Different Fish Meal and Fish Oil Dietary Levels in European Sea Bass: Welfare Implications After Acute Confinement Stress

To provide practical feeding management guidelines preceding a stressful episode during farming practices, European sea bass juveniles (initial weight: 72.3 g) were fed for 60-days different fish meal (FM) and oil (FO) dietary levels [high (30% FM, 15% FO, FM30/FO15), intermediate (20% 7% FM20/FO7), low (10% 3% FM10/FO3)] in triplicate conditions. Fish then fasted 36 h exposed to 2-h acute crowding (80 kg m –3 biomass). Plasma biochemistry, skin mucus parameters gene expression of stress immune-related genes performed before, at 2 24 after crowding. At the end trial, FM10/FO3 group showed lower final body weight, weight gain, specific growth rate compared other treatments. Most plasma mainly affected by condition rather than diet; however, stress, lactate was higher FM30/FO15 Similarly, protease, antiprotease, peroxidase lysozyme mostly conditions, while displayed mucosal IgM bactericidal activity against Vibrio anguillarum V. harveyi . stress-related considered ( hsp70 gr-1 brain; , gr-2 head kidney), an overall pattern that increased over time addition, kidney also up-regulated stress. Higher plasmatic together with up-regulation some transcripts suggest reactivity stress-response mechanism high FM FO levels. Otherwise, observed seems indicate able activate pro-inflammatory response this treatment. Overall, results present study seem 10% might affect immune responses.