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Biochemical adaptation by the tropical copepods Apocyclops royi (Lindberg 1940) and Pseudodiaptomus annandalei (Sewell 1919) to a PUFA-poor brackish water habitat

Bolette Lykke Holm Nielsen, Hans Van Someren Gréve, Thomas Allan Rayner, Benni Winding Hansen*

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ABSTRACT: The cyclopoid Apocyclops royi and the calanoid Pseudodiaptomus annandalei are two tropical copepods suspected of the capability to biosynthesize the physiologically important n-3 polyunsaturated fatty acids (n-3 PUFA) eicosapentaenoic acid (C20:5n-3, EPA) and docosahexaenoic acid (C22:6n-3, DHA). We demonstrated this suspected ability using 13C18 α-linolenic acid (C18:3n-3, ALA) fed to the copepods through liposomes and a subsequent fatty acid (FA) analysis by GC-MS at three different time points, 0, 24 and 48h. Two different diets were applied post liposome-exposure, baker’s yeast Saccharomyces cerevisiae and the microalgae Dunaliella tertiolecta. For both copepods, further elongated and desaturated 13C n-3 PUFA were found at all time points. At T48h, A. royi and P. annandalei contained 13C-labelled DHA contents of 1.3 ± 0.2 and 0.7 ± 0.3 µg 13C-FA · mg Ccopepod-1 when fed baker’s yeast, respectively, and 1.2 ± 0.1 and 1.6 ± 0.5 µg 13C-FA · mg Ccopepod-1 when fed D. tertiolecta, respectively, with significant differences observed only between P. annandalei diet treatments. The 13C-labelled EPA content of A. royi and P. annandalei at T48h was 0.6 ± 0.4 and 0.7 ± 0.4 µg 13C-FA · mg Ccopepod-1 when fed baker’s yeast and 0.8 ± 0.2 and 0.3 ± 0.1 µg 13C-FA · mg Ccopepod-1 when fed D. tertiolecta, with significant differences only between copepods fed D. tertiolecta. A. royi and P. annandalei exhibited an ability to produce n-3 PUFA from the precursor ALA in comparatively large quantities. This ability enables these two species to inhabit habitats characterized by PUFA-poor particulate material.