120
A.P.A. Wohrmann
Lipid Content and Seasonal Variations
The more pelagic notothenioid species live, the more they tend to reduce
heavy components such as bones and scales and the stronger the tendency
to accumulate lipids [9]. These modifications are important adaptations
towards neutral buoyancy, since all notothenioids lack swim-bladder.
However, lipids in high-Antarctic notothenioids are important for two
further features, for the development of gonads and as energy reserves for
the long winter period. Figure 1 shows the total lipid content in different
tissues and the gonado somatic index (GSI) of female Trematomus
eulepidotus in spring and summer. The GSI increased from 1.8 in spring
to 8.2 in summer. In this time the lipid content in percent of dry weight
decreased dramatically in the liver and in the gonad from 52.3% to 19.8%
and from 60.7% to 17.8%, respectively. By contrast, the lipid content in
the dorsal muscle was not significantly changed. However, according to
Eastman [9] the liver is not an important site for lipid storage in
notothenioid fishes, in contrast e.g. to the lean cod fishes which store most
of their lipid in the liver. Livers of male T. eulepidotus had higher lipid
contents as compared to livers of females, a phenomenon also reported for
the benthopelagic Notothenia rossii marmorata, presumably due to higher
protein contents required in females for the formation of ovaries. The
variability of lipid contents in the liver and the gonad may be explained by
the fact that these energy stores are utilized more rapidly than other fat
reserves when energy is required [10].
Sidell and coworkers emphasize the importance of lipids, particularly
monounsaturated fatty acids, as fuel for aerobic energy metabolism. They
determined higher lipid levels in serum and oxidative muscle of the
"mesopelagic" Trematomus newnesi as compared to the demersal
Gobionotothen gibberifrons, which corresponded with the higher
locomotory activity of the dusky notothen [11]. They also found high lipid
contents of oxidative muscles being correlated with high capacities for
fatty acid catabolism, in contrast to low glycolytic enzyme activities.
Furthermore, a high lipid content in oxidative tissues may accelerate
oxygen transfer from capillaries to mitochondria [12].
The tendency of lipid accumulation with an increasingly pelagic life
style is readily explained by energetic advantages due to improved
buoyancy characteristics. DeVries and Eastman [13] claimed that in
Pleuragramma antarcticum the lipid sacs are extracellular formations.
Hence, although the sacs are largely filled with triacylglycerols, they
should have no metabolic function as energy reserves and serve
exclusively as flotation devices. However, the cellular structures of the
A.P.A. Wohrmann
Lipid Content and Seasonal Variations
The more pelagic notothenioid species live, the more they tend to reduce
heavy components such as bones and scales and the stronger the tendency
to accumulate lipids [9]. These modifications are important adaptations
towards neutral buoyancy, since all notothenioids lack swim-bladder.
However, lipids in high-Antarctic notothenioids are important for two
further features, for the development of gonads and as energy reserves for
the long winter period. Figure 1 shows the total lipid content in different
tissues and the gonado somatic index (GSI) of female Trematomus
eulepidotus in spring and summer. The GSI increased from 1.8 in spring
to 8.2 in summer. In this time the lipid content in percent of dry weight
decreased dramatically in the liver and in the gonad from 52.3% to 19.8%
and from 60.7% to 17.8%, respectively. By contrast, the lipid content in
the dorsal muscle was not significantly changed. However, according to
Eastman [9] the liver is not an important site for lipid storage in
notothenioid fishes, in contrast e.g. to the lean cod fishes which store most
of their lipid in the liver. Livers of male T. eulepidotus had higher lipid
contents as compared to livers of females, a phenomenon also reported for
the benthopelagic Notothenia rossii marmorata, presumably due to higher
protein contents required in females for the formation of ovaries. The
variability of lipid contents in the liver and the gonad may be explained by
the fact that these energy stores are utilized more rapidly than other fat
reserves when energy is required [10].
Sidell and coworkers emphasize the importance of lipids, particularly
monounsaturated fatty acids, as fuel for aerobic energy metabolism. They
determined higher lipid levels in serum and oxidative muscle of the
"mesopelagic" Trematomus newnesi as compared to the demersal
Gobionotothen gibberifrons, which corresponded with the higher
locomotory activity of the dusky notothen [11]. They also found high lipid
contents of oxidative muscles being correlated with high capacities for
fatty acid catabolism, in contrast to low glycolytic enzyme activities.
Furthermore, a high lipid content in oxidative tissues may accelerate
oxygen transfer from capillaries to mitochondria [12].
The tendency of lipid accumulation with an increasingly pelagic life
style is readily explained by energetic advantages due to improved
buoyancy characteristics. DeVries and Eastman [13] claimed that in
Pleuragramma antarcticum the lipid sacs are extracellular formations.
Hence, although the sacs are largely filled with triacylglycerols, they
should have no metabolic function as energy reserves and serve
exclusively as flotation devices. However, the cellular structures of the