A possible explanation for the differences in the fatty acid composition of fresh-water and marine fishes

Farkas, Tibor (1971) A possible explanation for the differences in the fatty acid composition of fresh-water and marine fishes. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 38. pp. 143-152. ISSN 0365-3005

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Abstract

Considering the data concerning the metabolism of fatty acids in aquatic animals and comparing the fatty acid compositions in different levels of aquatic food chains for the differences observed in the fatty acid composition of fresh-water and marine fishes the following explanation is offered: 1. The differences in the levels of linoleic and linolenic acids can be traced back to the differences in species composition of phytoplankton in seas and inland waters. In marine phytoplankton predominate the diatoms with low level of linoleic and linolenic acids, in fresh-water bodies however the green and blue-green algae with high levels of both fatty acids. The distribution of these fatty acids in the fats of herbivoreous planktonic crustaceans shows the same pattern as in their food. 2. Although both marine and fresh-water fishes were shown to be able to desaturate and elongate linoleic and linolenic acids to long chain polyunsaturated fatty acids, the bulk of these fatty acids originates in lower trophic levels. Some planktonic crustacean species are able to regulate the levels of these fatty acids in their phospholipids according to the environmental temperature. Decrease in the environmental temperature results in an increase of eicosa-, and docosapolyenoic fatty acids in both fresh-water and marine crustaceans. The distribution of long chain polyunsaturated fatty acids in the triglycerides of marine and fresh-water fishes is similar to that in their natural food. 3. Planktonic crustaceans and fishes can dehydrogenate saturated fatty acids of both endogenous and exogenous origin. This process may modify the ratio of saturated to monounsaturated fatty acids in higher trophic levels as compared to the phytoplankton.

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