7. CHEMICAL COMPOSITION
209
with the accompanying very low temperatures an appreciable proportion of the bulk of the organism is made up of fats in storage. Even
within the same species, e.g. Nyctiphanes australis, in which fat storage
is of a low order, ether extracts indicate a difference in the amount of
fat stored a t the same time of year, when the northern part of the
range is compared to the southern.” He found that Thysanoessa
gregaria in late summer in latitude 34”s had 3-4% by volume of ether
extracted oil while the same species taken in the Bass Strait in latitude
40’5 had 6 4 % during the same season. Euphausia superba preserved
in formalin had 12-15% and Thysanoessa macrura, from the same area
in the Antarctic, l0-12% by volume as ether extracted oils. Littlepage
(1964) in his Fig. 1 presents his own data along with those of Sheard
and of Fisher et al. (1952, 1954, 1955) but there is an error in this figure
resulting from the fact that Littlepage compared his data, expressed as
per cent dry weight, with those of the other authors who expressed theirs
as per cent wet weight or volume; the two groups of data should be
converted to the same units and then the correlation between high lipid
content and high latitude is not as significant as is illustrated in the
figure. It is, however, probably true that euphausiids in higher latitudes
tend to accumulate greater reserves of lipids than those in lower
latitudes but more data are required before conclusive demonstration
of this can be made. An examination of the data in Tables XI, XII,
and XI11 (Fisher, 1962a and unpublished; Fisher et al., 1955) does not
provide any definite evidence to support this hypothesis but then
observations have not been made throughout the year. Further, in
assessing latitudinal variations in lipid content, especially within the
geographical range of an individual species, the differences in the
physiological conditions of the two populations sampled must be
known, especially the relative states of sexual maturity of the individuals in the samples.
From the above it becomes obvious that a few samples of
euphausiids taken a t one or two seasons of the year are liable to produce
an erroneous picture of the lipid content of these animals. Consequently,
regular samples throughout the year are required to elucidate the
seasonal variations in the amount of lipids stored. Estimates of the
lipid content of twenty-six species are presented in Tables XI, XII, and
XI11 and dates, general location of samples, and average weight per
organism in the samples have been included. The ranges in values of
lipid content are similar in all species and no species has obviously
higher or lower values than the others. The sex of the animals was not
determined in these analyses and sexual differences may account for
some of the variability found in replicate samples of a species but we
209
with the accompanying very low temperatures an appreciable proportion of the bulk of the organism is made up of fats in storage. Even
within the same species, e.g. Nyctiphanes australis, in which fat storage
is of a low order, ether extracts indicate a difference in the amount of
fat stored a t the same time of year, when the northern part of the
range is compared to the southern.” He found that Thysanoessa
gregaria in late summer in latitude 34”s had 3-4% by volume of ether
extracted oil while the same species taken in the Bass Strait in latitude
40’5 had 6 4 % during the same season. Euphausia superba preserved
in formalin had 12-15% and Thysanoessa macrura, from the same area
in the Antarctic, l0-12% by volume as ether extracted oils. Littlepage
(1964) in his Fig. 1 presents his own data along with those of Sheard
and of Fisher et al. (1952, 1954, 1955) but there is an error in this figure
resulting from the fact that Littlepage compared his data, expressed as
per cent dry weight, with those of the other authors who expressed theirs
as per cent wet weight or volume; the two groups of data should be
converted to the same units and then the correlation between high lipid
content and high latitude is not as significant as is illustrated in the
figure. It is, however, probably true that euphausiids in higher latitudes
tend to accumulate greater reserves of lipids than those in lower
latitudes but more data are required before conclusive demonstration
of this can be made. An examination of the data in Tables XI, XII,
and XI11 (Fisher, 1962a and unpublished; Fisher et al., 1955) does not
provide any definite evidence to support this hypothesis but then
observations have not been made throughout the year. Further, in
assessing latitudinal variations in lipid content, especially within the
geographical range of an individual species, the differences in the
physiological conditions of the two populations sampled must be
known, especially the relative states of sexual maturity of the individuals in the samples.
From the above it becomes obvious that a few samples of
euphausiids taken a t one or two seasons of the year are liable to produce
an erroneous picture of the lipid content of these animals. Consequently,
regular samples throughout the year are required to elucidate the
seasonal variations in the amount of lipids stored. Estimates of the
lipid content of twenty-six species are presented in Tables XI, XII, and
XI11 and dates, general location of samples, and average weight per
organism in the samples have been included. The ranges in values of
lipid content are similar in all species and no species has obviously
higher or lower values than the others. The sex of the animals was not
determined in these analyses and sexual differences may account for
some of the variability found in replicate samples of a species but we