7. CHEMICAL COMPOSITION
225
reason to suggest that carotenoids in bottom detrital material may
contribute to the formation of vitamin A in the euphausiids.
We mentioned, in Chapter 6, that several species of euphausiids
have been found with the remains of crustacean, and especially
euphausiid, compound eyes in their stomachs. These eyes, of course,
represent a source of preformed vitamin A to the predator but
the vitamin A of the majority of individual euphausiids must be
acquired from other sources and at present the possibility that astaxanthin may be its precursor is extremely attractive. It is difficult to ignore
the coincidence between the increased uptake of astaxanthin from copepods in the food of M . norvegiea and the simultaneous increase in the
vitamin A reserves. The only evidence that astaxanthin could be a
precursor is that of Grangaud and Massonet (1955) who claim that the
poeciliid fish, Gambusia holbrooki Grd. can convert astaxanthin,
prepared from penaeid prawns, to vitamin A. On the other hand,
Fisher and Goldie (1959) remark that “. . . we know that the food
chain is longer and more complex, involving both organic and inorganic
nutrients from the land. The phytoplankton flourishes on the former
and the zooplankton feeds, in turn, on it as well as on the land-derived
vegetable material with its carotenoids, especially p-carotene. Such a
diet produces specimens of Meganyctiphanes norvegica in Loch Fyne
larger than we have seen from other waters, including the North Sea,
the north Atlantic and the Mediterranean; these large animals are
much richer in vitamin A than those we have analysed from the other
localities mentioned (Fisher et al., 1955).” Consequently, there may be
more than one source of the precursors of vitamin A. This idea is
supported when we consider the variations in feeding habits of the
different species of euphausiids. A re-examination of the data in
Table XVII shows that there is a distinct tendency for the more
predatory species, those with elongated thoracic limbs belonging to the
genera Thysanoessa, Styloeheiron, and Nematoscelis, to have greater
concentrations of vitamin A. These species, however, also have ‘( divided
eyes ” and since most of the vitamin A is located in the eyes this may
be associated with the visual processes rather than with an increased
opportunity to procure suitable precursors in their diets. What are the
concentrations of vitamin A present in other invertebrates? The
coelenterate, Velella velella (L.) has 0.28 pg/g of vitamin A alcohol
present in its tissues. No vitamin A was present in the few species of
polychaetes examined. About half of the thirty species of molluscs
belonging to the Loricata, Bivalvia and Gastropoda had concentrations
of vitamin A, mainly located in the digestive gland or the visceral
mass. Vitamin A was present in every one of the fifteen or so species
225
reason to suggest that carotenoids in bottom detrital material may
contribute to the formation of vitamin A in the euphausiids.
We mentioned, in Chapter 6, that several species of euphausiids
have been found with the remains of crustacean, and especially
euphausiid, compound eyes in their stomachs. These eyes, of course,
represent a source of preformed vitamin A to the predator but
the vitamin A of the majority of individual euphausiids must be
acquired from other sources and at present the possibility that astaxanthin may be its precursor is extremely attractive. It is difficult to ignore
the coincidence between the increased uptake of astaxanthin from copepods in the food of M . norvegiea and the simultaneous increase in the
vitamin A reserves. The only evidence that astaxanthin could be a
precursor is that of Grangaud and Massonet (1955) who claim that the
poeciliid fish, Gambusia holbrooki Grd. can convert astaxanthin,
prepared from penaeid prawns, to vitamin A. On the other hand,
Fisher and Goldie (1959) remark that “. . . we know that the food
chain is longer and more complex, involving both organic and inorganic
nutrients from the land. The phytoplankton flourishes on the former
and the zooplankton feeds, in turn, on it as well as on the land-derived
vegetable material with its carotenoids, especially p-carotene. Such a
diet produces specimens of Meganyctiphanes norvegica in Loch Fyne
larger than we have seen from other waters, including the North Sea,
the north Atlantic and the Mediterranean; these large animals are
much richer in vitamin A than those we have analysed from the other
localities mentioned (Fisher et al., 1955).” Consequently, there may be
more than one source of the precursors of vitamin A. This idea is
supported when we consider the variations in feeding habits of the
different species of euphausiids. A re-examination of the data in
Table XVII shows that there is a distinct tendency for the more
predatory species, those with elongated thoracic limbs belonging to the
genera Thysanoessa, Styloeheiron, and Nematoscelis, to have greater
concentrations of vitamin A. These species, however, also have ‘( divided
eyes ” and since most of the vitamin A is located in the eyes this may
be associated with the visual processes rather than with an increased
opportunity to procure suitable precursors in their diets. What are the
concentrations of vitamin A present in other invertebrates? The
coelenterate, Velella velella (L.) has 0.28 pg/g of vitamin A alcohol
present in its tissues. No vitamin A was present in the few species of
polychaetes examined. About half of the thirty species of molluscs
belonging to the Loricata, Bivalvia and Gastropoda had concentrations
of vitamin A, mainly located in the digestive gland or the visceral
mass. Vitamin A was present in every one of the fifteen or so species