46
I.S. Christiansen et al.
Results
More than one data set was available for some species (Table I). For
clarity we have not identified the species in Figs. I to 4.
Egg Size
Egg size seems to be a characteristic of both zoogeography and mode of
oviposition (Fig. 1; Table 2). Within the group of pelagic spawning
species, polar species produce significantly larger eggs than boreal species.
By contrast, the size of demersal eggs does not differ between
zoogeographic regions (Table 2). Further, egg size generally increases with
body length irrespective of zoogeography and mode of oviposition. The
boreal pelagic spawners form an exception. For this group of species, egg
size is consistently small at all body lengths (Fig. 1). Thus, 1) egg size
usually increases with increasing body length and 2) egg sizes of pelagic
spawning species are largest towards the poles, whereas 3) substrate
spawners produce similar sized eggs irrespective of zoogeography.
8
Pelagic
7
e 6
§
5
0
...
o a
0
~
0
....
~
4
0
8
0
cu
3
:a
•
biI
2
•
biI
cfo
• •
r.1
~ .. .. Ie Boreal I
o Polar
0
0
500
1000
1500
2000
Body length (mm)
8~----------------~
7
o
6
5
oe
o
4 0
o~o 0
3 :t!
Demersal
•
e
o
I
e Boreal
o Polar
O~~~~~~~~
o
500
1000
1500
2000
Body length (mm)
Fig. 1. Scatter plots showing egg diameters and body lengths of boreal and polar fish
species with pelagic and demersal spawning modes.
Fecundity
Fecundity increases with body length irrespective of zoogeography and
mode of oviposition (Fig. 2; Table 2). Further, among pelagic spawners the
polar species are significantly less fecund at a given body length than
boreal species. This contrasts with substrate spawners in which fecundity
does not differ between polar and boreal species (Table 2).