Effect of short-chain fatty acids inclusion in a plant feedstuffs-based diet on growth, immune response, and disease resistance of European seabass

Novel aquafeeds usually include high levels of plant feedstuffs (PF). However, most PF has antinutritional factors (ANF) that may jeopardize nutrient digestion and metabolic utilization, increasing fish susceptibility to oxidative stress, intestine inflammation, and disease susceptibility. The main goal of this work is to evaluate the potential of using SCFAs as functional ingredients in PF-rich diets on growth performance, immune status, and disease resistance of European sea bass. European sea bass juveniles were randomly distributed into twenty-one tanks (twenty-five fish per tank) were fed for 56 days in triplicate tanks with seven isoproteic and isolipidic diets with different short chain fatty acids and different percentage supplementation: Control diet; Diet SA 0.25 (sodium acetate at 0.25%), Diet SA 0.50 (sodium acetate at 0.50 %), SP 0.25 (sodium propionate at 0.25%), SP 0.50 (sodium propionate at 0.50%) SB 0.25 (sodium butyrate at 0.25%), SB 0.50 (sodium butyrate at 0.50%). At the end of the growth trial in order to evaluate the immune status three fish per tank were collected. After the growth trial fish were relocated to the challenge room. Six fish per diet (eighteen in total) were randomly selected and infected intraperitoneally (p.i) injected with 100ul of vibrio anguillarum (1.2x10 7 CFU/ mL -1 ). Four and twenty-four hours after the p.i infection, fish were sampled to assess the hematological profile and innate immune parameters. To access the survival, fifteen fish per tank (thirty per diet) were injected. These fish were fed with the experimental diets and the mortality recorded for 3 weeks. Dietary treatment had no effects on the growth performance of European seabass juveniles. Regarding blood parameters, all decreased with time regardless of fatty acid or its level of supplementation in relation to time 0 (prior infection), except for mean corpuscular hemoglobin concentration (MCHC). All parameters showed a tendency to recover at 24h. Mean corpuscular volume (MCV) is higher in fish fed sodium butyrate than sodium acetate. In innate immune parameters, all diets present a decrease in lysozyme activity and peroxidase activity at 4 and 24h post-infection. This decrease may be related to the lower WBC values at 4h. Peroxidase activity showed recovery at 24h in sodium acetate at 0.25 and 0.5% and at sodium propionate at 0.25%. Lysozyme activity was higher in fish fed sodium butyrate when compared with sodium acetate, despite the inclusion level. The survival was highest in fish fed sodium butyrate 0.5% (93.3 vs. 66.7% SP 0.25%), there were no differences in survival between treatments and control.