II. Lipids in Marine and Freshwater Organisms
271
gravimetric methods. However, the lipid class detail available from even very
small samples cannot be matched by any other technology. There is also ample
opportunity for replicates or parallel analyses of different samples because of the
system of handling ten Chromarods as a unit. Other systems such as HPLC can
only handle one sample at a time. The ability to analyze lipid or other organic
materials particularly for nonvolatile materials, on a microgram level, can be
complemented by very careful GLC for the volatile materials (Yang et aI., 1996).
11.2.4. Fatty Acids
Invertebrate lipids are broken down by fish in varying degrees (Henderson and
Tocher, 1987), and all components are rearranged into appropriate fish lipid
classes or catabolized for energy. This process is the same in marine or freshwater
milieus. Finnish lakes were examined for invertebrate-to-fish transfers of fatty
acids by Muje et al. (1989). They concluded that young fish deposited zooplankton fatty acids in total lipids with little change, whereas older fish were more
selective in altering fatty acid deposits for specific bodily needs or functions. As a
rule of thumb, young fish have relatively much less (1-2%) total lipid than older
fish (5-15%). This indicates that the young fish are building up muscle and
require basically only more cellular phospholipids. In older fish, the triacylglycerols are accumulated as energy stores and for gonadal development. Edible
fish do not usually contain wax esters, diacyl glyceryl ethers, or hydrocarbons,
and sterols (primarily cholesterol) are relatively minor. Attention has recently
focused on fatty acids of fish and shellfish for human nutrition. There are firm
indications that two fatty acids, 20:5co3 and 22:6co3, provided by fish and shellfish, have different roles in the human body (Goodnight, 1996). They can be
exploited for better health from modified diets if the lipid class and individual
fatty acids, or both, are understood. Studies of aquatic life reporting only total
lipids, or fatty acids of total lipids, may be of some value to human nutritionists
and dieticians but are of only minor value to biologists. An example is the analysis
of white (dorsal) muscle of 56 species of Swedish fish, including those of both
Baltic and freshwater origins, by Ahlgren et al. (1994). They concluded that the
human nutritional values (i.e., selected fatty acids of the co6 and co3 families of
polyunsaturated fatty acids) were similar for marine, brackish, and freshwater
fish. We now expect that absolutely essential cellular phospholipids rich in DHA
will make up ~0.6% of the mass of such muscle tissue (Ackman, 1990), so when
less DHA is shown as a percentage of all fatty acids, it can only suggest energy
reserves of triacylglycerols that probably have less of this fatty acid (Table 11.1).
Because this pattern is not observed in all likely cases, the merit of the data for
assessing energy reserve levels in freshwater and marine fish is further diminished. Similarly, the analysis of 35 Icelandic fish species for lipid and fatty
acids (Sigurgislad6ttir and Palmad6ttir, 1993) is only a convenient record for
those promoting long-chain co3 fatty acids for good health.
The mixtures of fatty acids of the lipids of marine and freshwater fish do not
differ radically. Roughly a third are saturated, a third or more are monounsatu-
271
gravimetric methods. However, the lipid class detail available from even very
small samples cannot be matched by any other technology. There is also ample
opportunity for replicates or parallel analyses of different samples because of the
system of handling ten Chromarods as a unit. Other systems such as HPLC can
only handle one sample at a time. The ability to analyze lipid or other organic
materials particularly for nonvolatile materials, on a microgram level, can be
complemented by very careful GLC for the volatile materials (Yang et aI., 1996).
11.2.4. Fatty Acids
Invertebrate lipids are broken down by fish in varying degrees (Henderson and
Tocher, 1987), and all components are rearranged into appropriate fish lipid
classes or catabolized for energy. This process is the same in marine or freshwater
milieus. Finnish lakes were examined for invertebrate-to-fish transfers of fatty
acids by Muje et al. (1989). They concluded that young fish deposited zooplankton fatty acids in total lipids with little change, whereas older fish were more
selective in altering fatty acid deposits for specific bodily needs or functions. As a
rule of thumb, young fish have relatively much less (1-2%) total lipid than older
fish (5-15%). This indicates that the young fish are building up muscle and
require basically only more cellular phospholipids. In older fish, the triacylglycerols are accumulated as energy stores and for gonadal development. Edible
fish do not usually contain wax esters, diacyl glyceryl ethers, or hydrocarbons,
and sterols (primarily cholesterol) are relatively minor. Attention has recently
focused on fatty acids of fish and shellfish for human nutrition. There are firm
indications that two fatty acids, 20:5co3 and 22:6co3, provided by fish and shellfish, have different roles in the human body (Goodnight, 1996). They can be
exploited for better health from modified diets if the lipid class and individual
fatty acids, or both, are understood. Studies of aquatic life reporting only total
lipids, or fatty acids of total lipids, may be of some value to human nutritionists
and dieticians but are of only minor value to biologists. An example is the analysis
of white (dorsal) muscle of 56 species of Swedish fish, including those of both
Baltic and freshwater origins, by Ahlgren et al. (1994). They concluded that the
human nutritional values (i.e., selected fatty acids of the co6 and co3 families of
polyunsaturated fatty acids) were similar for marine, brackish, and freshwater
fish. We now expect that absolutely essential cellular phospholipids rich in DHA
will make up ~0.6% of the mass of such muscle tissue (Ackman, 1990), so when
less DHA is shown as a percentage of all fatty acids, it can only suggest energy
reserves of triacylglycerols that probably have less of this fatty acid (Table 11.1).
Because this pattern is not observed in all likely cases, the merit of the data for
assessing energy reserve levels in freshwater and marine fish is further diminished. Similarly, the analysis of 35 Icelandic fish species for lipid and fatty
acids (Sigurgislad6ttir and Palmad6ttir, 1993) is only a convenient record for
those promoting long-chain co3 fatty acids for good health.
The mixtures of fatty acids of the lipids of marine and freshwater fish do not
differ radically. Roughly a third are saturated, a third or more are monounsatu-