The invention relates to novel strains of microalgae belonging to the isochrysis genus, which enable the optimal production of polyunsaturated fatty acids, in particular EPA, in a mixotrophic mode, as well as to a method for selecting and culturing said strains which in particular makes use of supplying discontinuous light in the form of flashes.Linvention se rapporte à de nouvelles souches de microalgues appartenant au genre Isochrysis permettant une production optimale dacides gras polyinsaturés, notamment dEPA, en mode mixotrophe, ainsi quà un procédé de sélection et de culture de telles souches faisant appel, notamment, à un apport de lumière discontinu sous forme de flashs.