FISH NUTRITION
429
It appeared that the medium chain saturated acids (16:O and 18:O)
and long chain unsaturated acids (C20 and C22) decreased with depth,
whereas the levels of oleic acid (18 : 1) increased with depth. These
findings must reflect to aome extent at least, the known presence of
wax esters rich in oleic acid in certain mid water species (Nevenzel
et al., 1965, 1966; Nevenzel, 1970). It is, as yet, not clear whether
changes in fatty acid composition can occur under these conditions in
particular lipid classes, e.g. triglycerides, and if such changes occur
whether they are a direct result of increasing pressure or other environmen t a1 parameters .
A major environmental factor well established as causing changes
in the fatty acid composition of individual lipid classes is temperature.
A great deal of evidence now exists supporting the idea that a decrease
in the environmental temperature induces an increased degree of
unsaturation in fish lipids (Hilditch and Williams, 1964 ; Johnston
and Roots, 1964; Knipprath and Mead, 1968; Smith, 1967; Smith
and Kemp, 1969; Kemp and Smith, 1970). While most of the
experimental work in this field has been done on freshwater fish, and
especially the goldfish, the phenomenon also applies t o marine fish
(Lewis, 1962). The data of Knipprath and Mead (1966) showed that
when guppies were kept at 14-15' instead of 26-27' an increase
occurred in the level of 22:6 acid within one week and increases
occurred in 14 : 0, 16 : 1, 18 : 2 after four weeks. Subsequent work with
the goldfish (Kemp and Smith, 1970) has demonstrated that cold
adaptation in this species did not markedly alter the fatty acid
composition of the whole fish, but pronounced changes occurred in
fatty acids of phospholipids fiom cytomembrane fractions of intestinal
mucosa, a tissue that is known to turnover rapidly. At lower temperatures these membrane fatty acids were markedly enriched in 20 : 1,
20 : 4 and 22 : 6 acids and markedly decreased in 18 : 0 and 20 : 3 acids.
Fatty acids of choline phosphoglycerides or ethanolamine phosphoglycerides were more susceptible to temperature-induced changes than
were acids of inositol phosphoglycerides or serine phosphoglycerides.
It is interesting to note that such changes in fatty acid composition
induced by temperature are accompanied by functional changes in the
goldfish intestinal mucosa, in that as the temperature is raised the
magnesium-stimulated adenosine triphosphatase activity increases
and the sodiumlpotassium-stimulated adenosine triphosphatase activity
falls (Smith, 1967). More recently Smith and Kemp (1971) have shown
that the increased desaturation of intestinal lipids is accompanied by an
increased rate of transfer of the amino acid valine across the intestinal
mucosa. The significance of these findings to the dietary intake of the
429
It appeared that the medium chain saturated acids (16:O and 18:O)
and long chain unsaturated acids (C20 and C22) decreased with depth,
whereas the levels of oleic acid (18 : 1) increased with depth. These
findings must reflect to aome extent at least, the known presence of
wax esters rich in oleic acid in certain mid water species (Nevenzel
et al., 1965, 1966; Nevenzel, 1970). It is, as yet, not clear whether
changes in fatty acid composition can occur under these conditions in
particular lipid classes, e.g. triglycerides, and if such changes occur
whether they are a direct result of increasing pressure or other environmen t a1 parameters .
A major environmental factor well established as causing changes
in the fatty acid composition of individual lipid classes is temperature.
A great deal of evidence now exists supporting the idea that a decrease
in the environmental temperature induces an increased degree of
unsaturation in fish lipids (Hilditch and Williams, 1964 ; Johnston
and Roots, 1964; Knipprath and Mead, 1968; Smith, 1967; Smith
and Kemp, 1969; Kemp and Smith, 1970). While most of the
experimental work in this field has been done on freshwater fish, and
especially the goldfish, the phenomenon also applies t o marine fish
(Lewis, 1962). The data of Knipprath and Mead (1966) showed that
when guppies were kept at 14-15' instead of 26-27' an increase
occurred in the level of 22:6 acid within one week and increases
occurred in 14 : 0, 16 : 1, 18 : 2 after four weeks. Subsequent work with
the goldfish (Kemp and Smith, 1970) has demonstrated that cold
adaptation in this species did not markedly alter the fatty acid
composition of the whole fish, but pronounced changes occurred in
fatty acids of phospholipids fiom cytomembrane fractions of intestinal
mucosa, a tissue that is known to turnover rapidly. At lower temperatures these membrane fatty acids were markedly enriched in 20 : 1,
20 : 4 and 22 : 6 acids and markedly decreased in 18 : 0 and 20 : 3 acids.
Fatty acids of choline phosphoglycerides or ethanolamine phosphoglycerides were more susceptible to temperature-induced changes than
were acids of inositol phosphoglycerides or serine phosphoglycerides.
It is interesting to note that such changes in fatty acid composition
induced by temperature are accompanied by functional changes in the
goldfish intestinal mucosa, in that as the temperature is raised the
magnesium-stimulated adenosine triphosphatase activity increases
and the sodiumlpotassium-stimulated adenosine triphosphatase activity
falls (Smith, 1967). More recently Smith and Kemp (1971) have shown
that the increased desaturation of intestinal lipids is accompanied by an
increased rate of transfer of the amino acid valine across the intestinal
mucosa. The significance of these findings to the dietary intake of the