Optimisation of T-ISO biomass production rich in essential fatty acids II. Effect of different light regimes on the production of fatty acids Ioannis Tzovenis a, * , Niels De Pauw b , Patrick Sorgeloos a a Laboratory of Aquaculture and ‘‘Artemia Reference Centre’’, Ghent University, Rozier 44, B-9000 Ghent, Belgium b Department of Applied Ecology and Environmental Biology, Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium Received 29 November 2001; received in revised form 26 July 2002; accepted 26 July 2002 Abstract It is well documented that culture conditions affect the fatty acid content of microalgae. We report in this study the fatty acid profiles and n 3 HUFA productivity of T-ISO, a popular haptophyte in the aquaculture industry, cultured under three photoperiods (24:0, 16:08 and 12:12 h L:D) combined with three photon flux densities (PFD: 120, 220 and 460 Amol photon m 2 s 1 ), at 25 jC. Sampling took place in both the exponential and post-exponential (light-limited) phase. In general, fatty acid proportions were effected by a strong interaction of L:D Â PFD resulting in metabolic changes difficult to be modelled. At the 12:12 and 24:0 h L:D the fatty acid pattern can be summarised as PUFA>SAFA>MUFA, while at 16:08 h L:D as SAFA>PUFA>MUFA reflecting a differential acclimation of the strain under light –dark cycles. At the 12:12 h L:D the PUFA content of biomass was significantly higher than at the other photocycles. PUFA content differences were located in the n 3 fraction with the n 6 content being rather constant. The n 3/n 6 and DHA/ EPA ratios under 24:0 h or 12:12 h L:D were optimal according to the literature for fish and shellfish nutrition requirements. In contrast, the 16:08 h L:D regimes, especially at low PFD, produced inadequate ratios. The production of n 3 HUFA in T-ISO is essentially influenced by the total photon flux available per day in a similar manner with growth. The capacity of the strain for storing lipid is limited under the conditions tested; consequently, the fatty acid content follows the biomass yield 0044-8486/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. PII:S0044-8486(02)00375-7 * Corresponding author. Present address: Department of Ecology and Systematics, Faculty of Biology, University of Athens, Panepistimioupolis, Zografou 15784, Greece. Tel.: +30-1-7274042; fax: +30-1-7274885. E-mail address: itzoveni@eexi.gr (I. Tzovenis). www.elsevier.com/locate/aqua-online Aquaculture 216 (2003) 223 – 242