Palaemon serratus (Pennant, 1777) is a shrimp with a high market value. It can be extensively produced in salt marshes with good survival rates, and it takes a reasonable period (8–10 months) to attain marketable size. For these reasons, it seems to have a good aquaculture potential. However, little is known about the nutritional requirements of this species, especially at the larval stages, and this may impose constraints to its successful rearing. This paper describes the changes occurring in the fatty acid profile of four developmental stages of Palaemon serratus eggs, newly hatched Zoea I larvae, and Zoea I starved for 24 and 48 hours, with the purpose of assessing larval fatty acid requirements. We also studied the effects of eight diets composed of microalgae (Chlorella sp. and Isochrysis galbana), rotifer (Brachionus plicatilis) and non-enriched or enriched brine shrimp (Artemia franciscana) nauplii on the fatty acid profiles of P. serratus postlarvae. Analysis of the P. serratus eggs revealed a high PUFA and HUFA content, which confirms their nutritional importance. The best results, in terms of postlarval fatty acid profile, were achieved with a diet of Artemia nauplii enriched with Protein Selco®, followed by a diet of B. plicatilis, Artemia nauplii, and Isochrysis galbana. The results from the present study are compared with survival and growth data from a previous study, and it is concluded that Protein Selco® appears to be the best Artemia enrichment product for the larval rearing of P. serratus.