9. INTERNAL ANATOMY AND PHYSIOLOQY
279
of growth, as 6%. The amount of carbon lost by the animals at moulting
ranges from 6 to 11% during the experimental periods while 62 to 87%
of the carbon is respired. Lasker used the data, presented by Ponomareva (1963), on wild populations of E . pacijica and concluded that
9% of assimilated carbon is incorporated in the tissues, but this does
not include the amounts involved in moulting and reproduction. He
then calculated that a further 9% of assimilated carbon was lost from
females a t breeding because they produced 1400 eggs. This estimate
is probably too high because the volume of an egg of this species is
of the order of 3 x
ml and 1400 eggs would therefore have a
volume of 4.2 x
mI as compared to a total body volume of the
mother of 5 x
ml. Consequently, the fecundity of this species is
more likely to be about 100 to 200 eggs representing a volume of about
10% of that of the body of the female. If this value is entered in
Lasker’s calculations then the amount of assimilated carbon lost from
the females a t breeding is not 9% but nearer 1% (Table XXVI), and
the percentages of carbon incorporated become-growth,
10% ;
moults, 16.5% ; and 72.5% is respired.
I n feeding experiments using Artemia nauplii which had assimilated
carbon-14 by eating radioactive algae, Lasker found that Euphausia
pacijka assimilated 66-95% (average 84%) of ingested carbon. A large
portion of the carbon appeared in the tissues even although the total
amount of carbon assimilated was not sufficient to satisfy the animal’s
requirements. Lasker concludes that when a metabolic deficit is in
existence then the animal makes this good by drawing on its tissues
rather than directly utilizing ingested carbon. Incidentally, Conover
(1966), in a single experiment with Meganyctiphanes norvegica, estimated
that 6.5% of the natural organic matter in the food in the gut was
assimilated.
The feeding methods and diets of euphausiids were examined in
Chapter 6 but very littIe information is available from experiments to
confirm some of the aspects discussed. The only experimental study of
feeding of euphausiids is that of Lasker (1966) on Euphausia pacijica.
Newly hatched nauplii of Artemia were fed on by this species a t a rate
of 52 nauplii per mg dry wt euphausiid per day while large Artemia
nauplii were only eaten a t a rate of 2 nauplii per mg dry wt per day.
Consequently, size of prey organisms must govern, to some degree, their
relative importance in the diet of an euphausiid. When Artemia nauplii
were used to determine the filtering rate of Euphausia paciJica when
filter feeding it was found that they filtered 22-45 ml per animal per hr.
This is a large volume of water to pass through their mouthparts in an
hour and Lasker suggests that the “ filtering rate ” may in fact, in this
A.M.B.-7
10
279
of growth, as 6%. The amount of carbon lost by the animals at moulting
ranges from 6 to 11% during the experimental periods while 62 to 87%
of the carbon is respired. Lasker used the data, presented by Ponomareva (1963), on wild populations of E . pacijica and concluded that
9% of assimilated carbon is incorporated in the tissues, but this does
not include the amounts involved in moulting and reproduction. He
then calculated that a further 9% of assimilated carbon was lost from
females a t breeding because they produced 1400 eggs. This estimate
is probably too high because the volume of an egg of this species is
of the order of 3 x
ml and 1400 eggs would therefore have a
volume of 4.2 x
mI as compared to a total body volume of the
mother of 5 x
ml. Consequently, the fecundity of this species is
more likely to be about 100 to 200 eggs representing a volume of about
10% of that of the body of the female. If this value is entered in
Lasker’s calculations then the amount of assimilated carbon lost from
the females a t breeding is not 9% but nearer 1% (Table XXVI), and
the percentages of carbon incorporated become-growth,
10% ;
moults, 16.5% ; and 72.5% is respired.
I n feeding experiments using Artemia nauplii which had assimilated
carbon-14 by eating radioactive algae, Lasker found that Euphausia
pacijka assimilated 66-95% (average 84%) of ingested carbon. A large
portion of the carbon appeared in the tissues even although the total
amount of carbon assimilated was not sufficient to satisfy the animal’s
requirements. Lasker concludes that when a metabolic deficit is in
existence then the animal makes this good by drawing on its tissues
rather than directly utilizing ingested carbon. Incidentally, Conover
(1966), in a single experiment with Meganyctiphanes norvegica, estimated
that 6.5% of the natural organic matter in the food in the gut was
assimilated.
The feeding methods and diets of euphausiids were examined in
Chapter 6 but very littIe information is available from experiments to
confirm some of the aspects discussed. The only experimental study of
feeding of euphausiids is that of Lasker (1966) on Euphausia pacijica.
Newly hatched nauplii of Artemia were fed on by this species a t a rate
of 52 nauplii per mg dry wt euphausiid per day while large Artemia
nauplii were only eaten a t a rate of 2 nauplii per mg dry wt per day.
Consequently, size of prey organisms must govern, to some degree, their
relative importance in the diet of an euphausiid. When Artemia nauplii
were used to determine the filtering rate of Euphausia paciJica when
filter feeding it was found that they filtered 22-45 ml per animal per hr.
This is a large volume of water to pass through their mouthparts in an
hour and Lasker suggests that the “ filtering rate ” may in fact, in this
A.M.B.-7
10