Maternal Output in Polar Fish Reproduction
49
Discussion
Information regarding the modes of oviposition in polar fish is sparse, but
most members of the Antarctic Nototheniidae are considered to be
substrate spawners. For this family, the development of fully mature ova
seems to require two or more successive seasons, and eggs are probably
deposited in one batch annually thereafter [11,17].
Morphological characteristics of egg-shells are species-specific and
developing pelagic eggs have been identified from a few species i.e.
Notothenia rossii and Notothenia coriiceps [18]. Other species such as
Champsocephalus gunnari and Dissostichus eleginoides may also produce
pelagic eggs [18] and they have, therefore, been considered as being
pelagic spawners in this study (Table 1). On the other hand, Pleuragramma
antarcticum (G. Hubold, pers. comm.) and Dissostichus mawsoni have
been classified as demersal spawners although the latter have many
features in common with the pelagic spawning species, i.e. a high fecundity
and maternal output (Table 1).
Knowledge about the mode of oviposition among Arctic species is also
sparse. Most species are, however, believed to be substrate spawners [3].
Information is available for only two pelagic spawning species,
Boreogadus saida and Liopsetta glacialis [3,14]. The eggs of Boreogadus
saida are found in the uppermost part of the water column (own unpubl.
data) and often develop in close association with the Arctic sea-ice .[19].
One could, therefore, argue that Boreogadus saida is, in reality, a substrate
spawner, with sea-ice providing the substrate. Similar spawning traits may
apply for the Arctic gadoid species viz Arctogadus glacialis and perhaps
also Arctogadus borizovi [13].
Egg size and fecundity, and hence maternal output, may show a high
degree of intraspecific variation, which is modulated by ecological and
environmental conditions [20]. Further, estimations of egg size and
fecundity may be biased if samples are taken from ovaries in which the
oocytes are not fully developed (K.-H. Kock, pers. comm.). Although the
above mentioned uncertainties and limitations should be borne in mind, we
WOUld, nevertheless, suggest the following general reproductive traits for
polar and boreal marine fish species:
• Polar fish produce relatively few, large eggs when compared with their
boreal counterparts, but this trait appears to apply only among pelagic
spawning species.
• Substrate spawning species produce relatively few, large eggs
irrespective of zoogeographic regions.
49
Discussion
Information regarding the modes of oviposition in polar fish is sparse, but
most members of the Antarctic Nototheniidae are considered to be
substrate spawners. For this family, the development of fully mature ova
seems to require two or more successive seasons, and eggs are probably
deposited in one batch annually thereafter [11,17].
Morphological characteristics of egg-shells are species-specific and
developing pelagic eggs have been identified from a few species i.e.
Notothenia rossii and Notothenia coriiceps [18]. Other species such as
Champsocephalus gunnari and Dissostichus eleginoides may also produce
pelagic eggs [18] and they have, therefore, been considered as being
pelagic spawners in this study (Table 1). On the other hand, Pleuragramma
antarcticum (G. Hubold, pers. comm.) and Dissostichus mawsoni have
been classified as demersal spawners although the latter have many
features in common with the pelagic spawning species, i.e. a high fecundity
and maternal output (Table 1).
Knowledge about the mode of oviposition among Arctic species is also
sparse. Most species are, however, believed to be substrate spawners [3].
Information is available for only two pelagic spawning species,
Boreogadus saida and Liopsetta glacialis [3,14]. The eggs of Boreogadus
saida are found in the uppermost part of the water column (own unpubl.
data) and often develop in close association with the Arctic sea-ice .[19].
One could, therefore, argue that Boreogadus saida is, in reality, a substrate
spawner, with sea-ice providing the substrate. Similar spawning traits may
apply for the Arctic gadoid species viz Arctogadus glacialis and perhaps
also Arctogadus borizovi [13].
Egg size and fecundity, and hence maternal output, may show a high
degree of intraspecific variation, which is modulated by ecological and
environmental conditions [20]. Further, estimations of egg size and
fecundity may be biased if samples are taken from ovaries in which the
oocytes are not fully developed (K.-H. Kock, pers. comm.). Although the
above mentioned uncertainties and limitations should be borne in mind, we
WOUld, nevertheless, suggest the following general reproductive traits for
polar and boreal marine fish species:
• Polar fish produce relatively few, large eggs when compared with their
boreal counterparts, but this trait appears to apply only among pelagic
spawning species.
• Substrate spawning species produce relatively few, large eggs
irrespective of zoogeographic regions.