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The unicellular microalgae Haematococcus pluvialis is of great interest because it is an exclusive and the richest source of natural astaxanthin (3, 3'- dihydroxy-ß-carotene-4, 4'-dione). We carried out an isolation and screening of a new H. pluvialis strains with high astaxanthin production potential from Algerian freshwater. The isolated strains were assessed for their growth and astaxanthin accumulation under different stress conditions associated with high light intensity. The main goal of the present study was to select highly astaxanthin-producing H. pluvialis strains from the Algerian environment. Eighteen microalgae strains in total were isolated on a Bold's basal medium from 48 aseptically collected freshwater samples from 5 different regions of Algeria. The identification of H. pluvialis was made according to morphological criteria. Growth tests have led to the selection of the best H. pluvialis strain that will be grown under stress (nutrient starvation and variable salinity) associated to high light intensity (200 µmol photons.m-2.s-1) to determine the optimal conditions of astaxanthin accumulation. Optimal nitrate concentration giving rise to maximum biomass was 0.50 g/L. Nitrate starvation associated with high light irradiance was most effective in induction of astaxanthin accumulation which reached 67.25 ± 2.28 mg/L in H. pluvialis cells. H. pluvialis morphology under such stress has shown the occurrence of mature aplanospores with thick cell wall. These results clearly show that the isolated H. pluvialis strain has a good performance to synthesize astaxanthin under nitrate starvation associated with high light irradiance suggesting its possible industrial culture for the production of this pigment. [ABSTRACT FROM AUTHOR]