216
THE BIOLOQY OF EUPHAUSIIDS
gated this claim and examined the stomach contents of baleen whales
in the Arctic and Antarctic Oceans and found no 6-carotene. The
carotenoid pigment, astaxanthin, not mentioned by Wagner, was
present in large quantities as was vitamin A. The chemical structures
of these substances are shown in Fig. 73. Kon and Thompson further
found evidence that the whales were absorbing the vitamin through
the intestinal walls. They also analysed samples of Meganyctiphanes
norvegica and Thysanoessa raschii caught in Loch Fyne and found
appreciable quantities of vitamin A present in them. This work was
extended and Fisher et al. (1952) published the first of a series of
papers which showed that whales could obtain enough vitamin A from
euphausiids without synthesizing it for themselves from precursors
such as /3-carotene.
There are two chemically different forms of vitamin A but one,
vitamin A,, has not, as yet, been identified in an invertebrate animal.
I n the following discussions the one which concerns us is vitamin A,
which has a formula C,,H,,O and we shall refer to it simply as vitamin
A. It is an alcohol consisting of an aromatic ring structure, the 6-ionone
ring, and a long side chain of conjugated double bonds. Vitamin A, is
also present in the form of an ester in the storage sites such as the liver
of vertebrates and in its aldehyde form (retinene) it takes part in the
visual cycle. This vitamin occurs in animals which are unable to
synthesize it de novo but obtain it from other animals or by converting
carotenoid pigments, mostly of plant origin, to vitamin A. The carotenoid pigments consist of two substituted or unsubstituted ionone
rings connected by an unsaturated chain of the same kind as the side
chain of vitamin A, but twice as long. 6-carotene has unsubstituted
ionone rings and astaxanthin has substituted rings (Fig. 73)) these
being the most important carotenoids associated with the formation of
vitamin A in invertebrates,
Vitamin A is estimated by biological assay, and most of the earlier
analyses were by this method, and also by chemical and physical
techniques. The methods of assay used are reviewed by Fisher and Kon
(1959). The earlier papers of Fisher, Kon, and Thompson express the
concentrations of vitamin A in samples in international units but they
state (Fisher et ab., 1956a) that these units should be multiplied by a
factor of 0.39 to convert them to micrograms (pg), the unit of measurement they use in their later papers. All the results quoted here, except
those in Figs. 7 4 and 75, are in micrograms and where these have been
obtained from earlier papers the results presented there have been
multiplied by the above factor.
We shall restrict ourselves to the occurrence of vitamin A and
THE BIOLOQY OF EUPHAUSIIDS
gated this claim and examined the stomach contents of baleen whales
in the Arctic and Antarctic Oceans and found no 6-carotene. The
carotenoid pigment, astaxanthin, not mentioned by Wagner, was
present in large quantities as was vitamin A. The chemical structures
of these substances are shown in Fig. 73. Kon and Thompson further
found evidence that the whales were absorbing the vitamin through
the intestinal walls. They also analysed samples of Meganyctiphanes
norvegica and Thysanoessa raschii caught in Loch Fyne and found
appreciable quantities of vitamin A present in them. This work was
extended and Fisher et al. (1952) published the first of a series of
papers which showed that whales could obtain enough vitamin A from
euphausiids without synthesizing it for themselves from precursors
such as /3-carotene.
There are two chemically different forms of vitamin A but one,
vitamin A,, has not, as yet, been identified in an invertebrate animal.
I n the following discussions the one which concerns us is vitamin A,
which has a formula C,,H,,O and we shall refer to it simply as vitamin
A. It is an alcohol consisting of an aromatic ring structure, the 6-ionone
ring, and a long side chain of conjugated double bonds. Vitamin A, is
also present in the form of an ester in the storage sites such as the liver
of vertebrates and in its aldehyde form (retinene) it takes part in the
visual cycle. This vitamin occurs in animals which are unable to
synthesize it de novo but obtain it from other animals or by converting
carotenoid pigments, mostly of plant origin, to vitamin A. The carotenoid pigments consist of two substituted or unsubstituted ionone
rings connected by an unsaturated chain of the same kind as the side
chain of vitamin A, but twice as long. 6-carotene has unsubstituted
ionone rings and astaxanthin has substituted rings (Fig. 73)) these
being the most important carotenoids associated with the formation of
vitamin A in invertebrates,
Vitamin A is estimated by biological assay, and most of the earlier
analyses were by this method, and also by chemical and physical
techniques. The methods of assay used are reviewed by Fisher and Kon
(1959). The earlier papers of Fisher, Kon, and Thompson express the
concentrations of vitamin A in samples in international units but they
state (Fisher et ab., 1956a) that these units should be multiplied by a
factor of 0.39 to convert them to micrograms (pg), the unit of measurement they use in their later papers. All the results quoted here, except
those in Figs. 7 4 and 75, are in micrograms and where these have been
obtained from earlier papers the results presented there have been
multiplied by the above factor.
We shall restrict ourselves to the occurrence of vitamin A and