500 whilst the bar 
on the right shows 1000 pm. 
and common sole (Fig. 6, Table 4). From the perspective 
of fecundity methodology, the measurement of F d as 
well as the standing stock of fecundity make it possible 
to adjust the fecundity to the same point in matura- 
tion, defined by mean follicle size, close to the start of 
spawning. 
Autodiametric calibration 
The seven species examined, even when in an advanced 
stage of maturity, contained very different forms of 
fecundity size frequency distribution (Fig. 7) ranging 
from normal (Atlantic herring, European plaice, and 
redfish) to a more skewed shape (European hake and 
Atlantic mackerel). In two species (Atlantic cod and 
European plaice) samples with a hydrated, bimodal 
distribution were also included in the data set. 
The equations (Table 5) from the regression analy- 
sis, based on the autodiametric calibration applied 
individually to Atlantic cod, Atlantic mackerel, Atlan- 
tic herring, European plaice, and redfish (Fig. 8) for 
each institute, made it possible to predict F ow (Eqs. 
4 and 5) with high precision in most cases (Table 6). 
European hake and Atlantic mackerel are examples 
where the vitellogenic follicle distribution is continu- 
ous extending down to overlap with the PVF popula- 
tion (Fig. 7) and produced a higher CV to predict F ow 
from using Equation 2. In the case of European 
plaice, Atlantic cod, and European hake, some ova- 
ries contained both maturing and hydrated follicles 
