180
Y. Olsen
be concluded that differences in percentage 0)3 fatty acid contents of species
reported in the literature reflect genetic differences (or differences resulting from
methodological problems, see above) rather than environmental or experimental
conditions.
8.2.6.2. Zooplankton
Fatty acid and lipid accumulation by marine zooplankton depends on the type of
storage lipid (Fig. 8.3); WEs or TAGs. Zooplankton used as live feed, and normally also fish, store TAGs.
8.2.6.2.1. Lipid Content and Lipid Composition
The relative amounts of PL and TAG in species that store TAGs (TAG-zooplankton) depend mainly on the lipid content, or the nutritional state, of the
zooplankton (general scheme in Fig. 8.8). The contents of TAG are highly variable, whereas the quantitative content of PL for given species is believed to be
relatively less variable and independent of the nutritional state of the zooplankton
(Rainuzzo et aI., 1994). The percentage content of both TAG and PL of total lipids
will accordingly vary strongly (Fig. 8.8).
Young stages of WE-zooplankton show the same characteristic features as
TAG-zooplankton, and very high WE contents in young stages are most unlikely
in nature. Older stages may, however, be very rich in WE. This was thoroughly
demonstrated by Sargent and coworkers through their classical work on marine
copepods in the food web (Sargent, 1989; Sargent and Henderson, 1986). The fact
that many important herbivorous zooplankton (e.g., Calanus finmarchicus) synthesize WEs has a great impact on the oils that are extracted from planktivorous
fish such as capelin, herring, and salmon. The fatty alcohol moiety of WEs in
herbivorous zooplankton are normally long-chained and monounsaturated (22: I,
20: I) and are synthesized by the zooplankton themselves. Carnivorous zooplankton may incorporate larger fractions of short-chain saturated fatty alcohol
moieties than herbivorous zooplankton.
Fish that feed on WE-zooplankton will oxidize the monounsaturated fatty
alcohols, which are then transformed into monounsaturated fatty acids of equal
chain length. Long-chain monounsaturated fatty acids are major components of
marine oils derived from planktivorous fish. These characteristic fatty acids,
which originate from herbivorous WE-zooplankton, may be useful as tracers in
food web studies. These fatty acids are also selectively used as catabolic fuel
(Olsen and Skjervold, 1991; Sargent and Henderson, 1986). It is noteworthy that
the fatty acid metabolism of the zooplankton, and consequently the fatty acid
composition at higher levels in the food web, are partly controlled by zooplankton
metabolism or genetics.
The lipid content of marine zooplankton is partly dependent on the lipid content
of their food. B. plicatilis is a typical TAG species that shows optimum growth at
relatively high temperature (Olsen et aI., I 993a). The impact of the food lipid
content on the lipid contents of the rotifer is low in the lower and intermediate
Y. Olsen
be concluded that differences in percentage 0)3 fatty acid contents of species
reported in the literature reflect genetic differences (or differences resulting from
methodological problems, see above) rather than environmental or experimental
conditions.
8.2.6.2. Zooplankton
Fatty acid and lipid accumulation by marine zooplankton depends on the type of
storage lipid (Fig. 8.3); WEs or TAGs. Zooplankton used as live feed, and normally also fish, store TAGs.
8.2.6.2.1. Lipid Content and Lipid Composition
The relative amounts of PL and TAG in species that store TAGs (TAG-zooplankton) depend mainly on the lipid content, or the nutritional state, of the
zooplankton (general scheme in Fig. 8.8). The contents of TAG are highly variable, whereas the quantitative content of PL for given species is believed to be
relatively less variable and independent of the nutritional state of the zooplankton
(Rainuzzo et aI., 1994). The percentage content of both TAG and PL of total lipids
will accordingly vary strongly (Fig. 8.8).
Young stages of WE-zooplankton show the same characteristic features as
TAG-zooplankton, and very high WE contents in young stages are most unlikely
in nature. Older stages may, however, be very rich in WE. This was thoroughly
demonstrated by Sargent and coworkers through their classical work on marine
copepods in the food web (Sargent, 1989; Sargent and Henderson, 1986). The fact
that many important herbivorous zooplankton (e.g., Calanus finmarchicus) synthesize WEs has a great impact on the oils that are extracted from planktivorous
fish such as capelin, herring, and salmon. The fatty alcohol moiety of WEs in
herbivorous zooplankton are normally long-chained and monounsaturated (22: I,
20: I) and are synthesized by the zooplankton themselves. Carnivorous zooplankton may incorporate larger fractions of short-chain saturated fatty alcohol
moieties than herbivorous zooplankton.
Fish that feed on WE-zooplankton will oxidize the monounsaturated fatty
alcohols, which are then transformed into monounsaturated fatty acids of equal
chain length. Long-chain monounsaturated fatty acids are major components of
marine oils derived from planktivorous fish. These characteristic fatty acids,
which originate from herbivorous WE-zooplankton, may be useful as tracers in
food web studies. These fatty acids are also selectively used as catabolic fuel
(Olsen and Skjervold, 1991; Sargent and Henderson, 1986). It is noteworthy that
the fatty acid metabolism of the zooplankton, and consequently the fatty acid
composition at higher levels in the food web, are partly controlled by zooplankton
metabolism or genetics.
The lipid content of marine zooplankton is partly dependent on the lipid content
of their food. B. plicatilis is a typical TAG species that shows optimum growth at
relatively high temperature (Olsen et aI., I 993a). The impact of the food lipid
content on the lipid contents of the rotifer is low in the lower and intermediate