430
0. B. OOWEY AND J. R. SARGHINT
fish has yet to be established, but it would appear highly probable that
changes in dietary intake do occur and that these are intimately
involved with changes in the fluidity of the biomembranes a t different
temperatures. Increased fluidity of fatty acids may also of course be of
considerable importance in the actual process of absorption of dietary
lipid from the gut.
3. Dietary factors
The largest single factor in the environment affecting fatty acid
composition in fish is diet. The influence of diet on fatty acid pattern
became apparent from the different fatty acid compositions of freshwater and marine fish. Lovern had shown in the 1930s that changes
in dietary lipid could alter the fatty acid compositions of a number of
species including the eel, salmon and carp ; carp on a low-fat vegetable
diet were deficient in polyenoic acids (Lovern, 1964). Kelly et al.
(19588) were the first to feed a fat-free diet to aquarium-maintained
salt-water fish (the mullet, Mugil cephalus L.) and to demonstrate that,
in the absence of dietary fat, these fish became deficient in polyenoic
acids although the fatty acids (1 6 : 0 and 18 : 0) typical of land animals
on a similar diet were formed biosynthetically. Administration of
menhaden oil to fish on a fat-free diet caused deposition of the
menhaden oil essentially unchanged. Body fat in freshwater species
can also be changed to resemble dietary fat such as cottonseed or
linseed oils (Kelly et al., 1958b). Subsequently, Reiser et al. (1963)
demonstrated that dietary linoleic and linolenic acids could be deposited
in both freshwater fish (Carrassius auratus (L.)) and in salt-water fish
(Mugil cephulus and Pundulus grandis Baird and Girard), although
linolenic acid was deposited to a greater degree. Increasing amounts of
linoleic acid were deposited with increasing dietary linoleic acid up to
a dietary level of 5% after which body deposition tapered off. Similar
work by Brenner et al. (1963) showed that the freshwater
Parapimelodus valenciennesi could, like land mammals, regulate the
amounts of dietary fatty acids deposited in tissues. Dietary 18 : 2 acid
prevented the accumulation of 16:1, 18:l and 20:3w9 acids occurring on a fat-free diet, indicating an inhibition of the biosynthesis of
the latter acids. The fatty acid composition of fish, therefore,
represents a baIance between fatty acids derived from the diet and
fatty acids derived biosynthetically.
Pish, however, can also alter dietary fatty acids substantially. A
striking demonstration of this fact comes from a food-chain experiment by Kayama et al. (1963). These authors reared the brine shrimp,
Artemia, solely on the alga Chaetoceros. The major fatty acids of
0. B. OOWEY AND J. R. SARGHINT
fish has yet to be established, but it would appear highly probable that
changes in dietary intake do occur and that these are intimately
involved with changes in the fluidity of the biomembranes a t different
temperatures. Increased fluidity of fatty acids may also of course be of
considerable importance in the actual process of absorption of dietary
lipid from the gut.
3. Dietary factors
The largest single factor in the environment affecting fatty acid
composition in fish is diet. The influence of diet on fatty acid pattern
became apparent from the different fatty acid compositions of freshwater and marine fish. Lovern had shown in the 1930s that changes
in dietary lipid could alter the fatty acid compositions of a number of
species including the eel, salmon and carp ; carp on a low-fat vegetable
diet were deficient in polyenoic acids (Lovern, 1964). Kelly et al.
(19588) were the first to feed a fat-free diet to aquarium-maintained
salt-water fish (the mullet, Mugil cephalus L.) and to demonstrate that,
in the absence of dietary fat, these fish became deficient in polyenoic
acids although the fatty acids (1 6 : 0 and 18 : 0) typical of land animals
on a similar diet were formed biosynthetically. Administration of
menhaden oil to fish on a fat-free diet caused deposition of the
menhaden oil essentially unchanged. Body fat in freshwater species
can also be changed to resemble dietary fat such as cottonseed or
linseed oils (Kelly et al., 1958b). Subsequently, Reiser et al. (1963)
demonstrated that dietary linoleic and linolenic acids could be deposited
in both freshwater fish (Carrassius auratus (L.)) and in salt-water fish
(Mugil cephulus and Pundulus grandis Baird and Girard), although
linolenic acid was deposited to a greater degree. Increasing amounts of
linoleic acid were deposited with increasing dietary linoleic acid up to
a dietary level of 5% after which body deposition tapered off. Similar
work by Brenner et al. (1963) showed that the freshwater
Parapimelodus valenciennesi could, like land mammals, regulate the
amounts of dietary fatty acids deposited in tissues. Dietary 18 : 2 acid
prevented the accumulation of 16:1, 18:l and 20:3w9 acids occurring on a fat-free diet, indicating an inhibition of the biosynthesis of
the latter acids. The fatty acid composition of fish, therefore,
represents a baIance between fatty acids derived from the diet and
fatty acids derived biosynthetically.
Pish, however, can also alter dietary fatty acids substantially. A
striking demonstration of this fact comes from a food-chain experiment by Kayama et al. (1963). These authors reared the brine shrimp,
Artemia, solely on the alga Chaetoceros. The major fatty acids of