This study investigated the antifungal activity of five essential oils (EOs) towards yeasts recovered from diseased fishes and focused on the efficacy of the effective EO on the growth performance, non-specific immunity, and disease resistance of Nile tilapia (Oreochromis niloticus). Fish (n=150) were divided into five groups (30 fish/group (G)) with three replicates. Fish in G1 were fed 3 g kg−1 of carvacrol supplemented diet for one month then challenged with Cryptococcus uniguttulatus and kept on carvacrol post-challenge. G2 was treated with 3 g kg−1 of the carvacrol supplemented diet and G3 received 40 mg kg−1 of itraconazole for one week. G4 served as unchallenged control. G5 was kept as a positive control. Phagocytic activity, reactive oxygen species production, reactive nitrogen species production, myeloperoxidase, lysozyme activity, and total immunoglobulins were tested before and after challenge. Moreover, Relative Percent Survival (RPS) and mortality percent were determined as indicators for functional immunity. EOs displayed diverge degrees of antifungal activity and carvacrol was the most effective against the tested yeasts. The dietary additive of carvacrol significantly enhanced growth performance, all immunological parameters, and the RPS values (90 %) than in other treatments. This unique experimental model indicates that carvacrol seems promising not only for enhancing immunity and promoting fish growth, but also to control emerging fungal infections. It would be necessary to investigate different concentrations of carvacrol as well as the antifungal activity in different fish species in future studies.