1. FATTY ACID OCCURRENCE AND DISTRIBUTION
31
to that of the average marine type. Within the class, however, several
groups have been differentiated [cf. Tsujimoto (156)] which, on the
basis of their fatty acid compositions, may be described as follows:
(a) those with large proportions of highly unsaturated fatty acids and
low unsaponifiable content (1-2%, mainly sterols); (b) those with fatty
acids, mainly belonging to the monoethenoid series and containing 10%
or more of unsaponifiable matter, which may consist of cholesterol and
glyceryl ethers, known as selachyl, chimyl, and batyl alcohols, or of
the terpenoid hydrocarbon squalene, in proportions up to 80% of liver
oil; (c) those with fatty acids containing a high proportion, up to 50%,
of saturated fatty acids, and with relatively low proportions of unsaponifiable matter.
The classification outlined is evidently not a rigid one, as some
shark (Galeorhinus sp.) liver oils with moderate amounts (3-8%) of
unsaponifiable matter conform both in regard to fatty acid composition
and mean unsaturation of the C 20 and C 22 unsaturated acids to the
average marine type (160, 161). Furthermore, the fatty acid composition of the liver oil is not necessarily determined by biological origin,
as marked differences are shown between the same species taken from
different waters (see Table VI). On the other hand the data reviewed
by Pathak and Dey (162) suggest that different species of shark taken
off the coast of India are characterized by the high content of saturated
acids, as in Tsujimoto's classification (c) above. However, the difference
in fatty acid composition between the fetal liver fat of Galeocerdo
tigrinus (with a low content of C 20 and absence of C 22 unsaturated
acids) and that of the liver fat of the mother, which is of the normal
marine type, remains unexplained.
Among the teleostids the most notable exception is the castor oil fish
(Ruvettus pretiosus), the body fat of which is actually a liquid wax
consisting of cetyl, oleyl, and octadecyl alcohols combined with oleic
and dihydroxyoleic acids (163).
In teleostids, variations in fatty acid composition according to the
site of storage have been noted. Hilditch (3) observed that on the
whole the composition of the flesh fats is more regular and the difference between species less pronounced than in the liver fats. The major
component acids in most cases fall within the following limits, expressed as weight per cent of the total fatty acids: palmitic acid, 15-18;
unsaturated C 1G , 10; C 18 , 20-25; C 20 , 22-26; and C 22 , 18-22. Thus the
percentages of hexadecenoic, Ci 8 , and C 20 unsaturated acids are somewhat lower, and those of the unsaturated C 22 acids somewhat higher,
than in the typical marine fat.
In teleostids the fat reserves may be concentrated in the liver, as in
31
to that of the average marine type. Within the class, however, several
groups have been differentiated [cf. Tsujimoto (156)] which, on the
basis of their fatty acid compositions, may be described as follows:
(a) those with large proportions of highly unsaturated fatty acids and
low unsaponifiable content (1-2%, mainly sterols); (b) those with fatty
acids, mainly belonging to the monoethenoid series and containing 10%
or more of unsaponifiable matter, which may consist of cholesterol and
glyceryl ethers, known as selachyl, chimyl, and batyl alcohols, or of
the terpenoid hydrocarbon squalene, in proportions up to 80% of liver
oil; (c) those with fatty acids containing a high proportion, up to 50%,
of saturated fatty acids, and with relatively low proportions of unsaponifiable matter.
The classification outlined is evidently not a rigid one, as some
shark (Galeorhinus sp.) liver oils with moderate amounts (3-8%) of
unsaponifiable matter conform both in regard to fatty acid composition
and mean unsaturation of the C 20 and C 22 unsaturated acids to the
average marine type (160, 161). Furthermore, the fatty acid composition of the liver oil is not necessarily determined by biological origin,
as marked differences are shown between the same species taken from
different waters (see Table VI). On the other hand the data reviewed
by Pathak and Dey (162) suggest that different species of shark taken
off the coast of India are characterized by the high content of saturated
acids, as in Tsujimoto's classification (c) above. However, the difference
in fatty acid composition between the fetal liver fat of Galeocerdo
tigrinus (with a low content of C 20 and absence of C 22 unsaturated
acids) and that of the liver fat of the mother, which is of the normal
marine type, remains unexplained.
Among the teleostids the most notable exception is the castor oil fish
(Ruvettus pretiosus), the body fat of which is actually a liquid wax
consisting of cetyl, oleyl, and octadecyl alcohols combined with oleic
and dihydroxyoleic acids (163).
In teleostids, variations in fatty acid composition according to the
site of storage have been noted. Hilditch (3) observed that on the
whole the composition of the flesh fats is more regular and the difference between species less pronounced than in the liver fats. The major
component acids in most cases fall within the following limits, expressed as weight per cent of the total fatty acids: palmitic acid, 15-18;
unsaturated C 1G , 10; C 18 , 20-25; C 20 , 22-26; and C 22 , 18-22. Thus the
percentages of hexadecenoic, Ci 8 , and C 20 unsaturated acids are somewhat lower, and those of the unsaturated C 22 acids somewhat higher,
than in the typical marine fat.
In teleostids the fat reserves may be concentrated in the liver, as in