:This planktivorous mode, it arises that the near total of the preferential, secondary preys and some additional preys of the species consist of harmful kinds of alga to the quality of water (odors, taste, filling of the filters) and to human health (production of toxins).Indeed the examination of the mode of S. galilaeus made it possible to gather the preys according to the affected targets.The producing preys of tastes and odor in water consist of:Peridinium (preferential prey), Cosmarium (secondary prey) Synedra (secondary prey), Melosira (secondary prey), Anabeana (prey accessories), Microcystis (prey secondary), Scenedesmus (prey accessories) and Volvox (prey accessories).The preys colmatrices of filters are made up of:Peridinium (preferential prey), Cymbella (secondary prey) Synedra (secondary prey), Navicula (secondary prey), Melosira (secondary prey), Diatoma (additional prey), Tracholomonas (additional prey), Microcystis (secondary prey) and Anabeana (additional prey).The producing toxin preys include/understand kinds Ci afterwards: Nostoc (additional prey), Microcystis (secondary prey), Anabeana (additional prey) and Chroococcus sp (additional prey).Very harmful preys with human health as eggs of ascaris were also identified like prey preferential at the species. The analysis of the planktivorous mode of S. galilaeus from the MFI% cumulated, coupled with the multivariate regressions between the preys taken in dry season and rainy season and those introduced between the classes of size (88