Natural antimicrobial active packaging is an emerging technology for fresh fish preservation in which a chemical compound of natural origin is purposely incorporated into a packaging material to be released into the food surface in order to protect it from spoilage by foodborne microorganisms. The maximum efficiency of an antimicrobial package can only be obtained when an adequate activity is achieved immediately after the packaging operation and is maintained constant throughout the product's shelf life. This work develops an active package designed for the preservation of fresh farmed salmon in cubes or slices, made up of a rigid polypropylene (PP)/ethylene-vinyl alcohol copolymer (EVOH)/PP tray heat-sealed with an active PP/EVOH/PP film lid in which 6.5% carvacrol is incorporated in the EVOH kernel as an antimicrobial active agent. The work also includes the measurement of the carvacrol kinetics and equilibrium parameters in the preserved salmon fillets, and proposes a mathematical model based on the finite element method to describe and simulate the common performance of the developed package/food system, and to predict its behavior under different working conditions or system configurations with the objective of finding the optimum combination of variables that ensure the best packaging performance. The results obtained from the determination of parameters showed a rapid migration of the active compound through the fish muscle, and a low affinity of the agent molecules for the food matrix. The active package was successfully developed, and the proposed model was satisfactorily used to detect the key factors that govern the package performance, and also to improve the package design by modifying the thickness distribution of the multilayer active film. (C) 2013 Elsevier Ltd. All rights reserved.