The application of the classical selection of diatoms on the example of the genus Haslea is considered. The ability of some representatives of this genus to synthesize marennine and marennine-like pigments is interesting to researchers and owners of oyster farms because these unique pigments can colorise the tissues of mollusks in a greenish color and improve their organoleptic properties. It has been shown that marennine has antibacterial, antiviral, antioxidant and other biological activities. It is assumed that the efficiency of marennine biosynthesis can be increased by obtaining highly productive strains by selection, which was not previously carried out in diatoms. The assessment of the possibility and prospects of applying the methods of classical breeding in relation to representatives of the genus Haslea is given. It is shown that significant success has been achieved to date in the study of the life cycle, crossing systems and other features of the reproductive biology of representatives of the genus Haslea, which allows them to carry out classical selection by selection, hybridization and obtaining descendants of the next generation.