In order to determine the effect of different levels of arachidonic acid (AA) in microdiets on growth and survival of gilthead seabream larvae, two experiments were carried out. In the first experiment, 17-day old larvae were fed microdiets for 14 days. In this trial, we tested four diets with a similar docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio and AA in the range of 0.1%–1.8% dry weight (d.w.) and a fifth diet with 1.0% d.w. of AA and a different DHA/EPA ratio. In the second experiment, 16-day old larvae were fed for 21 days on two microdiets with levels of 0.1% and 1.0% d.w. AA. All diets in the two experiments had the same total n−3 HUFA level. Growth was measured by total length and dry body weight of larvae. Larval lipids were extracted and fatty acid compositions of total neutral lipid (NL) and total polar lipid (PL) fractions were determined by gas chromatography. In the first experiment, the diet containing 1.8% d.w. of AA showed the best survival (P<0.05) but did not improve growth rate. In the second experiment, an increase in the AA dietary level from 0.1% to 1.0% d.w. significantly improved (P<0.05) larval growth. EPA accumulation in the PLs of the larvae was negatively affected by the inclusion of dietary AA. When working with a fixed dietary n−3 HUFA level (2.2% d.w.), the effect of dietary AA on larval growth was masked by that of the dietary DHA/EPA ratio. However, when DHA/EPA ratio in diet was unchanged (∼1.8), it was possible to improve larval growth by supplementing the diet with 1.0 d.w. of AA. The negative effect produced by the increment of dietary AA on the EPA incorporation into the larval PLs may be related to a competition interaction.