FISH NUTRITION
453
possess anti-rachitic activity for young growing mammals. Irradiation
of these steroids with U.V. light results in opening of ring I1 between
carbon atoms 9 and 10 and the formation of a double bond between
carbon atoms 10 and 9 so forming the vitamin D nucleus (11). Molecules
with several different side chains (R) all possess anti-rachitic activity
for mammals; these have been referred to as vitamins D, t o D,.
A vitamin D deficiency in growing mammals leads to the development of ricketts, cartilage fails to ossify and mineralize and some
aspects of calcium and phosphate metabolism are deranged. Processes
which are influenced by vitamin D include (i) intestinal absorption
of calcium, (ii) retention of phosphate, (iii) the conversion of organic
to inorganic phosphate and (iv) the oxidation of citrate.
Experiments in various laboratories have so far failed to demonstrate
a requirement for vitamin D by fish. Poston (1968a) examined the
effect of large doses of the vitamins on brook trout fingerlings. By
contrast with mammals pathological changes were not evident in the
fish and growth was not significantly different from that of fish receiving
a control diet. There was a significant increase in the serum calcium concentration and in the haematocrit of fish receiving the high vitamin D,
food. These effects axe similar to those reported to occur in rats.
The biosynthesis of vitamin D, from 7-dehydrocholesterol by a
non-photochemical process has been shown to occur in liver homogenates of the Atlantic striped bass (Blondin et al., 1964). Radioactivity from 7-[4-14C] dehydrocholesterol was incorporated into carrier
vitamin D, in darkness by liver homogenates. The authors suggest, on
chemical grounds, that the 6,8-peroxide of 7-dehydrochoIestero1 may
be an intermediate in the process. This pathway may be of considerable significance because sea water absorbs virtually all the
ultra-violet light within a few metres.
The distribution of vitamin D in the tissues of fish has been examined
by Yamakawa (1964). There were marked differences between different
species and in different organs. I n particular non-bony fish, sharks and
lampreys contained little vitamin D.
3. Vitamin E
As with certain other vitamins, vitamin E activity is found in a
number of compounds (tocopherols) of basically similar structure. Of
these a-tocopherol has both the widest distribution and the highest
biological activity. Structurally a-tocopherol (111) is a 6-hydroxychroman with an isoprenoid side chain; other tocopherols differ in the
degree of saturation of this side chain and in minor substituents.
A.X.B.-lO
18
453
possess anti-rachitic activity for young growing mammals. Irradiation
of these steroids with U.V. light results in opening of ring I1 between
carbon atoms 9 and 10 and the formation of a double bond between
carbon atoms 10 and 9 so forming the vitamin D nucleus (11). Molecules
with several different side chains (R) all possess anti-rachitic activity
for mammals; these have been referred to as vitamins D, t o D,.
A vitamin D deficiency in growing mammals leads to the development of ricketts, cartilage fails to ossify and mineralize and some
aspects of calcium and phosphate metabolism are deranged. Processes
which are influenced by vitamin D include (i) intestinal absorption
of calcium, (ii) retention of phosphate, (iii) the conversion of organic
to inorganic phosphate and (iv) the oxidation of citrate.
Experiments in various laboratories have so far failed to demonstrate
a requirement for vitamin D by fish. Poston (1968a) examined the
effect of large doses of the vitamins on brook trout fingerlings. By
contrast with mammals pathological changes were not evident in the
fish and growth was not significantly different from that of fish receiving
a control diet. There was a significant increase in the serum calcium concentration and in the haematocrit of fish receiving the high vitamin D,
food. These effects axe similar to those reported to occur in rats.
The biosynthesis of vitamin D, from 7-dehydrocholesterol by a
non-photochemical process has been shown to occur in liver homogenates of the Atlantic striped bass (Blondin et al., 1964). Radioactivity from 7-[4-14C] dehydrocholesterol was incorporated into carrier
vitamin D, in darkness by liver homogenates. The authors suggest, on
chemical grounds, that the 6,8-peroxide of 7-dehydrochoIestero1 may
be an intermediate in the process. This pathway may be of considerable significance because sea water absorbs virtually all the
ultra-violet light within a few metres.
The distribution of vitamin D in the tissues of fish has been examined
by Yamakawa (1964). There were marked differences between different
species and in different organs. I n particular non-bony fish, sharks and
lampreys contained little vitamin D.
3. Vitamin E
As with certain other vitamins, vitamin E activity is found in a
number of compounds (tocopherols) of basically similar structure. Of
these a-tocopherol has both the widest distribution and the highest
biological activity. Structurally a-tocopherol (111) is a 6-hydroxychroman with an isoprenoid side chain; other tocopherols differ in the
degree of saturation of this side chain and in minor substituents.
A.X.B.-lO
18