INFLUENCE OF GROWTH-RATE ON PIGMENT AND LIPID-COMPOSITION OF THE MICROALGA ISOCHRYSIS AFF GALBANA CLONE T-ISO

A continuous culture of Isochrysis aff. galbana clone Tiso, used to fe ed Pecten maximus larvae at IFREMER (Brest, France), was carried out i n a chemostat at its optimum temperature for growth (26-degrees-C). Ch anges in pigments, lipid class (neutral, glyco- and phospholipids) and degree of fatty acid unsaturation were studied at three different gro wth rates (0.33, 0.5, 1 d-1). As predicted by chemostat theory, a slow growth rate produced higher cell numbers and higher biomass per unit volume. These cells were low in chlorophyll a and carotenoids, but ric h in neutral lipids. In contrast, cultures with a fast growth rate yie lded lower cell concentrations, buth higher chlorophyll a, carotenoid and membrane lipid contents per cell. Changes in polyunsaturated fatty acid distribution were related to differences in algal growth rates. Neutral lipids contained mainly saturated and monounsaturated fatty ac ids (C18:1omega9) at low growth rates whereas they were enriched in po lyunsaturated fatty acids, especially C22:6omega3, at high growth rate s. Therefore, it is suggested that the growth rate in continuous cultu res be controlled so as to adjust the relative proportions of polyunsa turated fatty acids in lipid classes of the diet meant for larval nutr ition. Abbrevations: For nomenclature of fatty acids, the term C c:nom egax is used where c is the number of carbon atoms, n is the number of double bonds, and omegax is the position of double bond relative to t he methyl end of the fatty acid chain.