Zeldis et al. : An estimate of biomass of Hoplostethus atlanticus 
597 
passed through the mesh. Atretic eggs, in particular, had 
dimensions of 0.5 to 1.0 mm (from histological observa- 
tions) and were found to wash through the sieve. The mean 
size of stage-3 oocytes was 1.56 mm (range 1.30-1.83 mm, 
SE=0.01). More advanced stages had larger oocytes (stage 
4=2.15 mm; stage 5= 2.55 mm; stage 8=2.20 mm) and 
therefore were fully retained. 
Eggs were then counted with an electronic egg counter 
incorporating a phototransistor (Bycroft, 1986). Eggs were 
siphoned from a large beaker into a perspex chamber with 
a vacuum pump attached to the top of the chamber. Water 
flow was regulated to keep this chamber about three-quar- 
ters full, so that any air bubbles rose to the top. Eggs 
passed from the bottom of the chamber through a small 
tube past a phototransistor and light source. The reduc- 
tion in light intensity (caused by the presence of the eggs) 
was detected by the phototransistor and was recorded on 
an electronic counter with digital readout. The rate of flow 
was regulated to avoid large numbers of eggs in the cham- 
ber and exit tube at any one time (which could result in 
multiple eggs passing the counter at the same time and 
being recorded as only as one egg). Again control (set very 
low) was used to alter the sensitivity of the counter so 
that small fragments of extraneous material that remained 
after the sieving were not counted. 
Checks of the accuracy of the electronic counter were 
made by comparing manual counts (made with a dissect- 
ing microscope) with electronic counts and no significant 
difference was found (f-test, P<0.01, number of compari- 
sons=4). Also, a reference set of a known number of eggs 
was regularly used to check the calibration. Up to four 
determinations were made in each trial, which produced 
CV’s of the mean count of generally less than 0.01. 
Total fecundity from both ovaries was initially calcu- 
lated from the number of oocytes/g x ovarian weight. Al- 
though this is common practice in fecundity studies, it may 
introduce bias because ovary weight includes ovary wall 
which does not contain eggs. Several comparisons were 
made between estimated fecundity based on the scaled- 
up subsample count, and actual counts of all oocytes in an 
ovary. Scaled-up subsample counts typically overestimated 
actual fecundity by 10-20%. The proportion of wall weight 
to total ovary weight (for stages 3, 4, 5, and 8) were esti- 
mated by stripping a number of weighed ovaries of all eggs 
and weighing the remaining wall (Appendix 4, Table 1). 
The proportions were then used to adjust the total fecun- 
dities of each fish in each stage. The higher proportions 
for stages 5 and 8 are to be expected because some stage- 
5 fish may be in the act of spawning and stage-8 fish have 
already spawned some of their eggs; therefore the ovary 
wall is a greater proportion of total ovary weight. 
Table 1 
The contribution (percentage) of the ovary wall to ovary 
weight at each ovarian stage. See text for stage definitions. 
Stage 
Mean 
SE 
n 
3 
9.6 
1.2 
15 
4 
6.6 
0.4 
14 
5 
13.9 
2.7 
14 
8 
29.7 
4.4 
19 
