Krill meal (KM) emerges as a promising alternative to fish meal (FM) in aquafeeds, providing a rich source of protein, amino acids, phospholipids, omega-3 fatty acids, and bioactive compounds. This study aimed to investigate the effects of partially replacing FM with increasing levels of KM (3, 5 and 7% of the diet) on growth performance, nutrient utilization, and antioxidant defenses in juvenile gilthead sea bream (Sparus aurata) exposed to a crowding stress challenge. The dietary inclusion of 7% KM could effectively replace up to 7% FM in the diet, resulting in a tendency to improve feed conversion ratio (FCR) and nutrient efficiency ratios compared to the control FM diet. Under stress conditions, a significant interaction between diet and time was observed in fish blood omega- 3 index (OI3). At 24h after the stress challenge, all dietary treatments except 3% KM presented a significant increase in OI3. At 7d post-stress, fish fed the Control diet led to a significant reduction in O3I down to the basal levels. On the contrary, those fish fed 5% KM and 7% KM diets kept increased O3I at the end of the stress challenge (Table). Fish fed 5% KM and 7%KM also showed a lower increase of cat and sod gene expression 24h after stress, which was inversely correlated with fish blood OI3. Therefore, these results show that KM modulates red blood cells fatty acid profile by increasing fish OI3 after crowding stress as well as potentially function as an antioxidant modulator in fish feeds for mitigating stressful conditions. Thus, KM could be a viable candidate for FM replacement in aquafeeds, aiming to expand the basket of raw materials with functional properties to be used in aquafeed formulation by demonstrating its efficacy in improving nutrient utilization, as well as exhibiting benefits in mitigating oxidative stress in fish.