Effect of dietary supplementation with citral-loaded nanostructured systems on innate immune responses and gut microbiota of silver catfish (Rhamdia quelen)

Citral is a monoterpenoid found in the essential oils of several plant species, recognized as a safe diet additive and extensively used in the food and cosmetic industries. This study evaluated the effects of dietary supplementation with citral (0.25 g/kg), loaded in nanosystems or unloaded on the gastrointestinal tract (GIT) pH, hepatosomatic and intraperitoneal fat index, innate immune responses and gut microbiota (GM) of silver catfish (Rhamdia quelen). The treatments were: control diet (CO), diet containing unloaded citral (UC), diet containing citral-loaded nanoemulsions (NE), and diet containing citral-loaded alginate nanoparticles (NP). After 21 days fish fed all diets containing citral showed an increased liver lysozyme activity, whereas fish fed UC showed reduced serum hemolytic activity and intestinal myeloperoxidase activity. Serum lysozyme activity was lower in fish fed diet containing NP, whereas fish fed NE showed a reduced blood macrophage phagocytic index. Citral reduced stomach pH (all delivery forms) and increased intestinal pH when loaded in NE. Both NE and NP reduced the total bacterial population in the fish intestine, whereas Aeromonas spp. in intestine were higher in fish fed diet containing NP. Citral modulated the silver catfish immune responses, GIT pH and GM in a delivery mode-dependent manner.