Benefits of dietary krill meal inclusion towards better utilization of nutrients, and response to oxidative stress in gilthead seabream (Sparus aurata) juveniles

Krill meal (KM) emerges as a promising sustainable marine ingredient 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 including 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 47 % FM in the diet (8 % FM in 7 % KM in comparison to 15 % FM in control diet), without compromising growth or feed conversion. Although not statistically different, dietary supplementation with 5 and 7 % KM showed a tendency to further optimize feed conversion ratio and nutrient efficiency ratios compared to the control FM diet. Under stressful conditions, a significant interaction between diet and time was observed in fish blood omega-3 index (O3I). At 24 h after the stress challenge, all dietary treatments except KM3 presented a significant increase in n-3 PUFA, EPA, DHA as well as OI3, whereas a decrease in MUFA. At 7d (168 h) post-stress, fish fed the control diet presented a significant reduction in O3I down to the basal levels. On the contrary, those fish fed KM5 and KM7 diets kept increased O3I levels as well as n-3 PUFA content to the end of the stress challenge. Indeed, 24 h after stress, fish fed KM5 and KM7 showed a lower increase of cat and sod gene expression in head kidney, which was further inversely correlated with fish blood OI3. Therefore, these results show that KM modulates red blood cells fatty acid profile by increasing fish OI3 after stress as well as potentially functioning as an antioxidant modulator in fish feeds for mitigating stressful conditions. Hence, KM is a valuable functional ingredient in aquafeeds, aiming to expand the basket of raw materials with functional properties to be used in aquafeed formulation to enhance fish robustness. • KM effectively substitutes FM up to 47 %, enhancing feed sustainability in aquaculture. • KM boosts omega-3 levels and mitigates oxidative stress, enhancing fish health. • Novel insights: KM acts as an antioxidant, improving fish resilience to stress. • Application: KM's functional benefits make it a valuable ingredient for robust aquafeed formulations .