(NZ613593-A)   NOVELTY - Method of producing diatom biomass, involves continuously culturing diatom in culture medium to produce volumetric production rate of biomass of at least 20 g dry weight/l/day, where the culture medium provides essential nutrients to maintain the diatom in log phase growth.    USE - The method is useful for producing diatom biomass (claimed).    ADVANTAGE - The method is cost-effective, and simple.    DETAILED DESCRIPTION - Method of producing diatom biomass, involves (a) continuously culturing diatom in culture medium to produce volumetric production rate of biomass of at least 20 g dry weight/l/day, where the culture medium provides essential nutrients to maintain the diatom in log phase growth, or (b) (i) cultivating the diatom in culture medium to produce an active culture, (ii) removing portion of the active culture to collect the biomass, (iii) adding fresh culture medium to the remaining active culture that is substantially equivalent in volume to the portion of the active culture removed in the step (ii) and again cultivating the diatom, and (iv) repeating the steps (ii) and (iii) in which at least 20 g dry cell weight of biomass/l active culture is collected within 24 hours, where the culture medium is designed to provide essential nutrients to maintain the diatom in log phase growth. INDEPENDENT CLAIMS are included for the following:    (1) active culture in continuous culture comprising the above-mentioned culture medium, and diatom at diatom biomass density of at least 20 g/l;    (2) biomass produced by the above-mentioned method;    (3) composition of highly unsaturated fatty acid or their ester obtained from the biomass produced by above-mentioned methods;    (4) method of producing composition of the HUFA or their ester, involves extracting the HUFA or their ester from the biomass produced by the above-mentioned methods; and    (5) nutritional supplement, medical food, food, feed additive, pharmaceutical product comprising the above-mentioned composition produced by the above-mentioned method.