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C. B. COWEY AND J. R. SARGENT
misconception, namely that fish contain more lipids than do land
animals and especially mammals. It is true that the livers and muscles
of certain fish are very much richer in lipids than are the corresponding
tissues from mammals. It is also true that fish rely to a larger extent
than most mammals, including man, on lipids (and possibly protein)
rather than on carbohydrate for energy provision. Nevertheless the
overall lipid content of fish is relatively similar t o that of most land
animals. The great interest in fish lipids stems rather from the much
wider diversity of lipid classes and fatty acids present in fish compared
to those present in mammals. This diversity stems from the much larger
range of species found in the marine environment and possibly because
lipids fulfd certain functions in fish which do not normally occur in land
animals.
Prior to dealing with their role in nutrition we shall first consider
briefly the chemical nature of the different classes of lipid found in
fish, as well as the function of these compounds in biological phenomena.
This approach is adopted because experience has shown that it is
frequently advantageous to fit nutritional data into L known biochemical
and physiological framework which is well developed in the case of
fish lipids. Thus biochemical knowledge is exploited in considering
areas of lipid nutrition in fish where information is marginal.
A . Lipid types and their functions
The inter-relationships between the various major lipid types
commonly found in fish are shown in Fig. 6. Two main categories are
distinguished, namely polar lipids which are soluble in relatively
aqueous solvents, and non-polar lipids which are soluble in organic
solvents. All the lipid types contain fatty acids; these may be of
different chain lengths and different degrees of saturation; they are
linked to the compounds shown in the right-hand column of Fig. 6
which also characterize the different lipid types. Structural diagrams
of a triglyceride and of phosphatidyl choline are shown in Fig. 8.
Limited quantities of free fatty acids also occur in fish tissues and
may be relatively polar or non-polar depending on their chain length
and degree of unsaturation. Thus increasing the number of double
bonds (i.e. increasing the amount of unsaturation) and shortening the
chain length tends to increase the polarity of the fatty acid. It is
noteworthy that all the lipids shown in Fig. 6 are also present in land
animals and mammals. This is to say that so far no major lipid class has
been found in fish that is not also present in mammals. More information on the neutral lipids of fish may be found in recent reviews (e.g.
Lovern, 1964; Hilditch and Williams, 1964) while phospholipids in
C. B. COWEY AND J. R. SARGENT
misconception, namely that fish contain more lipids than do land
animals and especially mammals. It is true that the livers and muscles
of certain fish are very much richer in lipids than are the corresponding
tissues from mammals. It is also true that fish rely to a larger extent
than most mammals, including man, on lipids (and possibly protein)
rather than on carbohydrate for energy provision. Nevertheless the
overall lipid content of fish is relatively similar t o that of most land
animals. The great interest in fish lipids stems rather from the much
wider diversity of lipid classes and fatty acids present in fish compared
to those present in mammals. This diversity stems from the much larger
range of species found in the marine environment and possibly because
lipids fulfd certain functions in fish which do not normally occur in land
animals.
Prior to dealing with their role in nutrition we shall first consider
briefly the chemical nature of the different classes of lipid found in
fish, as well as the function of these compounds in biological phenomena.
This approach is adopted because experience has shown that it is
frequently advantageous to fit nutritional data into L known biochemical
and physiological framework which is well developed in the case of
fish lipids. Thus biochemical knowledge is exploited in considering
areas of lipid nutrition in fish where information is marginal.
A . Lipid types and their functions
The inter-relationships between the various major lipid types
commonly found in fish are shown in Fig. 6. Two main categories are
distinguished, namely polar lipids which are soluble in relatively
aqueous solvents, and non-polar lipids which are soluble in organic
solvents. All the lipid types contain fatty acids; these may be of
different chain lengths and different degrees of saturation; they are
linked to the compounds shown in the right-hand column of Fig. 6
which also characterize the different lipid types. Structural diagrams
of a triglyceride and of phosphatidyl choline are shown in Fig. 8.
Limited quantities of free fatty acids also occur in fish tissues and
may be relatively polar or non-polar depending on their chain length
and degree of unsaturation. Thus increasing the number of double
bonds (i.e. increasing the amount of unsaturation) and shortening the
chain length tends to increase the polarity of the fatty acid. It is
noteworthy that all the lipids shown in Fig. 6 are also present in land
animals and mammals. This is to say that so far no major lipid class has
been found in fish that is not also present in mammals. More information on the neutral lipids of fish may be found in recent reviews (e.g.
Lovern, 1964; Hilditch and Williams, 1964) while phospholipids in