Witthames et al.: Advances in methods for determining fecundity in marine fishes 
157 
45 
0 +• 1 1 1 
0 15 30 45 
Histology (%) 
Figure 4 
Comparison of atretic follicles as a percentage of atretic 
follicles divided by the sum of vitellogenic and atretic 
follicles in whole mount and histology, respectively 
found in 2 year old aquaculture reared Atlantic cod 
(Gadus morhua) at Institute IMR in 2004. The equation 
for the fitted line is W=Hx0.85+4.20 (n = 18, r 2 =0.79, 
P <0.001). 
mercial vessels, 4) easily portable samples that can 
be distributed at lower cost to facilitate exchange of 
samples between laboratories carrying out international 
egg production based stock assessments (Armstrong et 
al., 2001) and, not least, 5) better preservation of his- 
tological detail to identify and determine proportions 
of atretic and postovulatory follicles. Our finding that 
POF in recently ovulated ovaries are spherical and 
not collapsed, compared to previous studies, may be 
attributed to less compression in a biopsy compared to 
ovaries fixed whole. 
A small difficulty in not returning the whole ovary 
back to the laboratory for subsampling means the ovary 
must be weighed at sea, sometimes in rough conditions, 
but this can be achieved using motion-compensated bal- 
ances. Although this equipment is perhaps beyond some 
research budgets it has been successful even on com- 
mercial vessel in rough conditions providing the mass 
for weighing is less than 75% of the upper weighing 
range. Also balances are available with a resolution of 
0.01 g making it feasible to weigh ovaries from probably 
all commercial species with an acceptable accuracy. If 
it is not feasible to use motion-compensated balances, 
it has been reported that ovaries can be returned for 
weighing after the end on of the cruise providing the 
ovary is packed to prevent water loss (Klibansky and 
Juanes, 2008). A further recommendation, in connection 
with using the pipette, is to complete at least duplicate 
samples and the follicles should not be larger than the 
pipette internal bore of 2 mm although exception can be 
made for hydrated follicles just larger than 2 mm. 
In this study it was shown that the ovary is homog- 
enous in regard to F ow and D f both for Atlantic cod and 
03 
c n 
o 
03 
0 ) 
> 
0) 
cc 
60 i 
B 
50 - 
40 - 
30 - 
20 - 
10 - 
0 - o 
o 
o 
8 
o 
1600 
>, 1400 - 
? 1200 • 
3 iooo - 
® 800 ■ 
d) 
■g 600 • 
I 400 ■ 
00 200 - 
0 ■ 
300 400 500 600 700 800 
Mean follicle diameter (pm) 
Figure 5 
Down regulation of fecundity during mat- 
uration in North and Irish Sea Atlantic 
cod ( Gadus morhua) collected in 2003 and 
2004. (A) Prevalence of atretic follicles 
(proportion of fish with atresia) plotted 
against the mean follicle diameter of the 
fecundity (Dp pm). (B) Relative intensity 
of atretic follicles (atretic follicles per g 
female whole weight) plotted against Dp, 
(pm). (C) The decline in relative fecun- 
dity (F 6u ,=fecundity/body weight [g] ) in 
relation to Dp (pm). The fitted line is 
from the equation xlnZT+ b where 
a=-581.9 and b = 4360 (r 2 = 0.30, P for a 
and b <0.0001). Open circles are used in 
A and B because they refer to regressing 
follicles and filled circles are used in C to 
denote normal vitellogenic follicles. 
European hake. Homogenous packing has also been 
reported for hydrated oocytes prior to ovulation in Eu- 
ropean hake (Murua et al., 2006). The posterior region 
of the ovary is the most variable and in some fish this 
part can be packed with significantly different sized 
follicles and should be avoided. However, it should not 
be assumed that F d is universally independent of loca- 
tion because small differences (2%) in F d heterogeneity 
have been reported in flatfish species such as yellowfin 
