FISH NUTRFJ!ION
427
However, more subtle differences have been brought out by Ackman
(1967) some of whose data are shown in Table XIII. Thus (i) total
saturated fatty acids are somewhat higher in freshwater than in
marine fish, (ii) 16: 1 and 18: 1 acids are higher in freshwater than in
marine oils while the converse is true for 20 : 1 and 22 : 1 acids, but the
overall quantity of monoenoic acids is marginally lower in freshwater
oils, (iii) freshwater oils contain higher proportions of dienoic acids,
trienoic acids, especially 18:2w6 and 18:3w6 and 18:3w3, and
tetraenoic acids, especially 20 : 4w6 and 22 : 4w6, (iv) 22 : 4w6 does not
usually occur in marine oils, (v) as the level of 16 : 0 is similar in the
total fatty acids from both sources the ratios 16:0/16:1 and
16 : 0116 : 1 + 18 : 1 are lower in freshwater fatty acids than in marine
fatty acids.
It is also worthy of note that the ratio total w3/totalw6 is much
less in freshwater fatty acids than in marine fatty acids reflecting a
higher dietary input of 18 : 2w6 and 18 : 3w6 in freshwater species. In
addition to a rise in 18 : 2w6 levels in freshwater oils, higher acids of the
w6 series 20 : 4w6 and 22 : 4w6 are also proportionally raised suggesting
that chain elongation in the w6 series has occurred readily. In contrast,
while 18 : 3w3 is raised in freshwater oils, higher acids of the w3 series
are not proportionally elevated suggesting that chain elongation of the
w3 series does not, or need not, occur in freshwater fish. Instead 18 : 303
may be deposited unaltered in the depot fat. On the other hand marine
oils are characterized by increased proportions of higher w 3 acids,
20 : 6w3, 22 : 6w3 and 22 : 6w3 (Gruger et al., 1964).
The foregoing account refers to depot fat. The mainly polar lipids
already described as constituents of biomembrane systems have aho
been examined. Fatty acid analyses of individual phospholipid classes
from fish have been carried out by a number of workers including
Richardson et uZ. (1962), Brockerhoff et uZ. (1963), Menzell and Olcott
(1964), Olley and Duncan (1965), Jangaard et al. (1967), Shimma and
Taguchi (1964) and Kemp and Smith (1970). Some of the data on fatty
acid analyses of phospholipids are reproduced in Table XIV. For the
present discussion “flesh lipids” are excluded since the extent to
which the latter represent different proportions of depot oil and tissue
phospholipids is not always clear. As with land animals (Carrol, 1965)
it is clear from Table XIV that fatty acids of the phospholipids of fish
are much more unsaturated than fatty acids from triglycerides (see also
Menzell and Olcott, 1964). The increased unsaturation in the fatty
acids from phospholipids is very largely due to the increased levels of
C20 and C22 unsaturated acids that may account for more than 50%
of the total fatty acids present. Differences are also apparent between
427
However, more subtle differences have been brought out by Ackman
(1967) some of whose data are shown in Table XIII. Thus (i) total
saturated fatty acids are somewhat higher in freshwater than in
marine fish, (ii) 16: 1 and 18: 1 acids are higher in freshwater than in
marine oils while the converse is true for 20 : 1 and 22 : 1 acids, but the
overall quantity of monoenoic acids is marginally lower in freshwater
oils, (iii) freshwater oils contain higher proportions of dienoic acids,
trienoic acids, especially 18:2w6 and 18:3w6 and 18:3w3, and
tetraenoic acids, especially 20 : 4w6 and 22 : 4w6, (iv) 22 : 4w6 does not
usually occur in marine oils, (v) as the level of 16 : 0 is similar in the
total fatty acids from both sources the ratios 16:0/16:1 and
16 : 0116 : 1 + 18 : 1 are lower in freshwater fatty acids than in marine
fatty acids.
It is also worthy of note that the ratio total w3/totalw6 is much
less in freshwater fatty acids than in marine fatty acids reflecting a
higher dietary input of 18 : 2w6 and 18 : 3w6 in freshwater species. In
addition to a rise in 18 : 2w6 levels in freshwater oils, higher acids of the
w6 series 20 : 4w6 and 22 : 4w6 are also proportionally raised suggesting
that chain elongation in the w6 series has occurred readily. In contrast,
while 18 : 3w3 is raised in freshwater oils, higher acids of the w3 series
are not proportionally elevated suggesting that chain elongation of the
w3 series does not, or need not, occur in freshwater fish. Instead 18 : 303
may be deposited unaltered in the depot fat. On the other hand marine
oils are characterized by increased proportions of higher w 3 acids,
20 : 6w3, 22 : 6w3 and 22 : 6w3 (Gruger et al., 1964).
The foregoing account refers to depot fat. The mainly polar lipids
already described as constituents of biomembrane systems have aho
been examined. Fatty acid analyses of individual phospholipid classes
from fish have been carried out by a number of workers including
Richardson et uZ. (1962), Brockerhoff et uZ. (1963), Menzell and Olcott
(1964), Olley and Duncan (1965), Jangaard et al. (1967), Shimma and
Taguchi (1964) and Kemp and Smith (1970). Some of the data on fatty
acid analyses of phospholipids are reproduced in Table XIV. For the
present discussion “flesh lipids” are excluded since the extent to
which the latter represent different proportions of depot oil and tissue
phospholipids is not always clear. As with land animals (Carrol, 1965)
it is clear from Table XIV that fatty acids of the phospholipids of fish
are much more unsaturated than fatty acids from triglycerides (see also
Menzell and Olcott, 1964). The increased unsaturation in the fatty
acids from phospholipids is very largely due to the increased levels of
C20 and C22 unsaturated acids that may account for more than 50%
of the total fatty acids present. Differences are also apparent between