206
THE BIOLOGY O F EUPHAUSIIDS
minimal value in November/December. The spring increase of the
phytoplankton populations takes place a t this time in the Antarctic
and the store of lipids within the euphausiid once again increases. An
examination of Fig. 76 which contains part of the data presented in
Fig. 71, shows the seasonal fluctuations in lipid stores in relation to the
fluctuations in the concentrations of vitamin A and astaxanthin in
Meganyctiphanes norvegica and Thysanoessa raschii. There is an
inverse relationship and high lipid content is not associated with
increased vitamin A or astaxanthin contents. We have no information
on the comparative seasonal fluctuations of these components in other
species of euphausiids.
Seasonal fluctuations in the lipid content of Meganyctiphanes
norvegica and Thysanoessa raschii can be related to the breeding and
growth of these organisms. During the late summer and the autumn
the levels of lipids stored increase and reach maximal values. These
species frequently have a life-span of two or three years. Fisher (1962a)
has pointed out that adolescents entering the adult population in the
summer have a high lipid content and this tends to raise the " average
values ) ) of the lipid content in the population as a whole. The reproductive systems of the adults which have bred in the spring are in a
rudimentary condition throughout the summer and consequently, they
redevelop at the same time as those of the adolescents. Development
starts in November/December and the males mature before the
females. Mating of these species takes place in JanuarylFebruary and
the ovaries continue to grow and are mature in March/April. The
mature ovary represents about 10% of the body weight and it is noticeable that the lipid content of the body decreases as the gonads mature.
The eggs have a high lipid content ; this has not been estimated quantitatively but sections of the eggs demonstrate the presence of many oil
globules in the cytoplasm. The eggs are laid in April/May and there is
plenty of food present in the water a t this time. The rate of growth in
body length of the euphausiids accelerates a t this time (see Chapter 10)
and the lipid content shows a small increase followed by a decrease.
This partial increase in the lipid content may originate from an increased
intake of lipids in the food of the euphausiids. Many of the eggs and
larvae of planktonic and other organisms have a high lipid content and
these organisms are eaten by the euphausiids. The lipid content of the
euphausiids increases throughout the summer and autumn and maximal
reserves are present just prior to the development of the gonads. No
such relationship between the seasonal fluctuations in lipid content and
growth and breeding is indicated in the data on Euphausia crystallorophias
(Littlepage, 1964). There is, instead, a gradual decrease throughout the
THE BIOLOGY O F EUPHAUSIIDS
minimal value in November/December. The spring increase of the
phytoplankton populations takes place a t this time in the Antarctic
and the store of lipids within the euphausiid once again increases. An
examination of Fig. 76 which contains part of the data presented in
Fig. 71, shows the seasonal fluctuations in lipid stores in relation to the
fluctuations in the concentrations of vitamin A and astaxanthin in
Meganyctiphanes norvegica and Thysanoessa raschii. There is an
inverse relationship and high lipid content is not associated with
increased vitamin A or astaxanthin contents. We have no information
on the comparative seasonal fluctuations of these components in other
species of euphausiids.
Seasonal fluctuations in the lipid content of Meganyctiphanes
norvegica and Thysanoessa raschii can be related to the breeding and
growth of these organisms. During the late summer and the autumn
the levels of lipids stored increase and reach maximal values. These
species frequently have a life-span of two or three years. Fisher (1962a)
has pointed out that adolescents entering the adult population in the
summer have a high lipid content and this tends to raise the " average
values ) ) of the lipid content in the population as a whole. The reproductive systems of the adults which have bred in the spring are in a
rudimentary condition throughout the summer and consequently, they
redevelop at the same time as those of the adolescents. Development
starts in November/December and the males mature before the
females. Mating of these species takes place in JanuarylFebruary and
the ovaries continue to grow and are mature in March/April. The
mature ovary represents about 10% of the body weight and it is noticeable that the lipid content of the body decreases as the gonads mature.
The eggs have a high lipid content ; this has not been estimated quantitatively but sections of the eggs demonstrate the presence of many oil
globules in the cytoplasm. The eggs are laid in April/May and there is
plenty of food present in the water a t this time. The rate of growth in
body length of the euphausiids accelerates a t this time (see Chapter 10)
and the lipid content shows a small increase followed by a decrease.
This partial increase in the lipid content may originate from an increased
intake of lipids in the food of the euphausiids. Many of the eggs and
larvae of planktonic and other organisms have a high lipid content and
these organisms are eaten by the euphausiids. The lipid content of the
euphausiids increases throughout the summer and autumn and maximal
reserves are present just prior to the development of the gonads. No
such relationship between the seasonal fluctuations in lipid content and
growth and breeding is indicated in the data on Euphausia crystallorophias
(Littlepage, 1964). There is, instead, a gradual decrease throughout the