2. Fatty Acids as Trophic and Chemical Markers
35
part responsible for a common fin disease. It is believed that the high proportions
of 20:4006 in wild salmon originates in the lipids of aquatic insects, which constitute an important portion of their natural food (Ackman and Takeuchi, 1986).
The analysis of several species of freshwater invertebrates that are natural food of
salmon indicated, however, that not only insects but also the Gammaridae and
Oligochaeta can be a source of 18:20)6 and 20:40)6 for fish (Bell et aI., 1994).
Growing environmental and conservationist concerns have stimulated the use
of alternative methods applied to the ecology of aquatic and semiaquatic mammals. Many of these investigations have used fatty acid markers to determine food
resources for populations of aquatic mammals (for a comparative discussion, see
also Landrum and Fisher, this volume). A comparison of the fatty acids in the
blubber of a population of harbor seals, Phoca vitulina from the Ungava Peninsula
(a land-locked environment in northern Quebec) and their marine counterpart,
showed that the inland animals have a fatty acid profile enriched in components of
freshwater origin, such as 18:2006, 18:30)3, and 20:40)6; the blubber of the marine
populations of P. vitulina contained higher concentrations of20: 10)9 and 22: 10)11
(Smith et aI., 1996). These MUFAs are characteristic components of the wax
esters of marine calanoid copepods, which are eaten by zooplanktivorus fish and
then are transferred to higher trophic levels of the food chain (Clarke et aI., 1987,
Sargent, 1976).
The contribution of marine versus freshwater fatty acids food sources can be
assessed by its 0)3/0)6 fatty acid ratio in the predator tissues. A typical 0)3/0)6 ratio
for freshwater fish ranges from 0.5 to 3.8, whereas for marine fish the ratio varies
from 4.7 to 14.4 (Henderson and Tocher, 1987). The 0)3/006 fatty acid ratio in the
blubber of "marine" and "freshwater" seals are >6.3 and 2.0, respectively (Smith
et aI., 1996). The fatty acids in the blubber of the river dolphin, Inia geoffrensis (an
entirely freshwater species), have a 0)3/0)6 ratio of 0.27 (Ackman et aI., 1971).
Comparable results on individual fatty acid components and 0)3/0)6 fatty acid
ratios have been obtained to distinguish marine from lake populations of the
ringed seal, Phoca hispida, from Finnish waters (Kiikelii, 1996; Kiikelii et aI.,
1995; KiikeIa et aI., 1993).
Endogenous and dietary fatty acids play an important role in maintaining the
optimal degree of membrane fluidity in the peripheral tissues of small homothermous animals exposed to near-zero water temperatures. The anatomical distribution and the fatty acid composition of adipose tissue of aquatic and semiaquatic
rodents from high-latitude environments present a valuable opportunity to study
the importance of dietary fatty acids in cold adaptation. Beavers (Castor canadensis and C. fiber) and the muskrats (Onidatra zibethicus) accumulate large
amounts of dietary 18:30)3 (up to 18% and 20% of the total fatty acids, respectively) in peripheral adipose tissues of the tail and feet (KakeIa and Hyvarinen,
1996). The concentrations of 18:30)3 in the core tissues such as the mesenteries,
the perirenal tissues, and the liver are much lower « 1 % of the total fatty acids).
Linolenic acid (18:30)3) is an essential fatty acid for many animals, and beavers
obtain it from green plants, bark, and wood (Peng, 1992; Dunlop-Johns et aI.,
1991). The lipids of cold water animals also contain substantial amounts of C20
35
part responsible for a common fin disease. It is believed that the high proportions
of 20:4006 in wild salmon originates in the lipids of aquatic insects, which constitute an important portion of their natural food (Ackman and Takeuchi, 1986).
The analysis of several species of freshwater invertebrates that are natural food of
salmon indicated, however, that not only insects but also the Gammaridae and
Oligochaeta can be a source of 18:20)6 and 20:40)6 for fish (Bell et aI., 1994).
Growing environmental and conservationist concerns have stimulated the use
of alternative methods applied to the ecology of aquatic and semiaquatic mammals. Many of these investigations have used fatty acid markers to determine food
resources for populations of aquatic mammals (for a comparative discussion, see
also Landrum and Fisher, this volume). A comparison of the fatty acids in the
blubber of a population of harbor seals, Phoca vitulina from the Ungava Peninsula
(a land-locked environment in northern Quebec) and their marine counterpart,
showed that the inland animals have a fatty acid profile enriched in components of
freshwater origin, such as 18:2006, 18:30)3, and 20:40)6; the blubber of the marine
populations of P. vitulina contained higher concentrations of20: 10)9 and 22: 10)11
(Smith et aI., 1996). These MUFAs are characteristic components of the wax
esters of marine calanoid copepods, which are eaten by zooplanktivorus fish and
then are transferred to higher trophic levels of the food chain (Clarke et aI., 1987,
Sargent, 1976).
The contribution of marine versus freshwater fatty acids food sources can be
assessed by its 0)3/0)6 fatty acid ratio in the predator tissues. A typical 0)3/0)6 ratio
for freshwater fish ranges from 0.5 to 3.8, whereas for marine fish the ratio varies
from 4.7 to 14.4 (Henderson and Tocher, 1987). The 0)3/006 fatty acid ratio in the
blubber of "marine" and "freshwater" seals are >6.3 and 2.0, respectively (Smith
et aI., 1996). The fatty acids in the blubber of the river dolphin, Inia geoffrensis (an
entirely freshwater species), have a 0)3/0)6 ratio of 0.27 (Ackman et aI., 1971).
Comparable results on individual fatty acid components and 0)3/0)6 fatty acid
ratios have been obtained to distinguish marine from lake populations of the
ringed seal, Phoca hispida, from Finnish waters (Kiikelii, 1996; Kiikelii et aI.,
1995; KiikeIa et aI., 1993).
Endogenous and dietary fatty acids play an important role in maintaining the
optimal degree of membrane fluidity in the peripheral tissues of small homothermous animals exposed to near-zero water temperatures. The anatomical distribution and the fatty acid composition of adipose tissue of aquatic and semiaquatic
rodents from high-latitude environments present a valuable opportunity to study
the importance of dietary fatty acids in cold adaptation. Beavers (Castor canadensis and C. fiber) and the muskrats (Onidatra zibethicus) accumulate large
amounts of dietary 18:30)3 (up to 18% and 20% of the total fatty acids, respectively) in peripheral adipose tissues of the tail and feet (KakeIa and Hyvarinen,
1996). The concentrations of 18:30)3 in the core tissues such as the mesenteries,
the perirenal tissues, and the liver are much lower « 1 % of the total fatty acids).
Linolenic acid (18:30)3) is an essential fatty acid for many animals, and beavers
obtain it from green plants, bark, and wood (Peng, 1992; Dunlop-Johns et aI.,
1991). The lipids of cold water animals also contain substantial amounts of C20