1. FATTY ACID OCCURRENCE AND DISTRIBUTION
29
1. Fats of Aquatic Flora
Lovern (152) has found that the fats of marine or freshwater
species, including those of algae and higher plants so far examined,
resemble somewhat those of freshwater animals. As noted by Hilditch
(3), there is an indication in the algae fats that the compositions fall
into groups agreeing with their botanical relationships, irrespective of
their habitat (freshwater or marine). The fat of the red alga alone has
C 20 and C 22 unsaturated acids in amounts corresponding to those of
marine animals. There has been no detailed analysis in regard to the
nature of the types of unsaturated acids, but Paschke and Wheeler
(153) found that Ci 8 unsaturated acids of the freshwater chlorella consisted mainly of linolenic acid, with lesser proportions of linoleic and
monoethenoid acids. The tetraenoic acids formed only a minor proportion. This appears to contrast with the fats of marine animals, in
which the polyenoic acids are largely tetraenoic (stearidonic) acid.
2. Fats of Aquatic Invertebrates and Differentiation into Marine and
Freshwater Types
Although the fats of aquatic plants show no marked differences between freshwater and saltwater species, the Crustacea feeding on
marine phytoplankton possess the marine type of fat, which then persists throughout marine animal life (154). The differences in the composition between the fats of marine and freshwater species are probably of dietary origin, as will be discussed later.
In most instances, the fats of marine and freshwater species conform
fairly closely in composition to the average marine and freshwater types
indicated in Table III. It will suffice, therefore, to mention a few of the
exceptions. The few observations made on the fats of invertebrates
show no unusual features, apart from those of sponges, which contain a
wide range (Ci 4 -C 28 ) of unsaturated acids, with the C 26 and C 28 constituents predominating (cf. Table V).
Bergmann and Swift (155) point out that the high molecular weight
acids may be present as cerebroside or phosphatide-like derivatives.
However, cerebrosides are not characteristic of the lower forms of life,
and as a rule the phospholipid fatty acids of aquatic species are similar
to the glyceride fatty acids. In this connection the phospholipids of the
mussel (Mytilus edulis) have also been found to contain about 10% of
higher molecular weight (ca. C 28 ) fatty acids (155).
3. Fats of Marine Fishes and Mammals
In the elasmobranchs the oil reserves are usually concentrated in
liver and the fatty acid composition of the liver oils conforms generally
29
1. Fats of Aquatic Flora
Lovern (152) has found that the fats of marine or freshwater
species, including those of algae and higher plants so far examined,
resemble somewhat those of freshwater animals. As noted by Hilditch
(3), there is an indication in the algae fats that the compositions fall
into groups agreeing with their botanical relationships, irrespective of
their habitat (freshwater or marine). The fat of the red alga alone has
C 20 and C 22 unsaturated acids in amounts corresponding to those of
marine animals. There has been no detailed analysis in regard to the
nature of the types of unsaturated acids, but Paschke and Wheeler
(153) found that Ci 8 unsaturated acids of the freshwater chlorella consisted mainly of linolenic acid, with lesser proportions of linoleic and
monoethenoid acids. The tetraenoic acids formed only a minor proportion. This appears to contrast with the fats of marine animals, in
which the polyenoic acids are largely tetraenoic (stearidonic) acid.
2. Fats of Aquatic Invertebrates and Differentiation into Marine and
Freshwater Types
Although the fats of aquatic plants show no marked differences between freshwater and saltwater species, the Crustacea feeding on
marine phytoplankton possess the marine type of fat, which then persists throughout marine animal life (154). The differences in the composition between the fats of marine and freshwater species are probably of dietary origin, as will be discussed later.
In most instances, the fats of marine and freshwater species conform
fairly closely in composition to the average marine and freshwater types
indicated in Table III. It will suffice, therefore, to mention a few of the
exceptions. The few observations made on the fats of invertebrates
show no unusual features, apart from those of sponges, which contain a
wide range (Ci 4 -C 28 ) of unsaturated acids, with the C 26 and C 28 constituents predominating (cf. Table V).
Bergmann and Swift (155) point out that the high molecular weight
acids may be present as cerebroside or phosphatide-like derivatives.
However, cerebrosides are not characteristic of the lower forms of life,
and as a rule the phospholipid fatty acids of aquatic species are similar
to the glyceride fatty acids. In this connection the phospholipids of the
mussel (Mytilus edulis) have also been found to contain about 10% of
higher molecular weight (ca. C 28 ) fatty acids (155).
3. Fats of Marine Fishes and Mammals
In the elasmobranchs the oil reserves are usually concentrated in
liver and the fatty acid composition of the liver oils conforms generally